&EPA   Method 1631:  Mercury in Water by
        Oxidation, Purge and Trap, and Cold
        Vapor Atomic Fluorescence
                                   ) Printed on Recycled Paper

Method 1631

This method was prepared under the direction of William A. Telliard of the Engineering and Analysis
Division (HAD) within the U.S. Environmental Agency's (EPA's) Office of Science and Technology
(OST).  The method was prepared by Nicholas Bloom of Frontier GeoSciences under EPA Contract
68-C3-0337 with the DynCorp Environmental Programs Division.  Additional assistance in preparing
the method was provided by DynCorp Environmental and Interface, Inc.
This method has been reviewed and approved for publication by the Analytical Methods Staff within
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
Engineering and Analysis Division (4303)
U.S. Environmental Protection Agency
401 M Street SW
Washington, DC 20460
Phone:  202/260-7134
Fax:   202/260-7185
                                                                               Draft, July 1996

                                                                                      Method 1631

 This analytical method supports water quality monitoring programs authorized under the Clean Water
 Act (CWA, the "Act"). CWA Section 304(a) 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.

 CWA Section 303 requires each state 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
 CWA Sections 301(b) and 306.

 In defining water quality standards, the state may use narrative criteria, numeric criteria, or both.
 However, the  1987 amendments to CWA 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 (58 FR 60848) and the Stay of Federal Water Quality Criteria for Metals (60 FR 22228). These
 rules include water quality criteria for 13 metals, and it is these criteria on which  the new sampling
 and analysis methods are based. Method 1631 was specifically developed to provide reliable
 measurements of mercury at EPA WQC levels.

 In developing  methods for determination of trace metals, EPA found that one of the greatest
 difficulties 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 method is
 designed to preclude contamination in nearly all situations.  It also contains procedures necessary to
produce reliable results at  the lowest ambient 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, Method  1631  is performance based.  Alternative procedures may be used so
long as those procedures are demonstrated to yield reliable results.

Requests for additional copies of this method should be directed to:
 11209 Kenwood Road
Cincinnati, OH 45242

Method 1631
    Note:  This method is performance based.  The laboratory is permitted to omit any step or
    modify any procedure provided that all performance requirements in this method are met.  The
    laboratory may not omit any quality control analyses.  The terms "shall" and "must"  define
    procedures required for producing reliable data at water quality criteria levels. The terms
    "should" and "may" indicate optional steps that may be modified or omitted if the laboratory
    can demonstrate that the modified method produces results equivalent or superior to results
    produced by this method.             	^	
                                                                                  Draft, July 1996

                                Method  1631
     Mercury in  Water by  Oxidation, Purge  and Trap,  and
 1.0   Scope and Application

 1.1     This method is for determination of mercury (Hg) in filtered and unfiltered water by oxidation,
        purge and trap, desorption, and cold-vapor atomic fluorescence spectrometry (CVAFS). This
        method is for use in EPA's data gathering and monitoring programs associated with the Clean
        Water Act, the Resource Conservation and Recovery Act, the Comprehensive Environmental
        Response, Compensation and Liability Act, and the Safe Drinking Water Act.  The method is
        based on a contractor-developed method (Reference 1) and on peer-reviewed, published
        procedures for the determination of mercury and in aqueous samples, ranging from sea water
        to sewage effluent (References 2-5).

 1.2     This method is accompanied by Method 1669: Sampling Ambient Water for Determination of
        Trace Metals at EPA Water Quality Criteria Levels (Sampling Method). The Sampling
        Method is necessary to preclude contamination during the sampling process.

 1.3     This method is designed for determination of Hg in the range of 0.5-100 ng/L and may be
        extended to higher levels by selection of a smaller sample size. 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 part-per-billion (ppb) range, whereas
        ambient mercury concentrations are normally in the low part-per-trillion  (ppt) 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. Section 4.0 gives these

 1.5     The detection limit and minimum level of quantitation in this method are usually dependent on
        the level of background  elements rather than instrumental limitations. The  method detection
        limit (MDL; 40 CFR 136, Appendix B) for mercury has been determined to be 0.2 ngTL when
        no background elements or interferences are present. The minimum level (ML) has been
        established as 0.5 ng/L.  An MDL as low as 0.05 ng/L can be achieved for low Hg samples by
        using larger sample sizes, lower BrCl levels (0.2%), and extra caution in sample handling.

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

 1.7    This method follows  the EPA Environmental Methods Management Council's "Format for
       Method Documentation."
Draft, July 1996

Method 1631
1.8    This method is "performance based."  The analyst is permitted to modify the method to
       overcome interferences or lower the cost of measurements if all performance criteria are met.
       Section 9.1.2 gives the requirements for establishing method equivalency.

1.9    Any modification of this method, beyond those expressly permitted, shall be considered a
       major modification subject to application and approval of alternate test procedures under 40
       CFR  136.4 and 136.5.

1.10   This method should be used only by analysts who are experienced in the use of CVAFS
       techniques and who are thoroughly trained in the sample handling and instrumental  techniques
       described in this method. Each analyst who uses this method must demonstrate the ability to
       generate acceptable results using the procedure in Section 9.2.

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

2.0   Summary  of Method

2.1    A 100-2000 mL sample is collected directly into specially cleaned, pretested, fluoropolymer
       bottle(s) using sample handling techniques specially designed for collection of mercury at trace
       levels (Reference 6).

2.2    For dissolved Hg, samples are filtered through a 0.45-um capsule filter.

2.3    Samples are preserved by adding 5 mL/L of pretested 12 N HC1 (to allow both total and
       methyl Hg determination) or 5 mL/L  BrCl solution, if total mercury only  is to be determined.

2.4    Prior to analysis, a 100-mL sample aliquot is placed in a specially designed purge vessel, and
0.2 N BrCl solution is added to oxidize all Hg compounds to Hg(II).

After oxidation, the sample is sequentially prereduced with NH2OH-HC1 to destroy the free
halogens, and then reduced with SnCl2 to convert Hg(II) to volatile Hg(0).
 2.6     The Hg(0) is separated from solution by purging with nitrogen onto a gold-coated sand trap.

 2.7     The trapped Hg is thermally desorbed from the gold trap into an inert gas stream that carries
        the released Hg(0) into the cell of a cold-vapor atomic fluorescence spectrometer (CVAFS) for

 2.8     Quality is ensured through calibration and testing of the oxidation, purging, and detection
                                                                                  Draft, July 1996

                                                                                    Method 1631
 3.0   Definitions
Total mercury—all BrCl-oxidizable mercury forms and species found in an unfiltered aqueous
solution. This includes, but is not limited to, Hg(II), Hg(0), strongly organo-complexed Hg(II)
compounds, adsorbed paniculate Hg, and several tested covalently bound organo-mercurials
(e.g., CH3HgCl, (CH3)2Hg, and  C6H5HgOOCCH3).  The recovery of Hg bound within
microbial cells may require the additional step of UV photo-oxidation.  In this method, total
mercury and total recoverable mercury are synonymous.

Dissolved mercury—-all BrCl-oxidizable mercury forms and species found in the filtrate of an
aqueous solution that has been filtered through a 0.45 micron filter.

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 that come in contact with the sample and therefore require careful cleaning will be
referred to collectively as the Apparatus.

Definitions of other terms used in this method are given in the glossary at the end of the
 4.0    Contamination and Interferences

 4.1     Preventing ambient water samples from becoming contaminated during the sampling and
        analysis 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.  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
        that contain high levels of zinc), containers, sampling equipment, reagents, and reagent water;
        improperly cleaned and stored equipment, labware, and reagents; and atmospheric inputs  such
        as dirt and dust. Even human contact can be a source of trace metals contamination.  For
        example, it has been demonstrated that dental work (e.g., mercury amalgam fillings) in the
        mouths of laboratory personnel can contaminate samples that are directly exposed to exhalation
        (Reference 5).

 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 mercury.

