Method 1630

Methyl Mercury in Water by Distillation, Aqueous Ethylation,
   Purge and Trap, and Cold Vapor Atomic Fluorescence
                       August, 1998
             U.S. Environmental Protection Agency
                      Office of Water
               Office of Science and Technology
            Engineering and Analysis Division (4303)
                      401 M Street SW
                   Washington, D.C. 20460

 Method 1630

This method was prepared under the direction of William A. Telliard of the Engineering and Analysis
Division (BAD) 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 draft 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.  EPA plans
further validation of this draft method. The method may be revised following validation to reflect results of
the study.

EPA welcomes suggestions for improvement of this method. Suggestions and questions concerning this
method or its application should be addressed to:

W.A. Telliard
Engineering and Analysis Division (4303)
U.S. Environmental Protection Agency
401M Street SW
Washington, D.C.  20460
Phone: 202/260-7134
Fax:  202/260-7185
                                                                             Draft, August, 1998

                                                                                              Method 1630

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 water body or a segment of a water body, 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 water body, 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 1630 was specifically  developed to provide reliable
measurements of methyl 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 1630 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
Draft, August,  1998

                                                                                    Method 1630
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," "must," and "may not" 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, August, 1998

                                   Method 1630

 Methyl  Mercury in Water by  Distillation, Aqueous  Ethylation,
     Purge and Trap, and  Cold Vapor Atomic Fluorescence

1.0    Scope and Application

1.1    This method is for determination of methyl mercury (CH3Hg) in filtered and unfiltered water by
       distillation, aqueous ethylation, 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 CH3Hg in aqueous samples, ranging
       from sea water to sewage effluent (References 2-7).

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 CH3Hg in the range of 0.02-5 ng/L and may be
       extended to higher levels by selection of a smaller sample size.

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 metal determinations and minimize contamination (Section 4.0).

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 CH3Hg has been determined to be 0.02 ng/L when no
       background elements or interferences are present. The minimum level  (ML) has been established
       as 0.06 ng/L. An MDL as low as 0.009 ng/L can be achieved for low CH3Hg samples by using
       extra caution in sample handling and reagent selection, particularly the use of "for ultra-low level
       only" distillation equipment.

1.6    Clean and ultraclean—The terms "clean" and "ultraclean" have been applied to the techniques
       needed to reduce or eliminate contamination in trace metal  determinations. These terms are not
       used in this method because they lack an exact definition. However, the information provided in
       this method is consistent with the summary guidance on clean and ultraclean techniques.
Draft, August, 1998

 Method 1630
1.7    This method follows the EPA Environmental Methods Management Council's "Format for Method

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 or
       borosilicate bottle(s) using sample handling techniques specially designed for collection of metals
       at trace levels (Reference  6).

2.2    For dissolved CH3Hg, samples are filtered through a 0.45-(jm capsule filter.

2.3    Fresh water samples are preserved by adding 4 mL/L of pretested 11.6 M HC1, while saline
       samples ([Cl~] > 500 ppm) are preserved with 2 mL/L of 9 M H2SO4 solution, to avoid distillation
       interferences caused by excess chloride.

2.4    Prior to analysis, a 45-mL sample aliquot is placed in a specially designed fluoropolymer
       distillation vessel, and 35  mL of the water is distilled into the receiving vessel at 125°C under N2

2.5    After distillation, the sample is adjusted to pH 4.9 with an acetate buffer and ethylated in a closed
       purge vessel by the addition of sodium tetraethyl borate (NaBEt4).
                                                                                Draft, August, 1998

                                                                                    Method 1630
2.6    The ethyl analog of CH3Hg, methylethyl mercury (CH3CH3CH2Hg), is separated from solution by
       purging with N2 onto a graphitic carbon (Carbotrap®) trap.

2.7    The trapped methylethyl mercury is thermally desorbed from the Carbotrap® trap into an inert gas
       stream that carries the released methylethyl mercury first through a pyrolytic decomposition
       column, which converts organo mercury forms to elemental mercury (Hg°), and then into the cell of
       a cold-vapor atomic fluorescence spectrometer (CVAFS) for detection.

2.8    Quality is ensured through calibration and testing of the distillation, ethylation, purging, and
       detection systems.

3.0   Definitions

3.1    Apparatus: Throughout this method, the sample containers, sampling devices, instrumentation,
       and all other materials and devices used in sample collection, sample processing, and sample
       analysis that come in contact with the sample and therefore require careful cleaning will be referred
       to collectively as the Apparatus.

3.2    Dissolved methyl mercury: All distillable CH3Hg forms and species found in the filtrate of an
       aqueous solution that has been filtered through a 0.45 micron filter.

3.3    Methyl mercury:  All acid-distillable Hg, which, upon reaction with NaBEt4 yields methylethyl
       mercury. This includes, but is not limited to, CH3Hg+, strongly organo-complexed CH3Hg
       compounds, adsorbed particulate CH3Hg, and CH3Hg bound in microorganisms. In freshly
       collected samples, dimethyl mercury ((CH3)2Hg) will not be recovered as CH3Hg, but in samples
       which have been acidified for several days, most (CH3)2Hg has broken down to CH3Hg.  In this
       method, CH3Hg and total recoverable CH3Hg are synonymous.

