United States
        Environmental Protection
Office of Water
April 1995
©EPA   Method 1640:  Determination of Trace
        Elements in Ambient Waters by On-
        Line Chelation Preconcentration and
        Inductively Coupled Plasma-Mass
                                       > Printed on Recycled Paper


®EPA  Method 1640: Determination of Trace
       Elements in Ambient Waters by On-
       Line Chelation Preconcentration and
       Inductively Coupled Plasma-Mass
                                   ) Printed on Recycled Paper


Method 1640
Method 1640  was prepared under the  direction of William  A. Telliard of the  U.S. Environmental
Protection Agency's (EPA's) Office of Water (OW), Engineering and Analysis Division (BAD).  The
method was prepared under EPA Contract 68-C3-0337 by the DynCorp Environmental Programs Division
with assistance from Interface, Inc.

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

Shier Herman, 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 Gill, 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
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:

J.T. Creed
T.D.  Martin
S.E. Long (DynCorp, formerly Technology Applications, Inc.)
 This method has been reviewed and approved for publication by the Engineering and Analysis Division
 of the U.S. Environmental 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
 Phone: 202/260-7120
 Fax:  202/260-7185
                                                                                    April 1995


                                                                                      Method 164Q

 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 that can be achieved
 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 in the National Toxics Rule (57
 FR 60848). This rule includes water quality criteria for 13  metals, and it is these criteria on which the
 new sampling and analysis methods are based.  Method 1640 was specifically  developed to provide
 reliable measurements of four of these metals at EPA WQC levels using on-line chelation preconcentration
 and inductively coupled plasma-mass spectrometry  techniques.

 In developing these methods, EPA found that one of the greatest difficulties in 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:

 11029 Kenwood Road
 Cincinnati, OH 45242
April 1995


Method 1640
    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 show  that data quality is not affected.
                                                                                       April 1995


                                                                         Method 1640
                             Method  1640
  Determination of Trace Elements in Ambient  Waters by
     On-Line Chelation Preconcentration and 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 on-line chelation preconcentration and 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 contained in EPA Method 200.10 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 (the "Sampling Method"). The Sampling Method is necessary to ensure that
       contamination will not compromise trace metals determinations during the sampling process.

1.2     This method is applicable to the following elements:
                                              Chemical Abstract
                 Analyte       Symbol        Services Registry
                                              Number (CASRN)
Table 1 lists the EPA WQC levels, the method detection limit (MDL) for each metal, and the
minimum level (ML) for each metal in this method.  Linear working ranges will be dependent
on the instrumentation and selected operating conditions but should be essentially independent
of the matrix because elimination of the matrix is a feature of the method.

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-
billion (ppb) range, whereas ambient metals concentrations are normally in the low part-per-
trillion (ppt) to low ppb range.
April 1995

Method 1640
1.4    The 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 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 they lack 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 0.45-/*m capsule filter
       at the field site.  The Sampling Method describes the filtering procedures.  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; provides procedures
       for laboratory preservation are provided in this method.

1.9    Acid solubilization is required before the determination of total recoverable elements to aid
       breakdown of complexes or colloids that might influence trace element recoveries.

1.10   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 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.

1.11   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     This method is used to preconcentrate trace elements using an iminodiacetate functionalized
        chelating resin (References 11-12).  Following acid solubilization, the sample is buffered
        prior to the chelating column using an on-line system.  Group I and II metals, as well as most
                                                                                      April 1995

                                                                                    Method 1640
       anions, are selectively separated from the analytes by elution with ammonium acetate at pH
       5.5. The analytes are subsequently eluted into a simplified matrix consisting of dilute nitric
       acid and are determined by ICP-MS" using a directly coupled on-line configuration.

2.2    The determinative step in this method is ICP-MS (Reference 13-15).  Sample material in
       solution is introduced by pneumatic nebulization 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 (m/z) ratio by a mass spectrometer having a minimum resolution
       capability of 1 amu peak width at 5% peak height at m/z 300.  An electron multiplier or
       Faraday detector detects ions transmitted through the mass analyzer, and a data handling
       system processes the resulting current. Interferences relating to the technique (Section 4)
       must be recognized and corrected.  Such corrections must  include compensation for isobaric
       elemental interferences and interferences from polyatomic  ions derived from the plasma gas,
       reagents,  or sample matrix.  Instrumental drift must be corrected for by the use of internal

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 the glossary (Section 18) 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 16). 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 that 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
        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).
 April 1995

                Method 1640
                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.

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

                     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.

                     Although 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 in 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 in 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 tune between cleaning and use will also minimize contamination.

