United States           Office of Water                  EPA821-R-95-030
          Environmental Protection      Engineering and Analysis Division (4303)       April 1995
          Agency             Washington, DC 20460
&EPA    Method 1637:  Determination of Trace
          Elements in Ambient Waters by
          Chelation Preconcentration with
          Graphite Furnace Atomic Absorption
                       I'.S. Environmental Protection Agency
                       region 5, Library (,r;i.-12J)
                       1' '-Vest Jackson Boulevard, 12th Floor
                       C.Mcago, IL  60604-3b90
                                                ) Printed on Recycled Paper

Method 1637
Method 1637  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 in marine chemistry contributed to  the philosophy behind this method. Their
contribution is gratefully acknowledged:

Shier Berman, National Research Council, Ottawa, Ontario, Canada
Nicholas Bloom, Frontier Geosciences Inc., Seattle, Washington
Paul Boothe and Gary Steinmetz, Texas A&M University, College Station, Texas
Eric Crecelius, Battelle Marine Sciences Laboratory, Sequim, Washington
Russell Flegal, University of California/Santa Cruz, California
Gary 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, J.T. Creed and T.D. Martin of 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.
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
U.S. Environmental Protection Agency
Office of Water
Analytical Methods Staff
Mail Code 4303
401 M Street SW
Washington, DC 20460
                                                                                    April 1995

                                                                                      Method 1637
This analytical method was designed to support water quality monitoring programs authorized under the
Clean Water Act.  Section 304(a) of the Clean Water Act requires EPA to publish water quality criteria
that reflect the latest scientific knowledge concerning the physical fate (e.g., concentration and dispersal)
of pollutants, the effects of pollutants on ecological and human health, and the effect of pollutants on
biological community diversity, productivity, and stability.

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

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

In some cases, these water quality criteria are as much as 280 times  lower than those achievable  using
existing EPA methods and required to support technology-based permits. Therefore, EPA developed new
sampling and analysis methods to specifically  address state needs  for measuring toxic metals at  water
quality criteria levels, when such measurements are necessary to protect designated uses in state  water
quality standards.  The latest criteria published by EPA are  those listed 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  1637 was  specifically developed to provide
reliable measurements of two of these metals at EPA WQC levels using off-line chelation preconcentration
and stabilized temperature graphite furnace atomic  absorption 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                                                                                       in

Method 1637
    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 procedure
    can be modified or omitted if the laboratory can demonstrate that data quality is not affected.
iv                                                                                     April 1995

                                                                            Method 1637
                              Method  1637

       Determination of Trace  Elements  in Ambient  Waters
      by Off-Line Chelation Preconcentration  and Stabilized
        Temperature Graphite Furnace Atomic Absorption

1.0    Scope and Application

1.1     This method provides procedures for the determination of dissolved elements in ambient waters
       at EPA water quality criteria (WQC) levels using off-line chelation preconcentration and stabilized
       temperature graphite furnace atomic absorption (GFAA). It may also be used for determination
       of total recoverable element concentrations in these waters.  This method was  developed by
       integrating the analytical procedures in EPA Method 200.13 with the stringent 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 ensure 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 analytes:
Chemical Abstract Services
Registry Number (CASRN)
       Table 1 lists the EPA WQC levels, the method detection limit (MDL) for each metal, and the
       minimum level (ML) set for each metal in this method.  Instrument operating conditions for the
       applicable elements are listed in Table 3. These are intended as a guide and are typical of a
       system optimized for the element employing commercial instrumentation.  However, actual linear
       working ranges will be dependent on the sample matrix, instrumentation, and selected operating

1.3     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.

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
April 1995

Method 1637
       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 EPA 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 and copied from  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  equivalent performance.

1.8    For dissolved metal determinations, samples must be filtered through a 0.45-pm 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; procedures for laboratory preservation are
       provided in this method.

1.9    For the determination of total recoverable analy tes in ambient water samples, a digestion/extraction
       is required before analysis when the elements are not in solution (e.g., aqueous samples that may
       contain paniculate and suspended solids).

1.10   The sensitivity and limited linear dynamic range (LDR) of GFAA often implies the need to dilute
       a sample before analysis. The actual magnitude of the dilution as well as the cleanliness of the
       labware used to perform the dilution can dramatically  influence the  quality of the  analytical
       results.  Therefore, sample  types requiring large dilutions (>50:1) should be analyzed by an
       another approved test procedure that has a larger LDR or is inherently less sensitive than GFAA.

1.11   This method should be used  by analysts experienced in the use of graphite  furnace  atomic
       absorption spectroscopy, the  interpretation of spectral and matrix interferences, and procedures for
       their correction, and 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.

1.12   This method is accompanied by a data verification and validation guidance  document,  Guidance
       on the Documentation and Evaluation of Trace  Metals Data Collected for CWA Compliance
       Monitoring.  Before using this method, data users should state the data quality objectives (DQOs)
       required for a project.
                                                                                      April 1995

                                                                                     Method 1637
2.0    Summary of Method

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

2.2     This method  is used to preconcentrate trace  elements using an iminodiacetate functionalized
        chelating resin (References 11 and 12). After a sample is prepared, it is buffered using an on-line
        system before it enters the chelating column.  Group I and II metals, as well as most 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 0.75 M nitric acid and are
        determined by stabilized temperature platform graphite furnace atomic absorption (STPGFAA).

2.3     In STPGFAA, the sample and the matrix modifier are first pipetted onto the platform or a device
        that provides delayed atomization.  The furnace chamber is then purged with a continuous flow
        of a premixed gas  (95%  argon-5% hydrogen) and  the sample is  dried  at  a relatively low
        temperature (about 120°C) to avoid spattering. Once dried, the sample is pretreated in a char or
        ashing step that is designed to minimize the interference effects caused by the concomitant sample
        matrix. After the char step, the furnace is allowed to cool before atomization.  The atomization
        cycle is characterized by rapid heating of the furnace to a temperature at which the metal (analyte)
        is atomized from the pyrolytic graphite surface into a stopped gas flow atmosphere of argon
        containing 5% hydrogen. The resulting atomic cloud absorbs the element specific atomic emission
        produced by a hollow cathode lamp  (HCL) or an electrodeless discharge lamp (EDL).   After
        analysis, the furnace is subjected to a cleanout period of high temperature and continuous argon
        flow. Because the resulting absorbance usually has a nonspecific component associated with the
        actual  analyte absorbance, an instrumental background correction device is  required to subtract
        from the total signal the component that is  nonspecific to the analyte.  In the  absence  of
        interferences,  the background corrected absorbance is directly related to the concentration of the
        analyte.  Interferences relating to STPGFAA  (Section 4.0)  must be recognized and corrected.
        Suppressions  or enhancements of instrument  response caused by  the sample matrix must be
        corrected by the method of standard  addition (Section 12.6).
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.
April 1995

Method 1637
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 with 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 13).
       Therefore, it is imperative that extreme care be taken to avoid contamination when collecting and
       analyzing ambient water samples for trace metals.