       The integrity of the results produced cannot be compromised by contamination
                      of  samples. This method and the Sampling Method give requirements and
                      suggestions for control of sample contamination.
Draft, July 1996

Method 1631
      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   Avoiding contamination—The best way to control contamination is to completely
               avoid exposure of the sample to contamination in the first place. Avoiding exposure
               means performing operations in an area known to be free from contamination.  Two of
               the most important factors in avoiding/reducing sample contamination are (1) an
               awareness of potential sources of contamination and (2) strict attention to work being
               done. Therefore, it is imperative that the procedures described in this method be
               carried out by well-trained, experienced personnel.

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

       4.3.4   Minimize exposure—The Apparatus that will contact samples, blanks, or standard
               solutions should be opened or exposed only in a clean room, clean bench,  or glove
               box so that exposure to an uncontrolled atmosphere is minimized.  When not being
               used, the Apparatus should be covered with clean plastic wrap,  stored 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 a given batch of samples is processed, all work surfaces
               in the hood, clean bench, or  glove box in which the samples will be processed should
               be cleaned by wiping with a lint-free cloth or wipe  soaked with reagent water.

       4.3.6   Wear gloves—Sampling personnel must wear clean, nontalc gloves 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 determination of mercury at
               ambient water quality criteria levels must be nonmetallic, free of material that  may
               contain metals, or both.

      Construction materials—Only fluoropolymer or borosilicate glass (if Hg is the
                      only target analyte) containers should be used for samples that will be
                      analyzed for mercury because mercury vapors can diffuse in or out of  other
                                                                                  Draft, July 1996

                                                                                      Method 1631
                       materials, resulting in results that are biased low or high. All materials,
                       regardless of construction, that-will directly or indirectly contact the sample
                       must be cleaned using the procedures in this method and must be known to be
                       clean and mercury free before proceeding.

       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 introduction 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 a low concentration  of mercury is processed immediately after a
                       sample containing a relatively high concentration of mercury.  When an
                       unusually concentrated sample is encountered, a bubbler blank should be
                       analyzed immediately following the sample to check for carryover.  Samples
                       known or suspected to contain the lowest concentration of mercury should be
                       analyzed first followed by samples containing higher levels.

       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 mercury are processed and
                       analyzed. 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 subsequently transfer the contamination to the  sample.  Therefore, it is
                       imperative that every piece of the Apparatus that is directly or indirectly used
                       in the collection, processing, and analysis of ambient water samples be
                       thoroughly cleaned (see Section 6.1.2).
Draft, July 1996

Method 1631
      Contamination by airborne participate 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
       4.4.1   Due to the BrCl oxidation step, there are no observed interferences in the
               determination of Hg by this method.

       4.4.2   The potential exists for destruction of the gold traps if free halogens are purged onto
               them, or if they are overheated (>500 °C).  When the instructions in this method are
               followed accurately, neither of these outcomes is likely.

       4.4.3   Water vapor may collect in the gold traps and subsequently condense  in the
               fluorescence cell upon desorption, giving a false peak due to scattering of the
               excitation radiation.  Condensation can be avoided by predrying the gold trap, and by
               discarding those traps that tend to absorb large quantities of water vapor.

       4.4.4   The fluorescent intensity is strongly dependent upon the presence of molecular species
               in the carrier gas that can cause "quenching" of the excited atoms. The dual
               amalgamation technique eliminates quenching due to trace gases,  but it still remains
               the analyst's responsibility to ensure high purity inert carrier gas and a leak-free
               analytical train.
5.0    Safety
The toxicity or carcinogenicity of each chemical used in this method has not been precisely
determined; however, each compound should be treated as a potential health hazard.  Exposure
to these compounds should be reduced to the lowest possible level.

       5.1.1   Chronic mercury exposure may cause kidney damage, muscle tremors, spasms,
               personality changes, depression, irritability and nervousness. Organo-
               mercurials may cause permanent brain damage.  Because of the toxicological
               and physical properties of Hg, pure standards should be handled only by
               highly trained personnel thoroughly familiar with handling and cautionary
               procedures and the  associated risks.

       5.1.2   It is recommended that the laboratory purchase a dilute standard solution of the
               Hg in this method.  If primary solutions are prepared, they  shall be prepared in
               a hood, and a NIOSH/MESA-approved toxic gas respirator shall be worn when
               high concentrations are handled.

This method does not address all safety issues associated with its use.  The laboratory is
responsible for maintaining a current awareness file of OSHA regulations for the safe handling
                                                                                   Draft, July 1996

                                                                                      Method 1631
         of the chemicals specified in this method.  A reference file of material -safety data sheets
         (MSDSs) should also be made available to all personnel involved in these analyses.  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.
         Additional information on laboratory safety can be found in References 7-10. The references
      •   and bibliography at the end of Reference 10 are particularly comprehensive in dealing with the
         general subject of laboratory safety.

 5.3     Samples suspected to contain high concentrations of Hg are handled using essentially the same
         techniques employed in handling radioactive or infectious materials. Well-ventilated,
         controlled access laboratories are required. Assistance in evaluating the health hazards of
         particular laboratory conditions may be obtained from certain consulting laboratories and from
         State Departments of Health or Labor, many of which have an industrial health service. Each
         laboratory must develop a strict safety program for handling Hg.

         5.3.1   Facility—When samples known or suspected of containing high concentrations of
                mercury are handled, all operations (including removal of samples from sample
                containers, weighing, transferring, and mixing) should be  performed in a glove box
                demonstrated to be leaktight or in a fume hood demonstrated to have adequate airflow.
                Gross losses to the laboratory ventilation system must not be allowed. Handling of the
                dilute solutions normally used in analytical and animal work presents no inhalation
                hazards except in  an accident.

        5.3.2   Protective equipment—Disposable plastic gloves, apron or lab coat, safety glasses or
                mask, and a glove box  or fume hood adequate for radioactive work should be used.
                During analytical operations that may give rise to aerosols or dusts, personnel should
                wear respirators equipped with activated carbon filters.

        5.3.3   Training—Workers must be trained in the proper method  of removing contaminated
                gloves and clothing without contacting the exterior surfaces.

        5.3.4   Personal hygiene—Hands and forearms should be washed thoroughly  after each
                manipulation and before breaks (coffee, lunch, and shift).

        5.3.5  Confinement—Isolated  work areas posted with signs, segregated glassware and tools,
               and plastic absorbent paper on bench tops will aid in confining contamination.

        5.3.6  Effluent vapors—The effluent from the CVAFS should pass through either a column
               of activated charcoal or a trap containing gold or sulfur to amalgamate or react
               mercury vapors.
Waste handling—Good technique includes minimizing contaminated waste.  Plastic
bag liners should be used in waste cans.  Janitors and other personnel must be trained
in the safe handling of waste.
        5.3.8   Decontamination

      Decontamination of personnel—Use any mild soap with plenty of scrubbing
Draft, July 1996

Method 1631
      Glassware, tools, and surfaces—Sulfur powder will reaet with mercury to
                      produce mercuric sulfide, thereby eliminating the possible volatilization of Hg.
                      Satisfactory cleaning may be accomplished by dusting a surface lightly with
                      sulfur powder, then washing with any detergent and water.

       5.3.9   Laundry—Clothing known to be contaminated should be collected in plastic bags.
               Persons who convey the bags and launder the clothing should be advised of the hazard
               and trained in proper handling.  If the launderer knows of the potential problem, the
               clothing may be put into a washer without contact. The washer should be run through
               a cycle before being used again for other clothing.

       5.3.10  Wipe tests—A useful method of determining cleanliness of work surfaces and tools is
               to wipe the surface with a piece of filter paper.  Extraction and analysis by this
               method can achieve a limit of detection of less than  1 ng per wipe. Less than 0.1 fig
               per wipe indicates acceptable cleanliness; anything higher warrants further cleaning.
               More than 10 ug on a wipe constitutes an acute hazard and requires prompt cleaning
               before further use of the equipment or work space, and indicates that unacceptable
               work practices have been employed.

6.0   Apparatus and  Materials

       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, materials, or cleaning procedures other than those suggested here. The laboratory
       is responsible for demonstrating equivalent performance.

