®EPA  Method 1638: Determination of Trace
       Elements in Ambient Waters by
       Inductively Coupled Plasma-Mass
       Spectrometry
                                  > Printed on Recycled Paper

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Method 1638
                                   Acknowledgements

Method 1638  was prepared under the direction of William A. Telliard of the U.S. Envkonmental
Protection Agency's (EPA's) Office of Water (OW), Engineering and Analysis Division (BAD). Ilie
method was prepared under EPA Contract 68-C3-0337 by the DynCorp Envkonmental Programs Division
with assistance from Interface, Inc.

The following researchers contributed to the philosophy behind this method.  Their contribution is
gratefully acknowledged:

Shier Berman, National Research Council, Ottawa, Ontario, Canada;
Nicholas Bloom, Frontier Geosciences Inc., Seattle, Washington;
Paul Boothe and Gary Steinmetz, Texas A&M University, College Station, Texas;
Eric Crecelius, Battelle Marine Sciences Laboratory, Sequim, Washington;
Russell Flegal, University of California/Santa Cruz, California;
Gary GUI, Texas A&M University at Galveston, Texas;
Carlton Hunt and Dion Lewis,  Battelle Ocean Sciences, Duxbury, Massachusetts;
Carl Watras Wisconsin Department of Natural Resources, Boulder Junction, Wisconsin; and
Herb Windom and Ralph Smith, Skidaway Institute of Oceanography, Savannah, Georgia.

In addition, the following personnel at the EPA Office of Research and Development's Environmental
Monitoring Systems Laboratory in Cincinnati, Ohio, are gratefully acknowledged for the development of
the analytical procedures described in this method:

 C.A. Brockhoff
J.T. Creed
 T.D. Martin
 E.R. Martin
 S.E. Long (DynCorp, formerly Technology Applications Inc.)


                                         Disclaimer


 This method has been reviewed and approved for publication by the Engineering and Analysis Division
 of the U.S. Envkonmental Protection Agency.  Mention of trade names or commercial products does not
 constitute endorsement or recommendation for use.


 Questions concerning this method or its  application should be addressed to:

 W.A. Telliard
 USEPA Office of Water
 Analytical Methods Staff
 Mail Code 4303"
 401 M Street, SW
 Washington, DC 20460
 202/260-7120
                                                                             Draft, January 1996

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                                                                                     Method 1638
  Introduction

  This analytical method was designed to support water quality monitoring programs authorized under the
  Clean Water Act.  Section 304(a) of the Clean Water Act requires EPA to publish water quality criteria
  that reflect the latest scientific knowledge concerning the physical fate (e.g., concentration and dispersal)
  of pollutants, the effects of pollutants on ecological and human health, and the effect of pollutants on
  biological community diversity, productivity, and stability.

  Section 303 of the Clean Water Act requires states to set a water quality standard for each body of water
  within its boundaries.  A state water quality standard consists of a designated use or uses of a waterbody
  or a segment of a waterbody, the water quality criteria that are necessary to protect the designated use or
  uses, and an antidegradation policy. These water quality standards serve two purposes: (1) they establish
  the water quality goals for a specific waterbody, and (2) they are the basis for establishing water quality-
  based treatment controls and strategies beyond the technology-based controls required by Sections 301(b)
  and 306 of the Clean Water Act.

  In defining water quality standards, the  state  may use narrative criteria, numeric  criteria, or  both.
 However, the 1987 amendments to the Clean Water Act required states to adopt numeric criteria for toxic
 pollutants (designated in Section 307(a) of the Act) based on EPA Section 304(a) criteria or  other
 scientific data, when the discharge or presence of those toxic pollutants could reasonably be expected to
 interfere with designated uses.

 In some cases, these water quality criteria are as much as 280 times lower than those achievable using
 existing EPA methods  and required to support technology-based permits. Therefore, EPA developed new
 sampling and analysis methods to specifically address state needs for measuring toxic metals at water
 quality criteria levels,  when such measurements are necessary to protect designated uses in state water
 quality standards.  The latest criteria published by EPA are those listed hi the National Toxics Rule (57
 FR 60848) and the Stay of Federal Water Quality Criteria for Metals (60 PR 22228).  These rules  include
 water  quality criteria for 13 metals, and it is these criteria  on which the new sampling and analysis
 methods are based.  Method 1638 was specifically developed to provide reliable measurements  of nine
 of these metals at EPA WQC levels using inductively coupled plasma-mass spectrometry techniques.

 In developing these methods, EPA found that one of the greatest difficulties hi measuring pollutants at
 these levels was precluding sample contamination during collection, transport, and analysis.  The degree
 of difficulty, however, is highly dependent on the metal and site-specific conditions.  This analytical
 method, therefore, is designed to provide the level of protection necessary to preclude contamination in
 nearly all situations. It is also designed to provide the procedures necessary to produce reliable results
 at the lowest possible water quality criteria published by EPA. In recognition of the variety of situations
 to which this method may be applied, and in recognition of continuing technological advances, the method
 is performance-based.  Alternative procedures may be used, so long as those procedures are demonstrated
 to yield reliable results.

 Requests for additional copies should be directed to:

 U.S.EPANCEPI
 11029  Kenwood Road
 Cincinnati, OH 45242
 513/489-8190
Draft, January 1996
                                                                                            Hi

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Method 1638
     Note-  This method is intended to be performance-based, and the laboratory is permitted to omit any
     step or modify any procedure provided that all performance requirements set forth in this method
     are met  The laboratory is not allowed to omit any quality control analyses.  The terms  must,
     "may " and  "should" are included  throughout this  method  and are intended to illustrate the
     importance of the procedures in producing verifiable data at water quality criteria levels. The term
     "must" is used to indicate that researchers in trace metals analysis have found certain procedures
     essential in successfully analyzing samples and avoiding contamination; however, these procedures
     can be modified or omitted if the laboratory can demonstrate that data quality is not affected.
  IV
                                                                                Draft, January 1996

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                                   Method  1638

              Determination of Trace Elements in Ambient Waters by
                 Inductively Coupled Plasma — Mass Spectrometry
  1.0   Scope and Application

  1.1    This method is for the determination of dissolved elements in ambient waters at EPA water
        quality criteria (WQC) levels using inductively coupled plasma-mass spectrometry (ICP-MS).
        It may also be used for determination of total recoverable element concentrations in these
        waters.  This method was developed by integrating the analytical procedures in EPA Method
        200.8 with the quality control (QC) and sample handling procedures necessary to avoid
        contamination and ensure the validity of analytical results during sampling and analysis for
        metals at EPA WQC levels. This method contains  QC procedures that will assure that
        contamination will be detected when blanks accompanying samples are analyzed. This method
        is accompanied by Method 1669:  Sampling Ambient Water for Determination of Trace Metals
        at EPA Water Quality Criteria Levels ("Sampling Method").  The Sampling Method is
        necessary to assure that trace metals determinations will not be compromised by contamination
        during the sampling process.

 1.2    This method is applicable to the following elements:
Analyte
Antimony
Cadmium
Copper
Lead
Nickel
Selenium
Silver
Thallium
Zinc
Symbol
(Sb)
(Cd)
(Cu)
(Pb)
(Ni)
(Se)
(Ag)
(Tl)
(Zn)
Chemical Abstract Services
Registry Number (CASRN)
7440-36-0
7440-43-9
7440-50-8
7439-92-1
7440-02-0
7782-49-2
7440-22-4
7440-28-0
7440-66-6
1.3
Table 1 lists the EPA WQC levels, the Method Detection Limit (MDL) for each metal, and the
minimum level for each metal in this method.  Linear working ranges will be dependent on the
sample matrix, instrumentation, and selected operating conditions.

This method is not intended for determination of metals at concentrations normally found in
treated and untreated discharges from industrial facilities. Existing regulations (40 CFR Parts
400-500) typically limit concentrations in industrial discharges to the mid to high part-per-
Droft, January 1996

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Method 1638
       billion (ppb) range, whereas ambient metals concentrations are normally in the low part-per-
       trillion (ppt) to low ppb range.

14    Hie ease of contaminating ambient water samples with the metal(s) of interest and interfering
       substances cannot be overemphasized.  This method includes suggestions for improvements in
       facilities and analytical techniques that should maximize the ability of the laboratory to make
       reliable trace metals determinations  and minimize contamination.  These suggestions are given
       in Section 4.0, "Contamination and Interferences" and are based on findings of researchers
       performing trace metals analyses (References 1-8).  Additional suggestions for improvement of
       existing facilities may be found in EPA's Guidance for Establishing Trace Metals Clean
       Rooms in Existing Facilities, which is available from the National Center for Environmental
       Publications and Information (NCEPI) at the address listed in the introduction to this
       document.

 1 5     Clean and ultraclean—The terms "clean" and "ultraclean" have been applied to the techniques
       needed to reduce or eliminate contamination in trace metals determinations. These terms are
        not used in this method because of their lack of an exact definition. However, the information
        provided in this method is consistent with the summary guidance on clean and ultraclean
        techniques (Reference 9).

 1.6     This method follows the EPA Environmental Methods Management Council's "Format for
        Method Documentation" (Reference 10).

 1 7     This method is "performance-based"; i.e., an alternate procedure or technique may be used as
        long as the performance requirements in the method are met. Section 9.1.2 gives details of the
        tests and documentation required to support and document equivalent performance.

 1.8    For dissolved metal determinations, samples must be filtered through a 0^5-pm capsule filter
        at the field site.  The filtering procedures are described in the Sampling Method. The filtered
        samples may be preserved in the field or transported to the laboratory for preservation.
        Procedures for field preservation are detailed in the Sampling Method; procedures for
        laboratory preservation are provided in this method.

 1 9    For the determination of total recoverable analytes hi ambient water samples, a
        digestion/extraction (see Section 12.2) is required before analysis when the elements  are not in
        solution (e.g., aqueous samples that may contain paniculate and suspended solids).

 110  The procedure given in this method for digestion of total recoverable metals is suitable for die
         determination of silver in aqueous samples containing concentrations up to 0.1 mg/L. For the
         analysis of samples containing higher concentrations of silver, succeedingly smaller volume,
         well-mixed sample aliquots must be prepared until the analysis solution contains <0.1 mg/L
         silver.

  111   This method should be used by analysts experienced in the use of inductively coupled plasma
         mass spectrometry (ICP-MS), including the interpretation of spectral and matrix interferences
         and procedures for their correction, and this method should be used only by personnel
         thoroughly trained in the handling and analysis of samples for determination of metals at EPA
         WQC levels. A minimum of six months experience with commercial instrumentation is
         recommended.
                                                                               Draft, January 1996

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                                                                                    Method2638
 1.12   This method is accompanied by a data verification and validation guidance document,
        Guidance on the Documentation and Evaluation of Trace Metals Data Collected for CWA
        Compliance Monitoring.  Before using this method, data users should state the data quality
        objectives (DQOs) required for a project.

 2.0   Summary of Method

 2.1    An aliquot of a well-mixed, homogeneous aqueous sample is accurately measured for sample
        processing.  For total recoverable analysis of an aqueous sample containing undissolved
        material, analytes are first solubilized by gentle refluxing with nitric and hydrochloric acids.
        After cooling, the sample is made to volume, mixed, and centrifuged or allowed to settle
        overnight prior to analysis.  For the determination of dissolved analytes in a filtered aqueous
        sample aliquot, the sample is made ready for analysis by the appropriate addition of nitric acid,
        and then diluted to a predetermined volume and mixed before analysis.

 2.2    The digested sample is introduced into a radiofrequency plasma where energy transfer
        processes cause desolvation, atomization, and ionization. The ions are extracted from the
        plasma through a differentially pumped vacuum interface and separated on the basis of their
        mass-to-charge ratio (m/z) by a mass spectrometer having a minimum resolution capability of
        1 amu peak width at 5% peak height at m/z 300. Ions transmitted through the mass analyzer
        are detected by an electron multiplier or Faraday detector and  the resulting current is processed
        by a data handling system (References 11-13).

 3.0   Definitions
 3.1
       Apparatus—Throughout this method, the sample containers, sampling devices, instrumentation,
       and all other materials and devices used in sample collection, sample processing, and sample
       analysis activities will be referred to collectively as the Apparatus.

3.2    Other definitions of terms are given in Section 18.0 at the end of this method.

4.0   Contamination and Interferences

4.1    Preventing ambient water samples from becoming contaminated during the sampling and
       analytical process constitutes one of the greatest difficulties encountered in trace metals
       determinations. Over the last two decades, marine chemists have come to recognize that much
       of the historical data on the concentrations of dissolved trace metals in seawater are
       erroneously high because the concentrations reflect contamination from sampling and analysis
       rather than ambient levels.  More recently, historical trace metals data collected from
       freshwater rivers and streams have been shown to be similarly biased because of contamination
       during sampling and analysis (Reference 14). Therefore,  it is imperative that extreme care be
       taken to avoid contamination when collecting and analyzing ambient water samples for trace
       metals.

4.2    There are numerous routes by which samples may become contaminated.  Potential sources of
       trace metals  contamination during  sampling include:  metallic or metal-containing labware
       (e.g., talc gloves which contain high levels of zinc), containers, sampling equipment, reagents,
       and reagent water; improperly cleaned and stored equipment, labware, and reagents;  and
       atmospheric  inputs such as dirt and dust. Even human contact can be a source of trace metals
Draft, January 1996

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Method 1638
       contamination. For example, it has been demonstrated that dental work (e.g., mercury
       amalgam fillings) in the mouths of laboratory personnel can contaminate samples that are
       directly exposed to exhalation (Reference 3).

4.3    Contamination Control

       4.3.1   Philosophy—The philosophy behind contamination control is to ensure that any object
               or substance that contacts the sample is metal-free and free from any material that may
               contain metals.

               4.3.1.1 The integrity of the results produced cannot be compromised by contamination
                      of samples.  Requirements and suggestions for control of sample contamination
                      are given in this method and the Sampling Method.