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

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.   This method  and the Sampling Method give  requirements and
                      suggestions for controlling sample contamination.

       Substances in a sample cannot be allowed to contaminate the laboratory work area
                      or instrumentation used for trace metals measurements.  This method  gives
                      requirements and suggestions for protecting the laboratory.

       Although contamination control is essential, personnel health and safety remain
                      the highest priority.  The Sampling  Method and Section 5 of this method give
                      requirements and suggestions for personnel safety.

       4.3.2   Avoid 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 or thought 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.
                                                                                     April 1995

                                                                                     Method 1637
               be performed in a class 100 clean bench or a nonmetal glove box fed by particle-free air
               or nitrogen.  Digestions must be performed in a nonmetal fume hood, ideally situated in
               the clean room.

        4.3.4   Minimize exposure—The Apparatus  that will contact  samples,  blanks, or  standard
               solutions must only be opened or exposed 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 in the clean bench or in a
               plastic box or glove box, or bagged in clean zip-type bags. Minimizing the time between
               cleaning and use will also minimize contamination.

        4.3.5   Clean work surfaces—Before processing a given batch of samples, all work surfaces in
               the hood, clean bench, or glove box 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 pair of clean gloves put on.  Wearing multiple layers of clean gloves
               will allow the old pair to be quickly stripped with minimal disruption to the work activity.

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

      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 must not be
                      used to hold liquids that come in contact with the sample or must not contact the
                      sample itself, 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 14).

      Serialization—It is recommended that  serial numbers be  indelibly marked  or
                      etched on  each piece of Apparatus  so that contamination can  be traced, and
April 1995

Method 1637
                      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.

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

      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 dirty plastic bag may pick up contamination from the bag
                      and then subsequently transfer the contamination to the sample.  Therefore, it is
                      imperative that every piece of the Apparatus that is directly or  indirectly used in
                                                                                       April 1995

                                                                                    Method 1637
                      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—Several interference sources may cause inaccuracies in the determination of trace
       elements by GFAA.  These interferences can be classified into three major subdivisions: spectral,
       matrix, and memory. Some of these interferences can be minimized through the preconcentration
       step, which reduces  the Ca, Mg,  Na, and chloride concentrations in the sample before GFAA

       4.4.1    Spectral interferences are  caused by  the absorbance of light by a molecule or atom that
               is not the analyte  of interest or emission from black body  radiation.

      Spectral interferences caused by an element only occur if there is a  spectral
                      overlap between the wavelength of the interfering element and the analyte of
                      interest.   Fortunately, this  type of  interference is relatively uncommon  in
                      STPGFAA because of the narrow atomic line widths associated with STPGFAA.
                      In addition, the use of appropriate furnace temperature programs and high spectral
                      purity  lamps as light sources can minimize the possibility of this type  of
                      interference.   However,  molecular  absorbances can   span  several  hundred
                      nanometers, producing broadband spectral interferences. This type of interference
                      is  far more common in STPGFAA.   The use of matrix modifiers,  selective
                      volatilization, and background correctors are all attempts to eliminate unwanted
                      nonspecific absorbance.  Since the nonspecific component of the total absorbance
                      can vary  considerably from sample  type to sample type, to  provide  effective
                      background correction and eliminate elemental spectral interferences, the exclusive
                      use of Zeeman background correction is specified  in this method.

      Spectral interferences are also caused by black body radiation produced during the
                      atomization furnace cycle. This black body emission reaches the photomultiplier
                      tube, producing erroneous results.   The magnitude of this interference can be
                      minimized by proper furnace  tube  alignment and monochromator design.   In
                      addition, atomization temperatures that adequately volatilize the analyte of interest
                      without producing unnecessary black body radiation can help reduce unwanted
                      background emission produced during atomization.

       4.4.2   Matrix interferences are caused by sample components that inhibit the formation of free
               atomic analyte atoms during the atomization cycle. In this method, the use of a delayed
               atomization  device that provides  warmer gas phase  temperatures is  required.  These
               devices provide an environment that is more conducive  to the formation of free analyte
               atoms and thereby minimize this type of interference.  This type of interference can be
               detected  by  analyzing the  sample plus  a sample  aliquot fortified with  a known
April 1995

Method 1637
               concentration of the analyte.  If the determined concentration of the analyte addition is
               outside a designated range, a possible matrix effect should be suspected (Section 9.3)

        4.4.3   Memory interferences result from analyzing a sample containing a high concentration of
               an element (typically  a high atomization temperature element) that cannot be removed
               quantitatively in one  complete set of furnace steps.  The  analyte  that remains in the
               furnace can produce false positive signals on subsequent sample(s). Therefore, the analyst
               should establish the  analyte concentration that can be injected into  the  furnace and
               adequately removed  in  one complete set of furnace cycles.  If this  concentration is
               exceeded, the sample should be diluted and a blank analyzed to ensure the memory effect
               has been eliminated before reanalyzing the diluted sample.

        4.4.4   Low recoveries may be encountered in the preconcentration cycle if the trace elements are
               complexed by competing chelators (humic/fulvic) 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.

        4.4.5   Memory  interferences from the chelating system may be encountered, especially  after
               analyzing a sample containing high  analyte concentrations.  A thorough column rinsing
               sequence following elution of the analytes is necessary to minimize such interferences.
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
               15-18).  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 18 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.  Acidification of samples should be done 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.
                                                                                       April 1995

                                                                                     Method 1637
 5.4     During atomization, the graphite tube emits intense UV radiation. Suitable precautions should be
        taken to protect personnel from such a hazard.

 5.5     The  use  of the argon/hydrogen gas mixture  during the  dry and char steps may evolve  a
        considerable amount of HC1 gas. Therefore, adequate ventilation is required.
 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 must
                      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 room.

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

 6.2     Graphite Furnace Atomic Absorbance Spectrophotometer

        6.2.1   The GFAA spectrometer must be capable of programmed heating of the graphite tube and
               the associated  delayed atomization device.  The instrument must be equipped with an
               adequate  background  correction device capable of  removing undesirable nonspecific
               absorbance over  the spectral region of interest and provide an analytical condition not
               subject to the  occurrence of interelement  spectral overlap interferences.  The furnace
               device must be capable  of using an alternate gas supply during  specified cycles of the
               analysis.  The capability to record relatively fast (< 1 s) transient signals and evaluate data
               on a peak  area  basis is preferred.   In addition, a  recirculating refrigeration bath  is
               recommended for improved reproducibility of furnace temperatures.