6.1    Sampling equipment

       6.1.1   Sample collection bottles-Fluoropolymer or borosilicate glass, 125- to 1000-mL, with
               fluoropolymer or fluoropolymer-lined cap.

       6.1.2   Cleaning

      New bottles are cleaned by heating to 65-75°C in 4 N HC1 for at least 48 h.
                      The bottles are cooled, rinsed three times  with reagent water, and filled with
                      reagent water containing 1% HC1.  These bottles are capped and placed in a
                       clean oven at 60-70°C overnight.  After cooling, they are rinsed three more
                      times with reagent water, filled with reagent water containing 0.4% (v/v) HC1,
                       and placed in a mercury-free class 100  clean bench until dry. The bottles are
                       then tightly capped (with a wrench), double-bagged in new polyethylene zip-
                       type bags until needed, and stored in wooden or plastic boxes until  use.

      Used bottles known not to have contained mercury  at high levels are cleaned
                       as above, except with only 6-12 h in hot 4 N HC1.

      Bottle blanks should be analyzed as described in Section to verify the
                       effectiveness of the cleaning procedures.
                                                                                  Draft, July 1996

                                                                                     Method 163]
         6.1.3   Filtration Apparatus

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

       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—styrene/ethylene/butylene/silicone (SEES) resin for use with
                       peristaltic pump, approx 3/8-in i.d. by approximately 3 ft (Cole-Parmer size
                       18, Catalog No. G-06464-18, or approximately 1/4-in i.d., Cole-Parmer size
                       17, Catalog No. G-06464-17, or equivalent). Tubing is cleaned by soaking in
                       5-10% HC1 solution for 8-24 h, rinsing with reagent water in a clean bench in
                       a clean room, and drying in the clean bench by purging with metal-free air or
                       nitrogen. After drying, the tubing is double-bagged in clear polyethylene bags,
                       serialized with a unique number, and stored until use.

 6.2    Equipment for bottle and glassware cleaning

        6.2.1    Vat, 100-200 L, high-density polyethylene (HOPE), half filled with 4 N HC1 in
                reagent water.

        6.2.2    Panel immersion heater, 500-W, all-fluoropolymer coated,  120 vac (Cole-Parmer H-
                03053-04, or equivalent)

        NOTE: Caution: Read instructions carefully!!  The heater will maintain steady state,
        without temperature feedback control, of 60-75°C in a vat  of the size described.
        However, the equilibrium temperature will be higher (up to boiling) in a smaller vat.
        Also, the heater plate MUST be maintained in a vertical position, completely
 	submerged and away from the vat walls to avoid melting the vat or burning out!

        6.2.3   Laboratory sink in class 100 clean area, with high-flow reagent water (Section 7.1) for

        6.2.4   Clean bench,  class 100, for drying rinsed bottles.

        6.2.5   Oven, stainless steel, in class 100 clean area, capable of maintaining  ± 5°C in the
               60-70°C temperature range.
Cold vapor atomic fluorescence spectrometer (CVAFS): The CVAFS system used may either
be purchased from a supplier, or built in the laboratory from commercially available

6.3.1   Commercially available:  Tekran (Toronto, ON) Model 2357 CVAFS, or Brooks-Rand
       (Seattle, WA)  Model m CVAFS, or equivalent

6.3.2   Custom-built CVAFS (Reference  11).  Figure 1  shows the schematic diagram.  The
       system consists of the following:
Draft, July 1996

Method 1631
      Low-pressure 4-W mercury vapor lamp

      Far UV quartz flow-through fluorescence cell—12 mm x 12 mm x 45 mm,
                      with a 10-mm path length (NSG Cells, or equivalent).

      UV-visible photomultiplier (PMT)—sensitive to < 230 nm. This PMT is
                      isolated from outside light with a 253.7-nm interference filter (Oriel Corp.,
                      Stamford, CT, or equivalent).

      Photometer and PMT power supply (Oriel Corp. or equivalent), to convert
                      PMT output (nanoamp) to millivolts

      Black anodized aluminum optical block—holds fluorescence cell, PMT, and
                      light source at perpendicular angles, and provides collimation of incident and
                      fluorescent beams  (Frontier Geosciences Inc., Seattle, WA, or equivalent).

      Flowmeter, with needle valve capable of reproducibly keeping the carrier gas
                      flow rate at 30 mL/min

      Ultra high-purity argon (grade 5.0)

6.4     Equipment for Hg purging system—Figure 2a shows the schematic diagram for the purging
        system. The system consists of the following:

        6.4.1   Flow meter/needle valve—capable of controlling and measuring gas flow rate to the
               purge vessel at 350 (± 50) mL/min.

        6.4.2   Fluoropolymer fittings—connections between components and columns are made using
               6.4-mm o.d. fluoropolymer tubing and fluoropolymer friction-fit or threaded tubing
               connectors.  Connections between components requiring mobility  are made with 3.2-
               mm o.d. fluoropolymer tubing because of its greater flexibility.

        6.4.3   Acid fume pretrap—10-cm long x 0.9-cm i.d. fluoropolymer tube containing 2-3 g of
               reagent grade, nonindicating, 8-14 mesh soda lime chunks, packed between wads of
               silanized glass wool. This trap is cleaned of Hg by placing on the output of a clean
               cold vapor generator (bubbler) and purging for 1 h with N2 at 350 mL/min.

        6.4.4   Cold vapor generator (bubbler)—200-mL borosilicate glass (15  cm high x 5.0 cm
               diameter) with standard taper 24/40 neck, fitted with a sparging stopper having a
               coarse glass frit that extends to within 0.2 cm of the bubbler bottom (Frontier
               Geosciences, Inc. or equivalent).

 6.5     Equipment for the  dual-trap Hg(0) preconcentrating system

        6.5.1   Figure 2b shows the schematic for the dual-trap amalgamation system (Reference 5).
                                                                                  Draft, July 1996

                                                                                      Method 1631
        6.5.2   Gold-coated sand traps—10-cm x 6.5-mm o.d. x 4-mm i.d. quartz tubing. The tube is
                filled with 3.4 cm of gold-coated 45/60 mesh quartz sand (Frontier Geosciences Inc.,
                Seattle, WA, or equivalent). The ends are plugged with quartz wool.

       Traps are fitted with 6.5-mm i.d. fluoropolymer friction-fit sleeves for making
                       connection to the system. When traps are not in use, fluoropolymer end plugs
                       are inserted in trap ends to eliminate contamination.

       At least six  traps are needed for efficient operation, one as the "analytical"
                       trap, and the others to sequentially collect samples on.

        6.5.3   Heating of gold-coated sand traps—To desorb Hg collected on a trap, heat for 3.0 min
                to 450-500°C (a barely visible red glow when the room is darkened) with a coil
                consisting of 75 cm of 24-gauge  Nichrome wire at a potential of 10-14 vac. Potential
                is applied and finely adjusted with an autotransformer.

        6.5.4   Timers—The heating interval is controlled by a timer-activated 120-V outlet (Gralab,
                or equivalent), into which the heating coil autotransformer is  plugged.  Two timers are
                required, one each for the "sample" trap and the "analytical" trap.

        6.5.5   Air blowers—After heating, traps are cooled by blowing air from a small squirrel-cage
                blower positioned immediately above the trap.  Two blowers  are required, one each for
                the "sample" trap and the "analytical" trap.

        Recorder—Any multi-range  millivolt chart recorder or integrator with a range compatible with
        the CVAFS is acceptable. By using a two pen recorder with pen sensitivity offset by a factor
        of 10, the dynamic range of the system is extended to 103.

        Pipettors—All-plastic pneumatic  fixed-volume and variable pipettors in the range of 10 uL to
        5.0 mL.
 6.8     Analytical balance capable of weighing to the nearest 0.01 g
7.0    Reagents and Standards
       Reagent water—18-MQ minimum, ultrapure deionized water starting from a prepurified
       (distilled, R.O., etc.) source.  Water should be monitored for Hg, especially after ion exchange
       beds are changed.