                       4.3.5   Clean work surfaces—Before a given batch of samples is processed, all work surfaces
                              in the hood, clean bench, or glove box in 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 6.10.7)
                              during all operations involving handling of the  Apparatus,  samples, and blanks.  Only
                              clean gloves may touch the Apparatus. If another object or substance  is touched, the
                              glove(s) must be changed before again handling the Apparatus. If it is even suspected
                              that gloves have become contaminated, work must be halted, the contaminated  gloves
                              removed, and a new pah- of clean  gloves put on.  Wearing multiple layers of clean
                                                                                                     April 1995

                                                                                       Method 1640
                 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.
  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 in 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 in 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
                in Section 11 and must be known to be clean and metal-free before
                proceeding.  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, polyvinylchloride,  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 17).  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. 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.

4.3.8   Avoid Sources of Contamination—Avoid contamination by being aware of potential
       sources and routes of contamination.
April 1995

Method 1640
      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

      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.

      Contamination by indirect contact—Apparatus that may not directly come in
                       contact with the samples  may still be a source of contamination.  For example,
                       clean tubing placed in a duly 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 in the collection, processing, and analysis of ambient water
                       samples be cleaned as specified in Section 11.

       Contamination by airborne particulate 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.

 4.4     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.  Internal
         standards should be used to correct for instrumental drift as well as suppressions or
         enhancements of instrument response caused by the sample matrix.

         4.4.1   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
                                                                                        April 1995

                                                                                     Method 1640
               minimum, one isotope free of isobaric elemental interferences. 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 hi the equation for
               data calculations.  Relative abundances should be established before any corrections are

       4.4.2   Abundance sensitivity—Is a property defining the degree to which the wings of a mass
               peak contribute to adjacent m/z's. Ion energy and quadruple operating pressure affect
               the abundance sensitivity.  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.

       4.4.3   Isobaric polyatomic ion interferences—Are caused by ions consisting of more than one
               atom which have  the same nominal m/z 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.  Such
               interferences must be recognized, and when they cannot be avoided by selecting
               alternative analytical isotopes, 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.

       4.4.4   Physical interferences—Are  associated with the physical processes that govern the
               transport of sample into the  plasma, sample conversion processes hi 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. Internal standardization may be effectively used to
               compensate for many physical interference effects (Reference 18).  Internal standards
               ideally should have similar analytical behavior to the elements being determined.

       4.4.5   Memory interferences—Result when isotopes of elements in a previous sample
               contribute to the signals measured in a new sample.  Memory  effects can result from
               sample deposition on the sampler and skimmer cones, and from the buildup of sample
               material hi the plasma torch and spray chamber. The site where these effects occur
               depends 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 tunes necessary for a particular element should be estimated
               before it is analyzed.  This estimation 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
April 1995

Method 1640
               intervals. The length of time required to reduce analyte signals below the ML should
               be noted. Memory interferences may also be assessed within an analytical run by
               using a minimum 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 in the previous sample to
               identify if the memory effect was high. If a memory interference is suspected, the
               sample should be reanalyzed after a long rinse period.

               A principal advantage of this method is the  selective elimination of species giving rise
               to polyatomic spectral interferences on certain transition metals (e.g., removal of the
               chloride interference on vanadium).  As most of the sample matrix is removed, matrix-
               induced physical interferences are also substantially reduced.

               Low recoveries may be encountered in the preconcentration cycle if the trace elements
               are complexed by competing chelators in the sample or are present as colloidal
               material.  Acid solubilization pretreatment is used to improve analyte recovery and to
               minimize adsorption, hydrolysis, and precipitation effects.
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.

        5.1.1   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
               19-22).  A reference file of material safety data sheets (MSDSs) should also be
               available to all personnel involved in 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 22 are particularly comprehensive
               in dealing with the general subject of laboratory safety.

        5.1.2   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.

5.2     The acidification of samples containing reactive materials may result in the release of toxic
        gases such as cyanides or sulfides. Samples should be acidified in a fume hood.

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

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.
                                                                                       April 1995

                                                                                    Method 1640
 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.  The laboratory is responsible for
        demonstrating equivalent performance.
 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.  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.  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

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.

Preconcentration system—System containing no metal parts in the analyte flow path,
configured as shown in Figure 1.
        NOTE: An alternate preconcentration system to the one described below may be used
        provided that all performance criteria listed in this method can be met.  If low
        recoveries are encountered in the preconcentration cycle for a particular analyte, it
        may be necessary to use an alternate preconcentration system.

        6.2.1   Column—Macroporous  iminodiacetate chelating resin (Dionex Metpac CC-1 or

        6.2.2   Sample loop—10-mL loop  constructed from narrow-bore, high-pressure inert tubing,
               Tefzel ETFE (ethylene tetra-fluoroethylene) or equivalent.

        6.2.3   Eluent pumping system  (PI)—Programmable-flow, high-pressure pumping system,
               capable of delivering either one of two eluents at a pressure up to 2000 psi and a flow
               rate of 1-5 mL/min.

