United States
         Environmental Protection
C ff ice of Water
April 1995
v°/EPA   Method 1636:  Determination of
         Hexavalent Chromium by Ion
                                             Printed on Recycled Paper


&EPA  Method 1636: Determination of
       Hexavaient Chromium by Ion
                                   * Printed on Recycled Paper


Method 1636

Method 1636  was prepared under the direction of William A. Telliard of the U.S. Environmental
Protection Agency's (EPA's) Office of Water (OW), Engineering and Analysis Division (BAD).  The
method was prepared under EPA Contract 68-C3-0337 by the DynCorp Environmental Programs Division
with assistance from Interface, Inc.

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

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

T.D. Martin
J.D. Pfaff
EJ. Arar (DynCorp, formerly Technology Applications, Inc.)
 S.E. Long (DynCorp, formerly Technology Applications, Inc.)


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

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

 W.A. Telliard
 USEPA Office of Water
 Analytical Methods Staff
 Mail Code 4303
 401 M Street, SW
 Washington, DC  20460
 Phone:  202/260-7120
 Fax:   202/260-7185
                                                                                      April 1995


                                                                                      Method 1636
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 about 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 1636 was specifically developed to provide
reliable measurements  of hexavalent chromium at EPA WQC levels using ion chromatography 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 Ken wood Road
Cincinnati, OH 45242
 April 1995


Method 1636
     Note:  This method is intended to be performance based, and the laboratory is permitted to omit any
     step or modify any procedure if all performance requirements set forth in this method are met. The
     laboratory is  not  allowed to omit  any quality control  analyses.  The terms "must," "may," and
     "should" are included throughout this method and are intended to illustrate the importance of the
     procedures in producing verifiable data at water quality criteria levels.  The term "must" is used to
     indicate that  researchers  in trace metals analysis  have  found certain procedures essential  in
     successfully analyzing samples and  avoiding  contamination; however, these procedures can  be
     modified or omitted if the laboratory can demonstrate that data quality is not affected.
 iv                                                                                      April 1995


                                                                              Method 1636
                              Method   1636
        Determination  of  Hexavalent Chromium  by  Ion
1.0    Scope  and  Application

1.1     This method is for the determination of dissolved hexavalent chromium (as CrO42) in ambient
       waters at EPA water quality criteria (WQC) levels using ion chromatography (1C).  This
       method was developed by integrating the analytical procedures in EPA Method 218.6 with the
       quality control (QC) and sample handling procedures necessary to avoid contamination and
       ensure the validity of analytical results during sampling and analysis for metals at EPA WQC
       levels.  This method contains QC procedures that will 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.
                                                 Chemical Abstract Services
                Analyte                          Registry Number (CASRN)

                Hexavalent Chromium (as CrO42)           18540-29-9
 1.2    Table 1 lists the EPA WQC level, the method detection limit (MDL), and the minimum level
       (ML) for hexavalent chromium (Cr(VI)).  Linear working ranges will be dependent on the
       sample matrix, instrumentation, and selected operating conditions.

 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
       facilities and analytical techniques that should maximize the ability of the laboratory to make
       reliable trace metals determinations and minimize contamination.  These suggestions are
       given in Section 4.0 and are based on findings of researchers  performing trace metals analyses
       (References 1-8).  Additional suggestions for improvement of existing  facilities may be found
       in EPA's Guidance for Establishing Trace Metals Clean Rooms in Existing Facilities, which is
       available from the National Center tor Environmental Publications and Information (NCEPI)
       at the address listed in the introduction to this document.
 April 1995

    Method 1636
          not used in this method
              and donation
   samples should be preserved in the field
 commercial instrumentation is recommended
 objectives (DQOs) required foa proc,
                                                        Management coundrs
                                                                       -  The filtered
                                                                          experience with
                                                       validation  ui
                                                                   *** the data
2.0   Summary of Method
introduced into the ion chromato/raph  A
before the Cr(VI), as CrO   is sted on  h  h
Postcolumn derivadzationof    CrvD wi* dnhe
colored complex at 530 nm                d,phenyl
                                                             fi,tra,e is adjusted to

                                                             °f "* Sample (50~250
                                                                       from "
                                                                        SeparatOr co'"mn-
                                                             ,s followed by detection of the
                                                                              April 1995

                                                                                   Method 1636
3.0   Definitions

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

3.2    Other definitions of terms are given  in the glossary (Section 18) at the end of this method.
4.0   Contamination and Interferences

4.1    Preventing ambient water samples from becoming contaminated during the sampling and
       analytical process constitutes one of the greatest difficulties encountered in trace metals
       determinations.  Over the last two decades, marine chemists have come to recognize that much
       of the historical data on the concentrations of dissolved trace metals in seawater are
       erroneously high because the concentrations reflect contamination from sampling and analysis
       rather than ambient levels.  More recently, historical trace metals data collected from
       freshwater rivers and streams have been shown to be similarly biased because of contamination
       during sampling and analysis (Reference 11).  Therefore, it is imperative that extreme care be
       taken to avoid contamination when collecting and analyzing ambient water samples for trace

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 3).