       Air—It is very important that the laboratory air be low in both paniculate and gaseous
       mercury. Ideally, mercury work should be conducted in a new laboratory with mercury-free
       paint on the walls.  Outside air, which is very low in Hg, should be brought directly into the
       class 100 clean bench air intake.  If this is impossible, air coming into the clean bench can be
       cleaned for mercury by placing a gold-coated cloth prefilter over the intake.

       7.2.1   Gold-coated cloth  filter: Soak 2  m2 of cotton gauze hi 500 mL of 2% gold chloride
              solution at pH 7.  In a hood, add 100 mL of 30% NH2OH-HC1 solution, and
              homogenize into the cloth with gloved hands. The material will turn black as colloidal
Draft, July 1996

Method 1631
               gold is precipitated. Allow the mixture to set for several hours; then rinse with
               copious amounts of deionized water. Squeeze-dry the rinsed cloth, and spread flat on
               newspapers to air-dry. When dry, fold and place over the intake prefilter of the
               laminar flow hood.

       CAUTION:  Great care should be taken to avoid contaminating the laboratory with
       gold dust.  This could cause interferences with the analysis if gold becomes
       incorporated into the samples or equipment.  The gilding procedure should be done in
       a remote laboratory if at all possible.	

7.3    Hydrochloric acid—trace-metal purified reagent HC1 containing less than 5 pg/mL Hg.  The
       HC1 should be preanalyzed for Hg before use.

7.4    Hydroxylamine hydrochloride—Dissolve 300 g of NH2OH-HC1 in reagent water  and bring to
       1.0 L.  This solution may be purified by the addition of 1.0 mL  of SnCL, solution and purging
       overnight at 500 mL/min with Hg-free N2.

7.5    Stannous chloride—Bring 200 g of SnCl2-2H2O and 100 mL concentrated HC1 to 1.0 L with
       reagent water.  Purge overnight with mercury-free N2 at 500 mL/min to remove all traces of
       Hg. Store tightly capped.

7.6    Bromine monochloride (BrCl)—In a fume hood, dissolve 27 g of reagent grade KBr in 2.5 L
       of low-Hg HC1.  Place a clean magnetic stir bar in the bottle and stir for approximately 1 h in
       the fume hood. Slowly add 38 g reagent grade KBrO3  to the acid while stirring.  When all of
       the KBrO3 has been added, the solution color should change from yellow to red  to orange.
       Loosely cap the bottle, and allow to  stir another hour before tightening the lid.

       CAUTION: This process generates copious quantities of free halogens (C12, Br2,
       BrCl), which are released from the bottle. Add the KBrO3 SLOWLY in a fume hood!

7.7    Stock mercury standard—NIST-certified 10,000-ppm aqueous Hg solution (NIST-3133).  This
       solution is stable at least until the NIST expiration date.

7.8    Secondary Hg standard—Add approx 0.5 L of reagent water and 5 mL  of BrCl solution
       (Section 7.6) to a 1.00-L class A volumetric flask.  Add 0.100 mL of the stock mercury
       standard (Section 7.7) to the flask and dilute to 1.00 L  with reagent water. This solution
       contains 1.00 ug/mL (1.00 ppm) Hg. Transfer the solution to a fluoropolymer bottle and cap
       tightly. This solution is stable indefinitely.

7.9    Working Hg standard—Dilute 1.00 mL of the secondary Hg standard (Section 7.8) to 100 mL
       in a class A volumetric flask with reagent water containing 0.5% by volume BrCl solution
       (Section 7.6).  This  solution  contains 10.0 ng/mL and should be replaced monthly.

7.10  IPR and OPR solutions—Using the working Hg standard (Section 7.9), prepare EPR and OPR
        solutions at a concentration of 5 ng/L Hg in reagent water.

7.11  Nitrogen—Grade 4.5 (standard laboratory grade) nitrogen that has been further purified by the
        removal of Hg using a gold-coated sand trap.
                                                                                  Draft, July 1996

                                                                                    Method 1631
 7.12   Argon—Grade 5.0 (ultra high-purity, GC grade) that has been further purified by the removal
        of Hg using a gold-coated sand trap.         ;

 8.0   Sample Collection, Preservation, and Storage

 8.1     Before samples are collected, consideration should be given to the type of data required, (i.e.,
        dissolved or total), 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.

 8.2     Samples are collected into rigorously cleaned fluoropolymer bottles with fluoropolymer or
        fluoropolymer-lined caps.  Borosilicate glass bottles may be used if Hg is the only target
        analyte. It is critical that the bottles have tightly sealing caps to avoid diffusion of
        atmospheric Hg through the threads (Reference 4). Polyethylene sample bottles must not be
        used (Reference 11).

 8.3     Collect samples using the Sampling Method (Reference 6).  Procedures in the Sampling
        Method are based on rigorous protocols for collection of samples for mercury (References 4
        and 11).

        NOTE: Discrete samplers have been found to contaminate samples with Hg at the
        ng/L level, and therefore,  great care should be exercised if this type of sampler is used
        to collect samples.  It may be necessary for the sampling team to use other means of
        sample collection if samples are found to be contaminated using the discrete sampler.

 8.4     Sample filtration—For dissolved Hg, samples and field blanks are filtered through a 0.45-nm
        capsule filter (Section  The Sampling Method describes filtering procedures.

 8.5     Preservation—Samples are preserved by adding 5 mL/L of concentrated HC1 (to allow both
        total  and methyl Hg determination) or 5 mL/L BrCl solution, if total mercury only is to be
        determined.  Acid- and BrCl-preserved samples are stable for a minimum of 6 months.

        8.5.1   Samples may be shipped to the laboratory unpreserved if they are (1) collected  in
               fluoropolymer bottles, (2) filled  to the top with no head space,  (3) capped tightly, and
               (4) maintained at 0-4°C from the time of collection until preservation.  The samples
               must be acid-preserved  within 48 h after sampling.

        8.5.2   Samples that are acid-preserved  may lose Hg to coagulated organic materials in the
               water or condensed on the walls (Reference 12).  The  best approach is to add BrCl
               directly to the sample bottle at least 24 hours before analysis. If other Hg species are
               to be analyzed, these aliquots must be removed prior to the addition of BrCl.  If BrCl
               cannot be added directly to the sample bottle, then the bottle must be shaken
               vigorously prior to sub-sampling.

        8.5.3   Handling of the samples in the laboratory should be undertaken in a mercury-free
               clean bench, after  rinsing the outside of the bottles with reagent water and drying in
               the clean air hood.
Draft, July 1996

Method 1631
       NOTE: Due to the potential for contamination, it is recommended that filtration and
       preservation of samples be performed in the clean room in the laboratory.  However,
       if circumstances in the field prevent overnight shipment of samples, then the samples
       should be filtered and preserved in a designated clean area in the field in accordance
       with the procedures given in Sections 8.3 and 8.4 of Method 1669.	

8.6    Storage—Sample bottles should be stored in clean (new) polyethylene bags until analysis.
       Refrigeration at 0-4°C is not necessary once samples are preserved.  If properly preserved,
       samples can be held up to 6 months before analysis.
9.0    Quality Control

9.1     Each laboratory that uses this method is required to operate a formal quality assurance
        program (Reference 13).  The minimum requirements of this program consist of an initial
        demonstration of laboratory capability, ongoing analysis of standards and blanks as a test of
        continued performance, and the analysis of matrix spikes (MS) and matrix spike duplicates
        (MSD) to assess accuracy and precision.  Laboratory performance is compared to established
        performance criteria to determine that the results of analyses meet the performance
        characteristics of the method.

        9.1.1   The analyst shall make an initial demonstration of the ability to generate acceptable
               accuracy and precision with this method.  This ability is established as described in
               Section 9.2.