        6.2.2   Single  element hollow cathode  lamps or single  element electrodeless discharge lamps
               along with the  associated power supplies

        6.2.3   Argon gas supply (high-purity grade, 99.99%) for use during the atomization of selenium,
               for sheathing the furnace tube when in operation, and during furnace cleanout
April 1995

Method 1637
        6.2.4   Alternate gas  mixture  (hydrogen 5%-argon 95%) for use as a continuous gas  flow
               environment during the dry and char furnace cycles

        6.2.5   Autosampler capable of adding matrix modifier solutions to the furnace, a single addition
               of analyte, and completing methods  of standard additions when required

6.3     Preconcentration system—System containing no metal parts in the analyte flow path, configured
        as shown with a sample loop in Figure 1 and without a sample loop in Figure 2.
        NOTE: An alternate preconcentration system to the one described below may be used if
        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.

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

        6.3.2   Control valves—Inert double stack, pneumatically operated four-way slider valves with

        6.3.3   Argon gas supply regulated at 80-100 psi

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

        6.3.5   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 with the sample collection vessel

        6.3.6   Eluent  pumping system (gradient pump)—Programmable  flow, high-pressure pumping
               system, capable of delivering either one of three eluents at  a pressure up to 2000 psi and
               a flow rate of 1-5 mL/min

        6.3.7   System setup, including sample loop (Figure 1)

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

       Auxiliary  pumps

                    On-line  buffer  pump—Piston pump (Dionex QIC  pump  or
                                     equivalent) for delivering 2 M ammonium acetate buffer solution

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

                    Sample pump—Peristaltic pump for loading sample loop
10                                                                                    April 1995

                                                                                     Method 1637
        6.3.8   System setup without sample loop (Figure 2)

      Auxiliary Pumps

                   Sample pump (Dionex  QIC  pump or equivalent) for loading
                                     sample on the column

                   Carrier pump  (Dionex QIC pump or equivalent)  used to flush
                                     collection line between samples

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

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

6.7     Gravity convection drying oven—with thermostatic control capable of maintaining 105°C (± 5°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 trace element sample  handling.   Sample containers  can
        introduce positive and negative errors in the determination of trace elements  by (1) contributing
        contaminants through surface desorption or  leaching, and (2) depleting element concentrations
        through adsorption processes. All labware must be metal free.  Suitable construction materials
        are  fluoropolymer  (FEP,  PTFE),  conventional or  linear  polyethylene, polycarbonate,  and
        polypropylene. Fluoropolymer should be used  when samples are to be analyzed for mercury.  All
        labware should be cleaned according to the procedure  in Section 11.4.  Gloves, plastic wrap,
        storage bags, and filters may all be used new without additional cleaning unless  results of the
        equipment blank pinpoint any of these materials as a source of contamination.  In this case, either
        an alternate supplier must be obtained or the materials must be cleaned.

        NOTE: Chromic acid must not be used for cleaning glassware.

        6.10.1  Volumetric flasks, graduated cylinders, funnels and centrifuge tubes

        6.10.2  Assorted calibrated pipets

        6.10.3  PTFE (or other suitable material) beakers—250-mL with PTFE covers

        6.10.4  Narrow-mouth storage bottles—FEP (fluorinated ethylene propylene) with ETFE (ethylene
               tetrafluorethylene) screw closure, 125-250 mL capacities
April 1995                                                                                     11

Method 1637
       6.10.5  One-piece stem FEP wash bottle—with screw closure, 125-mL capacity

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

       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  Nonmetallic brushes—for scrubbing Apparatus

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

       6.10.11        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
       who  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 9.5.3)  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.  The Sampling  Method describes various types of samplers.  Cleaned
               sampling devices should be stored in polyethylene bags or wrap.

       6.11.2  Sample  bottles—Fluoropolymer (FEP, PTFE),  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

             Filters, Gelman Supor 0.45-um,  15-mm diameter filter capsules (Gelman
                              12175), or equivalent

             Peristaltic pump—115-V a.c., 12-V d.c., internal battery, variable-speed,
                              single-head (Cole-Parmer, 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, approximately 3/8-in i.d. by approx 3 ft (Cole-Parmer size
                              18, Catalog No. G-06464-18, or approximately 1/4-in i.d., Cole-Parmer
 12                                                                                     April 1995

                                                                                     Method 1637
                              size 17, Catalog No. G-06464-17, or equivalent). Tubing is cleaned by
                              soaking in 5-10% HC1 solution for 8-24 h, rinsing with reagent water in
                              a clean bench in a clean room, and drying in the clean bench by purging
                              with metal-free air or nitrogen. After drying, the tubing is double-bagged
                              in clear polyethylene bags, serialized with a unique number, and stored
                              until use.
7.0    Reagents and Standards

        Reagents may contain elemental impurities that might affect analytical data. Only high-purity
        reagents should be used. If the purity of a reagent is in question, analyze for contamination. All
        acids used for this method must be of ultra high-purity grade or equivalent.  Suitable acids are
        available from a number of manufacturers. Redistilled acids prepared by sub-boiling distillation
        are acceptable.

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

        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 0.75 M—Dilute 47.7 mL (67.3 g) concentrated nitric acid to 1000 mL with
               reagent water.

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

        7.1.5   Hydrochloric acid, concentrated (sp gr 1.19)

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

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

        7.1.8   Hydrochloric acid (HC1)—IN trace metal grade

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

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

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

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

        7.1.13  Acetic acid,  glacial (sp gr  1.05)
April 1995                                                                                     13

Method 1637
       7.1.14  Ammonium hydroxide (20%)

       7.1.15  Ammonium acetate buffer 1 M, 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 water.

       7.1.16  Ammonium acetate buffer 2 M, pH 5.5—Prepare as for Section 7.1.15 using 116 mL (121
               g) glacial acetic acid and 130 mL (120 g) 20% ammonium hydroxide, diluted to 1000 mL
               with reagent water.
       NOTE: If the system is configured as shown in Figure 1, the ammonium acetate buffer
       solutions may be further purified by passing them through the chelating column at a flow
       rate of 5.0 mL/min.  Collect the purified solution in a container.  Then elute the collected
       contaminants from the column using 0.75 M nitric acid for 5 min at a flow rate of 4.0
       mL/min.  If the system is configured as shown in Figure 2, most of the buffer is being
       purified in an on-line configuration  through the cleanup column.

       7.1.17 Oxalic  acid  dihydrate  (CASRN  6153-56-6), 0.2  M—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    Matrix Modifier—Dissolve 300 mg palladium (Pd) powder in a minimum amount of concentrated
       HNO3 (1 mL of HNO3, adding  concentrated HC1  only  if necessary).  Dissolve 200 mg of
       Mg(NO3)2-6H2O in  reagent water.  Pour the two solutions together and dilute to  100 mL with
       reagent water.
        NOTE: It is recommended that the matrix modifier be analyzed separately to assess the
        contribution of the modifier to the overall laboratory blank.