        6.2.4   Auxiliary pumps
April 1995

Method 1640
               6.2A.I On-line buffer pump (P2)—Piston pump (Dionex QIC pump or equivalent) for
                      delivering 2M ammonium acetate buffer solution.

      Carrier pump (P3)—Peristaltic pump (Gilson Minipuls or equivalent) for
                      delivering 1% nitric acid carrier solution.

      Sample pump (P4)—Peristaltic pump for loading sample loop.

        6.2.5   Control valves—Inert, double-stack, pneumatically operated four-way slider valves
               with connectors.

        6.2.6   Argon gas supply regulated at 80-100 psi

        6.2.7   Solution reservoirs—Inert containers, e.g., high density polyethylene (HDPE), for
               holding eluent and carrier reagents.

        6.2.8   Tubing—High pressure, narrow bore, inert tubing (e.g., Tefzel ETFE or equivalent) for
               interconnection of pumps and valve assemblies and a minimum length for connection
               of the preconcentration system to the ICP-MS instrument.

6.3  Inductively coupled plasma mass spectrometer

        6.3.1   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.

        6.3.2   Radio-frequency generator compliant with FCC regulations.

        6.3.3   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.

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

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

        6.3.6   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
               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.

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

 6.5    Temperature-adjustable hot plate—capable of maintaining a temperature of 95°C.
April 1995

                                                                                     Method 1640
6.6     Centrifuge with guard bowl, electric timer, and brake (optional)

6.7     Drying oven—gravity convection, with thermostatic control capable of maintaining 105°C (±

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

6.9     pH meter or pH paper

6.10    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 handling trace element samples.  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.

        6.10.1  Volumetric flasks, graduated cylinders, funnels, and centrifuge tubes

        6.10.2  Assorted calibrated pipets

        6.10.3  Beakers—fluoropolymer (or other suitable material), 250-mL with fluoropolymer

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

        6.10.5  Wash bottle—One-piece stem fluoropolymer, with screw closure, 125-mL capacity.

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

        6.10.7  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.

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

        6.10.9  Brushes—Nonmetallic, for scrubbing Apparatus.
April 1995

Method 1640
Storage bags—Clean, zip-type, nonvented, colorless polyethylene (various
sizes) for storage of Apparatus.

Plastic wrap—Clean, colorless polyethylene for storage of Apparatus.
6.11   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 the equipment is shipped 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.

       6.11.1  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

       6.11.2  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.

        6.11.3  Filtration Apparatus

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

             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).

             Tubing for use with peristaltic pump—styrene/ethylene/butylene/
                              silicone (SEES) resin, approx 3/8-in i.d. by approximately 3 ft (Cole-
                              Parmer size  18, Catalog No. G-06464-18, or approximately  1/4-in i.d.,
                              Cole-Parmer 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 hi clear polyethylene bags, serialized with a
                              unique number, and stored until use.
                                                                 April 1995

                                                                                      Method 164Q
  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 ultra high-purity grade. Suitable acids are available
         from a number of manufacturers or may be prepared by sub-boiling distillation.

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

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

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

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

         7.1.4   Nitric acid 1.25M—Dilute 79 mL (112 g) concentrated nitric acid to 1000 mL with
               reagent water.

         7.1.5  Nitric acid 1%—Dilute 10 mL concentrated nitric^acid to 1000 mL with reagent water.

         7.1.6  Hydrochloric acid—concentrated (sp gr 1.19).

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

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

        7.1.9  Hydrochloric acid (HC1)—IN trace metal grade

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

        7.1.11  Hydrochloric acid (HC1)—1% wt, trace metal grade

        7.1.12  Hydrochloric acid (HC1)—0.5% (v/v), trace metal grade

        7.1.13  Hydrochloric acid (HC1)—0.1% (v/v) ultrapure grade

        7.1.14  Acetic acid, glacial (sp gr 1.05)

        7.1.15  Ammonium hydroxide (20%)
April 1995

Method 1640
       7.1.16  Ammonium acetate buffer 1M, pH 5.5—Add 58 mL (60.5 g) of glacial acetic acid to
               600 mL of reagent water.  Add 65 mL (60 g) of 20% ammonium hydroxide and mix.
               Check the pH of the resulting solution by withdrawing a small aliquot and testing with
               a calibrated pH meter, adjusting the solution to pH 5.5 (± 0.1) with small volumes of
               acetic acid or ammonium hydroxide as necessary.  Cool and dilute to 1 L with reagent

       7.1.17  Ammonium acetate buffer 2M, pH 5.5—Prepare as for Section 7.1.16 using 116 mL.
               (121 g) glacial acetic acid and 130 mL (120 g) 20%  ammonium hydroxide, diluted to
               1000 mL with reagent water.
        NOTE: The ammonium acetate buffer solutions may be further purified by passing
        them through the chelating column at a flow rate of 5.0 mLlmin. With reference to
        Figure 1, pump the buffer solution through the column using pump PI, with valves A
        and B off and valve C on.  Collect the purified solution in a container at the waste
        outlet.  Then elute the collected contaminants from the column using 1.25M nitric acid
        for 5 min at a flow rate of 4.0 mLlmin.	