        9.1.2   In recognition of advances that are occurring in analytical technology, the analyst is
               permitted certain options to  improve results or lower the cost of measurements.  These
               options include automation of the dual-amalgamation system, single-trap amalgamation
               (Reference 14), direct electronic data acquisition, calibration using gas-phase elemental
               Hg standards, changes in the bubbler design (including substitution of a flow-injection
               system) to maximize throughput, or changes in the detector (i.e., CVAAS), where less
               sensitivity is acceptable or desired. Changes in the principle of the determinative
               technique, such as the use of colorimetry, are not allowed.  If an analytical technique
               other than the CVAFS technique specified in this method is used, that technique must
               have  a specificity for mercury equal to or better than the specificity of the technique in
               this method.

       Each time this 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 one-third the regulatory compliance level  or
                       lower than the MDL of this method, 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:
                                                                                   Draft, July 1996

                                                                                       Method 1631
                    The names, titles, addresses, and telephone numbers of the
                                      analyst(s) who performed the analyses and modification, and
                                      the quality control officer who witnessed and will verify the
                                      analyses and modification

                    A narrative stating the 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 (Section 10)
                                      (b)      Initial  precision and recovery (Section 9.2)
                                      (c)      Analysis of blanks (Section 9.4)
                                      (d)      Matrix spike/matrix spike duplicate analysis (Section
                                      (e)      Ongoing precision and recovery (Section  9.5)
                                      (f)      Quality control sample (Section 9.6)

                    Data that will  allow an independent reviewer to validate each
                                      determination by tracking the instrument output to the final
                                      result.  These data are to include the following:

                                      (a)      Sample numbers and other identifiers
                                      (b)      Processing dates
                                      (c)      Analysis dates
                                      (d)      Analysis sequence/run chronology
                                      (e)      Sample weight or volume
                                      (f)      Copies of logbooks, chart recorder, or other raw data
                                      (g)     Calculations linking raw data to the results reported

        9.1.3   Analyses of MS and MSD samples are required to  demonstrate the accuracy and
               precision and to monitor matrix interferences.  Section 9.3 describes the procedure and
               QC criteria for spiking.

        9.1.4   Analyses of blanks are required to demonstrate acceptable levels of contamination.
               Section 9.4 describes the procedures and criteria for analyzing blanks.

        9.1.5   The laboratory shall, on an ongoing basis, demonstrate through analysis of the ongoing
               precision and recovery (OPR) sample and the quality control sample (QCS) that the
               system is in control.  Sections 9.5 and 9.6 describe these procedures, respectively.

        9.1.6   The laboratory shall maintain records to define the  quality of the data that are
               generated.  Sections 9.3.7 and 9.5.3 describe  the development of accuracy statements.

        9.1.7   The determination of Hg in water is controlled by an analytical batch.  An analytical
               batch is a set of samples oxidized with the same batch of reagents,  and analyzed
               during the  same 12-hour shift.  A batch may  be from 1 to as many as 20  samples.
               Each batch must be accompanied by at least three bubbler blanks (Section 9.4), an
Draft, July 1996

Method 1631
               OPR sample, and a QCS.  In addition, there must be one MS and one MSB sample for
               every 10 samples (a frequency of 10%).  Reagent blanks for this determination are
               required when the batch of reagents (bromine monochloride plus hydroxylamine
               hydrochloride) are made, with verification in triplicate each month until a new batch of
               reagents is needed.

9.2    Initial demonstration of laboratory capability

       9.2.1   Method detection limit—To establish the ability to detect Hg, the analyst shall
               determine the MDL determined according to the procedure at 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 Section 1.5 or one-third  the regulatory compliance limit,  whichever is greater.
               The MDL 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 the MDL 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 replicates of the IPR solution  (5 ng/L, Section 7.10)  according to
                      the procedure beginning in Section 11.

      Using the results of the set of four analyses, compute the average percent
                      recovery (X), and the standard deviation of the percent recovery (s) for Hg.

      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 samples may begin.  If,  however, s
                      exceeds the precision limit or X falls outside the acceptance range, system
                      performance is unacceptable. Correct the problem and repeat the test (Section

9.3    Matrix spike (MS) and matrix spike duplicate (MSD)—To assess the performance of the
       method on a given sample matrix, the laboratory must spike, in duplicate, a minimum of 10%
       (1 sample in 10) from a given sampling site or, if for compliance monitoring, from a given
       discharge. Therefore, an analytical batch of 20 samples would require two MS/MSD samples.

       9.3.1   The concentration of the spike in the sample shall be  determined  as follows:

      If, as in compliance monitoring, the concentration of Hg in the sample is being
                      checked against a regulatory concentration limit, the spiking level  shall be at
                      that limit or at 1-5 times the background concentration of the sample (as
                      determined in Section 9.3.2), whichever is greater.

      If the concentration of Hg in a sample is not being checked against a limit, the
                      spike shall be at 1-5 times  the background  concentration  or at 1-5 times the
                      ML in Table 1, whichever is greater.
Draft, July 1996

                                                                                      Method 1631
        9.3.2   To determine the background concentration (B), analyze one sample aliquot from each
                set of 10 samples from each site or discharge according to the procedure in Section 11.
                If the expected background concentration is known from previous experience or other
                knowledge, the spiking level may be established a priori.

       If necessary, prepare a standard solution to produce an appropriate level in the
                       sample (Section 9.3.1).

       Spike two additional sample aliquots with the spiking solution and analyze
                       these aliquots as described in Section 11.1.2 to  determine the concentration
                       after spiking (A).

        9.3.3   Calculate the percent recovery (P) in each aliquot  using the following equation:
                                         P = 100
                       A = Measured concentration of analyte after spiking
                       B = Measured concentration of analyte before spiking
                       T = True concentration of the spike
        9.3.4  Compare the percent recovery (P) with the QC acceptance criteria in Table 2.

       If results of the MS/MSD are similar and fail the acceptance criteria, and
                       recovery for the OPR standard (Section 9.5) for the analytical batch is within
                       the acceptance criteria in Table 2, an interference is present and the results
                       may not be reported for regulatory compliance purposes.  If the interference
                       can be attributed to sampling, the site or discharge should be resampled.  If the
                       interference can be attributed to a method deficiency, the analyst must modify
                       the method, repeat the test required in Section 9.1.2, and repeat analysis of the
                       sample and MS/MSD.  However, when this method was written, there were no
                       known interferences in  the determination of Hg using this method.. If such a
                       result is observed, the analyst should investigate it thoroughly.

       If the results of both the spike and the OPR test fall outside the acceptance
                       criteria, the analytical system is judged to be out of control. The analyst must
                       identify and correct the problem and reanalyze the sample batch.
Draft, July 1996

Method 1631
       9.3.5   Relative percent difference between duplicates—Compute the relative percent
               difference (RPD) between the MS and MSD results according to the following
               equation using the concentrations found in the MS and MSD. Do not use the
               recoveries calculated in Section 9.3.3 for this calculation because the RPD is inflated
               when the background concentration is near the spike concentration.
                                   RPD = 200 x
                  Dl = concentration of Hg in the MS sample
                  D2 = concentration of Hg in the MSD sample

       The RPD for the MS/MSD pair must not exceed the acceptance criterion in Table 2.
       If the criterion is not met, the system is judged to be out of control.  The problem
       must immediately be identified and corrected, and the analytical batch reanalyzed.

9.3.7   As  part of the QC program for the laboratory, method precision and accuracy for
       samples should be assessed and records maintained. After analyzing five samples in
       which the recovery passes the test in Section 9.3.4, compute the average percent
       recovery (Pa) and the standard deviation of the percent recovery (sp).  Express the
       accuracy assessment as a percent  recovery interval from Pa - 2sp to Pa + 2sp.  For
       example, if Pa = 90% and sp = 10% for five analyses,  the accuracy interval is
       expressed as 70-110%. Update the accuracy assessment regularly (e.g., after every
       five to ten new accuracy measurements).

Blanks—Blanks are critical to the reliable determination of Hg at low levels. The  sections
below give the  minimum requirements for analysis of blanks.  However, it is suggested that
additional blanks be analyzed as necessary to pinpoint sources of contamination in, and
external to, the laboratory.