7.4     Standard stock solutions—Stock standards may be purchased or prepared from ultra high-purity
        grade chemicals (99.99 to 99.999% pure).  All compounds must be dried for 1 h at 105°C, unless
        otherwise specified.  It is recommended that stock  solutions be stored in FEP bottles. Replace
        stock standards when succeeding dilutions for  preparation of calibration standards cannot be
14                                                                                    April 1995

                                                                                     Method 1637
        CAUTION:  Many of these chemicals are extremely toxic if inhaled or  swallowed
        (Section 5.1).  Wash hands thoroughly after handling.
        Below are typical stock solution preparation procedures for 1-L quantities, but for the purpose of
        pollution prevention,  the analyst is  encouraged to prepare smaller  quantities  when possible.
        Concentrations  are calculated  based  on the weight of the pure element or the weight of the
        compound multiplied by the fraction  of the analyte in the compound.

        From pure element,
                                  Concentration  - we*ht
                                                   volume (L)
        From pure compound,
                        Concentration  = **** <**> *
                                                    volume (L)

              gravimetric factor  = the weight fraction of the analyte in the compound.
        7.4.1   Cadmium solution, stock—1 mL - 1000 ug Cd:  Dissolve 1.000 g Cd metal, acid-cleaned
               with (1+9) HNO3, weighed accurately to at least four significant figures, in 50 mL (1+1)
               HNO3 with heating to effect dissolution. Let solution cool and dilute with reagent water
               in a 1-L volumetric flask.

        7.4.2   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.

7.5     Preparation of calibration standards—Fresh calibration standards should  be prepared every 2
        weeks, or as needed. Dilute each stock standard solution to levels appropriate to the operating
        range of the instrument using reagent water containing 1%  (v/v) HNO3.  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.  Calibration standards
        should be initially verified using a quality control sample (Section 7.7).

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 autosampler uptake system.  All diluent acids
        should be made from concentrated acids  (Section 7.1) and reagent water (Section 7.2). In addition
        to  these blanks, the  laboratory  may be required to analyze field blanks (Section 9.5.2)  and
        equipment blanks  (Section 9.5.3).
April 1995                                                                                     15

Method 1637
       7.6.1   Calibration blank—The calibration blank consists of 1% (v/v) HNO3 in reagent water.
               The calibration blank should be stored in a FEP bottle.

       7.6.2   Laboratory blank—Must contain all the reagents in the same volumes as those 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 9.5.1).

       7.6.3   The rinse blank is prepared  as needed by adding 1.0 mL of concentrated HNO3 and 1.0
               mL concentrated HC1 to 1 L of reagent water.

7.7    Quality control sample (QCS)—The QCS must be obtained from an outside source different from
       the  standard stock solutions and prepared in  the same acid mixture as that for the calibration
       standards.  The concentration of the analytes in the QCS solution should be such that the resulting
       solution will provide an absorbance reading of approximately 0.1.  The QCS solution should be
       stored in a FEP bottle and analyzed as needed to meet data quality needs. A fresh solution should
       be prepared quarterly or more frequently as needed.

7.8    Ongoing precision and recovery (OPR) sample—The OPR should be prepared in the same acid
       mixture as that for the calibration standards by combining method analytes at appropriate
       concentrations. The OPR must  be carried through the same entire preparation scheme as that for
       the samples including sample digestion, when applicable (Section 9.6).
8.0    Sample Collection, Filtration, Preservation, and Storage

8.1     Before an aqueous sample is collected, consideration should be given to the type of data required,
        (i.e., dissolved or total recoverable), so that appropriate preservation and pretreatment steps can
        be taken.  The pH of all aqueous samples  must be  tested immediately before aliquotting  for
        processing or direct analysis to ensure the sample has  been properly preserved. If properly acid-
        preserved, the sample can be held up to 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  urn
        capsule filter at the field site.  The Sampling Method describes the filtering procedures.  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 7.1.4) to bring the sample to pH
        < 2. For samples received at  neutral pH, approx 5 mL of 10% HNO3 per liter will be required.
 16                                                                                   April 1995

                                                                                    Method 1637
       8.4.1    Wearing clean gloves, remove the cap from the sample bottle, add the volume of reagent
               grade acid that will bring the pH to < 2, and recap the bottle immediately. If the bottle
               is full, withdraw the necessary volume using a precleaned pipet and then add the acid.
               Record the volume withdrawn and the amount of acid used.
       NOTE: Do not dip pH paper or a pH meter into the sample; remove a small aliquot with
       a clean pipet and test the aliquot.  When the nature of the sample is either unknown or
       known to be hazardous, acidification should be done in a fume hood (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 should then
              verified to be pH < 2 just before withdrawing an aliquot for processing or direct analysis.
              If for some reason such as high alkalinity the sample pH is verified to be > 2, more acid
              must be added and the sample held for 16 h until verified to be pH < 2 (Section 8.1).

       8.4.3  With each sample set,  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 19).  The minimum requirements of this program consist of an initial demonstration
       of laboratory  capability, analysis of  samples  spiked  with metals  of interest to evaluate and
       document data quality, and analysis of standards and blanks as tests of continued performance.
       To determine  that results of the analysis meet the performance  characteristics of the method,
       laboratory performance is compared to established performance criteria.

       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, concentration, and cleanup
               procedures, and changes  in instrumentation. Alternate determinative techniques, such as
               the substitution of a colorimetric technique or changes that degrade method performance,
               are not allowed.  If an analytical technique other than the techniques specified  in the
               method is  used, that  technique  must have a specificity equal  to or better than the
               specificity of  the techniques in the method for the analytes of interest.

      Each time the method is modified, the analyst is required to repeat the procedure
                      in Section 9.2. If 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
April 1995                                                                                    17

Method 1637
                      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
                                     analyst(s) 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 number

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

                   Results  from all quality  control  (QC)  tests  comparing the
                                     modified method to this method, including the following:

                                     (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 the
                                     following, 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 each 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 (autosampler, flow injection
                                             system, etc.)
                                     (m)    Operating   conditions   (background   corrections,
                                             temperature program, flow rates, etc.)
                                     (n)     Preconcentration system
                                     (o)     Detector  (type, operating conditions, etc.)
18                                                                                      April 1995

                                                                                      Method 1637
                                      (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 9.5
               describes the required types, procedures, and criteria for analyzing blanks.

        9.1.4   To monitor method performance, the laboratory shall spike at least 10% of the samples
               with the metal(s) of interest. 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 in this method, the result may
               not be reported for regulatory compliance purposes.

        9.1.5   The laboratory shall, on an ongoing basis, demonstrate through calibration verification and
               analysis of the ongoing precision and recovery aliquot that the  analytical system is in
               control.  Sections  10.8 and 9.6 describe these procedures.

        9.1.6   The  laboratory shall  maintain records to  define the quality of data that  are generated.
               Section 9.3.4 describes the development of accuracy statements.