        7.1.18  Oxalic acid dihydrate (CASRN 6153-56-6), 0.2M—Dissolve 25.2 g reagent grade
               C2H2O4.2H2O in 250 mL reagent water and dilute to 1000 mL with reagent water.
        CAUTION:  Oxalic acid is toxic; handle with care.
 7.2     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).

 7.3     Standard stock solutions—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.
        CAUTION:  Many metal salts are extremely toxic if inhaled or swallowed.  (Wash
        hands thoroughly after handling.) Stock solutions should be stored in plastic bottles.

        The following procedures may be used for preparing standard stock solutions:
        NOTE: Some metals, particularly those that form surface oxides, require cleaning
        before they are weighed.  This may be achieved by pickling the surface of the metal in
        acid. An amount over the desired weight should be pickled repeatedly, rinsed with
        water, dried, and weighed until the desired weight is achieved.
April 1995

                                                                                     Method 1640
       7.3.1   Bismuth solution, stock 1 mL = 1000 ug Bi—Dissolve 0.1115 g Bi2O3 in 5 mL
              concentrated nitric acid.  Heat to effect solution.  Cool and dilute to 100 mL with
              reagent water.

       7.3.2   Cadmium solution, stock 1 mL = 1000 ug 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.

       7.3.3   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.

       7.3.4   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.

       7.3.5   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.

       7.3.6   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.

       7.3.7   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.

       7.3.8   Terbium solution, stock 1 mL = 1000  ug Tb: Dissolve 0.1176 g Tb4O7 in 5 mL
              concentrated nitric acid, heating to  effect solution.  Cool and dilute to 100 mL with
              reagent water.

       7.3.9   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.

7.4    Multielement stock standard solution—When multielement stock standards  are prepared, care
       must be taken that the elements are compatible and stable. Originating element stocks should
       be checked for the presence of impurities that might influence the accuracy of the standard.
       Freshly prepared standards should be transferred to acid-cleaned, new FEP  or HDPE bottles
       for storage and monitored periodically for stability. A multielement stock standard solution
       containing cadmium, copper, lead, and nickel (1 mL = 10 ug) may be prepared by diluting 1
       mL of each single element stock in the  list to  100 mL with reagent water containing 1% (v/v)
       nitric acid.

       7.4.1    Preparation of calibration standards—Fresh multielement calibration standards should
               be prepared every 2 weeks  or as needed. Dilute the stock multielement standard
               solution 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 ML (Table  1),  and
               another that must be near the upper end of the linear dynamic range. If the direct
               addition procedure is being used (Method A, Section 10.3), add internal standards
April 1995

 Method 1640
                (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).

 7.5     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 HEP 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).
        NOTE: Bismuth should not be used as an internal standard using the direct addition
        method (Method A, Section 10.3) because it is not efficiently concentrated on the
        iminodiacetate column.

 7.6     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 in order 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   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.

        7.6.2   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
               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 1% (v/v) nitric acid in reagent water.

7.7     Tuning solution—This solution is used for instrument tuning and mass calibration before
        analysis (Section 10.2).  The  solution is prepared by mixing nickel, yttrium, indium, terbium,
        and lead  stock solutions (Section 7.3) in 1% (v/v) nitric acid to produce a concentration of 100
        pg/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)—The 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 pg/L in 1% (v/v)  nitric acid.  Because of lower sensitivity, selenium may be diluted to a
        concentration of < 500 pg/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.
                                                                                        April 1995

                                                                                    Method 1640
 7.9    Ongoing precision and recovery (OPR) Sample—To an aliquot of reagent water, add aliquots
        of the multielement stock standard (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 they are
        aliquotted for processing or direct analysis to ensure the sample  has been properly preserved.
        If properly acid-preserved, the sample can be held up to 6 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 in  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 when the samples are collected 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 2 weeks
        of collection.  Samples and field blanks should be preserved at the laboratory immediately
        when they are received.  For 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, the sample should be acidified 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  an aliquot is withdrawn 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 16 h until verified to be
              pH <2. See Section 8.1.
April 1995

Method 1640
        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 23). The rninimum 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   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.

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

       Each time the method is modified, the analyst is required to repeat the
                       procedure in Section 9.2.  If the the change will affect the  detection limit of
                       the method, 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 the
                       change will affect calibration, the analyst must recalibrate the instrument
                       according to Section 10.

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

                   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.