4.3    Contamination Control

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

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

      Substances in a sample cannot be allowed to contaminate the laboratory  work
                      area or instrumentation used  for trace metals measurements.  Requirements and
                      suggestions for protecting the laboratory  are given in this method.
April 1995

Method 1636
            the most important factors in avoiding/reducin/^6]   fr°m contaminati°n. Two of
            awareness of potential sources X^^^^^"^011 ^ (1) an
            done.  Therefore it is imperative that to      d            attention to work being
            carried out by well-trained ™~:.	fJ"    U™S described in this method
                                                                         1S a class ,00
           should be Performed   a  la
                                           e an
  box so that exposure to m
  used, the AppLus shouTd
  bench or in a plastic box o
  - t,me betJen
                                                        samples- blanks- or
                                                         r°°m' C'ean bench' or «love
                                                c     e,'S minimiZed  Whe" not
                                                       S"C Wrap' St0red in the
          be deaned by wiping Wlh
                                                         isessed- a11 work
                                                     - nomaic
                                            ot                             -
          clean gloves may touch the AppTam   If 1  » ^^ SampleS' 3nd blanks'
          glove(s) must r/changed LforeT' in ha ndlin Th  f" " ^^ " Wuched' the
          that gloves have become con^inted wo"f m§u I Ed^h " " * ^ SUSPeC'e
          work activity.                  q    y Stllpped Wlth mmima^ disruption to the
metals, or both.
                                                                of metals at amMen,
                                       "onmetamc, tree of material that may contain
                                                                           // 7P95

                                                                                    Method 1636
                     of the other materials, resulting either in contamination or low-biased results
                     (Reference 3).  Stainless steel is a major source of chromium contamination.
                     All materials, regardless of construction, that will directly or indirectly contact
                     the sample must be cleaned using the procedures described in Section 11 and
                     must be known to be clean and metal free before proceeding.

     The following materials have been found to contain trace metals and should
                     not contact the sample or be used to hold liquids that contact the sample,
                     unless these materials have been  shown to be free of the metals  of interest at
                     the desired level:  Pyrex, Kimax, methacrylate, polyvinylchloride, nylon, and
                     Vycor (Reference 6). In addition, highly colored plastics, paper cap liners,
                     pigments used to mark increments on plastics, and rubber all contain trace
                     levels of metals and must be avoided (Reference 12).

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

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

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

      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
April 1995

    Method 1636
         Contamination by samples-Significant laboratory or instrument contamination
                         may result when untreated effluents, in-process waters, landfillkachaTs atd
                         other samples containing high concentrations of inorganic sub ta^este
                         processed and ana.yzed.  As stated in Section 1.0, thfs methodTn

                         Lu norrDe°nl r.'T'r' Td Samt"eS C°mainin« hi*h -ncentrad
                         should not be permitted into the clean room  and laboratory dedicated for
                         processing trace metals samples.                           uiuirea ror
                Therefore, it is imperative that every piece of the Apparatus that is
                indirectly used in ,he collection, processing, and analysis of amtiem
                samples be cleaned as specified in Section 11.
 4.4 Contamination by airborne paniculate matter-Less obvious substances caoable
               of contaminating samples include airborne particles.  Samples mayl    *
               contaminated by airborne dust, dirt, particles, or vapors from unfiUered air
               supplies; nearby corroded or rusted pipes, wires, or other fixture?or metal-
               contaimng pamt. Whenever possible, sample processing and analysisThould
               be done as far as possible from sources of airborne confamination

Interferences which affect the accurate determination of Cr(VI) may come from several

44-'   fcfd^l^ ™ f~ » *e P£—e of reducing species in an
                                          HK C3PaCity Wi* **h —trations of anionic
               species, especially chlonde and sulphate, will cause a loss of Cr(VI)   The column
5.0   Safety

                                                                                     April 1995

                                                                                    Method 1636
5.2    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 14-17).  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 17 are  particularly comprehensive in dealing with the general subject of laboratory

5.3    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.
6.0    Apparatus, Equipment, and Supplies

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

6.1     Facility

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

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

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

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

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

6.2     Ion Chromatograph

        6.2.1   Instrument equipped with a pump capable of withstanding a minimum  backpressure of
               2000 psi and of delivering a constant flow in the range of 1-5 mL/min and containing
               no metal parts in the sample, eluent, or reagent flow path
 April 1995

  Method 1636
         6.2.2   Helium gas supply (high purity, 99.995%)

         6.2.3   Pressurized eluent container, plastic, 1- or 2-L size

         6.2.4   Sample loops of various sizes (50-250uL)

         6.2.5   A pressurized reagent deliver)' module with a mixing tee and beaded mixing coil

         6.2.6   Guard Column-A column placed before  the separator column and containing a
                sorbent capable of removing strongly absorbing organics and particles that would
                otherwise damage the separator column (Dionex lonPac NG1  or equivalent).