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  (IPR)—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
April 1995                                                                                      19

Method 1637
                      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 dynamic range (LDR)—The upper limit of the LDR must be established for the
               wavelength used for each analyte by determining the signal responses from a minimum
               of six different concentration standards across the range, two of which are close to the
               upper limit of the LDR. Determined LDRs must be documented and kept on file. The
               analyst  should judge the linear calibration range that may be used for the analysis of
               samples from the resulting data.  The upper LDR limit should be an observed signal no
               more than  10% below the level extrapolated from the four lower standards.  The LDRs
               should  be  verified  whenever, in the judgment of the analyst, a change in analytical
               performance caused by either a change in instrument hardware or  operating conditions
               would dictate they be redetermined.
       NOTE: Multiple cleanout furnace cycles may be necessary to fully define or utilize the
       LDR for certain elements such as  chromium.  For this reason, the upper limit of the
       linear calibration range may not correspond to the upper LDR limit.

               Determined sample analyte concentrations  that exceed the upper  limit of the linear
               calibration range must either be diluted and reanalyzed with concern for memory effects
               (Section 4.4.3) or analyzed by another approved method.

       9.2.4   Quality control sample (QCS)—When beginning the use of this method, quarterly or as
               required to meet data quality  needs, verify the calibration  standards and  acceptable
               instrument performance with the preparation and analyses of a QCS (Section 7.7). To
               verify the calibration standards the determined mean concentration from 3 analyses of the
               QCS must be within  ± 10% of the stated QCS  value.  If the QCS  is not  within the
               required limits, an immediate second analysis of the QCS is recommended  to confirm
               unacceptable  performance.    If  the  calibration   standards,  acceptable  instrument
               performance, or both cannot be verified, the source of the problem must be identified and
               corrected before proceeding with further analyses.

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

       9.3.1    Determine the concentration of the MS and MSD 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 one to five times the background concentration, whichever
                      is greater.
20                                                                                   April 1995

                                                                                      Method 1637
      If the concentration is not  being checked against a  regulatory  limit,  the
                      concentration must be at one to five times the background concentration or at one
                      to five times the ML in Table 1, whichever is greater.

       9.3.2   Assess 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.

      For a metal that has failed the acceptance criteria, analyze the ongoing precision
                      and recovery standard (Section 9.6). 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 is attributable to the sample  matrix.  This situation should  be rare
                      because of the matrix elimination preconcentration step before analysis.  If a  low
                      recovery is found, check the pH of the sample plus the buffer  mixture.  The
                      resulting pH  should be about 5.5.  The pH of the sample strongly influences the
                      column's ability to preconcentrate the metals; therefore, a low  pH may cause a
                      low recovery.

      For samples  that  show 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   Assess recovery for samples and maintain records.

      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%.
April 1995                                                                                      21

Method 1637
      Update the accuracy assessment for each metal in each matrix on a regular basis
                      (e.g., after each 5-10 new measurements).

9.4    Precision of MS and MSD

       9.4.1   Calculate the relative percent difference (RPD) between the MS and MSD according to
               the equation below using the concentrations found in the MS and MSD.  Do not use the
               recoveries calculated in Section for this calculation because the RPD is inflated
               when the background concentration is near the spike concentration.
                                     RPD =
                      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 MS and the MSD must be less than 20%.  If
               this criterion is not met, the analytical system is judged to be out of control. Correct the
               problem and reanalyze all samples in the sample batch associated with the MS/MSD that
               failed the RPD test.

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

        9.5.1   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
                      analysis of the OPR (Section 9.6) 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

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

      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.
 22                                                                                    April 1995

                                                                                     Method 1637
       9.5.2   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.

      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 (three 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
                      before the next sampling event.

       9.5.3   Equipment Blanks—Before any sampling equipment is used at a given site, the laboratory
               or cleaning facility is required to generate equipment blanks to show 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

      Sampler check blanks—Sampler check blanks are generated in the laboratory or
                      at the equipment cleaning contractor's facility by processing reagent water
                      through the sampling devices using the same procedures that are used in the field
                      (see Sampling Method).  Therefore, the "clean hands/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 in the field (see Sampling Method). For
April 1995                                                                                     23

Method 1637
                                    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.

                  The sampler check blank must be analyzed using the procedures
                                    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 shown to be free from  the
                                    metal(s)  of interest before the equipment may be used  in  the

                  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

9.6    Ongoing precision and recovery

       9.6.1    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.

       9.6.2   Analyze the OPR sample before analyzing the method blank and samples from the same

       9.6.3   Compute the percent recovery of each metal in the OPR sample.

       9.6.4   For each metal, compare the concentration to the limits for ongoing recovery in 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 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 9.6).

       9.6.5   Add results that pass the specifications in Section 9.6.4  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%.
24                                                                                    April 1995

                                                                                    Method 1637
 9.7     The specifications 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.

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

 10.0  Calibration and  Standardization

 10.1    Table 3 lists recommended wavelengths and instrument operating conditions. However, because
        of differences among makes and models of spectrophotometers and electrothermal furnace devices,
        the actual instrument conditions selected may vary  from those listed.

 10.2    The preconcentration system can be configured using a sample loop to define the sample volume
        (Figure 1) or the system can be configured such that a sample pump rate and a pumping time
        defines the sample volume (Figure 2). The system illustrated in Figure 1  is recommended for
        sample sizes of <  10 mL.  A thorough rinsing of the sample loop between samples with HNO3
        is required. This rinsing will minimize the cross-contamination that may be caused by the sample
        loop.  The system  in Figure 2 should be used for sample volumes of > 10 mL.  The sample pump
        used in  Figure  2  must  be calibrated to ensure that  a reproducible/defined volume is  being

 10.3    Before this method is used, the instrument operating conditions must be optimized. The analyst
        should follow the  instructions provided by the manufacturer while using the conditions in Table
        3 as a guide. Of particular importance is the determination of the charring temperature limit for
        each analyte. This limit is the furnace temperature setting at which a loss in analyte  will occur
        before atomization. This limit should be determined by conducting char temperature profiles for
        each analyte and when necessary, in the matrix of question.  The charring temperature selected
        should minimize background absorbance while providing some furnace temperature variation
        without loss of analyte.  For routine analytical operation, the charring temperature is usually set
        at least 100°C below this  limit.  The optimum conditions selected should provide the lowest
        reliable MDLs and be similar to those in Table 1.  Once the optimum operating conditions are
        determined, they should be recorded and available for daily reference.

 10.4    Before an initial calibration, the linear dynamic range of the analyte must be determined (Section
        9.2.3) using the optimized instrument operating conditions.  For all determinations allow an
        instrument and hollow cathode lamp warm-up period of not less than 15 min. If an EDL is to be
        used, allow 30 min for warm-up.