                   A listing of metals measured, by name and CAS Registry

                    A narrative stating reason(s) for the modification(s).
April 1995

                                                                                      Method 1640
                    Results from all quality control (QC) 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

                    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 before the extraction/concentration step
                                      (g)     Volume after each extraction/concentration step
                                      (h)     Final volume before analysis
                                      (i)     Injection volume
                                      (j)     Dilution data, differentiating between dilution of a
                                             sample  or extract
                                      (k)     Instrument and operating conditions  (make, model,
                                             revision, modifications)
                                      (1)     Sample introduction system (ultrasonic nebulizer, flow
                                             injection system, etc.)
                                      (m)    Preconcentration system
                                      (n)     Operating conditions (background corrections,
                                             temperature program, flow rates, etc.)
                                      (o)     Detector (type, operating conditions, etc.)
                                      (p)     Mass spectra, printer tapes, and other recordings of raw
                                      (q)     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. Section
               9.6 describes the required types, procedures, and criteria for analysis of blanks.

        9.1.4   The laboratory shall spike at least 10%  of the samples with the metal(s) of interest to
               monitor method performance. Section 9.3  describes this test.  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.
April 1995

Method 1640
        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 in control.  These procedures are described in Sections 10.5 and 9.7 of this

        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 in
               the practice of this method. The laboratory must produce an MDL that is less than or
               equal to the MDL listed in Table 1, or one-third the regulatory compliance limit,
               whichever is greater. MDLs should be determined when a new operator begins work
               or whenever, in the judgment of the analyst, a change in instrument hardware or
               operating conditions would dictate that they be redetermined.

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

      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 in Section 12.  All
                      digestion, extraction, and concentration steps, and the containers, labware, and
                      reagents that will be used with samples must be used in this test.

      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
                      (s) for  each metal.

      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

        9.2.3   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 analyst
               should judge the linear calibration range that may be used for the analysis of samples
               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, in the judgement of the
April 1995

                                                                                      Method 1640
                analyst, a change in analytical performance caused by either a change in instrument
                hardware or operating conditions would dictate they be redetermined.
         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.

 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: If, as in compliance monitoring, the concentration of a specific metal in the
               sample is being checked against a regulatory concentration limit, the spike
               must be at that limit or at 1-5 times the background concentration, whichever
               is greater. 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 Determine the background concentration (B)  of each metal by analyzing one
               sample aliquot according to the procedure in  Section 12. 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. Spike a second sample aliquot with the QC check sample concentrate and
               analyze it to determine the concentration after spiking (A) of each metal. 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.
April 1995

Method 1640
      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.

      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).

      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.

      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%.

      Update the accuracy assessment for each metal in each matrix on  a regular
                       basis (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 hi  Section for this calculation because the RPD is inflated
               when the background concentration is near  the spike concentration.

                       Dl = concentration of the analyte in  the MS sample
                       D2 ~ concentration of the analyte in  the MSD sample
         9.4.2   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 be 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 that failed the RPD test.
                                                                                         April 1995

                                                                                       Method 1640
 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 in 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 2, add the
 internal standards, and reanalyze. If, after flushing, the response 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
 tuning condition of the instrument.

 Blanks—Blanks are analyzed to demonstrate freedom from contamination.

 9.6.1   Laboratory (method) blank  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
                the OPR is  analyzed (Section 9.7) to demonstrate  freedom from contamination.  If the metal of interest or any potentially interfering substance is found in the
                blank at a concentration equal to or greater than the MDL (Table 1), sample
                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. Alternatively, if a sufficient number  of blanks (3 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. 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  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.
April 1995

              Method 1640
                    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,
                                     results for associated samples may be the result of contamination and may not
                                     be reported for regulatory compliance purposes.

                    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.

                    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.

                      9.6.3  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.

                     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
                                     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.

                     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 hi the
                                      field (see Sampling  Method). Therefore, the "clean hands/duty hands"
                                      technique used during field sampling should be followed when preparing
                                      sampler check blanks at the laboratory or cleaning facility.

                                    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.
                                                                                                       April 1995

                                                                                      Method 164Q
                    The sampler check blank must be analyzed using the
                                      procedures given in 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 in the field.

                    Sampler check blanks must be run on all equipment that will
                                      be used in 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 the method blank and samples from the same batch
               are analyzed.

        9.7.3   Compute the percent recovery of each metal in 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 outside of the range given, the analytical processes are not being performed
               properly for that metal.  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%.

9.8     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.

9.9     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
April 1995

Method 1640
        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

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 in this  method.  Table 5 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 min 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 nickel isotopes 60, 61, 62.  Resolution at high mass is indicated
               by lead isotopes 206, 207, 208.  For good performance, adjust the 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%.

10.3    Internal standardization—Internal standardization must be used in all analyses to correct for
        instrument drift and physical interferences.  For full mass range scans,  a minimum of three
        internal standards must be used.  Internal  standards  must be present in  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). The concentration of the internal standard should be
        sufficiently high that good precision is obtained 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 in the sample. Internal standards should be added to blanks, samples, and
        standards in a like way so that dilution effects resulting from the addition may be disregarded.
        NOTE: Bismuth should not be used as an internal standard using the direct addition
        method (Method A, Section 10.3) because it is not efficiently concentrated on the
        iminodiacetate column.