        6.2.7   Separator Column-A column packed with a high capacity anion exchange resin
                capable of separating  CK)42  from other sample constituents (Dionex lonPac AST or

        6.2.8    A low-volume  flow-through cell, visible lamp detector containing no metal parts in
               contact with the eluent flow path, Detection wavelength is at  530 nm.

        6.2.9   Recorder, integrator, or computer for receiving analog or digital signals for recording
               detector response (peak height  or area) as a function of time                      §

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

6.4    pH meter or pH paper

                          with capability to measure to ai mg- for - »
                  0' *termi"alion of trace lev^ of elements, contamination and loss are of prime
              ation  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 des,gnated  for trace element sample handling  Sample

        lT iThT1 '"      C P°SltiVe ^ "egatiVe 6IIOrS  in *e Determination of trace elenZ by
       (1) contributing contammams through surface desorption or leaching, and (2) depleting element
       concentrates through adsorption processes.  All labware must be Lai free  SuU able
       construcnon materials are fluoropolymer (PEP. PTFE), conventional or linear polyethylene
       anlT^f   '     P0l™lene' F'— polymer should be used when samples LTobe
       analyzed for mercury.  All labware should be cleaned according to the procedure in Section
       11.4.  Gloves, plasuc wrap, storage bags, and filters may all be used new without additional

                 685       * "*                  ''    * °f these  ™«<^ ™* sou™ of
                                                           USt "e °btained or the
      NOTE: Chromic acid must not be used for cleaning glassware.
      6.6.1   Glassware-Class A volumetric flasks and a graduated cylinder.
                                                                                    April 1995

                                                                                     Method 1636
       6.6.2   Assorted Class A calibrated pipets

       6.6.3   10-mL male luer-lock disposable syringes

       6.6.4   0.45-um syringe filters

       6.6.5   Storage bottle—High density polypropylene, 1-L capacity.

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

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

       6.6.8   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.

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

       6.6.10 Brushes—Nonmetallic, for scrubbing Apparatus.

       6.6.11 Storage bags—Clean, zip-type, nonvented, colorless polyethylene  (various sizes) to
              store the Apparatus.

       6.6.12 Plastic wrap—Clean, colorless polyethylene to store the  Apparatus.

6.7    Sampling Equipment—The sampling team may contract with the laboratory or a cleaning
       facility that is responsible for cleaning, storing, and shipping all sampling devices, sample
       bottles, filtration equipment,  and  all other Apparatus used for the collection of ambient water
       samples.  Before  the equipment is shipped to the field site, the laboratory or facility must
       generate an acceptable equipment blank (Section 9.5.3) to demonstrate that the sampling
       equipment is free from contamination.

       6.7.1    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.

       6.7.2   Sample bottles—Fluoropolymer, conventional or linear polyethylene, polycarbonate, or
               polypropylene; 500-mL with lids. Cleaned sample bottles should be filled with 0.1%
               HC1 (v/v) until use.
        NOTE: If mercury is a target ana/yte, fluoropolymer or glass bottles must be used.
        6.7.3   Filtration Apparatus
       Filter—Gelman Supor 0.45-um, 15-mm diameter capsule filter (Gelman 12175,
                       or equivalent).
April 1995

   Method 1636
         Peristaltic pump-115-V a.c., 12-V d.c., internal battery, variable-speed
                         single-head (Cole Farmer, portable, "Masterflex US," Catalog No  H-07570-10
                         drive with Quick Load pump head, Catalog No. H-07021-24, or equivalent).
                          ecc             peristaltic Pump-styrene/ethylene/butylene/ silicone
                         (SEES) resin, approx 3/8-in i.d. by approximately 3 ft (Cole-Parmer size 18
                         Catalog No. G-06464-18, or approximately 1/4-in i.d., Cole-Parmer size 17
                         ?±g± G;°6464-17' or equivalent). Tubing is cleaned by soaking in '
                         5-0% HC1 solution for 8-24 h, rinsing with reagent  water in a clean bench in
                         a clean room, and drying m the clean bench by purging with metal-free air or
                         nitrogen   After drying, the tubing is double-bagged in clear polyethylene bags
                         serialized with a unique number, and stored until use.