               4.3.1.2 Substances in a sample cannot be allowed to contaminate the laboratory work
                      area or instrumentation used for trace metals measurements.  Requirements and
                      suggestions for protecting the laboratory are given in this method.

               4.3.1.3 While contamination control is essential, personnel health and safety remain
                      the highest priority.  Requirements and suggestions for personnel safety are
                      given in Section 5 of this method and the Sampling Method.

        4.3.2   Avoiding contamination—The best way to control contamination is to completely
               avoid exposure of the sample to contamination in the first place.  Avoiding exposure
               means performing operations in an area known to be free from contamination.  Two of
               the most important factors in avoiding/reducing sample contamination are: (1) an
               awareness of potential  sources  of contamination and (2) strict attention to work being
               done. Therefore it is imperative that the procedures described hi this method be
               carried out by well-trained, experienced personnel.

        4.3.3   Use a clean environment—The ideal environment for processing samples is a class 100
               clean room (Section 6.1.1).  If a clean room is not available, all sample preparation
               should be performed in a class 100 clean bench or a nonmetal glove box fed by
               particle-free air or nitrogen.  Digestions should be performed hi a nonmetal fume hood
               situated, ideally, hi the clean room.

        4.3.4  Minimize exposure—The Apparatus that will contact samples, blanks, or standard
               solutions should be opened or  exposed only in a clean room, clean bench, or glove
               box so that exposure to an uncontrolled atmosphere is minimized.  When not being
               used, the Apparatus should be covered with clean plastic wrap, stored hi the clean
               bench or in a plastic box or glove  box, or bagged in clean zip-type  bags. Minimizing
               the time between cleaning and use will also minimize contamination.

        4.3.5  Clean work surfaces—Before processing a given batch of samples,  all work surfaces in
               the hood, clean bench, or glove box hi which the samples will be processed should be
               cleaned by wiping with a lint-free cloth or wipe soaked with reagent water.

        4.3.6  Wear gloves—Sampling personnel must wear clean, nontalc gloves (Section 6.9.7)
                during all operations involving handling of the Apparatus, samples, and blanks. Only
                                                                               Draft, January 1996

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                                                                                      Method 1638
         4.3.7
 clean gloves may touch the Apparatus. If another object or substance is touched, the
 glove(s) must be changed before handling the Apparatus again.  If it is even suspected
 that gloves have become contaminated, work must be halted, the contaminated gloves
 removed, and a new pair of clean gloves put on.  Wearing multiple layers of clean
 gloves will allow the old pair to be quickly stripped with minimal disruption to the
 work activity.

 Use metal-free Apparatus—All Apparatus used for determination of metals at ambient
 water quality criteria levels must be nonmetallic, free of material that may contain
 metals, or both.

 4.3.7.1 Construction materials—Only the following materials should come in contact
        with samples:  fluoropolymer (FEP, PTFE), conventional or linear
        polyethylene, polycarbonate, polypropylene, polysulfone, or ultrapure quartz.
        PTFE is less desirable than FEP because the sintered material hi PTFE may
        contain contaminates and is susceptible to serious memory contamination
        (Reference 6).  Fluoropolymer or glass containers should be used for samples
        that will be analyzed for mercury because mercury vapors can diffuse hi or out
        of the other materials resulting either in contamination or low-biased results
        (Reference 3).  All materials, regardless of construction, that will directly or
        indirectly contact the sample must be cleaned using the procedures described
        hi Section 11 and must be known to be clean and metal-free before
        proceeding.

 4.3.7.2 The following materials have been found to  contain trace metals and should
        not contact the sample or be used to hold liquids that contact the sample,
        unless these materials have been shown to be free of the metals of interest at
        the desired level:  Pyrex, Kimax, methacrylate, polyvinylcbloride, nylon, and
        Vycor (Reference 6).  In addition, highly colored plastics, paper cap liners,
       pigments  used to mark increments on plastics, and rubber all contain trace
       levels of metals and must be avoided (Reference 15).

 4.3.7.3 Serialization—It is recommended that serial numbers be indelibly marked or
       etched on each piece of Apparatus so that contamination can be traced, and
       logbooks should be maintained to track the sample from the container through
       the labware to injection into the instrument.  It may be useful to dedicate
       separate sets of labware to  different sample types; e.g., receiving waters vs.
       effluents.  However, the Apparatus used for processing blanks and standards
       must be mixed with the Apparatus used to process samples so that
       contamination of all labware can be detected.

4.3.7.4 The laboratory or cleaning facility is responsible for cleaning the Apparatus
       used by the sampling team. If there are any  indications that the Apparatus is
       not clean when received by the sampling team (e.g., ripped storage bags), an
       assessment of the likelihood of contamination must be made. Sampling must
       not proceed if it is possible that the Apparatus is contaminated. If the
       Apparatus is contaminated,  it must be returned to the laboratory or cleaning
       facility for proper cleaning before any sampling activity resumes.
Draft, January 1996

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Method 1638
  4.4
4.3.8   Avoid Sources of Contamination—Avoid contamination by being aware of potential
       sources and routes of contamination.

       4.3.8.1 Contamination by carryover—Contamination may occur when a sample
              containing low concentrations of metals is processed immediately after a
              sample containing relatively high concentrations of these metals.  To reduce
              carryover, the sample introduction system may be rinsed between samples with
              dilute acid and reagent water. When an unusually concentrated sample is
              encountered, it is followed by analysis of a laboratory blank to check for
              carryover. For samples containing high levels of metals, it may be necessary
              to acid clean or replace the connecting tubing or inlet system to ensure that
              contamination will not affect subsequent measurements.  Samples known or
              suspected to contain the lowest concentration of metals should be analyzed
              first followed by samples containing higher levels.  For instruments containing
              autosamplers, the laboratory should keep track of which  station is used for a
              given sample. When an unusually high concentration of a metal is detected in
              a sample, the station used for that sample should be cleaned more thoroughly
              to prevent contamination of subsequent samples, and the results for subsequent
               samples should be checked for evidence of the metal(s) that occurred in high
               concentration.

        4382 Contamination by samples—Significant laboratory or instrument contamination
               may result when untreated effluents, in-process waters, landfill leachates, and
               other samples containing high concentrations of inorganic substances are
               processed and analyzed.  As stated in Section 1.0,  this method is not intended
               for application to these samples, and  samples containing high concentrations
               should not be permitted into the clean room and laboratory dedicated for
               processing trace metals samples.

        4383 Contamination by indirect contact—Apparatus that may not directly come hi
               contact with the samples may still be a source of contamination. For example,
               clean tubing placed in a dirty plastic  bag may pick up contamination from the
               bag  and then subsequently transfer the contamination to the sample.
               Therefore, it is imperative that every piece of the Apparatus that is directly or
               indirectly used hi the collection, processing, and analysis of ambient water
               samples be cleaned as  specified in Section 11.

        4.3.8.4 Contamination by airborne paniculate matter—Less obvious substances capable
               of contaminating samples include airborne particles. Samples may be
               contaminated by airborne dust, dirt, particles, or vapors from  unfiltered air
               supplies; nearby corroded or rusted pipes, wires, or  other fixtures; or metal-
               containing paint. Whenever possible, sample processing and analysis should
                occur as far as possible from sources of airborne contamination.

  Interferences—Interference sources that may cause inaccuracies in the determination of trace
  elements by ICP-MS are given below and must be recognized and corrected for. Instrumental
  drift, as well as suppressions or enhancements of instrument response caused by the sample
  matrix, should be corrected for by the use of internal standards.
                                                                               Draft, January 1996

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                                                                                      Method 1638
         4.4.1
        4.4.2
        4.4.3
        4.4.4
 Isobaric elemental interferences—Are caused by isotopes of different elements that
 form singly or doubly charged ions of the same nominal m/z and that cannot be
 resolved by the mass spectrometer.  All elements determined by this method have, at a
 minimum, one isotope free of isobaric elemental interferences. Of the isotopes
 recommended for use with this method (Table 5), only selenium-82 (krypton)  has an
 isobaric elemental interference.  If an alternative isotope that has a higher natural
 abundance is  selected to achieve greater sensitivity, an isobaric interference may occur.
 All data obtained under such conditions must be corrected by measuring the signal
 from another  isotope of the interfering element and subtracting the contribution the
 isotope of interest based on the relative abundance of the alternate isotope and isotope
 of interest.  A record of this correction  process should be included with the report of
 the data.  It should be noted that such corrections will only be as accurate as the
 accuracy of the relative abundance used in the equation for data calculations. Relative
 abundances should be established before applying any corrections.

 Abundance sensitivity—Is a property defining the degree to which the wings of a mass
 peak contribute to adjacent m/z's. The abundance sensitivity is affected by ion energy
 and quadruple operating pressure. Wing overlap interferences may result when a small
 m/z peak is being measured adjacent to a  large one.  The potential for these
 interferences should be recognized and the spectrometer resolution adjusted to
 minimize them.

 Isobaric polyatomic ion interferences—Are caused by ions consisting of more than one
 atom which have the same nominal mass-to-charge ratio as the isotope of interest, and
 which cannot  be resolved by the mass spectrometer in use. These  ions are commonly
 formed in the plasma or interface system from support gases or sample components.
 Most of the common interferences have been identified (Reference 13), and these are
 listed in Table 3 together with elements affected. Such interferences must be
 recognized, and when they cannot be avoided by the selection of an alternative m/z,
 appropriate corrections must be made to the data. Equations for the correction of data
 should be established at the time of the  analytical run sequence because the polyatomic
 ion interferences will be highly dependent on the sample matrix and" chosen instrument
 conditions.  In particular, the common 82Kr interference that affects the determination
 of both arsenic and selenium can be greatly reduced with the use of high-purity
 krypton-free argon.

 Physical interferences—Are associated with the physical processes  which govern the
 transport of sample into the plasma, sample conversion processes in the plasma, and
 the transmission of ions through the plasma-mass spectrometer interface.  These
 interferences may result in differences between instrument responses for the sample
 and the calibration standards. Physical interferences may occur in the transfer of
 solution to the nebulizer (e.g., viscosity effects), at the point of aerosol formation and
 transport to the plasma (e.g., surface tension), or during excitation and ionization
processes within the plasma itself. High levels of dissolved solids hi the sample may
contribute deposits of material on the  extraction cone, skimmer cone, or both, reducing
the effective diameter of the orifices and therefore ion transmission. Dissolved solids
levels not exceeding 0.2% (w/v) have been recommended (Reference 13) to reduce
such effects. Internal standardization may  be effectively used to compensate for many
Draft, January 1996

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Method 1638
               physical interference effects (Reference 16). Internal standards ideally should have
               analytical behavior similar to the elements being determined.

       445   Memory interferences—Result when isotopes of elements hi a previous sample
               contribute to the signals measured hi a new sample. Memory effects can result from
               sample deposition on the sampler and skimmer cones, and from the buildup of sample
               material in the plasma torch and spray chamber. The  site where these effects occur is
               dependent on the element and can be minimized by flushing the system with a rinse
               blank between samples (Section 7.6.3). The possibility of memory interferences
               should be recognized within an analytical run and suitable rinse times  should be used
               to reduce them.  The rinse times necessary for a particular element should be estimated
               before analysis.  This may be achieved by  aspirating a standard containing elements
               corresponding to ten times the upper end of the linear range for a normal sample
               analysis period, followed by analysis of the rinse blank at designated intervals. The
               length of time required to reduce analyte signals below the minimum level (ML)
               should be noted.  Memory interferences may also be assessed within an  analytical run
               by using a rrjinimum of three replicate integrations for data acquisition.  If the
               integrated signal values drop consecutively, the analyst should be alerted to the
               possibility of a memory effect, and should examine the analyte concentration m the
               previous sample to identify if this was high.  If a memory interference is suspected,
               the sample should be reanalyzed after a long rinse period.

 5.0   Safety

 5 1     The toxicity or carcinogenicity of reagents used in this method have not been fully established.
        Each chemical should be regarded as a potential health hazard and exposure to these
        compounds should be as low as reasonably achievable.

        511   Each laboratory is responsible for maintaining  a current awareness file of OSHA
               regulations for the safe handling of the chemicals specified in this method (References
               17-20).  A reference file of material safety data sheets (MSDSs)  should also be
               available to all personnel involved hi the chemical analysis. It is also suggested that
               the laboratory perform personal hygiene monitoring of each analyst who uses this
               method and that the results of this monitoring  be made available to the  analyst.  The
               references and bibliography at the end of Reference 20 are particularly comprehensive
               hi dealing with the general subject of laboratory safety.

        512  Concentrated nitric and hydrochloric acids present various hazards and are moderately
               toxic and extremely irritating to skin and mucus membranes.  Use these reagents in a
               fume hood whenever possible and if eye or skin contact occurs, flush with large
               volumes of water. Always wear protective clothing and safety glasses or a shield for
               eye protection, and observe proper mixing when working with these reagents.

  52   The acidification of samples containing reactive materials may result hi the release of toxic
        gases, such as cyanides or sulfides. Acidification of samples should be done in a fume hood.

  5.3   All personnel handling environmental samples known to contain or to have been hi contact
        with human waste should be immunized against known disease-causative agents.
                                                                               Draft, January 1996

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                                                                                    Method 1638
 5.4    Analytical plasma sources emit radiofrequency radiation in addition to intense UV radiation.
        Suitable precautions should be taken to protect personnel from such hazards. The inductively
        coupled plasma should only be viewed with proper eye protection from UV emissions.

 6.0   Apparatus, Equipment, and Supplies


        Disclaimer:  The mention of trade names or commercial products in this method is for
        illustrative purposes only and does not constitute endorsement or recommendation for use by
        the Environmental Protection Agency.  Equivalent performance may be achievable using
        apparatus and materials other than those suggested here.  Demonstration of equivalent
        performance is the responsibility of the laboratory.

 6.1    Facility

        6.1.1    Clean room—Class 100, 200-ft2 minimum, with down-flow, positive-pressure
                ventilation, air-lock entrances, and pass-through doors.

                6.1.1.1 Construction materials—Nonmetallic, preferably plastic sheeting attached
                      without metal fasteners. If painted, paints that do not contain the metal(s) of
                      interest should be used.