 10.4    Calibration—Before initial calibration, set up proper instrument software routines for
        quantitative analysis and connect the ICP-MS instrument to the preconcentration apparatus.
April 1995

                                                                                     Method 1640
       The instrument must be calibrated at a minimum of three points for each analyte to be

       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 ML
              (Table 1), and another that must be near the upper end of the linear dynamic range.
              The calibration solutions should be processed through the preconcentration system
              using the procedures described in Section 12.  A minimum of three replicate
              integrations are 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 =
                C  = concentration of the analyte in the standard or blank solution
               C.  = concentration of the internal standard in the solution
                As - 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.

       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,

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.
April 1995

 Method 1640
        10.5.4 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

 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

 11.0  Procedures for Cleaning the  Apparatus

 11.1    All sampling equipment, sample containers, and labware should be cleaned in 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 24), labware cleaning
        areas as described by Patterson and Settle (Reference 6), or clean benches.

 11.2    Materials, such as gloves (Section 6.10.7),  storage bags (Section 6.10.10), and plastic wrap
        (Section 6.10.11), 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.
        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 of analytes
        above the MDL, those cleaning steps that do not eliminate these artifacts may be
        omitted if all performance criteria outlined in Section 9 are met.

        11.3.1  Bottles, labware, and sampling equipment

             Fill  a precleaned basin (Section 6.10.8) with a sufficient quantity of a
                              0.5% solution of liquid detergent (Section 6.8), and completely
                              immerse each piece  of ware.  Allow to soak in the detergent for at
                              least 30 min.

             Using a pair of clean gloves (Section 6.10.7) and clean nonmetallic
                              brushes (Section 6.10.9), thoroughly scrub down all materials with the

             Place the scrubbed materials in a precleaned basin.  Change gloves.
                                                                                      April 1995

                                                                                       Method 1640
 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 h.

 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 in a hot (50-60°C) bath of
 IN trace metal grade HC1 (Section 7.1.9), and allow  to soak for at
 least 48 h.

 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

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

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

         11.3.3  Fluoropolymer sample bottles—These bottles should be used if mercury is a target
After cleaning, fill sample bottles with 0.1% (v/v) ultrapure HC1
(Section 7.1.13) and cap tightly. It may be necessary to use a strap
wrench to assure a tight seal.

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
Apply the steps outlined in Sections to all bottles,
labware, and sampling equipment. Proceed with Section for.
bottles or Section for labware and sampling equipment.

After cleaning, fill each bottle with 0.1% (v/v) ultrapure HC1  (Section
7.1.13).  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.
April 1995

                Method 1640
                            After rinsing labware and sampling equipment, air-dry in a class 100
                                             clean air bench. After drying, wrap each piece of ware or 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 for vapors tp
                        diffuse through the polyethylene.	

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

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

                                  Dry by hanging upside down from a plastic line with a plastic

                        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 7.1.10) 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 6.10.9) should be used to scrub the pole with reagent water and the pole
                               wiped down with acids described in Section 11.3.4.  After cleaning, the pole should be
                               wrapped in polyethylene film.

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

                        All cleaning solutions and acid baths should be periodically  monitored for accumulation of
                        metals that could lead to contamination. When levels of metals in the solutions become too
                        high, the solutions and baths should be changed and the old solutions neutralized and
                        discarded in 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 in 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 in the calculations.
                                                                                      April 1995

  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
         12.2.1-12.2.6 in a fume hood that is located in a clean room.  An alternate digestion
         procedure is provided in Section 12.2.7; 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 6.10.3).  If appropriate, a smaller sample volume may be used.

         12.2.2  Add 2 mL (1+1) nitric acid to the beaker and place the beaker on the hot plate for
                digestion.  The hot plate should be located in 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 so 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.)

         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 h 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 min. (Slight boiling may occur, but vigorous boiling
               must be  avoided.)

        12.2.5 Allow the beaker to cool. Quantitatively transfer the sample solution to a 100-mL
               volumetric flask, 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.)  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

        12.2.7  Alternate total recoverable digestion procedure
April 1995

Method 1640
            Open the preserved sample under clean conditions. Add ultrapure
                             nitric acid at the rate of 10 mL/L.  Remove the cap from the original
                             container only long enough to add the aliquot of acid. The sample
                             container should not be filled to the lip by the addition of the acid.
                             However, only minimal headspace is needed to avoid leakage during

            Tightly recap the container and shake thoroughly. Place the container
                             hi 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
                             h.  (Total time will be 2.5-3 h depending on the sample size).
                             Temperature can be monitored using an identical sample container with
                             distilled  water and a thermocouple to standardize heating tune.