 10.5    Before daily instrument calibration, inspect the graphite furnace, the sample uptake system and
        autosampler injector for any change that would affect instrument performance.  Clean the system
        and replace the graphite tube, platform, or both when needed or daily.  A cotton swab dipped in
        a 50/50 mixture of isopropyl alcohol (IPA) and H2O (so that it is damp but not dripping) can be
        used to remove most of the salt buildup. A  second cotton swab is dipped in IPA and the contact
        rings are wiped down to ensure they are clean. The  rings are then allowed to thoroughly dry and
April 1995                                                                                   25

Method 1637
       then  a new  tube  is  placed in the  furnace  and  conditioned  according to  the  instrument
       manufacturer's specifications.

10.6   After the warm-up period but before calibration, instrument stability must be demonstrated by
       analyzing a standard solution with a concentration three times the ML at least five times.  The
       resulting relative standard deviation (RSD) of absorbance  signals must be < 5%.  If the RSD is
       > 5%, determine and correct the cause before calibrating the instrument.

10.7   For initial and daily operation, calibrate the instrument according to the instrument manufacturer's
       recommended procedures using the  calibration blank (Section 7.6.1) and calibration standards
       (Section 7.5) 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.

       10.7. 1  Calculate the response factor (RF) for each metal in each CAL solution using the equation
               below and the height or area produced by the metal.

                         Rx  = height or area of the signal for the metal
                         C  = concentration of compound injected (ug/L)
        10.7.2  For each metal, calculate the mean RF (M), the standard deviation of the RF (SD), and
               the relative standard deviation  (RSD) of the mean, where RSD = 100 x SD/M.

        10.7.3  Linearity—If the RSD of the mean RF for any metal is less than 25% over the calibration
               range, an averaged response factor may be used for that analyte.  Otherwise, a calibration
               curve for that metal must be used over the calibration range.

10.8    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.

        10.8.1  Analyze the mid-point calibration standard (Section 10.7).

        10.8.2  Compute the percent recovery  of each metal using the calibration curve obtained in the
               initial calibration.

        10.8.3  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.  Locate and correct the problem and/or
               prepare a new calibration check standard and repeat the test (Sections 10.8.1-10.8.3), or
               recalibrate the system according  to Section  10.7.
26                                                                                     April 1995

                                                                                     Method 1637
        10.8.4  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 reanalyzed.

10.9    A calibration blank must be analyzed following every calibration verification to show 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 10.8), and repeat the analysis of the calibration blank.
11.0  Procedures for Cleaning the  Apparatus

11.1    All  sampling equipment, sample  containers,  and labware should be cleaned 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 20), 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  9.5) from an 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.

             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
April 1995                                                                                     27

Method 1637
             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 7.1.8), and allow to soak for at least 48

             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
                              7.1.12) and cap tightly.  To ensure a tight seal, it may be necessary to use
                              a strap wrench.

             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
                              7.1.12).   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.

             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.
28                                                                                     April 1995

                                                                                     Method 1637
        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 to 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
               7.1.9) 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 just
               described. 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

 11.4    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.

 11.5    All cleaning solutions and acid baths should be periodically monitored for accumulation of metals
        that could lead  to contamination.  When levels of metals in the solutions become too high, the
        solutions and baths should be changed and the old solutions neutralized and discarded to comply
        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).  Cap the tube and mix.  The sample is now ready for
               analysis. Allowance for sample dilution should be made in the calculations.
April 1995                                                                                    29

Method 1637
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. Section 12.2.7 provides an
       alternate  digestion procedure, but the procedure has not undergone interlaboratory
        12.2.1  To determine 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.)  To prevent sample contamination from the fume hood environment, the
               beaker should be covered or other necessary steps should be taken.
       NOTE: For proper heating, adjust the temperature control of the hot plate so that an
       uncovered Griffin beaker containing 50 mL of water placed in the center of the hotplate
       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 to prevent loss of the HC1-H2O azeotrope.)

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

        12.2.6  Allow any undissolved material to settle overnight, or centrifuge a portion of the prepared
               sample until  clear.  (If, after centrifuging or standing overnight, the  sample contains
               suspended solids that would clog the nebulizer, a portion of the sample may be filtered
               to remove  the solids  before analysis.  However,  care  should  be exercised  to  avoid
               potential contamination from filtration.)   The sample is now  ready  to  be  analyzed.
               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
30                                                                                     April 1995

                                                                                      Method 1637
        12.2.7  Alternate total recoverable digestion procedure

             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 heating.

             Tightly recap the container and shake thoroughly. Place the container in
                              an  oven preheated to 85°C.   The container  should be placed  on an
                              insulating piece of material such as wood rather than directly on the
                              typical metal grating.  After the samples have reached 85°C, heat for 2
                              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 time.

             Allow the  sample to cool.  The sample is now  ready  to be  analyzed.
                              Remove aliquots for analysis under clean conditions.

 12.3    Before the preconcentration system is used for the first time, it should be thoroughly cleaned and
        decontaminated using 0.2 M oxalic acid.

        12.3.1   Precleaning the preconcentration system

              Place approximately 500 mL 0.2 M  oxalic  acid in  each of  the
                              sample/eluent containers. Flush the entire system by running the program
                              used for sample analysis  three times.

             Rinse the containers with  reagent water and repeat the sequence described
                              in Section using 0.75 M nitric acid and again using reagent water
                              in place of the 0.2 M oxalic acid.

              Rinse the containers thoroughly with reagent water, fill  them with their
                              designated  reagents, and run  through the program  used for sample
                              analysis to prime the pump and all eluent lines with the correct reagents.

        12.3.2  Peak profile determination

              The peak elution time or the collection window  should be determined
                              using an ICP-AES (or Flame AA). Figure 3 is a plot of time vs emission
                              intensity for Cd and  Pb.  The collection window  is  marked in Figure 3
                              and should provide about 30 seconds buffer on either side of the peak.
                              If an ICP-AES is not available, it is recommended that the peak profile
                              be determined by collecting 200-uL samples during the elution part of the
                              preconcentration cycle and then reconstructing the peak profile from the
                              analysis of the 200-uL samples.
April 1995                                                                                     31

Method 1637
12.4   Sample preconcentration

       12.4.1   Preconcentration using a sample loop

             Loading sample loop—With valve 1 in the off position and valve 2 in the
                             on position, load the sample through the sample loop to waste using the
                             sample pump for 4 min at 4 mL/min.  Switch on the carrier pump and
                             pump 1% nitric acid to flush the sample collection line.

             Column loading—With valve 1 in the on position, load the sample from
                             the loop onto the column using 1 M ammonium acetate for 4.5 min at 4.0
                             mL/min.  Switch on the buffer pump, and pump 2 M ammonium acetate
                             at a flow rate of 1 mL/min. The analytes are retained on the column, and
                             most of the matrix is passed through to waste.