                6.1.1.2 Adhesive mats—for use at entry points to control dust and dirt from shoes.

        6.1.2   Fume hoods—nonmetallic, two minimum, with one installed internal to the clean
               room.

        6.1.3   Clean benches—class 100, one installed in the clean room; the other adjacent to the
               analytical instrument(s) for preparation of samples and standards.

 6.2 Inductively coupled plasma mass spectrometer:

        6.2.1   Instrument capable of scanning the mass range 5-250 amu with a minimum resolution
               capability of 1 amu peak width at 5% peak height. Instrument may be fitted with a
               conventional or extended dynamic range detection system.

        6.2.2   Radio-frequency generator compliant with FCC regulations.

        6.2.3   Argon gas supply—High-purity grade (99.99%). When analyses are conducted
               frequently, liquid argon is more economical and requires less frequent replacement of
               tanks than compressed argon in conventional cylinders (Section 4.1.3).

        6.2.4   A variable-speed peristaltic pump is required for solution delivery to the nebulizer.

        6.2.5   A mass-flow controller on the nebulizer gas supply is required.  A water-cooled spray
               chamber may be of benefit hi reducing some types of interferences (e.g., from
               polyatomic oxide species).

        6.2.6   If an electron multiplier detector is being used, precautions should be taken, where
               necessary, to prevent exposure to high ion flux. Otherwise changes in instrument
Draft, January 1996

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Method 1638
               response or damage to the multiplier may result. Samples having high concentrations
               of elements beyond the linear range of the instrument and with isotopes falling within
               scanning windows should be diluted before analysis.

6.3     Analytical balance—with capability to measure to 0.1 mg, for use in weighing solids and for
        preparing standards.

6.4     Temperature adjustable hot plate—capable of maintaining a temperature of 95°C.

6.5     Centrifuge with guard bowl, electric timer, and brake (optional).

6.6     Drying oven—gravity convection, with thermostatic control capable of maintaining 105°C (±
        5°C).

6.7     Alkaline detergent—Liquinox®, Alconox®, or equivalent.

6.8     pH meter or pH paper.

6.9     Labware—For determination of trace levels of elements, contamination and loss are of prime
        consideration.  Potential contamination sources include improperly cleaned laboratory
        apparatus and general contamination within the laboratory environment from dust, etc. A
        clean laboratory work area should be designated for trace element sample handling.  Sample
        containers can introduce positive and negative errors in the determination of trace elements by
        (1) contributing contaminants through surface desorption or leaching, and (2) depleting element
        concentrations through adsorption processes.  All labware must be metal-free. Suitable
        construction materials are fluoropolymer (FEP, PTFE), conventional or linear polyethylene,
        polycarbonate, and polypropylene.  Fluoropolymer should be used when samples are to be
        analyzed for mercury. All labware should be cleaned according to the procedure in Section
        11.4.  Gloves, plastic wrap, storage bags, and filters may all be used new without additional
        cleaning unless results of the equipment blank pinpoint any of these materials as a source of
        contamination.  In this case, either an alternate supplier must be obtained or the materials must
        be cleaned.
        NOTE: Chromic acid must not be used for cleaning glassware.    	

        6.9.1  Volumetric flasks, graduated cylinders, funnels and centrifuge tubes.

        6.9.2  Assorted calibrated pipettes.

        6.9.3  Beakers—fluoropolymer (or other suitable material), 250-mL with fluoropolymer
               covers.

        6.9.4  Storage bottles—Narrow-mouth, fluoropolymer with fluoropolymer screw closure, 125-
               to 250-mL capacities.

        6.9.5  Wash bottle—One-piece stem fluoropolymer, with screw closure, 125-mL capacity.
 10
                                                                               Draft, January 1996

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  	.	 	Method 2638


         6.9.6   Tongs—For removal of Apparatus from acid baths.  Coated metal tongs may not be
                used.

         6.9.7   Gloves—clean, nontalc polyethylene, latex, or vinyl; various lengths. Heavy gloves
                should be worn when working in acid baths since baths will contain hot, strong acids.

         6.9.8   Buckets or basins—5- to 50-L capacity, for acid soaking of the Apparatus.

         6.9.9   Brushes—Nonmetallic, for scrubbing Apparatus.

         6.9.10  Storage bags—Clean, zip-type, nonvented, colorless polyethylene (various sizes) for
                storage of Apparatus.

         6.9.11  Plastic wrap—Clean, colorless polyethylene for storage of Apparatus.

 6.10    Sampling Equipment—The sampling team may contract with the laboratory or a cleaning
         facility that is responsible for cleaning, storing, and shipping all sampling devices, sample
         bottles, filtration equipment, and all other Apparatus used for the collection of ambient water
         samples.  Before shipping the equipment to the field site, the laboratory or facility must
         generate an acceptable equipment blank (Section 9.6.3) to demonstrate that the sampling
         equipment is free from contamination.

         6.10.1  Sampling Devices—Before ambient water samples are collected, consideration should
                be given to the type of sample to be collected and the devices to be used (grab,
                surface, or subsurface samplers).  The laboratory or cleaning facility must clean all
                devices used for sample collection.  Various types of samplers are described in the
                Sampling Method.  Cleaned sampling devices should be stored in polyethylene bags or
                wrap.

        6.10.2  Sample bottles—Fluoropolymer, conventional or linear polyethylene, polycarbonate, or
                polypropylene; 500-mL with lids. Cleaned sample bottles should be filled with  0.1%
                HC1 (v/v) until use.
        NOTE: If mercury is a target analyte, fluoropolymer or glass bottles must be used.

        6.10.3  Filtration Apparatus

               6.10.3.1        Filter—Gehnan Supor 0.45-um, 15-mm diameter capsule filter
                              (Gelman 12175, or equivalent)

               6.10.3.2        Peristaltic pump—115-V a.c., 12-V d.c., internal battery, variable-
                              speed, single-head (Cole-Farmer, portable, "Masterflex L/S," Catalog
                              No. H-07570-10 drive with Quick Load pump head, Catalog No. H-
                              07021-24, or equivalent).

               6.10.3.3        Tubing for use with peristaltic pump—styrene/ethylene/butylene/
                              silicone (SEES) resin, approximately 3/8-in Ld. by approx 3 ft (Cole-
                             Parmer size 18, Catalog No. G-06464-18, or approximately 1/4-in i.d.,
Draft, January 1996
                                                                                             11

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Method 1638
                             Cole-Farmer size 17, Catalog. No. G-06464-17, or equivalent). Tubing
                             is cleaned by soaking in 5-10% HC1 solution for 8-24 h, rinsing with
                             reagent water in a clean bench in a clean room, and drying in the clean
                             bench by purging with metal-free air or nitrogen.  After drying, the
                             tubing is double-bagged in clear polyethylene bags, serialized with a
                             unique number, and stored until use.
7.0    Reagents and Standards
        Reagents may contain elemental impurities that might affect the integrity of analytical data.
        Because of the high sensitivity of ICP-MS, high-purity reagents should be used. Each reagent
        lot should be tested for the metals of interest by diluting and analyzing an aliquot from the lot
        using the techniques and instrumentation to be used for analysis of samples.  The lot will be
        acceptable if the concentration of the metal of interest is below the MDL listed in this method.
        All acids used for this method must be of ultra high-purity grade. Suitable acids are available
        from a number of manufacturers or may be prepared by sub-boiling distillation. Nitric acid is
        preferred for ICP-MS to minimize polyatomic ion interferences. Several polyatomic ion
        interferences result when hydrochloric acid is used (Table 3); however, hydrochloric acid is
        required to maintain stability in  solutions containing antimony and silver. When hydrochloric
        acid is used, corrections for the  chloride polyatomic ion interferences must be applied to all
        data.

 7.1     Reagents for cleaning Apparatus, sample bottle storage, and sample preservation.

        7.1.1   Nitric acid—concentrated (sp gr 1.41), Seastar or equivalent

        7.1.2  Nitric acid (1+1)—Add  500 mL cone, nitric acid to 400 mL of regent water and dilute
               to 1 L.

        7.1.3  Nitric acid (1+9)—Add 100 mL cone, nitric acid to 400 mL of reagent water and
               dilute to 1 L.

        7.1.4  Hydrochloric acid—concentrated (sp gr 1.19).

        7.1.5  Hydrochloric acid (1+1)—Add 500  mL concentrated hydrochloric acid to 400 mL of
                reagent water and dilute to 1 L.

        7.1.6   Hydrochloric acid (1+4)—Add 200 mL concentrated hydrochloric acid to 400 mL of
                reagent water and dilute to 1 L.

        7.1.7   Hydrochloric acid (HC1)—IN trace metal grade.

        7.1.8   Hydrochloric acid (HC1)—10% wt, trace metal grade.

        7.1.9   Hydrochloric acid (HC1>—1% wt, trace metal grade.

        7.1.10 Hydrochloric acid (HC1)—0.5% (v/v), trace metal grade.
  12
                                                                               Draft, January 1996

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                                                                                      Method 1638
  7.2
 7.3
7.1.11  Hydrochloric acid (HC1)—0.1% (v/v) ultrapure grade.

7.1.12  Tartaric acid (CASRN 87-69-4).

Reagent water—Water demonstrated to be free from the metal(s) of interest and potentially
interfering substances at the MDL for that metal listed in Table 1.  Prepared by distillation,
deionization, reverse osmosis, anodic/cathodic stripping voltammetry, or other technique that
removes the metal(s) and potential interferent(s).

Stock standard solutions—Stock standards may be purchased from a  reputable commercial
source or prepared from ultra high-purity grade chemicals or metals (99.99-99.999% pure).
All salts should be dried for 1 h at 105°C, unless otherwise specified. Stock solutions should
be stored in FEP bottles.  Replace stock standards when succeeding dilutions for preparation of
the multielement stock standards can not be verified.
         CAUTION:  Many metal salts are extremely toxic if inhaled or swallowed.  Wash
         hands thoroughly after handling.

         The following procedures may be used for preparing standard stock solutions:
        NOTE: Some metals, particularly those which form surface oxides, require cleaning
        prior to being weighed.  This may be achieved by pickling the surface of the metal in
        acid. An amount in excess of the desired weight should be pickled repeatedly, rinsed
        with water, dried, and weighed until the desired weight is achieved.

        7.3.1  Antimony solution, stock 1 mL = 1000 ug Sb—Dissolve 0.100 g antimony powder in
               2 mL (1+1) nitric acid and 0.5 mL concentrated hydrochloric acid, heating to effect
               solution. Cool, add 20 mL reagent water and 0.15-g tartaric acid.  Warm the solution
               to dissolve the white precipitate. Cool and dilute to  100 mL with reagent water.
        7.3.2
        7.3.3
       Beryllium solution, stock 1 mL - 1000 ug Be—Dissolve 1.965 g  BeSO^HjO (DO
       NOT DRY) in 50 mL reagent water. Add 1 mL concentrated nitric acid. Dilute to
       100 mL with reagent water.

       Bismuth solution, stock 1 mL = 1000 pg Bi—Dissolve 0.1115 g Bif)3 in 5 mL
       concentrated nitric acid. Heat to effect solution. Cool and dilute to 100 mL with
       reagent water.
        7.3.4   Cadmium solution, stock 1 mL = 1000 pg Cd—Pickle cadmium metal in (1+9) nitric
               acid to an exact weight of 0.100 g. Dissolve in 5 mL (1+1) nitric acid, heating to
               effect solution. Cool and dilute to  100 mL with reagent water.

        7.3.5   Cobalt solution, stock 1 mL = 1000 pg Co—Pickle cobalt metal in (1+9) nitric acid to
               an exact weight of 0.100 g. Dissolve in 5 mL (1+1) nitric acid, heating to effect
               solution. Cool and dilute to 100 mL with reagent water.
Draft, January 1996
                                                                                             13

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Method 1638
  7.4
736   Copper solution, stock 1 mL - 1000 ug Cu—Pickle copper metal in (1+9) nitric acid
       to an exact weight of 0.100 g. Dissolve in 5 mL (1+1) nitric acid, heating to effect
       solution. Cool and dilute to 100 mL with reagent water.

737   Indium solution, stock 1 mL - 1000 ug In—Pickle indium metal in (1+1) nitric acid to
       an exact weight of 0.100 g. Dissolve in 10 mL (1+1) nitric acid, heating to effect
       solution. Cool and dilute to 100 mL with reagent water.

7.3.8   Lead solution, stock 1  mL =  1000 ug Pb—Dissolve 0.1599 g PbNO3 in 5 mL (1+1)
       nitric acid.  Dilute to 100 mL with reagent water.

739   Magnesium solution, stock 1  mL = 1000 ug Mg—Dissolve 0.1658 g MgO in 10 mL
  ' '   (1+1) nitric acid, heating to effect solution. Cool and dilute to 100 mL with reagent
       water.

7.3.10 Nickel solution, stock 1 mL = 1000 ug Ni-Dissolve 0.100 g nickel powder^in 5 mL
        concentrated nitric acid, heating to effect solution. Cool and dilute to 100 mL with
       reagent water.

7311  Scandium solution, stock 1 mL = 1000 ug Sc—Dissolve 0.1534 g Sc2O3 in 5 mL
        (1+1) nitric acid, heating to effect solution. Cool and dilute to 100 mL with reagent
        water.

7.3.12  Selenium solution, stock 1 mL = 1000 ug Se—Dissolve 0.1405 g SeO2 in 20 mL
        reagent water. Dilute to 100 mL with reagent water.

 7 3.13  Silver solution, stock  1 mL = 1000 ug Ag-Dissolve 0.100 g silver metal in 5 mL
        (1+1) nitric acid, heating to effect solution. Cool and dilute to 100 mL with reagent
        water. Store in dark container.

 7 3.14 Terbium solution, stock 1 mL = 1000 ug Tb—Dissolve 0.1176 g Tbp, in 5 mL
        concentrated nitric acid, heating to effect solution.  Cool and dilute to 100 mL with
        reagent water.