            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.

 12.3    Before first use, the preconcentration system should be thoroughly cleaned and decontaminated
        using 0.2M oxalic acid.

        12.3.1  Place approximately 500 mL 0.2M oxalic acid hi all the eluent/solution containers and
               fill the sample loop with 0.2M oxalic acid using the sample pump (P4) at a flow rate
               of 3-5 mL/min.  With the preconcentration system disconnected from the ICP-MS
               instrument, use the pump program sequence listed in Table 3, to flush the complete
               system with oxalic acid., Repeat the flush sequence three times.

        12.3.2  Repeat the sequence described in Section 12.3.1 using  1.25M nitric acid and again
               using reagent water hi place of the 0.2M oxalic acid.

        12.3.3  Rinse the containers thoroughly with reagent water, fill them with their designated
               reagents  (see Figure 1),  and run through the sequence in Table 3 once to prime the
               pump and all eluent lines with the correct reagents.

 12.4    Sample Analysis

        12.4.1  Initiate ICP-MS  instrument operating configuration.  Tune the instrument for the
               analytes  of interest (Section 10).

        12.4.2  Establish instrument software run procedures for quantitative analysis. Because the
               analytes  are eluted from the preconcentration column in a transient manner, it is
               recommended that the instrument software be configured hi a rapid scan/peak hopping
               mode. The instrument is now ready to be calibrated.

        12.4.3  Reconnect the preconcentration system to the ICP-MS  instrument. With valves A and
               B hi the off position and valve C in the on position, load the sample through the
               sample loop to waste using pump P4 for 4 nun at 4 mL/min.  Switch on the carrier
April 1995

                                                                                  Method 1640
              pump (P3) and pump 1% nitric acid to the nebulizer of the ICP-MS instrument at a
              flow rate of 0.8-1.0 mL/min.

       12.4.4 Switch on the buffer pump (P2), and pump 2M ammonium acetate at a flow rate of
              1.0 mL/min.

       12.4.5 Preconcentration of the sample may be achieved by running through an eluent pump
              program (PI) sequence similar to that illustrated in Table 3.  The exact timing of this
              sequence should be modified according to the internal volume of the connecting tubing
              and the specific hardware configuration used.

           Inject sample—With valves A, B and C on, load sample from the loop
                            onto the column using 1M ammonium acetate for 4.5 min at 4.0
                            mL/min.  The analytes are retained on the column, while most of the
                            matrix is passed through to waste.

          Elute analytes—Turn off valves A and B  and begin eluting the
                            analytes by pumping 1.25M nitric acid through the column at 4.0
                            mL/min, then turn off valve C and pump  the eluted analytes into the
                            ICP-MS instrument at 1.0 mL/min.  Initiate ICP-MS software data
                            acquisition and integrate the eluted analyte profiles.

          Column Reconditioning—Turn on valve C to direct column effluent to
                            waste, and pump 1.25M nitric acid, 1M ammonium acetate, 1.25M
                            nitric acid and 1M ammonium acetate alternately through the column
                            at 4.0 mL/min. During this process, the next sample can be loaded
                            into the sample loop using the sample pump  (P4).

       12.4.6 Repeat the sequence described in Section  12.4.5 for each  sample to be analyzed. At
              the end of the analytical run, leave the column filled with 1M ammonium acetate
              buffer until it is next used.

       12.4.7 Samples having concentrations higher than the established linear dynamic range should
              be diluted into range with 1% HNO3 (v/v) and reanalyzed.
13.0  Data Analysis and  Calculations

13.1   Elemental equations recommended for sample data calculations are listed in Table 4. Sample
       data should be reported hi 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   Compute the concentration of each analyte in the sample using the response factor determined
       from calibration data (Section 10.4) and the following equation:
April 1995

Method 1640
                                     C (mglL) =
                                                  Ats x RF
                        Where the  terms are as defined in Section 10.4.2.
 13.4    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.

 13.5    If an element has more than one monitored m/z, examination of the concentration calculated
        for each m/z, or the 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.

 13.6    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.

 13.7    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 25) for dissolved
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. Many 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
        properly.  Standards should be prepared in volumes consistent with laboratory use to minimize
        the volume of expired standards to be disposed.
                                                                                     April 1995

                                                                                  Method 1640
 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 the 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, VA, 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. "Accuracy in Trace Analysis"; In National Bureau of Standards
       Special Publication 422; LaFleur, P.D., Ed., U.S. Government Printing Office, Washington,
       DC, 1976.

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, Martha 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, Oct. 1, 1993.
April 1995

Method 1640
10     "Format for Method Documentation", Distributed by the EPA Environmental Monitoring
       Management Council, Washington, DC, Nov. 18, 1993.