  7.0    Reagents and Standards

         Reagents may contain elemental impurities that  might affect the integrity of analytical data

               e                                          reagent Srade salts'  Since a concentrated
         tes ed fo  tnern,     f      T     * adjUSt ^ PH °f SHmpeS' 6aCh W lot sho^ be
         tested for the metals of interest by diluting and analyzing an aliquot from the lot using the
         techniques and instrumentation to he used for analysis of samples.  The lot will be acceptable
         if the concentration of  the metal of interes, is below the  MDL listed in this method  All acids
         used for this method must be of ultra high-purity grade.  Suitable acids are available from a
         number of manufacturers or may be prepared by sub-boiling distillation.

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

         7.1.1   Nitric acid-concentrated (sp gr  1 .41 ), Seastar or equivalent

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

         7.1.3   Nitric acid  ( 1 +9)-Add  1 00 mL concentrated nitric add  to 400 mL of reagent water
                and dilute to 1 L.

         7.1.4   Hydrochloric acid — concentrated  (sp gr 1.19).

        7. 1 .5    Hydrochloric acid (1 + 1 )_ Add 500 mL concentrated hydrochloric acid to 400 mL of
                reagent water and dilute to i  L.

        7. 1 .6    Hydrochloric acid ( 1 +4)-Add 200 mL concentrated hydrochloric acid to 400 mL of
                reagent water and  dilute to I  L.

        7. 1 .7   Hydrochloric acid  (HC1)— I N trace metal grade

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

        7.1.9   Hydrochloric acid (HC1)— J 
                                                                                     Method 1636
       7.1.10 Hydrochloric acid (HC1)—0.5% (v/v), trace metal grade

       7.1.11  Hydrochloric acid (HCD—0.1% (v/v) ultrapure grade

       7.1.12 Ammonium hydroxide, NH,OH, (sp gr 0.902), (CASRN 1336-21-6)

       7.1.13 Ammonium sulphate, (NH4.2SO4, (CASRN 7783-20-2)

       7.1.14  1,5-Diphenylcarbazide, (CASRN 140-22-7)

       7.1.15 Methanol, HPLC grade

       7.1.16 Sulfuric acid, concentrated (sp gr  1.84)

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    Cr(VI) Stock  Standard Solution—To prepare a 1000 mg/L solution, dissolve 4.501 g of
       Na2CrO4.4H2O in reagent water and dilute to 1 L. Transfer to a polypropylene storage

       7.3.1   Preparation of calibration standards—Fresh calibration standards should be prepared
               every 2 weeks or as needed.  Dilute the siock standard solution to levels appropriate to
               the operating range of the instrument using reagent water.  Before final dilution, the
               standards should be adjusted to pH 9-9.5 with the buffer solution (Section 7.6).
               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  verified initially using a
               quality control  sample (Section 7.8).

7.4    Eluent—Dissolve 33 g  of ammonium sulphate in 500 mL of reagent water and add 6.5 mL of
       ammonium hydroxide.  Dilute to 1  L with reagent water.

7.5    Postcolumn Reagent—Dissolve 0.5 g of 1.5-diphenylcarbazide in 100 mL of HPLC grade
       methanol.  Add to about  500  mL of reagent water containing 28 mL of 98% sulfuric acid
       while stirring. Dilute  with reagent water to 1 L in a volumetric flask.  Reagent is stable for 4
       or 5 days  but should be prepared only as needed.

7.6     Buffer Solution—Dissolve 33 g of ammonium sulphate  in 75 mL of reagent water and add 6.5
        mL of ammonium hydroxide.  Dilute to 100 mL with reagent water.

7.7     Blanks	The laboratory should prepare the following types of blanks.  A calibration blank is
        used to  establish the analytical calibration curve; and the laboratory (method) blank is used to
        assess possible contamination from the sample preparation procedure.  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                                                                                     ll

    Method 1636

   <- .00 ug/L in reagen
   The QCS should be analyzed a. neerie i  ,n
   be prepared quarterly or n^re fte.uentt as

   Ongoing precision and recovery (OPR) Samnle  Tn ^
   from the stock standard (Section  5 L prelreTh^ °OTR
   the same entire preparation scheme as the Lmples
                                                               bfT- '° '
                                                               b"ffer S°lutlon (Section 7-6>
                                                            ****• ^ " ^ S°lu«°"
  8.0    Sample Collection, Filtration, Preservation, and Storage

              , pe.or.ed at the ,,   of sample
                                                                   <*** -uired so that
  Sample coHecuon-Samples are ,,,llec,ed as described in the Samphng

                                                          ™st be analyzed w.thin 24 h of

 .6    Samples should be stored in polyethylene bags a, 0-4°C until analysis
9.0    Quality Assurance/Quality Control

       and document da
                                                                C°nSist °f an initial
                                                                               Y 7995