             Elution matrix—With valve 1  in the on position, the gradient pump is
                             allowed to elute the matrix using the  1 M ammonium acetate.  At this
                             time, the carrier, buffer, and the sample pumps are all off.

             Elute  analytes—Turn off valve 1 and begin  eluting the analytes by
                             pumping 0.75 M nitric acid through the column and turn off valve 2 and
                             pump the eluted analytes into the collection flask. The analytes should
                             be eluted  into a 2-mL sample volume.

             Column reconditioning—Turn on valve 2 to direct the column effluent to
                             waste, and pump 0.75 M nitric acid,  1 M ammonium acetate, 0.75  M
                             nitric acid and 1 M ammonium acetate alternately through the column at
                             4.0 mL/min.  Each solvent should be pumped through the column for 2
                             min.  During this process, the next sample can be loaded into the sample
                             loop using the sample pump.

             Preconcentration of the sample may be achieved by running through  an
                             eluent pump  program.  The exact timing of this sequence  should  be
                             modified according to the internal volume  of the connecting tubing and
                             the specific hardware configuration used.

       12.4.2   Preconcentration using an auxiliary pump to determine sample volume

             Sample loading—With valves 1 and 2 on and the sample pump on, load
                             the sample on the column buffering the sample using the gradient pump
                             and the 2 M buffer. The actual sample volume is determined by knowing
                             the sample pump rate and the time.  While the sample is being loaded,
                             the carrier pump can be used to flush the collection line.

             Elution matrix—With valve 1  in the off position the gradient pump is
                             allowed to elute the matrix using the 1 M ammonium acetate. At this
                             time, the carrier, buffer, and the sample pumps are all off.
32                                                                                   April 1995

                                                                                      Method 1637
             Elution of analytes—With valves 1 and 2 in the off position the gradient
                              pump is switched to 0.75 M HNO3 and the analytes are eluted into the
                              collection vessel.  The analytes should be eluted into a 2-mL sample

             Column reconditioning—Turn on valve 2 to direct the column effluent to
                              waste, and pump 0.75 M nitric  acid, 1 M ammonium acetate, 0.75  M
                              nitric acid and 1 M ammonium acetate alternately through the column at
                              4.0 mL/min.
        NOTE: When switching the gradient pump from nitric acid back to the ammonium
        acetate, it is necessary to flush the line connecting the gradient pump to valve 2 with the
        ammonium acetate before switching the valve. Otherwise, if the line contains nitric acid,
        it will elute the metals from the cleanup column.
              Preconcentration of the sample may be achieved by running through an
                              eluent pump program.  The exact  timing  of this sequence should be
                              modified according to the internal volume of the connecting tubing and
                              the specific hardware configuration used.

 12.5    Sample analysis

        12.5.1   Before beginning daily calibration, the instrument should be reconfigured to the optimized
                conditions as determined in Section  10.  Initiate data system and allow a period of not
                less than 15 min for instrument and hollow cathode lamp warm-up. If an EDL is to be
                used, allow 30 min for warm-up. Tune and calibrate the instrument for the analytes of

        12.5.2   An autosampler must be used to introduce all solutions into the  graphite furnace.  Once
                the standard, sample or QC  solution plus the matrix modifier  is injected, the furnace
                controller completes furnace cycles and cleanout period as programmed. Analyte signals
                must be integrated and collected as peak area measurements.  Background  absorbances,
                background  corrected analyte signals, and  determined analyte concentrations  on all
                solutions must be able to be displayed on a CRT for immediate review by the analyst and
               be available as hard copy for documentation to be kept on file.  Flush the autosampler
                solution uptake system with the rinse blank (Section 7.6.3) between each solution injected.

        12.5.3  Repeat the sequence described in Section 12.4.1 or 12.4.2 for each sample to be analyzed.
               At the end of the analytical run, leave the column filled with 1 M ammonium acetate
               buffer until it is next used.

        12.5.4  Determined sample analyte concentrations that are > 90% of the upper limit of calibration
               must  either be diluted with  acidified reagent water and reanalyzed with concern for
               memory  effects  (Section  4.4.3), or  determined by another  approved test procedure.
               Samples with a background absorbance > 1.0  must be appropriately diluted with acidified
               reagent water and reanalyzed. If the method of standard additions is required, follow the
               instructions in Section 12.6.
April 1995                                                                                     33

Method 1637
       12.5.5  During sample analyses, the laboratory must comply with the required quality control
               described in Sections 9 and  10.

12.6   Method  of standard  additions  (MSA) — If MSA  is  required, the  following  procedure is

       12.6.1  MSA (Reference 21) involves preparing new standards in the sample matrix by adding
               known  amounts of standard to one or  more aliquots of the processed sample solution.
               This technique compensates for a  sample constituent  that enhances  or depresses the
               analyte signal, thus producing a different slope from that of the calibration standards. It
               will not correct for additive  interference, which causes a baseline shift.  The simplest
               version of this technique is the single-addition method.  The  procedure is as follows:
               Two identical aliquots of the sample solution, each of volume Vx, are taken.  To the first
               (labeled A) is added a small volume Vs of a standard analyte solution of concentration Cs.
               To the  second (labeled B) is added the same volume Vs of the solvent.  The analytical
               signals  of A and B are measured and  corrected for nonanalyte signals.  The unknown
               sample concentration Cx is calculated:
               where SA and SB are the analytical signals of solutions A and B, respectively. Vs and Cs
               should be chosen so that SA is roughly twice SB on the average.  To avoid excess dilution
               of the sample matrix, it is best if Vs  is made much less than Vx, and Cs is thus much
               greater than Cx.  If a separation or concentration step is used, the additions are best made
               first and carried through the entire procedure.  For  the results from this technique to be
               valid,  the following limitations must be taken into consideration:

               1 .      The response vs amount must be linear.

               2.      The chemical form of the analyte added must respond in the same manner as the
                      analyte in the sample.

               3.      The interference effect must be constant over the working range of concern.

               4.      The signal must be corrected for any additive interference.
13.0  Data Analysis and Calculations

13.1   Sample data should be reported in units of ug/L (parts per billion; ppb).  Report results at or
       above the ML for metals found in samples and determined in standards.  Report all results for
       metals found in blanks, regardless of level.
34                                                                                    April 1995

                                                                                     Method 1637
 13.2    Compute the concentration of each analyte in the sample using the averaged RF determined from
        the calibration data (Section  10.7) according to the following equation:
                          where the terms are defined in Section 10.6.1.
 13.3    For total recoverable aqueous analytes (Sections 12.2.1-12.2.6), if a different aliquot volume other
        than 100 mL is used for sample preparation, adjust the dilution factor accordingly. Also, account
        for any additional dilution of the prepared sample solution needed to complete the determination
        of analytes exceeding the upper limit  of the calibration  curve.  Do not report data below the
        determined analyte MDL concentration or below an adjusted detection limit reflecting smaller
        sample aliquots used in processing or additional  dilutions required to complete the analysis.