9.4.1   Bubbler blanks—Bubbler blanks are analyzed to demonstrate freedom from system
       contamination. The mean bubbler blank for an analytical batch, if within acceptance
       criteria, is subtracted from all raw data for that batch prior to the calculation  of results.  Immediately after analyzing a sample for Hg,  place a clean gold trap on the
               bubbler, purge and analyze the sample a second time using the procedure in
               Section  11, and determine the amount of Hg remaining in the system.  If the bubbler blank is found to contain more  than 50 pg Hg, the system is  out
               of control.  The problem  must be investigated and remedied, and the samples
               run on that bubbler must  be reanalyzed.  The  remedy for a contaminated
               bubbler usually involves rigorously cleaning the bubbler or changing the soda
               lime trap on the affected  bubbler. If the blanks from other bubblers  contain
               less than 50 pg Hg, the data associated with those bubblers remain valid.  The mean result for all bubbler blanks (from bubblers passing the  specification
               in Section in an analytical batch (at least three bubbler blanks) is
               calculated at the end of the batch. The mean  result must be < 25 pg with a
                                                                                  Draft, July 1996

                                                                                      Method 1631
                       standard deviation of < 10 pg for the batch to be considered valid. If the
                       mean is < 25 pg, the value is subtracted from all raw data before results are

       If the bubbler blank QC exceeds the acceptance criteria in Section, then
                       the system is out of control, and the problem must be resolved, and the
                       samples reanalyzed.  Usually, the bubbler blank is too high for one of the
                       following reasons:

                              (a)     Bubblers need rigorous cleaning;

                              (b)     Soda-lime is contaminated;  or

                              (c)     Carrier gas  is contaminated.

       At least three bubble blanks must be run per analytical batch.  One of the
                       blanks must be  analyzed following each OPR.

        9.4.2   Reagent blanks—Since  even reagent water often contains measurable Hg, blanks must
                be determined on solutions of reagents by adding these reagents to previously purged
                reagent water in the bubbler.

       Reagent blanks  are required when the batch of reagents (bromine monochloride
                       plus hydroxylamine hydrochloride) are made, with verification  in triplicate
                       each month until a new batch of reagents is needed.

       Add aliquots of BrCl (0.5 mL), NH2OH (0.2 mL) and SnCl2 (0.5 mL) to
                       previously purged reagent water in the bubbler.

       The presence of more than 25 pg of Hg indicates a problem with the reagent
                       solution.  The purging of certain reagent solutions, such as SnCl2 or NH2OH)
                       with mercury-free nitrogen or argon can reduce Hg to acceptable levels.
                       Because BrCl cannot be purified, a new batch should be made from different
                       reagents and should be tested for Hg levels  if the level of Hg in the BrCl
                       solution is too high.

        9.4.3   Field blanks

       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 Hg 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.
Draft, July 1996

Method 1631
      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.

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

      Bottle blanks—After undergoing the cleaning procedures in this method,
                      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 the sample will be in contact with the bottle.
                      After standing, the water  should be analyzed for any signs of contamination.
                      If any bottle shows signs  of contamination, the problem must be identified, the
                      cleaning procedures corrected or cleaning solutions changed, and  all affected
                      bottles recleaned.

      Sampler check blanks—Sampler check blanks are generated in the laboratory
                      or at the equipment cleaning contractor's facility  by processing reagent water
                      through the sampling devices using the same procedures that are used 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 7.1) and processing
                                      the reagent water through the equipment using the same
                                      procedures that are 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 submersible pump or intake tubing
                                      into the water and pumping water into a sample container.

                     The sampler check blank must be analyzed using the
                                      procedures in this method.   If mercury 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
                                                                                   Draft, July 1996

                                                                                     Method 1631
                                     free from mercury and interferences before the equipment may
                                     be used in the field.

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

 9.5     Ongoing precision and recovery (OPR)—To demonstrate that the analysis system is in control
        and that acceptable precision and accuracy is being maintained within each analytical  batch,
        the analyst shall perform the following operations:

        9.5.1   Analyze the OPR solution (5 ng/L, Section 7.10) followed by a bubbler blank prior to
               the analysis of each analytical batch according to the procedure beginning in Section
               11. An OPR must also be analyzed at the end of an  analytical run or  at the end of
               each 12-hour shift.  Subtract the peak height (or peak area) of the bubbler blank from
               the height (or area) for the OPR and compute, the  concentration for the blank-
               subtracted OPR.

        9.5.2   Compare the concentration with the limits for ongoing precision and recovery in Table
               2.  If the concentration is in the range specified, the analysis system is in control and
               analysis of samples and blanks may proceed. If, however, the concentration is not in
               the specified range, the analytical process is not in control.  Correct the problem and
               repeat the ongoing precision and recovery test.

        9.5.3   The laboratory should add results that pass the specification in Section 9.5.2 to DPR
               and previous OPR data and update QC charts to form a graphic representation of
               continued laboratory performance.  The laboratory should also develop a statement of
               laboratory data quality for each analyte by calculating the average percent recovery (R)
               and the standard deviation of the percent recovery (sr).  Express the accuracy as a
               recovery interval from R - 2sr to R + 2sr. For example, if R = 95% and sr = 5%,  the
               accuracy is 85-105%.

 9.6     Quality control sample (QCS)—The laboratory must obtain a QCS from a source different
        from the Hg used  to produce the standards used routinely  in this method (Sections 7.7-7.10).
        The QCS should be analyzed as an independent check of instrument calibration in the middle
        of the analytical batch (e.g., for a batch of 14 samples, the QCS should  be analyzed after the
        seventh sample).

 9.7     Depending on specific program requirements, the laboratory may be required to analyze field
        duplicates and field spikes collected to assess the precision and accuracy of the sampling,
        sample transportation, and storage techniques.  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.
Draft, July 1996

Method 1631
10.0  Calibration and Standardization

10.1   Establish the operating conditions necessary to purge Hg from the bubbler and to desorb Hg
       from the traps in a sharp peak.  The system is calibrated using standards traceable to NIST
       standard reference material, as follows:
        10.1.1 Calibration


The calibration must contain five or more non-zero points and the
results of analysis of two bubbler blanks.  The lowest calibration point
must be at the Minimum Level (ML).

Standards are analyzed by the addition of aliquots of the Hg working
standard (Section 7.9)  directly into the bubblers. Add a 0.05 ng
aliquot of the standard and 0.5 mL SnCl, to the bubbler, swirling to
mix, and purge as above to produce a standard of 0.5 ng/L.
Sequentially follow with aliquots of 0.1, 0.5, 2.5, and 10 ng Hg with
0.5 mL SnCl2 to produce standards  of 1,  5, 25, and 100 ng/L.

Calculate the response factor (RF) for Hg in for each of the five
standards using the peak height or area produced and the following
                                          RF =
         Rx = height or area of the signal for Hg
         C  = net concentration (minus mean  bubbler blank) of standard analyzed (ngfL)
            Calculate the mean response factor (RFm), the standard deviation of the
                             RFm (SD), and the relative standard deviation (RSD) of the mean,
                             where RSD = 100 x SD/RFm. If the RSD of RFm is less than 15%
                             over the calibration range, then RFm may be used to calculate sample

            The net concentration recovery (minus mean bubbler blank) for the
                             lowest standard must be in the range of 75% to 125% of the expected
                             value to continue with sample analysis.

10.2   Ongoing precision and recovery—Perform the ongoing precision and recovery test to verify
       calibration prior to analysis of samples in each analytical batch.  An OPR must also be
       analyzed at the end of an analytical run or at the end of each 12-hour shift.
                                                    Draft, July 1996

                                                                                    Method 1631
 11.0  Procedure
        NOTE: The following procedures for analysis of samples are provided as guidelines.
        Analysts may find it necessary to optimize the procedures, such as drying time or
        potential applied to the Nichrome wires, for the laboratory's specific instrumental set-
 11.1    Sample Preparation

        11.1.1  Pour a 100-mL aliquot from a thoroughly shaken, acidified sample, into a 125-mL
               fluoropolymer bottle.  If BrCl was not added as a preservative (Section 8.5), add the
               amount of BrCl solution (Section 7.6) given below, cap the bottle, and digest at room
               temperature for 12 h minimum.