 7 3 15 ThaUium solution, stock 1 mL = 1000 ug Tl-Dissolve 0.1303 g T1NO3 in a solution
        mixture of 10 mL reagent water and 1 mL concentrated nitric acid. Dilute to 100 mL
        with reagent water.

  7 3 16 Yttrium solution, stock 1 mL = 1000 ug Y—Dissolve 0.1270 g Y2O3 in 5 mL (1+1)
        nitric  acid, heating to effect solution.  Cool and dilute to 100 mL with reagent water.

  7 3 17 Zinc solution, stock 1 mL - 1000 ug Zn—Pickle zinc metal in (1+9) nitric acid to an
         exact weight of 0.100 g. Dissolve in 5 mL (1+1)  nitric acid, heating to effect
         solution. Cool and dilute to 100 mL with reagent water.

  Multielement stock standard  solutions—Care must be taken in the preparation of multielement
  stock standards so that the elements are compatible and stable.  Originating element stocks
  should be checked for the presence of impurities which might influence the accuracy of the
  standard Freshly prepared standards should be transferred to acid-cleaned, not previously
  14
                                                                               Draft, January 1996

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                                                                                      Method 1638
         used, FEP fluorocarbon bottles for storage and monitored periodically for stability.  The
         following combinations of elements are suggested:
                           Standard Solution A
                         Antimony      Nickel
                         Cadmium     Selenium
                          Copper      Thallium
                           Lead          Zinc
                                              Standard Solution B
                                                    Silver
 7.5
 7.6
 Except for selenium, multielement stock standard solutions A and B (1 mL = 10 pg) may be
 prepared by diluting  1.0 mL of each single element stock standard in the combination list to
 100 mL with reagent water containing 1% (v/v) nitric acid.  For selenium in solution A, an
 aliquot of 5.0 mL of the stock standard should be diluted to the specified 100 mL (1 ml = 50
 pg Se).  Replace the multielement stock standards when succeeding dilutions for preparation of
 the calibration standards cannot be verified with the quality control sample.

 7.4.1   Preparation of calibration standards—Fresh multielement calibration standards  should
        be prepared every two weeks or as needed.  Dilute each of the stock multielement
        standard solutions A and B to levels appropriate to the operating range of the
        instrument using reagent water containing 1% (v/v) nitric acid. Calibration standards
        should be prepared at  a minimum of three concentrations, one of which must be at the
        minimum level (Table 1), and another which must be near the upper end of the linear
        dynamic range. It should be noted the selenium concentration is always a factor of 5
        > the other analytes. If the direct addition procedure is being used (Method A, Section
        10.3), add internal standards (Section 7.5) to the calibration standards and store in
        fluoropolymer bottles.  Calibration standards should be verified initially using a quality
        control sample (Section 7.8).

Internal standard stock solution—1 mL = 100 pg.  Dilute 10 mL  of scandium, yttrium, indium,
terbium, and bismuth stock standards (Section 7.3) to 100 mL with reagent water, and  store in
a FEP bottle.  Use this solution concentrate for addition to blanks, calibration standards and
samples, or dilute  by an appropriate amount using 1% (v/v) nitric acid, if the internal standards
are being added by peristaltic pump (Method B, Section 10.3).

Blanks—The laboratory should prepare the following types of blanks.  A calibration blank is
used to establish the analytical calibration curve; the laboratory (method) blank is used to
assess possible contamination from the sample preparation procedure and to assess spectral
background; and the rinse blank is used  to flush the instrument between samples to reduce
memory interferences. In addition to these blanks, the laboratory may  be required to analyze
field blanks (Section 9.6.2) and equipment blanks (Section 9.6.3).
        7.6.1
       7.6.2
       Calibration blank—Consists of 1% (v/v) nitric acid in reagent water.  If the direct
       addition procedure (Method A, Section 10.3) is being used, add internal standards.

       Laboratory blank—Must contain all the reagents in the same volumes as used in
       processing the samples. The laboratory blank must be carried through the same entire
Draft, January 1996
                                                                                             15

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Method 1638
               preparation scheme as the samples including digestion, when applicable (Section
               9.6.1).  If the direct addition procedure (Method A, Section 10.3) is being used, add
               internal standards to the solution after preparation is complete.

       7.6.3   Rinse blank—Consists of 2% (v/v) nitric acid in reagent water.

77    Tuning solution—This solution is used for instrument tuning and mass calibration prior to  '
       analysis  The solution is prepared by mixing beryllium, magnesium, cobalt, radium, and lead
       stock solutions (Section 7.3) in 1% (v/v) nitric acid to produce a concentration of 100 ug/L of
       each element.  Internal standards are not added to this solution. (Depending on the sensitivity
       of the instrument,  this solution may need to be diluted 10-fold.)

7 8    Quality control sample (QCS)—Hie QCS should be obtained from a source outside the
       laboratory  The concentration of the QCS solution analyzed will depend on the sensitivity of
       the instrument. To prepare the QCS, dilute an appropriate aliquot of analytes to a concentration
       <: 100 ug/L in  1% (v/v) nitric acid.  Because of lower sensitivity, selenium may be diluted to a
        concentration of < 500 ug/L. If the direct addition procedure (Method A, Section 10.3) is
       being used, add internal standards after dilution, mix, and store in a FEP bottle. The QCS
        should be analyzed as needed to meet data quality needs and a fresh solution should be
       prepared quarterly or more frequently as  needed.

 7 9     Ongoing precision and recovery (OPR) Sample—To an aliquot of reagent water, add aliquots
        from multielement stock standards A and B (Section 7.4) to prepare the OPR.  The OPR must
        be carried through the same entire preparation scheme as the samples including sample
        digestion, when applicable (Section 9.7). If the direct addition procedure (Method A, Section
        10.3) is being  used, add internal standards to this solution after preparation has been
        completed.

 8.0   Sample Collection, Filtration, Preservation, and Storage

 8 1    Before an aqueous sample is collected, consideration should be given to the type of data
        required (i e., dissolved or total recoverable), so that appropriate preservation and pretreatment
        steps can be taken.  The pH of all aqueous samples must be tested immediately before
        aliquotting for processing or direct analysis to ensure the sample has been properly preserved.
        If properly acid-preserved, the sample can be held up to six months before analysis.

  8.2    Sample collection—Samples are collected as described in the Sampling Method.

  8 3    Sample filtration—For dissolved metals, samples and field blanks are filtered through a 0.45-
        um capsule filter at the field site. Filtering procedures are described in the Sampling Method.
        For the determination of total recoverable elements, samples are not filtered but should be
        preserved according to the procedures hi Section 8.4.

  8 4     Sample preservation—Preservation of samples and field blanks for both dissolved and total
         recoverable elements may be performed in the field at time of collection or in the laboratory.
         However, to avoid the hazards of strong acids in the field and transport restrictions, to
         minimize the potential for sample contamination, and to expedite field operations, the sampling
         team may prefer to ship the samples to the laboratory within two weeks of collection.
         Samples and  field blanks should be preserved at the laboratory immediately upon receipt  For
  16
                                                                              Draft, January 1996

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       	Method 1638


         all metals, preservation involves the addition of 10% HNO3 (Section 7.1.3) to bring the sample
         to pH <2. For samples received at neutral pH, approx 5 mL of 10% HNO3 per liter will be
         required.

         8.4.1   Wearing clean gloves, remove the cap from the sample bottle, add the volume of
                reagent grade acid that will bring the pH to <2, and recap the bottle immediately. If
                the bottle is full, withdraw the necessary volume using a precleaned pipet and then add
                the acid.  Record the volume withdrawn and the amount of acid used.
        NOTE: Do not dip pH paper or a pH meter into the sample; remove a small aliquot
        •with a clean pipet and test the aliquot.  When the nature of the sample is either
        unknown or known to be hazardous, acidification should be done in a fume hood. See
        Section 5.2.
        8.4.2  Store the preserved sample for a minimum of 48 h at 0-4°C to allow the acid to
               completely dissolve the metal(s) adsorbed on the container walls. The sample pH
               should be verified as <2 immediately before withdrawing an aliquot for processing or
               direct analysis.  If, for some reason such as high alkalinity, the sample pH is verified
               to be >2, more acid must be added and the sample held for sixteen hours until verified
               tobepH<2.  See Section 8.1.

        8.4.3   With each sample batch, preserve a method blank and an OPR sample in the same way
               as the sample(s).

        8.4.4   Sample bottles should be stored in polyethylene bags at 0-4 °C until analysis.
 9.0   Quality Assurance/Quality Control

 9.1     Each laboratory that uses this method is required to operate a formal quality assurance
        program (Reference 21).  The minimum requirements of this program consist of an initial
        demonstration of laboratory capability, analysis of samples spiked with metals of interest to
        evaluate and document data quality, and analysis of standards and blanks as tests of continued
        performance.  Laboratory performance is compared to established performance criteria to
        determine that results of the analysis meet the performance characteristics of the method.
        9.1.1
        9.1.2
The analyst shall make an initial demonstration of the ability to generate acceptable
accuracy and precision with this method. This ability is established as described in
Section 9.2.

In recognition of advances that are occurring in analytical technology, the analyst is
permitted to exercise certain options to eliminate interferences or lower the costs of
measurements. These options include alternate digestion, concentration, and cleanup
procedures, and changes in instrumentation. Alternate determinative techniques, such
as the substitution of a colorimetric technique or  changes that degrade method
performance,  are not allowed. If an analytical technique other than the techniques
Draft, January 1996
                                                                                           17

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Method 1638
               specified in the method is used, that technique must have a specificity equal to or
               better than the specificity of the techniques in the method for the analytes of interest.

               9 1 2.1 Each time the method is modified, the analyst is required to repeat the
                      procedure in Section 9.2. If the detection limit of the method will be affected
                      by the change, the laboratory is required to demonstrate that the MDL (40
                      CFR Part 136, Appendix B) is lower than the MDL for that analyte in this
                      method, or one-third the regulatory compliance level, whichever is higher.  If
                      calibration will be affected by the change, the analyst must recalibrate the
                      instrument according to Section 10.

               9.1.2.2 The laboratory is required to maintain records of modifications made to this
                      method. These records include the following, at a minimum:

                      9.1.2.2.1      The names, titles, addresses, and telephone numbers of the
                                     analyses) who performed the analyses and modification, and of
                                     the quality control officer who witnessed and will verify the
                                     analyses and modification.

                      9.1.2.2.2      A listing of metals measured, by name and CAS Registry
                                     number.

                       9.1.2.2.3      A narrative stating reason(s) for the modification(s).

                       9.1.2.2.4      Results from all  quality control (QQ tests comparing the
                                     modified method to this method, including:

                                      (a)     Calibration.
                                      (b)     Calibration verification.
                                      (c)     Initial precision and recovery (Section 9.2).
                                      (d)     Analysis of blanks.
                                      (e)     Accuracy assessment.

                       9.1.2.2.5      Data that will allow an independent reviewer to validate each
                                      determination by tracing the instrument output (peak height,
                                      area, or other signal) to the final result. These data are to
                                      include, where possible:

                                      (a)      Sample  numbers and other identifiers.
                                      (b)     Digestion/preparation or extraction dates.
                                      (c)      Analysis dates and times.
                                      (d)     Analysis sequence/run chronology.
                                      (e)     Sample  weight or volume.
                                      (f)      Volume prior to extraction/concentration step.
                                      (g)     Volume after each extraction/concentration step.
                                      (h)     Final volume prior to analysis.
                                      (i)      Injection volume.
                                      (j)      Dilution data, differentiating between dilution of a
                                              sample  or extract
  18
                                                                                 Draft, January 1996

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                                                                                      Method 1638
                                      (k)     Instrument and operating conditions (make, model,
                                              revision, modifications).
                                      (1)      Sample introduction system (ultrasonic nebulizer, flow
                                              injection system, etc).
                                      (m)     Operating conditions (background corrections,
                                              temperature program, flow rates, etc).
                                      (n)     Detector (type, operating conditions, etc).
                                      (o)     Mass spectra, printer tapes, and other recordings of raw
                                              data.
                                      (p)     Quantitation reports, data system outputs, and other
                                              data to link raw data to results reported.

        9.1.3   Analyses of blanks are required to demonstrate freedom from contamination. The
                required types, procedures, and criteria for analysis of blanks are described in Section
                9.6.

        9.1.4   The laboratory shall spike at least 10% of the samples with the metal(s) of interest to
                monitor method performance.  This test is described in Section 9.3 of this method.
                When results of these spikes indicate atypical method performance for samples, an
                alternative extraction or cleanup technique must be used to bring method performance
                within acceptable limits.  If method performance for spikes cannot be brought within
                the limits given in this method, the result may not be reported for regulatory
                compliance purposes.

        9.1.5   The laboratory shall, on an ongoing basis,  demonstrate through calibration verification
                and through analysis of the ongoing precision and recovery aliquot that the analytical
                system is hi control.  These procedures are described in Sections 10.2 and 9.7 of this
                method.

        9.1.6   The laboratory shall maintain records to define the quality of data that are generated.
                Development of accuracy statements is described in Section 9.3.4.

 9.2     Initial demonstration of laboratory capability

        9.2.1    Method detection limit—To establish the ability to detect the trace metals of interest,
                the analyst shall determine the  MDL for each  analyte according to the procedure in 40
                CFR  136, Appendix B using the apparatus, reagents, and standards that will be  used hi
                the practice of this method. The laboratory must produce an MDL that is less than or
                equal to the MDL listed hi Table 1, or one-third the regulatory compliance limit,
                whichever is greater.  MDLs should be determined when a new operator begins work
                or whenever, hi the judgment of the analyst, a change hi instrument hardware or
                operating  conditions would dictate that they be redetermined.

        9.2.2    Initial precision and recovery (IPR)—To establish the ability to generate acceptable
               precision and recovery, the analyst shall perform the following operations.

               9.2.2.1 Analyze four aliquots of reagent water spiked with the metal(s) of interest at
                      2-3 times the ML (Table 1), according to the procedures hi Section 12.  All
Draft, January 1996
19

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Method 1638
                      digestion, extraction, and concentration steps, and the containers, labware, and
                      reagents that will be used with samples, must be used in this test.