                                                                                      Method 1636
       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 colonmetric 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 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

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

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

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

                     Data that will  allow an independent reviewer to validate each
                                      determination by tracing  the instrument output (peak height,
April 1995                                                                                       13

   Method 1636
                                        area, or other signal) to the final result.  These data are to
                                        include, where possible:

                                        (a)     Sample numbers and other identifiers
                                        (b)     Digestion/preparation or extraction dates
                                        (c)    Analysis dates and times
                                        (d)    Analysis sequence/run chronology
                                        (e)    Sample weight or volume
                                        (0     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)     Columns (type, resin, etc.)
                                        (m)    Operating conditions (background corrections,
                                               temperature program, flow rates, etc.)
                                        (n)     Detector (type, operating conditions, etc.)
                                        (o)     Printer tapes and other recordings of raw data
                                        (p)     Quantitation reports, data system outputs, and other
                                               data to link raw data to results reported

         9.1.3    Analyses of blanks are required to demonstrate freedom from contamination. Section
                 ¥.:> describes the required  types, procedures, and criteria for analysis of blanks.

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

                The laboratory  shall, on  an ongoing basis, demonstrate through calibration verification
                and through analysis of the ongoing precision and recovery aliquot that the  analytical
                system is in control. Sect.ons  10.4 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 hexavalent chromium  the
                analyst shall determine  the MDL for Cr(VI) 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 ], or one-third the regulatory compliance limit
14                                      '                                   -—	
                                                                                        April 1995

                                                                                     Method 1636
               whichever is greater. MDLs should be determined when a new operator begins work
               or whenever, in the judgement 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 Cr(VI) 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 Cr(VI) in each aliquot and the standard deviation of the recovery
                      (s) for each metal.

      Compare s and X with the corresponding limits for initial precision and
                      recovery in Table 2.  If s and X meet the acceptance criteria, system
                      performance is  acceptable and analysis of blanks and samples may begin. If,
                      however, s exceeds the precision limit or X falls outside the range for
                      accuracy, system performance is unacceptable.  Correct the problem and  repeat
                      the test  (Section

       9.2.3   Linear dynamic range (LDR)-- The LDR should  be determined by analyzing a
               minimum of 7 calibration standards ranging in concentration from 1 ug/L to 5,000
               ug/L across all  sensitivity settings of the spectrophotometer.  To normalize responses,
               divide the response by  the sensitivity setting multiplier. Perform the linear regression
               of normalized response vs. concentration and obtain the constants m and b, where m is
               the slope of the line and b is the y-mtercept.  Incrementally analyze standards of
               higher concentration until the measured absorbance response, /?, of a standard no
               longer yields a  calculated concentration, Cc, that  is ± 10%  of the known concentration,
               C, where Cc = (R - b)/m. That concentration defines the upper limit of the LDR for
               that instrument  and analytical operating conditions.  Samples having a concentration
               that is :> 90% of the upper limit of the LDR must be diluted to fall within the bounds
               of the current calibration curve concentration range and reanalyzed.

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

9.3    Method accuracy—To assess the performance of the method on a given sample matrix, the
       laboratory must perform matrix spike (MS) and matrix spike duplicate (MSD) sample analyses
       on 10% of the samples  from each site being  monitored, or at least one MS sample analysis
April 1995                                                                                      15

Method 1636
                B,anks (e.,, fie,d
       9.3. 1   TT,e concentration of the MS and MSD is determined as follows-
      9.3.2   Assessing spike recover Calculate each percent recovery (P) as lOOfA   RVT   u   ^P •
                 true value of the spike.                   (  " B)/T' Where T ls the

  9.3.3   Compare the percent recovery (P) for CrfVn
         criteria found in Table 2. If P fa 1  outside
         acceptance criteria have no, been met
                                                                           QC acceptance
                                                                       f°r recovery' the
  If the acceptance criteria were not met  anal™ ^
                  recovery standard (Section 9 6)   Hhe OPR      ,1 ^"^ PreC1Si°n and
                  2), the analytical system is in ont ol and th   ^ "  '"^ ^ Cr(VI) (Table
                  sample matrix.                      ^ the pr°blem can be a«nbuted to the
9.3.4   Recovery for samples should be as
                                       assessed and records maintained
                                                                                   V 7995

                                                                                    Method 1636
                      average percent recovery (R) and the standard deviation of the percent
                      recovery (SR).  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

      Update the accuracy assessment for Cr(VI) in each matrix on a regular basis
                      (e.g., after each five to ten new measurements).

9.4    Precision of matrix spike and duplicate

       9.4.1    Calculate the relative percent difference (RPD) between the MS and MSD per the
               equation below using the concentrations found in the MS and MSD. Do not use the
               recoveries calculated in Section for this calculation because the RPD is inflated
               when the background concentration is near the spike concentration.