11     Siraraks, A.; Kingston, H.M.; Riviello,  J.M. Anal Chem. 1990, 62, 1185.

12     Heithmar, E.M., Hinners, T.A.; Rowan, J.T.; Riviello, J.M. Anal Chem. 1990, 62, 857.

13     Gray, A.L.; Date, A.R. Analyst, 1983, 708, 1033.

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

15     Houk, R.S. Anal. Chem.  1986, 58, 97A.

16     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.

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

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

19     Carcinogens - Working With Carcinogens; Department of Health, Education, and Welfare,
       Public Health Service. Centers 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.

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

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

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

23     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.

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

25     "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.
April 1995

                                                                                      Method 1640
  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.
 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.

 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).

 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

 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).

 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 they are used.

 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.

 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.
April 1995

Method 1640
18.10  Initial Precision and Recovery (IPR)—Four aliquots of the OPR standard analyzed to
       establish the ability to generate acceptable precision and accuracy. IPRs are performed before
       the first time a method is used 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 (MSD).

 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.
April 1995

                                                                                     Method 164Q
 18.24  Method Blank—See Laboratory Blank.

 18.25  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).

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

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

 18.28  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).

 18.29  Preparation Blank—See Laboratory Blank.

 18.30  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.

 18.31  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.

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

 18.33  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

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

Tuning Solution—A solution used to determine acceptable instrument performance before
calibration and sample analyses (Section 7.7).
April 1995

Method 1640
                                                        Table 1

   List of Analytes Amenable to Analysis Using Method 1640:  Lowest Water Quality Criterion
                   for Each Metal  Species, Method Detection Limits, Minimum Levels,
                                     and Recommended Analytical Masses


Water Quality
Method Detection Limit
(MDL) and Minimum
Level (ML); ug/L

Analytical m/z

206, 207, 208
1.        Lowest of the freshwater, marine, and human health WQC promulgated by EPA for 14 states at 40 CFR Part 131 (57 FR 60848), with hardness-dependent
          freshwater aquatic life criteria adjusted In accordance with 57 FR 60848 to reflect the worst case hardness of 25 mg/L CaCO, and all aquatic life criteria
          adjusted In accordance with the Oct. 1,1993 Office of Water guidance to reflect dissolved metals criteria.

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 BAD and described In the EPA Draft National Guidance for the Permitting, Monitoring, and Enforcement of Water Quality-Based
          Effluent Limitations Set Below Analytical Deteetion/Quantitatlon Levels, March 22,1994.
April 1995

                                                                   Method 1640
                             IN EPA METHOD 16401
Initial Precision and
Recovery (Section 9.2)
s X
23 75-121
43 67-154
44 56-144
27 74-128
Calibration Verification
(Section 10.5)
Ongoing Precision and
Recovery (Section 9.7)
Spike Recovery
(Section 9.3)
All specifications expressed as percent
April 1995

Method 1640
                                OF TRACE ELEMENTS
                     Time     Flow
                     (min)   (mL/min)
Valve  Valve
 A,B     C
                      0.0      4.0      1M ammonium acetate   ON     ON
                      4.5      4.0         1.25MHN03       ON     ON
                      5.1      1.0         1.25MHNO3       OFF    ON
                      5.5      1.0         1.25MHNO3       OFF    OFF
                      7.5      4.0         1.25MHNO3       OFF    ON
                      8.0      4.0      1M ammonium acetate   OFF    ON
                      10.0      4.0         1.25MHNO3       OFF    ON
                      11.0      4.0      1M ammonium acetate   OFF    ON
                      12.5      0.0                        OFF    ON
                       April 1995

                                                                          Method 1640
                                     FOR DATA CALCULATIONS
Elemental Equation


  C—counts at specified m/Z.
  (1)—correction for MoO interference. An additional isobaric elemental correction should be made if
  palladium is present.
  (2)—allowance for variability of lead isotopes.

  NOTE:  As a minimum, all isotopes  listed should be monitored.  Isotopes recommended for analytical
  determination are underlined.
April 1995

 Method 1640

         Preconcentration column
Dionex chelation system
Dionex MetPac CC-1
         ICP-MS Instrument Conditions

         Plasma forward power
         Coolant flow rate
         Auxiliary flow rate
         Nebulizer flow rate

         Internal standards

         Data Acquisition

         Detector mode
         Mass range
         Dwell time
         Number of MCA channels
         Number of scan sweeps
VG PlasmaQuad Type I
1.35 kW
13.5 L/min
0.6 L/min
0.78 L/min

Sc, Y, In, Tb
Pulse counting
45-240 amu
160 us
                                                                            April 1995

                                                                          Method 1640
                   Figure 1. Configuration of Preconcentration System
 2M NH4OAc
                                      1M NH4OAc 1.25 M Nitric Acid
                                                                    1% Nitric Acid
                                                            • Mixing Tee
                                                            Qoff Q
April 1995