               9.2.2.2 Using results of the set of four analyses, compute the average percent recovery
                      (X) for the metal(s) in each aliquot and the standard deviation of the
                      recovery(ies) for each metal.

               9.2.2.3 For each metal, compare s and X with the corresponding limits for initial
                      precision and recovery in Table 2.  If s and X for all metal(s) meet the
                      acceptance criteria, system performance is acceptable and analysis of blanks
                      and samples may begin. If, however, any individual s exceeds the precision
                      limit or any individual X falls outside the range for accuracy, system
                      performance is unacceptable for that metal.  Correct the problem and repeat the
                      test (Section 9.2.2.1).

        9.2.3   Linear calibration ranges—Linear calibration ranges are primarily detector limited.
               The upper limit of the linear calibration range should be established for each analyte
               by determining .the signal responses from a minimum of three different concentration
               standards, one of which is close to the upper limit of the linear range.  Care should be
               taken to avoid potential damage to the detector during this process. The linear
               calibration range that may be used for the analysis of samples should be judged by the
               analyst from the resulting data. The upper limit should be an observed signal no more
               than 10% below the level extrapolated from lower standards. Determined sample
               analyte concentrations that are greater than 90% of the determined upper limit must be
               diluted and reanalyzed.  The upper limits should be verified whenever, hi  the judgment
               of the analyst, a  change in analytical performance caused by either a change in
               instrument hardware or operating conditions would dictate they be redetermined.

        9.2.4   Quality control sample (QCS)—When beginning the use of this method, quarterly or
               as required to meet data quality needs, verify the calibration standards and acceptable
               instrument performance with the preparation and analyses of a QCS (Section 7.8). To
               verify the calibration standards the determined mean concentration from 3 analyses of
               the QCS must be within ±10% of the stated QCS value.  If the QCS is not within the
               required limits, an immediate second analysis of the QCS is recommended to confirm
               unacceptable performance.  If the calibration standards, acceptable instrument
               performance, or  both cannot be verified, the source of the problem must be identified
               and corrected before proceeding with further analyses.

 9.3     Method accuracy—To assess the performance of the method on a given sample matrix, the
        laboratory must perform matrix spike (MS) and matrix spike duplicate (MSD) sample analyses
        on 10% of the samples from each site being monitored, or at least one MS sample analysis
        and one MSD sample analysis must be performed for each sample batch (samples collected
        from the same site at the same time, to a maximum of 10 samples), whichever is  more
        frequent  Blanks (e.g., field blanks) may not be used for MS/MSD analysis.

        9.3.1   The concentration of the MS and MSD is determined as follows:

               9.3.1.1  If, as in compliance monitoring, the concentration of a specific metal hi the
                       sample is being checked against a regulatory concentration limit, the spike
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                                                                                     Method 1638
                       must be at that limit or at 1-5 times the background concentration, whichever
                       is greater.

               9.3.1.2 If the concentration is not being checked against a regulatory limit, the
                       concentration must be at 1-5 times the background concentration or at 1-5
                       times the ML in Table 1, whichever is greater.

        9.3.2  Assessing spike recovery

               9.3.2.1  Determine the background concentration (B) of each metal by analyzing one
                       sample aliquot according to the procedure in Section 12.

               9.3.2.2  If necessary, prepare a QC check sample concentrate that will produce the
                       appropriate level (Section 9.3.1) in the sample when the concentrate is added.

               9.3.2.3  Spike a second sample aliquot with the QC check sample concentrate and
                       analyze it to determine the concentration after spiking (A) of each metal.

               9.3.2.4  Calculate each percent recovery (P) as 100(A-B)/T, where T is the known true
                       value of the spike.

        9.3.3   Compare the percent recovery (P) for each metal with the corresponding QC
               acceptance criteria found in Table 2. If any individual P falls outside the designated
               range for recovery, that metal has failed the acceptance criteria.

               9.3.3.1  For a metal that has failed the acceptance criteria, analyze the ongoing
                       precision and recovery standard (Section 9.7).  If the OPR is within its
                       respective limit for the metal(s) that failed (Table 2), the analytical system is in
                       control and the problem can be attributed to the sample matrix.

               9.3.3.2  For samples that exhibit matrix problems, further isolate the metal(s) from the
                       sample matrix using dilution, chelation, extraction,  concentration, hydride
                       generation, or other means, and repeat the accuracy test (Section 9.3.2).

               9.3.3.3  If the recovery for the metal remains outside the acceptance criteria, the
                       analytical result for that metal in the unspiked  sample is suspect and may not
                       be reported for regulatory compliance purposes.

        9.3.4   Recovery for samples should be assessed and records maintained.

               9.3.4.1 After the analysis of five samples of a given matrix type (river water, lake
                      water, etc.) for which the metal(s) pass the tests in Section 9.3.3, compute the
                      average percent recovery (R) and the standard deviation of the percent
                      recovery (SR) for the metal(s). Express the accuracy assessment as a percent
                      recovery interval from R - 2SR to R + 2SR for each matrix.  For example, if
                      R = 90% and SR - 10% for five analyses of river water, the accuracy interval
                      is expressed as 70-110%.
Draft, January 1996
21

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Method 1638
               9.3.4.2 Update the accuracy assessment for each metal in each matrix regularly (e.g.,
                      after each five to ten new measurements).

9.4    Precision of matrix spike and duplicate

       9.4.1   Calculate the relative percent difference (RPD) between the MS and MSD per the
               equation below using the concentrations found in the MS and MSD.  Do not use the
               recoveries calculated in Section 9.3.2.4 for this calculation because the RPD is inflated
               when the background concentration is near the spike concentration.
                                                 (DI+Z>2)/2
                      Where:
                      Dl = concentration of the analyte in the MS sample
                      D2 = concentration of the analyte in the MSD sample
        942   The relative percent difference between the matrix spike and the matrix spike duplicate
               must be less than 20%.  If this criterion is not met, the analytical system is judged to
               be out of control.  In this case, correct the problem and reanalyze all samples in the
               sample batch associated with the MS/MSD which failed the RPD test.

 9 5    Internal standards responses—The analyst is expected to monitor the responses from the
        internal standards throughout the sample batch being analyzed. Ratios of the internal standards
        responses against each other should also be monitored routinely. This information may be
        used to detect potential problems caused by mass dependent drift, errors incurred m adding the
        internal standards, or increases in the concentrations of individual internal standards caused by
        background contributions from the sample.  The absolute response of  any one internal standard
        must not deviate more than 60-125% of the original response in the calibration blank. If
        deviations greater than these are observed, flush the instrument with the rinse blank and
        monitor the responses in the calibration blank. If the responses of the internal standards are
        now within the limit, take a fresh aliquot of the sample, dilute by a further factor of two, add
        the internal standards, and reanalyze. If, after flushing, the responses of the internal standards
        in the calibration blank are out of limits, terminate the analysis and determine the cause of the
        drift.   Possible causes of drift may be a partially blocked sampling cone or a change in the
        timing condition of the instrument.

 9.6    Blanks—Blanks are analyzed to demonstrate freedom from contamination.

        9.6.1   Laboratory (method) blank

                9.6.1.1 Prepare a method blank with  each sample batch (samples of the same matrix
                       started through the sample preparation process (Section 12) on the same 12-
                       hour shift, to a maximum of 10 samples).  Analyze the blank immediately after
                       analysis of the OPR (Section 9.7) to demonstrate freedom from contamination.

                9.6.1.2 If the metal of interest or any potentially interfering substance is found hi the
                       .blank at a concentration equal to or greater than the MDL (Table 1), sample
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                                                                                      Method 1638
                       analysis must be halted, the source of the contamination determined, the
                       samples and a new method blank prepared, and the sample batch and fresh
                       method blank reanalyzed.

                9.6.1.3 Alternatively, if a sufficient number of blanks (three minimum) are analyzed to
                       characterize the nature of a blank, the average concentration plus two standard
                       deviations must be less than the regulatory compliance level.

                9.6.1.4 If the result for a single blank remains above the MDL or if the result for the
                       average concentration plus two standard deviations of three or more blanks
                       exceeds the regulatory compliance level, results for samples associated with
                       those blanks may not be reported for regulatory compliance purposes.  Stated
                       another way,  results for all  initial precision and recovery tests (Section 9.2)
                       and all samples must be associated with an uncontaminated method blank
                       before these results may be reported for regulatory compliance purposes.
        9.6.2  Field blank
        9.6.3
9.6.2.1  Analyze the field blank(s) shipped with each set of samples (samples collected
        from the same site at the same time, to a maximum of 10 samples).  Analyze
        the blank immediately before analyzing the samples in the batch.

9.6.2.2  If the metal of interest or any potentially interfering substance is found in the
        field blank at a concentration equal to or greater than the ML (Table 1), or
        greater than one-fifth the level  in the associated sample, whichever is greater,
        then results for associated samples may be the result of contamination and may
        not be reported for regulatory compliance purposes.

9.6.2.3  Alternatively, if a sufficient number of field blanks (3 minimum) are analyzed
        to characterize the nature of the field blank, the average concentration plus two
        standard deviations must be less than the regulatory compliance level or less
        than one-half the level in the associated sample, whichever is greater.

9.6.2.4  If contamination of the field blanks and associated samples is known or
        suspected, the laboratory should communicate this to the sampling team so that
        the source of contamination can be identified and corrective measures taken
        prior to the next sampling event.

Equipment Blanks—Before any sampling equipment is  used at a given  site, the
laboratory or cleaning facility is required to generate equipment blanks  to demonstrate
that the sampling equipment is free from contamination. Two types of equipment
blanks are required:  bottle blanks and sampler check blanks.

9.6.3.1  Bottle blanks—After undergoing appropriate cleaning procedures (Section
        11.4), bottles  should be subjected to conditions  of use to verify  the
        effectiveness of the cleaning procedures. A representative set of sample bottles
        should be filled with reagent water acidified to pH<2 and allowed to  stand for
        a minimum of 24 h. Ideally, the time that the bottles are allowed to stand
        should be as close as possible to the actual time that sample will be in contact
Draft, January 1996
                                                                               23

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Method 1638
                      with the bottle. After standing, the water should be analyzed for any signs of
                      contamination.  If any bottle shows signs of contamination, the problem must
                      be identified, the cleaning procedures corrected or cleaning solutions changed,
                      and all affected bottles recleaned.

               9.6.3.2 Sampler check blanks—Sampler check blanks are generated in the laboratory
                      or at the equipment cleaning contractor's facility by processing reagent water
                      through the sampling devices using the same procedures that are used in the
                      field (see Sampling Method). Therefore, the "clean hands/dirty hands"
                      technique used during field sampling should be followed when preparing
                      sampler check blanks  at the laboratory or cleaning facility.

               9.6.3.2.1        Sampler check blanks are generated by filling a large carboy or other
                              container with reagent  water (Section 7.2) and processing the reagent
                              water through the equipment using the same procedures that are used
                              hi the field (see Sampling Method).  For example, manual grab
                              sampler check blanks are collected by directly submerging a sample
                              bottle into the water, filling the bottle, and capping. Subsurface
                              sampler check blanks are collected by immersing the sampler into the
                              water and pumping water into a  sample container.

               9.6.3.2.2       The sampler check blank must be analyzed using the procedures given
                              hi this method.  If any metal of interest or any potentially interfering
                              substance is detected in the blank, the source of contamination or
                              interference must be identified, and the problem corrected. The
                              equipment must be demonstrated to be free from the metal(s) of
                              interest before the equipment may be used hi the field.

               9.6.3.2.3       Sampler check blanks must be run on all equipment that will be used
                              hi the field. If, for example, samples are to  be collected using both a
                              grab sampling device and a subsurface sampling device, a sampler
                              check blank must be run on both pieces of equipment.

 9.7    Ongoing precision and recovery

        9.7.1   Prepare an ongoing precision and recovery sample (laboratory-fortified method blank)
               identical to  the initial precision and recovery aliquots (Section 9.2) with each sample
               batch (samples of the same matrix started through the sample preparation process
               (Section 12) on the same 12-hour shift, to  a maximum of 10 samples) by spiking an
               aliquot of reagent water with the metal(s) of interest.

        9.7.2  Analyze the OPR sample before analyzing the method blank and  samples from the
               same batch.

        9.7.3  Compute the percent recovery of each metal hi the OPR sample.

        9.7.4  For each metal, compare the concentration to the limits for ongoing recovery hi Table
               2.  If all metals meet the acceptance criteria, system performance is acceptable and
               analysis of  blanks and samples may proceed. If, however, any individual recovery falls
 24
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                                                                                    Method 1638
 9.8
9.9
        outside of the range given, the analytical processes are not being performed properly
        for that metal.  In this event, correct the problem, reprepare the sample batch, and
        repeat the ongoing precision and recovery test (Section 9.7).

9.7.5   Add results that pass the specifications in Section 9.7.4 to initial and previous ongoing
        data for each metal in each matrix. Update QC charts to form a graphic representation
        of continued laboratory performance. Develop a statement of laboratory accuracy for
        each metal in each matrix type by calculating the average percent recovery (R) and the
        standard deviation of percent recovery (SR). Express the accuracy as a recovery
        interval from R - 2SR to R + 2SR. For example, if R = 95% and SR = 5%, the
        accuracy is 85-105%.

The specifications contained in this method can be met if the instrument used is calibrated
properly and then maintained in a calibrated state. A given instrument will provide the most
reproducible results if dedicated to the  settings and conditions required for the analyses of
metals by this method.

Depending on specific program requirements, the laboratory may be required to analyze field
duplicates collected to determine the precision of the sampling technique. The relative percent
difference (RPD) between field duplicates should be less than 20%.  If the RPD of the field
duplicates exceeds 20%, the laboratory should communicate this to the sampling team so that
the source of error can be identified and corrective measures taken before the next sampling
event.
 10.0  Calibration and Standardization

 10.1    Operating conditions—Because of the diversity of instrument hardware, no detailed instrument
        operating conditions are provided.  The analyst is advised to follow the recommended
        operating conditions provided by the manufacturer. The analyst is responsible for verifying
        that the instrument configuration and operating conditions satisfy the quality control
        requirements hi this method.  Table 7 lists instrument operating conditions that may be used as
        a guide for analysts in determining instrument configuration and operating conditions.