 13.4    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.

 13.5    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.
14.0  Method Performance

14.1    The MDLs in Table 1 and the quality control acceptance criteria in Table 2 were validated in two
        or three laboratories (Reference 22) for all dissolved analytes.
 15.0  Pollution Prevention

 15.1    Pollution prevention encompasses any technique that reduces or eliminates the quantity or toxicity
        of waste at  the  point of  generation.   Many  opportunities for pollution  prevention exist  in
        laboratory operation.  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.  To minimize the volume  of
        expired standards to be disposed of, standards should be  prepared in volumes consistent with
        laboratory use.
April 1995                                                                                    35

Method 1637
15.2   For information  about pollution prevention  that may  be applied to laboratories and research
       institutions, consult Less  is Better:  Laboratory Chemical Management for Waste Reduction,
       available from the American Chemical Society's Department of Government Relations and Science
       Policy, 1155  16th Street NW, Washington DC 20036, 202/872-4477.
16.0  Waste Management

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

1      Adeloju, S.B.; Bond, A.M. "Influence of Laboratory Environment on the Precision and Accuracy
       of Trace Element Analysis," Anal. Ghent. 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.O., Ed., U.S.  Government Printing Office, Washington, DC,

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

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

9      Prothro, M.G.  "Office  of  Water  Policy  and  Technical  Guidance  on  Interpretation and
       Implementation of Aquatic  Life Metals Criteria,"  EPA Memorandum  to Regional Water
       Management and Environmental Services Division Directors, Oct. 1, 1993.
36                                                                                  April 1995

                                                                                  Method 1637
 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     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.

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

 15     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.

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

 17     "Safety in Academic Chemistry  Laboratories,"  American Chemical Society  Committee  on
        Chemical Safety, 3rd ed., 1979.

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

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

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

 21     Winefordner, J.D.  'Trace Analysis: Spectroscopic Methods for Elements," Chemical Analysis,
        46, pp 41-42.

 22     "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.

 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.
April 1995                                                                                 37

Method 1637
18.2   Analyte—A metal tested for by the methods referenced in this method. The analytes are listed
       in Table 1.

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

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

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

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

18.7   Equipment Blank—An aliquot of reagent water that is subjected in the laboratory to all aspects
       of sample collection and analysis, including contact with all sampling devices and apparatus.  The
       purpose of the equipment blank is to determine whether the sampling devices and apparatus for
       sample collection have been adequately cleaned before they were 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 whether these materials are free
       from contamination before use.

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

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

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

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

18.12  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 whether method analytes or
 38                                                                                     April 1995

                                                                                   Method 1637
        interferences are present in the laboratory environment, the reagents, or the Apparatus (Sections
        7.6.2 and 9.5.1).

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

 18.14   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.

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

 18.16   Laboratory  Fortified Sample Matrix (LFM)—See  Matrix  Spike (MS) and Matrix Spike
        Duplicate (MSD).

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

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

 18.19   Matrix Modifier—A substance added to the graphite furnace along with the sample to minimize
        the interference effects by selective volatilization of either analyte or matrix components.

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

 18.22   May Not—This action, activity, or procedural step is prohibited.

 18.23   Method Blank—See Laboratory Blank.

 18.24   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).

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

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

 18.27   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 ensure that the results produced by the
April 1995                                                                                  39

Method 1637
       laboratory remain within the method-specified limits for precision and accuracy (Sections 7.8 and

18.28  Preparation Blank—See Laboratory Blank.

18.29  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.

18.30  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

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

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

18.33  Standard Addition—The addition  of a known amount of analyte to the sample to determine the
       relative response of the detector to an analyte within the sample matrix.  The relative response is
       then used to assess either an operative matrix effect or the sample analyte concentration (Section

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

18.35  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).
40                                                                                      April 1995

                                                                                                       Method 1637
                                                      Table 1

        List of Analytes Amenable to Analysis Using Method 1637:  Lowest Water Quality Criterion
                    for Each Metal Species, Method Detection Limits, and Minimum Levels
Lowest EPA
Water Quality
Criterion fag/L)1
Method Detection Limit
(MDL) and Minimum
Level (ML); ugfl.

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 CaCO3 and all aquatic life criteria adjusted in accordance with the Oct. 1, 1993 Office of Water guidance to reflect dissolved
metals criteria.

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

Minimum Level (ML) calculated by multiplying laboratory-determined MDL by 3.18 and rounding result to nearest multiple of 1, 2,
5, 10, 20, 50, etc. in accordance with procedures used by EAD and described in EPA Draft National Guidance for the Permitting,
Monitoring, and Enforcement of Water Quality-Based Effluent Limitations Set Below Analytical Detection/Quantitation Levels, March
22, 1994.
                                                      Table 2

                       Quality Control Acceptance Criteria for Performance Tests1


Initial Precision and
Recovery (Section 9.2)
8 X
23 70-116
27 63-117
(Section 10.8)

Ongoing Precision
Recovery (Section

(Section 9.3)

         All specifications expressed as percent.
April 1995

     Method 1637
                                              Table 3

      Recommended Graphite Furnace Operating Conditions and Recommended Matrix Modifier1"3
Wavelength Slit
228.8 0.7
283.3 0.7
Temperature pCf
Char Atom
800 1600
1250 2000
1   Matrix Modifier = 0.015 mg Pd + 0.01 mg Mg(NO3)2.

2   A 5% H2 in Ar gas mix is used during the dry and char steps at 300 mL/min for all elements.

3   A cool-down step between the char and atomization is recommended.

4   Actual char and atomization temperatures may vary from instrument to instrument and are best determined on
   an individual basis. The actual drying temperature may vary depending on the temperature of the water used
   to cool the furnace.
     42                                                                                April 1995

                                                                        Method 1637
   Figure   "I   Sample   Loop   Conf7 i Qur at  i on

Samp 1 e Loop
Load I ng
Co 1 umn
Load i ng
E 1 ut I on of
Matr i x
E 1 ut ion Of
Ana 1 ytes
Co 1 umn
Recond 1 t. I on

I ves


Carr i er

Samp I e


P I ug
I 1


Method 1637
 Figure   2   System   Diagram   Without.   Sample   Loop
Samp 1 e
Load I ng
E 1 ut 1 on of
Matr 1 x
El union Of
Ana 1 y tes
Co 1 umn
Recond 1 "t I on
Va 1 ves
1 2
On On
Off On
Off Off
Off On
Car r r er
Samp I e
April 1995


                                                            Method 1637
 Figure 3          Peak Collection Window  from  ICP-AES
       ,_ cn

        "> 1
        C $

        0) i
                    Start of Col lection
                '+  Cu
                                                  End of Col lection
                                                           l	I
                              40          80

April 1995