                                     RPD = 100(|D7-D2)
                                                (Dl +D2)/2
                      Dl  = concentration of the analyte in the MS sample
                      D2  = concentration of the analyte in the MSD sample
       9.4.2   The relative percent difference between the matrix spike and the matrix spike duplicate
               must be less than 20%.  If this criterion is not met, the analytical system  is be judged
               to be out of control.  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).  To demonstrate freedom from
                      contamination,  analyze the blank immediately after analysis of the OPR
                      (Section 9.6).

      If Cr(VI) 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.
April 1995                                                                                    17

Method 1636
      If the result for a single blank remains above the MDL or if the result for the
                      average concentrat.on plus two standard deviations of three or rrTre blanks
                      A^W *7 re8ulatol> compliance level, results for samples associatec
                      Aose blanks may not be reported for regulatory compliance purposes  Sfc
                      another way results for all initial precision and recovery tests Section 92

                     tefore Zf" T* * IT*"'6'1 Wi* M ^ntamirlted method Wank
                     before these results may be reported for regulatory compliance purposes
      9.5.2   Field blank

                                         With each « of san>P'es
                     from                u                                   ^Pe
                     from the same site at the same time, to a maximum of 10 sampled)
                     the blank immediately before analyzing the samples in the batch
    If Cr(VI) or any potentially interfering substance is found in the field blank at
                    a c°ncemra.,on e<,uai to or greater man me ML (Table 1), or grealer thaHne
                    fifth the level m the associated sample, whichever is greater, results for
                    associated samples may be the result of contamination and may nm te reported
                    for regulatory compliance purposes.                                 reported

    Alternatively, if a sufficient number  of field blanks (three minimum) are
                    analyzed to characterize the nature of the field blank, the averageTonc^ntration
                    plus two standard deviations must be less than the regulatory compU»cetveT
                    or less than one-half the level  in the  associated sampfe, whkhev™ is^eater

    If contamination of the field blanks and associated samples is known or
                    suspected, the laboratory should communicate this to the san^UngT™ so that

                                °                   identified and
Equipment Blanks-Before any sampling equipment is used at
                                                                      a given site the
            blanks are required: bottle blanks and sampler check blanks.
                                      undergoing appropriate cleaning procedures (Section
                        , bottles should be subjected to conditions of use to verify the
                    h.^™ °] theucleanin8 Pr°<*d«res.  A representative set of sample bottles
                   shou d be filled with reagent water adjusted to a pH 9-9.5 with the buffer
                   solution (Section 7.6) and allowed to stand for a minimum of 24 h  Ideally

                   *e IT fr   K60"'68 "* aU°Wed l° Stand Should >» - <*<** as possible"^
                   the actual time that sample will be in contact with the bottle. After standing
                   U* > water should be analyzed for any signs of contamination. If any "
                   shows signs of contammation, me problem must be identified, the deanng

                             °       °r deanin  SOlU              and a"
  Sampler check blanks-Sampler check blanks are generated in the laboratory
                  or at the equipment cleamng contractor's facility by processing reagent wato
                                                                                 April 1995

                                                                                     Method 1636
                       through the sampling devices using the same procedures that are used in the
                       field (see Sampling Method).  Therefore, the "clean hands/dirty hands"
                       technique used during field sampling should be followed when preparing
                       sampler check blanks at the laboratory or cleaning facility.

                    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 used in the field (see Sampling Method).  For
                                     example, manual grab sampler check blanks are collected by
                                     directly submerging  a sample bottle into the water, filling the
                                     bottle, and capping.  Subsurface sampler check blanks are
                                     collected by immersing the sampler into the water and
                                     pumping water into a sample container.

                    The sampler check blank must be analyzed using  the
                                     procedures given in this method.  If Cr(VI) or any potentially
                                     interfering substance is detected in the blank, the source of
                                     contamination or interference must be identified, and the
                                     problem corrected.  The equipment must be demonstrated to be
                                     free from  Cr(VI) 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 equipment.

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 analysis of the method blank and samples from the
               same batch.

        9.6.3   Compute the percent recovery of Cr(VI) in the OPR sample.

        9.6.4   Compare the concentration to the  limits for ongoing recovery in Table 2.  If the
               acceptance criteria are met, system performance is acceptable and analysis of blanks
               and samples may proceed.  If, however, the recovery falls outside of the range given,
               the analytical processes are not being performed properly.  Correct the problem,
               reprepare the sample batch, and repeat the ongoing precision and recovery test (Section
April 1995                                                                                     79

   Method 1636


  10.0  Calibration and Standardization
       detector is 2.0 mL/min  Thi reire m    |POSCOumn reagent (Se«ion 7.5) from the
                                         based on anticipated sample

                                                                           // 7PP5

                                                                                     Method 1636
10.4   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.