             For clear water and filtered samples, add 0.5 mL of BrCl; for brown
                              water and turbid samples, add 1.0 mL of BrCl.  If the yellow color
                              disappears because of consumption by organic matter or sulfides, more
                              BrCl should be added until a permanent (12-h) yellow color is

             Some highly organic matrices, such as sewage effluent, will require
                              high levels of BrCl (i.e., 5 mL/100 mL of sample), and longer
                              oxidation times, or elevated temperatures (i.e.; place sealed bottles in
                              oven at 50°C for 6 h).  The oxidation always must be continued until a
                             permanent yellow color remains.

        11.1.2  Matrix spikes and matrix spike duplicates—For every 10 or fewer  samples, pour two
               additional 100-mL aliquots from a randomly selected sample, spike at the level
               specified in Section 9.3,  and process in the same manner as the samples.  There should
               be 2 MS/MSD pairs for each analytical batch of 20 samples.

 11.2    Hg reduction and purging—Place 100 mL of reagent water in each bubbler, add 1.0 mL of
        SnCl2, and purge with Hg-free N2 for 20 min at 300-400 mL/min.

        11.2.1  Connect a gold sand trap to the output of the soda lime pretrap,  and purge the water
               another 20 min to obtain a bubbler blank.

        11.2.2  Add 0.2 mL of 30% NH2OH to the BrCI-oxidized sample in the 125-mL
               fluoropolymer bottle. Cap the bottle and swirl the sample. The yellow color will
               disappear, indicating the  destruction of the BrCl. Allow the sample to react for 5 min
               with periodic swirling to be sure that no traces of halogens remain.

        NOTE: Purging of free halogens onto the gold trap will result in damage  and low or
        irreproducible results.
Draft, July 1996

Method 1631
        11.2.3  After discarding the water from the standards, connect a fresh -trap to the bubbler, pour
               the reduced sample into the bubbler, add 0.5 mL of 20% SnCl2 solution, and purge the
               sample onto a gold sand trap with N2 for 20 min.

        11.2.4  When analyzing Hg samples, the recovery is quantitative, and organic interferents are
               destroyed. Thus, standards, bubbler blanks, and small amounts of high-level samples
               may  be run directly in the water of previously purged samples.  After very high
               samples, a small degree of carryover (<0.01%) may occur.  Bubblers that contained
               such samples should be blanked prior to proceeding with low level samples.

11.3    Desorption of Hg from the gold trap

        11.3.1  Remove the gold (sample) trap from the bubbler, place the Nichrome  wire coil around
               the sample trap and connect the sample trap into the analyzer train between the
               incoming Hg-free argon and the second gold-coated (analytical) sand trap (Figure la).

        11.3.2  Pass argon through the sample and analytical traps at a flow rate of approximately 30
               mL/min for approximately 2 min to drive off condensed water vapor.

        11.3.3  Apply power to the coil around the sample trap for 3 minutes to thermally desorb the
               Hg (as Hg(0)) from the sample trap onto the analytical gold trap.

        11.3.4  After the 3-min desorption time, turn off the power to the Nichrome coil, and cool the
               sample trap using the cooling fan.

        11.3.5  Turn on the chart recorder or other data acquisition device  to start data collection, and
               apply power to the Nichrome wire coil around the analytical trap.  Heat the analytical
               trap  for 3 min (1 min beyond the point at which the peak returns to baseline).

        11.3.6  Stop data collection, turn off the power to the Nichrome coil, and cool the analytical
               trap  to room temperature using the cooling fan.

        11.3.7  Place the next sample trap in line and proceed with analysis of the next sample.

        NOTE:  Under no circumstance should a sample trap be heated -while the analytical
        trap is still warm; otherwise, the analyte may be lost by passing through the analytical
        trap.                  ^	

11.4    Peaks generated using this technique should be very sharp and almost symmetrical.  Mercury
        elutes at approximately 1 min and has a width at half-height of about 5 seconds.

        11.4.1  Broad or asymmetrical peaks  indicate a problem with the desorption train, such as low
               gas flow rate, water vapor on the trap(s), or an analytical trap damaged by chemical
               fumes or overheating.

        11.4.2  Damage to an analytical trap is also indicated by a sharp peak, followed by a small,
               broad peak.
Draft, July 1996

                                                                                     Method 1631
        11.4.3  If the analytical trap has been damaged, the trap and the fluoropolymer tubing
                downstream from it should be discarded because of the possibility of gold migration
                onto downstream surfaces.

        11.4.4  Gold-coated sand traps should be tracked by unique identifiers so that any trap
                producing poor results can be quickly recognized and discarded.
 12.0  Data Analysis and Calculations

 12.1    For each analytical batch, the following parameters must first be calculated:

        12.1.1  Mean bubbler blank, "BB" (n = at least 3)

        12.1.2  The mean response factor (RFm, Section

 12.2    Compute the concentration of Hg in ng/L (parts-per-trillion; ppt) according to the following
                                     Kg] (ng/L) =

                   Rx = gross peak height (or area) of signal for Hg in sample
                   BB = mean bubbler blank (peak height or area units)
                   RFm = mean response factor
 12.3    The reagent blank may be subtracted on the same basis, using the peak height (or peak area)
        for the amount of reagents added to the sample aliquot (i.e., 0.5 mL BrCl), and the volume (V)
        of the sample. This result (in ng/L) may be subtracted from the concentration calculated
        above to obtain the net in situ Hg concentration.

 12.4    Reporting

        12.4.1  All results are reported after subtraction of mean bubbler blanks.

        12.4.2  Unless otherwise requested, net concentrations (after subtracting mean reagent blank)
               should be reported.

        12.4.3  Report all values in ng/L to three significant figures. Report results below the ML as
               <0.5 ng/L, or as required by the permitting authority or in the permit.  If the laboratory
               achieved  an MDL lower than 0.2 ng/L (Section 1.5), a new ML may be calculated by
               multiplying the laboratory-determined MDL by 3.18 and rounding the result to the
               nearest multiple of 1, 2, 5, 10, etc. in accordance with procedures described in the
               EPA Draft National Guidance for the Permitting, Monitoring, and Enforcement of
               Water Quality-Based Effluent Limitations Set Below Analytical Detection/Quantitation
Draft, July 1996

Method 1631
              Levels, March 22, 1994. Results below this level should be reported as less than the
              calculated ML.
13.0  Method Performance

13.1   The method detection limit (MDL) listed in Table 1 and the quality control acceptance criteria
       listed in Table 2 were validated in four laboratories (Reference 15). In addition, the
       techniques in this method have has been intercompared with other techniques for low-level
       mercury determination in water under a variety of studies, including ICES-5 (Reference 16)
       and the International Mercury Speciation Intercomparison Exercise (Reference 17).
14.0  Pollution Prevention

14.1   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.  Standards should be  prepared in volumes consistent with laboratory use to minimize
       the disposal of excess volumes of expired standards.

14.2   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 Governmental Relations and
       Science Policy, 1155 16th Street NW, Washington DC 20036, 202/872-^477.
15.0  Waste Management

15.1    The laboratory is responsible for complying with all federal, state, and local regulations
        governing waste management, particularly hazardous waste identification rules and land
        disposal restrictions, and for protecting the air, water, and land by minimizing and controlling
        all releases from fume hoods and bench operations. Compliance with all sewage discharge
        permits and regulations is also required.

15.2    Acids, samples at pH  <2, and BrCl solutions must be neutralized before being disposed of, or
        must be handled as hazardous waste.

15.3    For further information on waste management, consult The Waste Management Manual for
        Laboratory Personnel and Less  is Better: Laboratory Chemical Management for Waste
        Reduction, both available from the American Chemical Society's Department of Government
        Relations and Science Policy, 1155 16th Street NW,  Washington, DC 20036.
                                                                                Draft, July 1996

                                                                                  Method 1631
  16.0  References







 Frontier Geosciences, Inc., Purchase Order 8762 from DynCorp Viar, Inc., August 22, 1994.