 10.2    Precalibration routine—The following precalibration routine should be completed before
        calibrating the instrument until it can be documented with periodic performance data that the
        instrument meets the criteria listed below  without daily tuning.

        10.2.1  Initiate proper operating configuration of instrument and data system. Allow  a period
               of not less than 30 minutes for the instrument to warm up. During this period,
               conduct mass calibration and resolution checks using the tuning solution. Resolution
               at low mass is indicated by magnesium isotopes 24, 25, 26. Resolution at high mass
               is indicated by lead isotopes 206,  207, 208. For good performance adjust spectrometer
               resolution to produce a peak width of approximately 0.75 amu at 5% peak height.
               Adjust mass calibration if it has shifted by more than 0.1 amu from unit mass.

        10.2.2  Instrument stability must be demonstrated by running the tuning solution (Section 7.7)
               a minimum of five times with resulting relative standard deviations of absolute signals
               for all analytes of less than 10%.
Draft, January 1996
                                                                                    25

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Method 1638
10.3   Internal Standardization—Internal standardization must be used in all analyses to correct for
       instrument drift and physical interferences.

        10.3.1  A list of acceptable internal standards is provided in Table 4.  For full mass range
               scans, a minimum of three internal standards must be used. Procedures described in
               this method for general application detail the use of five internal standards:  scandium,
               yttrium, indium, terbium, and bismuth.

        10.3.2  Internal standards must be present hi all samples, standards, and blanks at identical
               levels. This may be achieved by  directly adding an aliquot of the internal standards to
               the CAL standard, blank, or- sample solution (Method A), or alternatively by mixing
               with the solution before nebulization using a second channel of the peristaltic pump
               and a mixing coil (Method B).

        10.3.3  The concentration of the internal standard should be sufficiently high to obtain good
               precision in the measurement of the isotope used for data correction and to minimize
               the possibility of correction errors if the internal standard is naturally present hi the
               sample. Depending on the sensitivity of the instrument, a concentration range of 1
               ug/L to 200 ug/L of each internal standard is recommended.  Internal standards should
               be added to blanks, samples, and  standards in a like manner, so that dilution effects
               resulting from the addition may be disregarded.

 10.4   Calibration—Before initial calibration, set up proper instrument software routines for
        quantitative analysis.  The instrument must be calibrated at a minimum of three points for each
        analyte to be determined.

        10.4.1  Inject the calibration blank (Section 7.6.1) and calibration standards A and B (Section
               7.4.1) prepared at three or more concentrations, one of which must be at the Minimum
               Level (Table 1), and another that must be near the upper end of the linear dynamic
               range. A minimum of three  replicate integrations is required for data acquisition. Use
               the average of the integrations for instrument calibration and data reporting.

        10.4.2 Compute the response factor at each concentration, as follows:
                                         RF =
                Where:
                 C  - concentration of the analyte in the standard or blank solution
                C.  = concentration of the internal standard in the solution
                 A  = height or area of the response at the mlz for the analyte
                A.  = height or area of the mlz for the internal standard
         10.4.3  Using the individual response factors at each concentration, compute the mean RF for
                each analyte.
 26
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                                                                                   Method 1638
        10.4.4  Linearity—If the RF over the calibration range is constant (<20% RSD), the RF can be
               assumed to be invariant and the mean RF can be used for calculations.  Alternatively,
               the results can be used to plot a calibration curve of response ratios^ A/A^, vs. RF.

10.5    Calibration verification—Immediately following calibration, an initial calibration verification
        should be performed. Adjustment of the instrument is performed until verification criteria are
        met.  Only after these criteria are met may blanks and samples be analyzed.

        10.5.1  Analyze the mid-point calibration standard (Section 10.4).

        10.5.2  Compute the percent recovery of each metal using the mean RF or calibration curve
               obtained in the initial calibration.

        10.5.3  For each metal, compare the  recovery with the corresponding limit for calibration
               verification in Table 2.  If all metals meet the acceptance criteria, system performance
               is acceptable and analysis of blanks and samples may continue using the response from
               the initial calibration. If any individual value falls outside the range given, system
               performance is unacceptable for that compound. In this event, locate and correct the
               problem and/or prepare a new calibration check standard and repeat the  test (Sections
               10.5.1-10.5.3), or recalibrate the system according to Section 10.4.

        10.5.5  Calibration must be verified following every ten samples by analyzing the mid-point
               calibration standard. If the recovery does not meet the acceptance criteria specified in
               Table 2, analysis must be halted, the problem corrected, and the instrument
               recalibrated.  All samples after the last acceptable calibration verification must be
               reanalyzed.

10.6    A calibration blank must be analyzed following every calibration verification to  demonstrate
        that there is no carryover of the analytes of interest and that the analytical system is free from
        contamination.  If the concentration of an analyte in the blank result exceeds the MDL, correct
        the problem, verify the calibration (Section  10.5), and repeat the analysis of the  calibration
        blank.
11.0  Procedures for Cleaning the Apparatus

11.1    All sampling equipment, sample containers, and labware should be cleaned hi a designated
        cleaning area that has been demonstrated to be free of trace element contaminants.  Such areas
        may include class 100 clean rooms as described by Moody (Reference 22), labware cleaning
        areas as described by Patterson and Settle (Reference 6), or clean benches.

11.2    Materials, such as gloves (Section 6.9.7), storage bags (Section 6.9.10), and plastic wrap
        (Section 6.9.11), may be used new without additional cleaning unless the results of the
        equipment blank pinpoint any of these materials as a source of contamination.  In this case,
        either an alternate supplier must be obtained or the materials must be cleaned.

11.3    Cleaning procedures—Proper cleaning of the Apparatus is extremely important, because the
        Apparatus may not only contaminate the samples but may also remove the analytes of interest
        by adsorption onto the container surface.
Draft, January 1996
27

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Method 1638
        NOTE: If laboratory, field, and equipment blanks (Section 9.6) from the Apparatus
        cleaned with fewer cleaning steps than those detailed below show no levels ofanalytes
        above the MDL, those cleaning steps that do not eliminate these artifacts may be
        omitted provided all performance criteria outlined in Section 9 are met.	

        11.3.1  Bottles, labware, and sampling equipment

               11.3.1.1        Fill a precleaned basin (Section 6.9.8) with a sufficient quantity of a
                              0.5% solution of liquid detergent (Section 6.7), and completely
                              immerse  each piece of ware.  Allow to soak in the detergent for at
                              least 30 minutes.
               11.3.1.2



               11.3.1.3

               11.3.1.4



               11.3.1.5



               11.3.1.6


               11.3.1.7



               11.3.1.8
Using a pair of clean gloves (Section 6.9.7) and clean nonmetallic
brushes (Section 6.9.9), thoroughly scrub down all materials with the
detergent.

Place the scrubbed materials in a precleaned basin. Change gloves.

Thoroughly rinse the inside and outside of each piece with reagent
water until there is no sign of detergent residue (e.g., until all soap
bubbles disappear).

Change gloves, immerse the rinsed equipment in a hot (50-60°C) bath
of concentrated reagent grade HNO3 (Section 7.1.1) and allow to soak
for at least 2 hours.

After soaking, use clean gloves and tongs to remove the Apparatus and
thoroughly rinse with distilled, deionized water (Section 7.2).

Change gloves and immerse the Apparatus hi a hot (50-60°C) bath of
IN trace metal grade HC1 (Section 7.1.7), and allow to soak for at
least 48 hours.

Thoroughly rinse all equipment and bottles with reagent water.
Proceed with Section 11.3.2 for labware and sampling equipment
Proceed with Section 11.3.3 for sample bottles.
        11.3.2 Labware and sampling equipment

               11.3.2.1       After cleaning, air-dry hi a class 100 clean air bench.

               11.3.2.2       After drying, wrap each piece of ware and equipment in two layers of
                              polyethylene film.

        11.3.3 Huoropolymer sample bottles—These bottles should be used if mercury is a target
               analyte.
28
                                                 Draft, January 1996

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                                                                                      Method 1638
                11.3.3.1        After cleaning, fill sample bottles with 0.1% (v/v) ultrapure HC1
                               (Section 7.1.11) and cap tightly. It may be necessary to use a strap
                               wrench to assure a tight seal.

                11.3.3.2        After capping, double-bag each bottle in polyethylene zip-type bags.
                               Store at room temperature until sample collection.

        11.3.4  Bottles, labware, and sampling equipment (polyethylene  or material other than
                fluoropolymer)

                11.3.4.1        Apply the steps outlined above in Sections 11.3.1.1-11.3.1.8 to all
                               bottles, labware, and sampling equipment.  Proceed with Section
                               11.3.4.2 for bottles or Section 11.3.4.3 for labware and sampling
                               equipment.

                11.3.4.2        After cleaning, fill each bottle with 0.1% (v/v) ultrapure HC1 (Section
                               7.1.11).  Double-bag each bottle in a polyethylene bag to prevent
                               contamination of the surfaces with dust and dirt.  Store at room
                               temperature until sample collection.

                11.3.4.3        After rinsing labware and sampling equipment, air-dry in a class 100
                               clean air bench. After drying, wrap each piece of ware and equipment
                               in two layers of polyethylene film.
        NOTE: Polyethylene bottles cannot be used to collect samples that will be analyzed
        for mercury at trace (e.g., 0.012 ug/L) levels because of the potential of vapors
        diffusing through the polyethylene.

                11.3.4.4       Polyethylene bags—If polyethylene bags need to be cleaned, clean
                              according to the following procedure:

                       11.3.4.4.1      Partially fill with cold, (1+1) HNO3 (Section 7.1.2) and rinse
                                      with distilled deionized water (Section 7.2).

                       11.3.4.4.2      Dry by hanging upside down from a plastic line with a plastic
                                      clip.

        11.3.5  Silicone tubing, fluoropolymer tubing, and other sampling apparatus—Clean any
               silicone, fluoropolymer, or other tubing used to collect samples by rinsing with 10%
               HC1 (Section 7.1.8) and flushing with water from the site before sample collection.

        11.3.6  Extension pole—Because of its length, it is impractical to submerse the 2-m
               polyethylene extension pole (used in with the optional grab sampling device) in acid
               solutions as described above.  If such an extension pole is used, a nonmetallic brush
               (Section 6.9.9) should be used to scrub the pole with reagent water and the pole wiped
               down with acids described in Section 11.3.4 above. After cleaning, the pole should be
               wrapped in polyethylene film.
Draft, January 1996
29

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Method 1638
11.4   Storage—Store each piece or assembly of the Apparatus hi a clean, single polyethylene zip-
       type bag.  If shipment is required, place the bagged apparatus hi a second polyethylene zip-
       type bag.

11.5   All cleaning solutions and acid baths should be periodically monitored for accumulation of
       metals that could lead to contamination.  When levels of metals hi the solutions become too
       high, the solutions and baths should be changed and the old solutions neutralized and
       discarded hi compliance with state and federal regulations.


12.0 Procedures for Sample Preparation and Analysis

12.1   Aqueous sample preparation—dissolved analytes

       12.1.1  For determination of dissolved analytes hi ground and surface waters, pipet an aliquot
              (£ 20 mL) of the filtered, acid-preserved sample into a clean 50-mL polypropylene
              centrifuge tube.  Add an appropriate volume of (1+1) nitric acid to adjust the acid
              concentration of the aliquot to approximate a 1% (v/v)  nitric acid solution (e.g., add
              0.4 mL (1+1) HNO3 to a 20-mL aliquot of sample).  Add the internal standards, cap
              the tube, and mix.  The sample is now ready for analysis.  Allowance for sample
              dilution should be made hi the calculations.

12.2   Aqueous sample preparation—total recoverable analytes


       NOTE: To preclude contamination during sample digestion, it may be necessary to
       perform the open beaker, total-recoverable digestion procedure described in Sections
       12.2.1-12.2.7 in a fume hood that is located in a clean room.  An alternate digestion
       procedure is provided in  Section 12.2.8; however, this procedure has not undergone
       interlaboratory testing. 	

       12.2.1 For the determination of total recoverable analytes in ambient water samples, transfer a
               100-mL (±1 mL) aliquot from a well-mixed, acid-preserved sample to a 250-mL
              Griffin beaker (Section 6.9.3). If appropriate,  a smaller sample volume may be used.

       12.2.2 Add 2 mL (1+1)  nitric acid and  1.0 mL of (1+1) hydrochloric acid to the beaker and
              place the beaker on the hot plate for digestion. The hot plate should be located hi a
              fume hood and previously adjusted to provide evaporation at a temperature of
               approximately but no higher than 85°C.  (See  the following note.)  The beaker should
              be covered or other necessary steps  should be taken to prevent sample contamination
              from the fume hood environment.
        NOTE: For proper heating, adjust the temperature control of the hotplate such that
        an uncovered Griffin beaker containing 50 mL of water placed in the center of the hot
        plate can be maintained at a temperature approximately but no higher than 85°C.
        (Once the beaker is covered with a watch glass, the temperature of the water will rise
        to approximately 95°C.)             	^	
 30
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                                                                                     Method 1638
         12.2.3  Reduce the volume of the sample aliquot to about 20 mL by gentle heating at 85°C.
                Do not boil. This step takes about 2 hours for a 100-mL aliquot with the rate of
                evaporation rapidly increasing as the sample volume approaches 20 mL.  (A spare
                beaker containing 20 mL of water can be used as a gauge.)

         12.2.4  Cover the lip of the beaker  with a watch glass to reduce additional evaporation and
                gently reflux the sample for 30 minutes. (Slight boiling may occur, but vigorous
                boiling must be avoided to prevent loss of the HCl-K^O azeotrope.)