       10.4.1  Analyze the mid-point calibration standard (Section 10.3).

       10.4.2  Compute the percent recovery of Cr(VI) using the calibration curve obtained in the
               initial calibration.

       10.4.3  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 the value falls outside the range given, system performance is
               unacceptable.  Locate and correct the problem and/or prepare a new calibration check
               standard and repeat the test (Sections 10.4.1-10.4.3), or recalibrate the system
               according to Section 10.3.

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

10.5   A calibration blank must be analyzed following every calibration verification to demonstrate
       that there is no carryover of Cr(VI) 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 10.4), 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 6.6.8), storage bags (Section 6.6.11),  and plastic wrap
       (Section 6.6.12) 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 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.
April 1995                                                                                      21

Method 1636
      11.3.1  Bottles, labware, and sampling equipment

        RH a precleaned basin (Section 6.6.9) with a sufficient quantity of

                           ^fr 1 'f'd.^ge" (Secti°" "X and compete./



Using a pair of clean gloves (Section 6.6.8) and clean
Place the scrubbed materials in a precleaned basin. Change gloves.
Thoroughly rinse the inside and outside of each piece with reagent
               no sign of detergent
Change gloves, immerse the rinsed equipment in a hot
           "AU       iztt^ttzzzzr-Md
           "AI-7       |»~S"^

          IIM*      s^t^TSrand b°"ies with reagent—
                      Proceed with Section 11.3.3 fc
    11.3.2  Labware and sampling equipment

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

           '3'2'2                      each piece of warc
   11.3.3  Fh^ropolymer samp.e bott.es-These bottles should be used if mercury is a Urge,

         1 1 O O 1        ...
                                    *«inpie Dottles with 0.1% (v/v) ultra.Diirp Hr^l
                     (Section 7.1.11) and cap tightly. To ensure a tight seal, it may be
                     necessary to use a strap wrench.                       y

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

                                                                                      Method 1636
        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
                              7.1.11). Double-bag each bottle in a polyethylene bag to prevent
                              contamination of the surfaces with dust and dirt.  Store at room
                              temperature until sample collection.

             After rinsing labware and  sampling equipment, air-dry in a class 100
                              clean air bench.  After drying, wrap each piece of ware or equipment
                              in two layers of  polyethylene film.
        NOTE: Polyethylene bottles cannot be used to collect samples that will be analyzed
       for mercury at trace (e.g., 0.012 ug/L) levels because of the potential for vapors 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 7.1.8) and flushing with water from the site before sample collection.

        11.3.6  Extension pole—Because of its length, it is impractical to submerse the 2-m
               polyethylene extension pole (used in with the optional grab sampling device) in acid
               solutions as described above.  If such an extension pole is used, a nonmetallic brush
               (Section 6.6.10) should be used to scrub the pole with reagent water and the pole
               wiped down with acids described in Section 11.3.4.  After cleaning,  the pole should be
               wrapped  in polyethylene film.

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
April 1995                                                                                      23

   Method 1636

   12.0  Procedures for Sample Preparation and Analysis

                                           e br°Ught '° amb-< '-P-ature before

        Initiate .nstrument operat.ng configurat.cn and caHbrate the .nstrument as described in Section
        range should bracket

        correction (r) for the
                                             (peak height or area) vs-
                                           6 °' '"" "" °f mag"«ude- The calibration
        exceed the calibration
 13.0  Data Analysis and Calculations

       Report al, resuHs for metals found
14.0  Method Performance


15.0  Pollution Prevention
     in .borato, operate.    e

                                                       3 mL °f sam"k-  ^« «*
                                                               C°nCentrati°nS that
                                                       21) for dissolved hexavalent
                                                             the quan«ity or
                                                                    April 1995

                                                                                   Method 1636
       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, standards should  be
       prepared in volumes consistent with laboratory use.

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. Chem. 1985, 57, 1728.

2       Herman, S.S.; Yeats, P.A. "Sampling of Seawater for Trace Metals," CRC Reviews in
        Analytical Chemistry 1985,  76, 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, 79, 175.

6       Patterson, C.C.; Settle, D.M. "Accuracy in Trace Analysis," In National Bureau of Standards
        Special Publication 422\ LaFleur, P.D., Ed., U.S. Government Printing Office: Washington,
        DC, 1976.
April 1995                                                                                  25

    Method 1636




           Fi.zge.ld, W.F, Watras, C.J. Science oflhe Total Environment 1989, 87,88, 223.