 Fitzgerald, W.F.; Gill, G.A. "Sub-Nanogram Determination of Mercury by Two-Stage Gold
 Amalgamation and Gas Phase Detection Applied to Atmospheric Analysis," Anal Chem  1979
 75, 1714.

 Bloom, N.S; Crecelius, E.A. "Determination of Mercury in Sea water at Subnanogram per
 Liter Levels," Mar. Chem. 1983, 14, 49.

 Gill, G.A.; Fitzgerald, W.F. "Mercury Sampling of Open Ocean Waters at the Picogram
 Level," Deep Sea Res 1985, 32, 287.

 Bloom, N.S; Fitzgerald, W.F. "Determination of Volatile Mercury Species at the Picogram
 Level by Low-Temperature Gas Chromatography with Cold-Vapor Atomic Fluorescence
 Detection," Anal. Chim. Acta. 1988, 208, 151.

 Method 1669, "Method for Sampling Ambient Water for Determination of Metals at EPA
 Ambient Criteria Levels," U.S. Environmental Protection Agency, Office of Water, Office of
 Science and Technology, Engineering and Analysis Division (4303), 401 M Street SW,
 Washington, DC 20460, April 1995 with January 1996 revisions.

 "Working with Carcinogens," Department of Health, Education, and Welfare, Public Health
 Service. Centers for Disease Control. NIOSH Publication 77-206, Aug 1977  NTIS PB-

 "OSHA Safety and Health  Standards, General Industry," OSHA 2206, 29 CFR 1910.

 "Safety in Academic Chemistry Laboratories," ACS Committee on Chemical Safety, 1979.

 "Standard Methods for the  Examination of Water and Wastewater," 18th ed. and later
 revisions, American Public Health Association, 1015 15th Street NW, Washington DC 20005
 1-35: Section 1090 (Safety), 1992.

 Bloom, N.S. "Trace Metals & Ultra-Clean Sample Handling," Environ. Lab. 1995, 7, 20.

 Bloom, N.S. "Influence of Analytical Conditions on the Observed 'Reactive Mercury,'
 Concentrations in Natural Fresh Waters." In Mercury as a Global Pollutant; Huckabee, J. and
 Watras, C.J., Eds.; Lewis Publishers, Ann Arbor, MI:  1994.

 "Handbook of Analytical Quality Control in Water and Wastewater Laboratories,"  U.S.
 Environmental Protection Agency. Environmental Monitoring Systems Laboratory  Cincinnati
 OH 45268, EPA-600/4-79-019, March 1979.

Liang, L.; Bloom, N.S. "Determination of Total Mercury by Single-Stage Gold Amalgamation
with Cold Vapor Atom Spectrometric Detection," J. Anal. Atomic Spectrom. 1993, 8, 591.
Draft, July 1996

Method 1631
15     "Results of the EPA Method 1631 Validation Study," July 1996.  Available from the EPA
       Sample Control Center, 300 N. Lee St., Alexandria, VA, 22314; 703/519-1140.

16     Cossa, D.; Couran, P. "An International Intercomparison Exercise for Total Mercury in Sea
       Water," App. Organomet. Chem.  1990, 4, 49.

17     Bloom, N.S.; Horvat, M.; Watras, CJ. "Results of the International Mercury Speciation
       Intercomparison Exercise,"  Wat. Air. Soil Pollut., in press.
17.0  Glossary

The definitions and purposes below are specific to this method, but have been conformed to common
usage as much as possible.

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

17.2   Analytical Batch—A batch of up to 20 samples that are oxidized with the same batch of
       reagents  and analyzed during the same 12-hour shift.  Each analytical batch must also include
       at least three bubbler blanks, an OPR, and .a QCS.  In addition, MS/MSD samples must be
       prepared at a frequency of 10% per analytical batch (one MS/MSD for every 10 samples).

17.3   Bubbler Blank—Analyzed to demonstrate freedom from system contamination. Immediately
       after analyzing a sample, water in the bubbler is purged and analyzed using the same
       procedure as for the samples to determine Hg.  The blank is somewhat different between days,
       and a minimum of three bubbler blanks must be analyzed per analytical batch.  The average of
       the results for the three bubbler blanks is subtracted from the result of analysis of each sample
       to produce a final result.

17.4   Intercomparison Study—An exercise in which samples are prepared and split by a reference
       laboratory, then analyzed by one or more testing laboratories and the reference laboratory.
       The intercomparison, with a reputable laboratory as the reference laboratory, serves as the best
       test of the precision and accuracy of the analyses at natural environmental levels.

17.5   Matrix Spike (MS) and Matrix Spike Duplicate (MSD)—Aliquots of an environmental
       sample to which known quantities of the  analyte(s) of interest is 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 these background concentrations.

17.6   May—This action,  activity, or procedural step is allowed but not required.

17.7   May not—This action, activity, or procedural step  is prohibited.

17.8   Minimum Level (ML)—The lowest level at which the entire analytical system must give a
       recognizable signal and acceptable calibration point for the analyte.  It is  equivalent to the
       concentration of the lowest calibration standard, assuming that all method-specified sample
                                                                                 Draft, July 1996

                                                                                      Method 1631
         weights, volumes, and cleanup procedures have been employed.  The ML is calculated by
         multiplying the MDL by 3.18 and rounding the result to the number nearest to (1, 2, or 5) x
         10°, where n is an integer.

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

 17.9    Quality Control Sample (QCS)—A sample containing Hg 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 as an independent check of
         instrument calibration.

 17.10   Reagent Water—Prepared from 18 MQ ultrapure deionized water starting from a prepurified
         source.  Reagent water is used to wash bottles, as trip and field blanks, and in the preparation
         of standards and reagents.

 17.11   Shall—This action, activity, or procedure is required.

 17.12   Should—This action, activity, or procedure is  suggested, but not required.

 17.13   Stock Solution—A solution containing an analyte that is prepared from a reference material
         traceable to EPA, NIST, or a source  that will attest to the purity and authenticity of the
         reference material.

 17.14   Ultraclean Handling—A series of established procedures designed to ensure that samples are
        not contaminated for Hg during sample collection,  storage, or analysis.
Draft, July 1996

Method 1631
                                              Table 1

             Mercury Analysis Using Method 1631: Lowest Water Quality Criterion,
                           Method Detection Limit, and Minimum Level
Mercury (Hg)
Lowest Ambient Water
Quality Criterion1
Method Detection Limit (MDL) and
Minimum Level (ML)
0.5 ng/L
1.       Lowest of the freshwater, marine, and human health ambient water quality criteria promulgated by EPA for 9 States and the District
        of Columbia at 40 CFR Part 131 on May 4, 1995 (60 FR 22229)

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

3.       Minimum Level (ML)
                                              Table 2

         Quality Control Acceptance Criteria for Performance Tests In EPA Method 1631
IPR (Section 9.2)
s X
21% 79-121%
OPR (Section 9.5)
Bubbler Blanks
(Section 9.4)
Max Mean
<50 pg <25 pg
(Section 9.3)
75-125% 24%
                                                                                     Draft, July 1996

                                                                                   Method 163I
              02 Removal
                           0-1000 volt DC
                           Power Supply
               Hg Removal Trap
                       Sample Trap      Analytical Trap
Chart Recorder
Figure 1.      Schematic Diagram of the Cold Vapor Atomic Fluorescence Spectrometer (CVAFS)
Draft, July 1996

Method 1631
           He Gas
   Hg Free
                           Soda Lime Pre-Trap       Gold Sample Trap
                                  Aqueous Sample+SnCl2
                      Gold Sample Trap           Gold Analysis Trap
                                                                          He Gas
                                                                          AFS Detector
 Figure 2.      Schematic Diagram of Bubbler Setup (a), and Dual-amalgamation System (b), Showing
               Orientation of Gold Traps and Soda Lime Pretraps
Draft, July 1996