         12.2.5  Allow the beaker to cool. Quantitatively transfer the sample solution to a 50-mL
                volumetric flask or 50-mL class A stoppered graduated cylinder, make to volume with
                reagent water, stopper, and mix.

         12.2.6  Allow any undissolved material to settle overnight, or centrifuge a portion of the
                prepared sample until clear. (If, after centrifuging  or standing overnight, the sample
                contains suspended solids that would clog the nebulizer, a portion of the sample may
                be filtered to remove the solids before  analysis. However, care should be exercised to
                avoid potential contamination from filtration.)

         12.2.7  Prior to analysis, adjust the  chloride concentration by pipetting 20 mL of the prepared
                solution into a 50-mL volumetric flask, dilute to volume with reagent water and mix.
                (If the dissolved solids in this solution  are >0.2%, additional dilution may be required
                to prevent clogging of the extraction and/or skimmer cones.) Add the internal
                standards and mix.  The sample is now ready for analysis. Because the effects of
                various matrices on the stability of diluted samples cannot be characterized, all
                analyses should be performed as soon as possible after the completed preparation.

        12.2.8  Alternate total recoverable digestion procedure
               12.2.8.1
               12.2.8.2
               12.2.8.3
12.3    Sample Analysis
Open the preserved sample under clean conditions. Add ultrapure
nitric and hydrochloric acid at the rate of 10 mL/L and 5 mL/L,
respectively. Remove the cap from the original container only long
enough to add each aliquot of acid. The sample container should not
be filled to the lip by the addition of the acids.  However,  only
minimal headspace is needed to avoid leakage during heating.

Tightly recap the container and shake thoroughly.  Place the container
in an oven preheated to 85°C. The container should be placed on an
insulating piece of material such as wood rather than directly on the
typical metal grating.  After the samples have reached 85°C, heat for 2
hours. (Total time will be 2.5-3 hours depending  on the sample size).
Temperature can be monitored using an identical sample container with
distilled water and a thermocouple to standardize heating time.

Allow the sample to cool. Add the internal standards and mix. The
sample is now ready for analysis. Remove aliquots for analysis under
clean conditions.
Draft, January 1996
                                                                31

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Method 1638
        12.3.1  For every new or unusual matrix, it is highly recommended that a semiquantitative
               analysis be carried out to screen the sample for elements that may be present at high
               concentration.  Information gained from this screening may be used to prevent
               potential damage to the detector during sample analysis and to identify elements that
               may exceed the linear range. Matrix screening may be carried out using intelligent
               software, if available, or by diluting the sample by a factor of 500 and analyzing in a
               semiquantitative mode.  The sample should also be screened for background levels of
               aH elements chosen for use as internal standards to prevent bias  hi the calculation of
               the analytical data.

        12.3.2  Initiate instrument operating configuration. Tune and calibrate the instrument for the
               analytes of interest (Section 10.0).

        12.3.3  Establish instrument software run procedures for quantitative analysis.  For all sample
               analyses, a minimum of three replicate integrations is required for data acquisition.
               Use the average of the integrations for data reporting.

        12.3.4  All m/z's that may affect data quality must be monitored during the analytical run.  As
               a nunimum, those m/z's prescribed in Table 5 must be monitored hi the same scan as
               is used for the collection of the data.  This information should be used to  correct the
               data for identified interferences.

        12.3.5  The rinse blank should be used to flush the system between samples. Allow sufficient
               time to remove traces of the previous sample or a minimum of  1 minute.  Samples
               should be aspirated for 30 seconds before data is collected.

        12.3.6  Samples having concentrations higher than the established linear dynamic range should
               be  diluted into range and reanalyzed. The sample should first be analyzed for the
               trace elements in the sample, protecting the detector from  the high concentration
               elements if necessary, by the selection of appropriate scanning windows.  The sample
               should then be diluted for the determination of the remaining elements. Alternatively,
               the dynamic range may be adjusted by selecting an alternative isotope of  lower natural
               abundance, if quality control data for that isotope have been established.  The dynamic
               range must not be adjusted by altering instrument conditions to an uncharacterized
               state.

 13.0 Data Analysis and Calculations

 13.1   Table 6 lists  elemental equations recommended for sample data calculations. Sample data
        should be reported in units of ug/L (parts-per-billion;  ppb). Report results at or above the ML
        for metals found in samples and determined in standards.  Report all results for metals found
        in blanks, regardless of level.

 13.2   For data .values less than the ML, two significant figures should be used for reporting element
        concentrations. For data values greater than or equal to the ML, three  significant figures
        should be used.

 13.3   For aqueous  samples prepared by total recoverable procedure (Sections 12.2.1-12.2.7),
        multiply solution concentrations by the dilution factor 1.25. If additional dilutions were made
 32
                                                                               Draft, January 1996

-------
                                                                                   Method 1638
        to any samples, the appropriate factor should be applied to the calculated sample
        concentrations.                     -s:          :

 13.4   Compute the concentration of each analyte in the sample using the response factor determined
        from calibration data (Section 10.4) and the following equation:
                                     rCs (VglL) =
                                                 A... x RF
                        Where the terms are as defined in Section 10.4.2.
 13.5    Corrections for characterized spectral interferences should be applied to the data.  Chloride
        interference corrections should be made on all samples, regardless of the addition of
        hydrochloric acid, because the chloride ion is a common constituent of environmental samples.

        13.6   If an element has more than one monitored m/z, examination of the concentration
               calculated for each m/z, or die relative abundances, will provide useful information for
               the analyst in detecting a possible spectral interference.  Consideration should therefore
               be given to both primary and secondary m/z's in the evaluation  of the element
               concentration.  In some cases, the secondary m/z may be less sensitive or more prone
               to interferences than the primary recommended m/z; therefore, differences between the
               results do not necessarily indicate a problem with data calculated for the primary m/z.

        13.7   The QC data obtained during the analyses provide an indication of the quality of the
               sample data and should be provided with the sample results.

        13.8   Do not perform blank subtraction on the sample results. Report results for samples
               and accompanying blanks.

 14.0  Method  Performance

 14.1    The method detection limits (MDLs) listed in Table 1 and the quality control  acceptance
        criteria listed in Table 2 were validated in two laboratories (Reference 23) for dissolved
        analytes.

 15.0  Pollution Prevention

 15.1    Pollution prevention encompasses any technique that reduces or eliminates the quantity or
        toxicity of waste at the point of generation. Numerous opportunities for pollution prevention
        exist in laboratory operation. The EPA has established a preferred hierarchy of environmental
        management techniques that places pollution prevention as the management option of first
        choice. Whenever feasible, laboratory personnel should use pollution prevention techniques to
        address their waste generation.  When wastes cannot be feasibly reduced at the source, the
        Agency recommends recycling  as the next best option. The acids used in this method should
        be reused as practicable by purifying by electrochemical techniques.  The only other chemicals
        used in this method are the neat materials used in preparing standards. These standards are
        used in extremely small amounts and pose little threat to the environment when managed
Draft, January 1996
33

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r
               Method 1638
                      properly.  Standards should be prepared in volumes consistent with laboratory use to minimize
                      the volume of expired standards to be disposed.

                15.2   For information about pollution prevention that may be applicable to laboratories and research
                      institutions, consult Less is Better: Laboratory Chemical Management for Waste Reduction,
                      available from the American Chemical Society's Department of Government Relations and
                      Science Policy, 1155 16th Street NW, Washington DC 20036, 202/872-4477.

                16.0 Waste  Management

                16.1   The Environmental Protection Agency requires that laboratory waste management practices  be
                      conducted consistent with all applicable rules and regulations. The Agency urges laboratories
                      to protect the air, water, and land by minimizing and controlling all releases from hoods and
                      bench operations, complying with the letter and spirit of any sewer discharge permits and
                      regulations, and by complying with all solid and hazardous waste regulations, particularly the
                      hazardous waste identification rules and land disposal restrictions.  For further information on
                      waste management consult The Waste Management Manual for Laboratory Personnel,
                      available from the American Chemical Society at the address listed in Section 15.2.

                17.0  References

                1     Adeloju, S.B.; Bond, A.M. "Influence of Laboratory Environment on the Precision and
                      Accuracy of Trace Element Analysis," Anal. Chem. 1985,57, 1728.

                2     Berman, S.S.; Yeats, P.A. "Sampling of Seawater for Trace Metals," CRC Reviews in
                      Analytical Chemistry 1985,16, 1.

                3      Bloom, N.S. "Ultra-Clean Sampling, Storage, and Analytical Strategies for the Accurate
                       Determination of Trace Metals in Natural Waters"; Presented at the 16th Annual EPA
                       Conference on the Analysis of Pollutants in the Environment, Norfolk, Virginia, May 5,1993.

                4      Bruland, K.W. 'Trace Elements in Seawater," Chemical Oceanography 1983, 8, 157.

                5      Nriagu, J.O.; Larson, G.; Wong, H.K.T.; Azcue, J.M. "A Protocol for Minimizing
                       Contamination in the Analysis of Trace Metals in Great Lakes Waters," J. Great Lakes
                       Research 1993,19, 175.

                6      Patterson, C.C.; Settle, D.M. In National Bureau of Standards Special Publication 422',
                       LaFleur, P.D., Ed., U.S. Government Printing Office, Washington, DC, 1976. "Accuracy in
                       Trace Analysis."

                7      Fitzgerald, W.F.; Watras, C.J. Science of the Total Environment 1989, 87/88, 223.

                8      Gill, G.A.; Fitzgerald, W.F. Deep Sea Res. 1985, 32, 287.

                9      Prothro, M.G. "Office of Water Policy and Technical Guidance on Interpretation and
                       Implementation of Aquatic Life Metals Criteria," EPA Memorandum to Regional Water
                       Management and Environmental Services Division Directors, October 1, 1993.
                34
                                                                                           Draft, January 1996

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                                                                     	Method 1638


 10     "Format for Method Documentation," Distributed by the EPA Environmental Monitoring
        Management Council, Washington, DC, November 18, 1993.

 11     Gray, A.L.; Date, A.R. Analyst 1983,108, 1033.

 12     Houk, R.S. et al. Anal Chem. 1980, 52, 2283.

 13     Houk, R.S. Anal Chem. 1986, 55, 97A.

 14     Windom, H.L; Byrd, J.T.; Smith, R.G., Jr.; Huan, F. "Inadequacy of NASQAN Data for
        Assessing Metal Trends in the Nation's Rivers," Environ. Sci. Technol. 1991, 25, 1137.

 15     Zief, M.; Mitchell, J.W. "Contamination Control in Trace Metals Analysis"; In Chemical
        Analysis 1976, Vol. 47, Chapter 6.

 16     Thompson, J.J.; Houk, R.S. Appl. Spec. 1987, 41, 801.

 17     Carcinogens - Working With Carcinogens, Department of Health, Education, and Welfare,
        Public Health Service, Center for Disease Control, National Institute for Occupational Safety
        and Health, Publication No. 77-206, Aug. 1977. Available from the National Technical
        Information Service (NTIS) as PB-277256.

 18     "OSHA Safety and Health Standards, General Industry,"  Occupational Safety and Health
        Administration, OSHA 2206, 29 CFR 1910 (Revised, January 1976).

 19     "Safety in Academic Chemistry Laboratories," American Chemical Society Publication,
        Committee on Chemical Safety, 3rd Edition,  1979.

 20     "Proposed OSHA Safety and Health Standards, Laboratories, Occupational Safety and Health
        Administration," Fed. Regist. July 24, 1986.

 21      Handbook of Analytical Quality Control in Water and Wastewater Laboratories; U.S.
        Environmental Protection Agency. EMSL-Cincinnati, OH, March 1979; EPA-600/4-79-019.

 22     Moody, J.R. "NBS Clean Laboratories for Trace Element Analysis," Anal Chem. 1982, 54,
        1358A.

 23      "Results of the Validation Study for Determination of Trace Metals at EPA Water Quality
        Criteria Levels," April 1995.  Available from the Sample Control Center (operated by
        DynCorp), 300 N. Lee Street, Alexandria, VA 22314, 703/519-1140.

 24     Hinners, T.A. "Interferences in ICP-MS by Bromine Species"; Presented at Winter Conference
        on Plasma Spectrochemistry, San Diego, CA, January 10-15, 1994.
Draft, January 1996
35

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Method 1638
18.0  Glossary

        Many of the terms and definitions listed below are used in the EPA 1600-series methods, but
        terms have been cross-referenced to terms commonly used in other methods where possible.

18.1    Ambient Water—Waters in the natural environment (e.g., rivers, lakes, streams, and other
        receiving waters), as opposed to effluent discharges.

18.2    Analyte—A metal tested for by the methods referenced in this method. The analytes are
        listed in Table 1.                 •

18.3    Apparatus—The sample container and other containers, filters, filter holders, labware, tubing,
        pipets, and other materials and devices used for sample collection or sample preparation, and
        that will contact samples, blanks, or analytical standards.

18.4    Calibration Blank—A volume of reagent water acidified with the same acid matrix as in the
        calibration standards.  The calibration blank is a zero standard and is used to calibrate the ICP
        instrument (Section 7.6.1).

18.5    Calibration Standard (CAL)—A solution prepared from a dilute mixed  standard and/or stock
        solutions and used to calibrate the response of the instrument with respect to analyte
        concentration.

 18.6    Dissolved Analyte—The concentration of analyte in an aqueous sample that will pass through
        a 0.45-um membrane filter assembly prior to sample acidification (Section 8.3).

 18.7    Equipment Blank—An aliquot of reagent water that is subjected in the laboratory to all
        aspects of sample collection and analysis, including contact with all sampling devices and
        apparatus. The purpose of the equipment blank is to determine if the sampling devices and
        apparatus for sample collection have been adequately cleaned before they are shipped to the
        field site. An acceptable equipment blank must be achieved before the sampling devices and
        apparatus are used for sample collection.  In addition,  equipment blanks should be run on
        random, representative sets of gloves, storage bags, and plastic wrap for each lot to determine
        if these materials are free from contamination before use.