           Gill, G.A.; Fitzgerald, W.F. Deep Sea Res. 1985, 32, 287.
           Manage^ and Environmema,
                                                     EPA Envi™
                                      Contro1 m Trace Metals
  Dionex Technical Note No. 26, May 1990.
 and Health, Publication No. 77-206 i  ST, 977  AV^ Tl   '"T for OccuPati°nal Safety
 Information Service (NTIS) as PB-277256.                        Nati°nal Teclffii

 "OSHA Safety and Health Standards, General Industry"- 29 CFK loin r>
 and Health Administration, OSHA 2206 (revisedCary 197™     ' °CCUPatIonal

                             Laboratories'' American
                                           La—ories, Occupational Safety and Hea,th

Grohse, P. Research Triangle Zns.Hute, Tnstitute Drive, Building 6, Research Triangle Park, NC

       OynCorp), 300 N.   e      .
                                                                                     // 7995

                                                                                     Method 1636
18.0  Glossary

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

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

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

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

18.4    Calibration Blank—A volume of reagent water acidified with the same acid matrix as in the
        calibration standards.  The calibration blank is a zero standard and is used to calibrate the ICP
        instrument (Section 7.7.1).

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

18.6    Dissolved Analyte—The concentration of analyte in an aqueous sample that will pass through
        a 0.45-um 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 if the sampling devices and
        apparatus for sample collection have been adequately cleaned before shipment to the field site.
        An acceptable equipment blank must be achieved before the sampling devices and apparatus
        are used for sample collection.  In addition,  equipment blanks should be run on random,
        representative sets of gloves, storage bags, and plastic wrap for each lot to determine if these
        materials  are free from contamination before use.

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

18.9    Field Duplicates (FD1 and FD2)—Two separate samples collected in separate sample bottles
        at the same time  and place under identical circumstances and treated exactly the same
        throughout field and laboratory procedures.  Analyses of FD1 and  FD2 give a measure of the
        precision  associated  with sample collection,  preservation, and storage, as well as with
        laboratory procedures.
April 1995                                                                                     27

 Method 1636
     1810  Initial Precision and
           establish the ability to
                                          P™   i
                                                        ** °PR Standard
    18.11   Instrument Detection Limit
           » equal ,o three ,imes the
           cahbrauon blank signal a, the selected analytical wavelength
          are used with samples.  ^ la™^              '
                     - Present in the labora^
                                                               .   "» «"^ sig»<" *hich
                                                                    meaSUrcments <* «*
                                                                     '  Qr ^^ ^ ^ ^.^

18.22   Method Blank-See Laboratory Blank.

18.23   Method Detection Limit (MDL)—Th
       identified, measured, and reported with yy%, ,
       greater than zero (Section 9.2.1 and Table  1)
                                                         * - "»** ** ca« »
                                                    * ** ***** Concentration is
                                                                          April 1995

                                                                                      Method 1636
 18.24  Minimum Level (ML)—The lowest level at which the entire analytical system gives a
        recognizable signal and acceptable calibration point (Reference 9).

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

 18.26  Ongoing Precision and Recovery (OPR) Standard—A laboratory blank spiked with known
        quantities of the method analytes.  The OPR is analyzed exactly like a sample.  Its purpose is
        to determine whether the methodology is in control and to assure  that the results produced by
        the laboratory remain within the method-specified limits for precision and accuracy (Sections
        7.9 and 9.6).

 18.27  Preparation Blank—See Laboratory Blank.

 18.28  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.

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

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

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

 18.32  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
April 1995                                                                                     29

     Method 1636
                                                      Table 1


Hexavalent Chromium
                                          Lowest Ambitnt Water
                                         Quality Criterion (ug/L)1
                     Method Detection Limit (MDL)
                     and Minimum Level (ML); ug/L

           Method Detection Limit as determined by 40 CFR Pan 156, Appendix B.
                   cvei ^IV1L_) calculated bv multinlvino ioK^.^oi.^_. j_»-..  •  .  .	

                                                   Table 2
          QuaUty Control Acceptance Criteria for Performance Tests in EPA Method ,636'

Hexavalent Chromium
                        Initial Precision and
                       Recovery (Section 9.2)
Calibration Verification
     (Section 10.4)
                                                     Ongoing Precision and
                                                     Recovery (Section 9.6)
         All specifications expressed as percent.
Spike Recovery
 (Section 9.3)
                                                                                                April 1995

                                                                             Method 1636
                 Table 3:  Recommended Ion Chromatographic Conditions
               Postcolumn Reagent:

               Retention Time:
Guard Column—Dionex lonPac NG1
Separator Column—Dionex lonPac AS7

250 mM (NH4)2SO4
100 mM NH4OH
Flow rate =1.5 mL/min

2mM Diphenylcarbohydrazide
10% v/v CH3OH
IN H2S04
Flow rate = 0.5 mL/min

Visible 530 nm

3.8 min
April 1995