 18 8   Field Blank—An aliquot of reagent water that is placed in a sample container in the
        laboratory, shipped to the field, and treated as a sample in all respects, including contact with
        the sampling devices and exposure to sampling site conditions, storage, preservation, and all
        analytical procedures, which may include filtration.  The purpose of the field blank is to
        determine if the field or sample transporting procedures and environments have contaminated
        the sample.

 18.9   Field Duplicates (FD1 and FD2)—Two separate samples collected in separate sample bottles
        at the same time and place under identical circumstances and treated exactly the same
        throughout field and laboratory procedures.  Analyses  of FD1 and FD2 give a measure of the
        precision associated with sample collection, preservation, and storage, as well as with
        laboratory procedures.
 36
                                                                               Draft, January 1996

-------
                                                                                   Method 1638
 18.10  Initial Precision and Recovery (BPR)—Four aliquots of the OPR standard analyzed to
        establish the ability to generate acceptable precision and accuracy. IPRs are performed before
        a method is used for the first time and any time the method or instrumentation is modified.

 18.11  Instrument Detection Limit (IDL)—The concentration equivalent to the analyte signal which
        is equal to three times the standard deviation of a series of ten replicate measurements of the
        calibration blank signal  at the selected analytical mass(es).

 18.12  Internal Standard—Pure analyte(s) added to a sample, extract, or standard solution in known
        amount(s) and used to measure the relative responses of other method analytes that are
        components of the same sample or solution.  The internal standard must be an analyte that is
        not a sample component (Sections 7.5 and 9.5).

 18.13  Laboratory Blank—An aliquot of reagent water that is treated exactly as a sample including
        exposure to all glassware, equipment, solvents,  reagents, internal standards, and surrogates that
        are used with samples.  The laboratory blank is used to determine if method analytes or
        interferences are present in the laboratory environment, the reagents, or the apparatus (Sections
        7.6.2 and 9.6.1).

 18.14  Laboratory Control Sample (LCS)—See Ongoing Precision and Recovery (OPR) Standard.

 18.15  Laboratory Duplicates (LD1 and LD2)—Two aliquots of the same sample  taken in the
        laboratory and analyzed separately with identical procedures.  Analyses of LD1 and LD2
        indicates precision associated with laboratory procedures, but not with sample collection,
        preservation, or storage procedures.

 18.16  Laboratory Fortified Blank (LFB)—See Ongoing Precision and Recovery (OPR) Standard.

 18.17  Laboratory Fortified Sample Matrix (LFM)—See Matrix Spike (MS) and Matrix Spike
        duplicate (MSB).

 18.18  Laboratory Reagent Blank (LRB)—See Laboratory Blank.

 18.19  Linear Dynamic Range (LDR)—The concentration range over which the instrument response
        to an analyte is linear (Section 9.2.3).

 18.20  Matrix Spike (MS) and Matrix Spike Duplicate (MSD)—Aliquots of an environmental
        sample to which known  quantities of the method analytes are added in the laboratory.  The
        MS and MSD are analyzed exactly like a sample. Their purpose is to quantify the bias and
        precision caused by the sample matrix.  The background concentrations of the analytes in the
        sample matrix must be determined in a separate aliquot and the measured values in the MS
        and MSD corrected for background concentrations (Section 9.3).

 18.21   m/z—mass-to-charge ratio

 18.22   May—This action, activity, or procedural step is optional.

 18.23   May Not—This action, activity, or procedural step is prohibited.
Draft, January 1996
37

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Method 1638
18.24

18.25



18.26


18.27

18.28
 18.29

 18.30


 18.31
 18.32


 18.33

 18.34
 18.35
 18.36
Method Blank—See Laboratory Blank.

Method Detection Limit (MDL)—The minimum concentration of an analyte that can be
identified, measured, and reported with 99% confidence that the analyte concentration is
greater than zero (Section 9.2.1 and Table 1).

Minimum Level (ML)—The lowest level at which the entire analytical system gives a
recognizable signal and acceptable calibration point (Reference 9).

Must—This action, activity, or procedural step is required.

Ongoing Precision and Recovery (OPR) Standard—A laboratory blank spiked with known
quantities of the method analytes.  The OPR is analyzed exactly like a sample. Its purpose is
to determine whether the methodology is in control and to assure  that the results produced by
the laboratory remain within the method-specified limits for precision and accuracy (Sections
7.9 and 9.7).

Preparation Blank—See Laboratory Blank.

Primary Dilution Standard—A solution containing the analytes  that is purchased or prepared
from stock solutions and diluted as needed to prepare calibration solutions and other solutions.

Quality Control Sample (QCS)—A sample containing all or a subset of the method analytes
at known concentrations. The QCS is obtained from a source external to the laboratory or is
prepared from a source of standards different from the source of calibration standards. It is
used to check laboratory performance with test materials prepared external to the normal
preparation process.

Reagent Water—Water demonstrated to be free from the method analytes and potentially
interfering substances at the MDL for that metal hi the method.

Should—This action, activity, or procedural step is suggested but not required.

Stock Standard Solution—A solution containing one or  more method analytes that is
prepared using a reference material traceable to EPA, the National Institute of Science and
Technology (NIST), or a source that will attest to the purity and authenticity of the reference
material.

Total Recoverable Analyte—The concentration of analyte determined by analysis of the
solution extract of an unfiltered aqueous sample following digestion by refiuxing with hot
dilute mineral acid(s) as specified in the method (Section 12.2).

Timing Solution—A solution which is used to determine acceptable instrument performance
before calibration and sample analyses (Section 7.7).
 38
                                                                      Draft, January 1996

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                                                                                                      Method 1638
                                                      Table 1

    List of Analytes Amenable to Analysis Using Method 1638:  Lowest Water Quality Criterion
                  for Each Metal Species, Method Detection Limits, Minimum Levels,
                                     and Recommended Analytical M/Z's
Metal
Antimony
Cadmium
Copper
Lead
Nickel
Selenium
Silver
Thallium
Zinc
Lowest
Ambient
Water Quality
Criterion
WLf
14
0.37
2.4
0.54
8.2
5
0.32
1.7
32
Method Detection
Limit (MDL) and
Minimum Level (ML);
vgn-
MDL2
0.0097
0.025
0.087
0.015
0.33
0.45
0.029
0.0079
0.14
ML3
0.02
0.1
0.2
0.05
1
1
0.1
0.02
0.5
Recommended
Analytical m/z
123
111
63
206, 207, 208
60
82
107
205
66
Notes:
1.   Lowest of the freshwater, marine, or human health WQC at 40 CFR Part 131 (57 FR 60848 for human health criteria and 60 FR 22228
     for aquatic criteria).  Hardness-dependent freshwater aquatic life criteria also calculated to reflect a hardness of 25 mg/L CaCO3, and all
     aquatic life criteria, except chronic criteria for Se, have been adjusted to reflect dissolved levels in accordance with the equations provided
     in 60 FR 22228. Hardness-dependent dissolved criteria conversion factors for Cd and Pb also calculated at a hardness of 25 mg/L per 60
     FR 22228.

2.   Method Detection Limit as determined by 40 CFR Part 136, Appendix B.

3.   Minimum Level (ML) calculated by multiplying laboratory-determined MDL by 3.18 and rounding result to nearest multiple of 1,2,5,10,
     etc. in accordance with procedures used by HAD and described in the EPA Draft National Guidance for the Permitting, Monitoring, and
     Enforcement of Water Quality-Based Effluent Limitations Set Below Analytical DetectionlQuantitation Levels, March 22, 1994.
Draft, January 1996
39

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Method 1638
                                           Table 2
       Quality Control Acceptance Criteria for Performance Tests in EPA Method 16381
Metal
Antimony
Cadmium
Copper
Lead
Nickel
Selenium
Silver
Thallium
Zinc
Initial Precision and
Recovery (Section
92)
s X
20 81-120
13 85-112
43 55-141
30 75-140
30 71-131
41 63-145
19 82-120
30 66-134
43 55-142
Calibration
Verification
(Section 10.5)
90-111
91-105
76-120
91-120
86-116
69-127
81-107
82-118
76-121
Ongoing Precision
and
Recovery (Section
9.7)
79-122
84-113
51-145
72-143
68-134
59-149
74-119
64-137
46-146
Spike
Recovery
(Section 9.3)
79-122
84-113
51-145
72-143
68-134
59-149
74-119
64-137
46-146
 1 All specifications expressed as percent
 40
                                                                             Draft, January 1996

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                                                                              Method 1638
TABLE 3: COMMON MOLECULAR ION INTERFERENCES IN ICP-MS
BACKGROUND MOLECULAR IONS
Molecular Ion
NIT
Off
OH,*

-------
     Method 1638
                                       TABLE 3 (continued)
                                    MATRIX MOLECULAR IONS
BROMIDE (Reference 24)
Molecular Ion

"BrH*
"BiO*
"BrO*
"BrOH*

Ar"Br+
                                             m/z

                                             82
                                             95
                                             97
                                             98

                                             121
                        Element Interference

                                Se
                                Mo
                                Mo
                                Mo

                                Sb
CHLORIDE
Molecular Ion
MCIOH*
"CIO*
                                             m/z

                                             51
                                             52
                                             53
                                             54
                        Element Interference

                                V
                                Cr
                                Cr
                                Cr
                                             75
                                             77
                                                                             As
                                                                             Se
SULFATE
Molecular Ion

"SO*
MSOH*
"SO*
SO/,
                                             m/z

                                             48
                                             49
                                             50
                                             51
                                             64
                                                                      Element Interference
                                V,Cr
                                V
                                Zn
Ar^S*
Ar«S*
                                             72
                                             74
PHOSPHATE
Molecular Ion

PO*
POH*
P02*
m/z

47
48
63
                                                                      Element Interference
                                                                              Cu
ArP*
GROUP I, H METALS
Molecular Ion
ArNa*
ArK*
ArCa*
                                              71
                                             m/z

                                             63
                                             79
                                             80
                         Element Interference

                                Cu
     42
                                                                                Draft, January 1996

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                                                                                        Method 1638
                                          TABLE 3 (continued)
                                     MATRIX MOLECULAR IONS
MATRIX OXIDES*
Molecular Ion

TiO
ZrO
MoO
m/z's
62-66
106-112
108-116
Element Interference
     Ni,Cu,Zn
     Ag,Cd
     Cd
    Oxide interferences will normally be very small and will only impact the method elements when present at relatively high
    concentrations. Some examples of matrix oxides of which the analyst should be aware are listed.
     Draft, January 1996
                                                   43

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    Method 1638
                 TABLE 4: INTERNAL STANDARDS AND LIMITATIONS OF USE
Internal Standard
^Lithium
Scandium
Yttrium
Rhodium
Indium
Terbium
Holmium
Lutetium
Bismuth
mlz
6
45
89
103
115
159
165
175
209
Possible Limitation
a


polyatomic ion interference
a,b

isobaric interference by



a


Sn




(a)  May be present in environmental samples.
(b)  In some instruments, yttrium may form measurable amounts of YO+ (105 amu) and YOH+ (106 amu). If this
    is the case, care should be taken in the use of the cadmium elemental correction equation.
Note:
Internal standards recommended for use with this method are shown hi boldface. Preparation
procedures for these are included in Section 7.3.
     44
                                                            Draft, January 1996

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                                                                                     Method 1638
TABLE 5: RECOMMENDED ISOTOPES AND ADDITIONAL
M/Z'S THAT MUST BE MONITORED
Isotope
27
121.123
25
135.137
9
106.108.111.114
52,53
59
63,65
206.207.208
55
95,97,98
60,62
77,82
107.109
203.205
232
238
51
66,67,68
83
99
105
118
Element of Interest
Aluminum
Antimony
Arsenic
Barium
Beryllium
Cadmium
Chromium
Cobalt
Copper
Lead
Manganese
Molybdenum
Nickel
Selenium
Silver
Thallium
Thorium
Uranium
Vanadium
Zinc
Krypton
Ruthenium
Palladium
Tin
Note:
Isotopes recommended for analytical determination are underlined.
Draft, January 1996
                                                                                45

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     Method 1638
       TABLE 6: RECOMMENDED ELEMENTAL EQUATIONS FOR DATA CALCULATIONS
Element
Sb
Cd
Cu
Pb
Ni
Se
Ag
•n
Zn
Elemental Equation
(1.000)(mC)
(1.000)(nlC)-(1.073)[(I08C)-(0.712)(106C)]
(l.OOO^C)
(1.000)(20SC)+(1.000)(207C)+(1.000)f!8C)
(1.000)(60C)
(LOOOC^Q
(i.ooo)(107q>
(LOOO^C)
(1.000)(«C)
Note

(1)

(2)

(3)



INTERNAL STANDARDS
Element
Bi
In
Sc
Tb
Y
Elemental Equation
(LOOOfC)
(1.000)("5C)-(0.016)(118C)
(1.000)(45C)
(1.000)(15'C)
(l.OOOJ^Q
Note

(4)



C—counts at specified m/z                                                                    ,     .  .,  „  ,.
(1>—Conection for MoO interference. M/z 106 must be from Cd only, not ZrO+. An additional correction should be made if palladium is

present.
(2)—allowance for variability of lead isotopes
(3)—Some argon supplies contain krypton as an impurity.  Selenium is corrected for  Kr by background subtraction.

(4)—correction for tin
      46
                                                                                     Draft, January 1996

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                                                                                               Method 1638
                       TABLE 7: RECOMMENDED INSTRUMENT OPERATING CONDITIONS
Instrument
Plasma forward power
Coolant flow rate
Auxiliary flow rate
Nebulizer flow rate
Solution uptake rate
Spray chamber temperature
Data Acquisition
Detector mode
Replicate integrations
Mass range
Dwell time
Number of MCA channels
Number of scan sweeps
Total acquisition time
VG PlasmaQuad Type I
1.35 kW
13.5 L/min
0.6iymin
0.78 L/min
0.6 mL/min
15°C

Pulse counting
3
8-240 amu
320 us
2048
85
3 minutes per sample
    Draft, January 1996
                                                                                                      47

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