3.4    Definitions of other terms  used in this method are given in the glossary at the end of the method.

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.
Draft, August, 1998

 Method 1630
4.2    Samples may become contaminated by numerous routes. Potential sources of trace metal
       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 metal contamination.  For example, it
       has been demonstrated that dental work (e.g., mercury amalgam fillings) in the mouths of
       laboratory personnel can contaminate samples that are directly exposed to exhalation (Reference

4.3    Contamination control

       4.3.1   Philosophy—The philosophy behind contamination control is to ensure that any object or
               substance that contacts the sample is metal free and free from any material that may
               contain Hg or CH3Hg.

            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.

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

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

       4.3.2  Avoid contamination—The best way to control contamination is to completely avoid
               exposure of the sample to contamination in the first place. Avoiding exposure means
               performing operations in an area known 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 the 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-free and particle-free
               air or nitrogen.  Digestions should be performed in  a nonmetal fume hood situated, ideally
               in the clean room.
                                                                                Draft, August, 1998

                                                                                      Method 1630
       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 in use, 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, non talc 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 CH3Hg at ambient
               water quality criteria levels must be nonmetallic and free of material that may contain

             Construction materials—Only fluoropolymer or borosilicate glass
                              containers should be used for samples that will be analyzed for Hg
                              because Hg vapors can diffuse in  or out of other 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
Draft, August, 1998

Method 1630
                             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 CH3Hg is processed immediately after a
                             sample containing a relatively high concentration. When an unusually
                             concentrated  sample is encountered, a ethylation blank should be analyzed
                             immediately following the sample to check for carryover. Samples known
                             or suspected to contain the lowest concentration of CH3Hg 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 Hg
                             or CH3Hg are processed and analyzed. This method is not intended for
                             application to these samples, and samples containing high concentrations
                             of trace metals 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 samples be thoroughly cleaned (see Section 6.1.2).

           Contamination by airborne particulate matter—Airborne particles are less
                             obvious substances capable of contaminating samples.  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
                                                                                Draft, August, 1998

                                                                                       Method 1630
4.4     Interferences

        4.4.1  When the method is properly applied, no significant interferences have been observed in
               the analysis of ambient waters.

        4.4.2  Distillation of CH3Hg from solution requires a carefully controlled level of HC1 in
               solution. Distillation will not be quantitative if too little HC1 is added, but too much HC1
               results in co-distillation of HC1 fumes, which interfere with the ethylation procedure.
               Therefore fresh water samples must be preserved only with between 0.3% and 0.5% (v/v)
               11.6 M HC1, and salt water samples with between 0.1% and 0.2% (v/v) 9 M H2SO4.

        4.4.3  Samples preserved with nitric acid (HNO3) cannot be analyzed for CH3Hg as the analyte is
               partially decomposed in the distillation step by this reagent.

        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 Carbotrap® trap
               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.  In some rare cases
               (such as oil polluted water) low molecular weight organic compounds may purge with the
               methylethyl mercury and collect on the Carbotrap® trap, subsequently resulting in signal
               quenching during elution.  Such cases are best treated by sample dilution prior to

        4.4.5  Recent investigations have shown that a positive artifact is possible with the distillation
               procedure in cases where high inorganic Hg concentrations are present (Reference 7).  In
               natural waters, approximately 0.01 to 0.05% of the ambient inorganic Hg in solution may
               be methylated by ambient organic matter during the distillation step. In most waters,
               where the percent CH3Hg is 1-30% of the total, this effect is trivial.  However, the analyst
               should be aware that in inorganic Hg contaminated waters, the fraction CH3Hg can be <
               1% of the total, and so flagging of the data (as representing a maximum estimate of
               CH3Hg concentration) may be warranted. In samples with high levels of divalent mercury
               (Hg(II)), solvent extraction may be  preferable to distillation (Reference 7).

5.0    Safety

5.1     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. It is suggested that the laboratory
        perform personal hygiene monitoring of each analyst using this method and that the results of this
        monitoring be made available to the analyst.
Draft, August, 1998

 Method 1630
       5.1.1  Chronic Hg 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 CH3Hg,
               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 CH3Hg for
               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

5.2    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 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.  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

5.3    Samples suspected of containing high concentrations of CH3Hg 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 CH3Hg.

       5.3.1  Facility—When samples known or suspected to contain high concentrations of CH3Hg 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 leakproof
               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 hazard 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.
                                                                                 Draft, August, 1998

                                                                                      Method 1630
       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 with Hg

       5.3.7  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 action.

            Glassware, tools, and surfaces—Activated carbon powder will adsorb
                              CH3Hg, eliminating the possible volatilization of CH3Hg. Satisfactory
                              cleaning may be accomplished by dusting a surface lightly with activated
                              carbon 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 (jg per wipe  indicates acceptable cleanliness; anything higher warrants further
                       cleaning.  More than 10 (ig on  a wipe constitutes an acute hazard, requires prompt
                       cleaning before further use of the equipment or work space, and indicates that
                       unacceptable work practices have been employed.
Draft, August, 1998

 Method 1630
6.0    Equipment and Supplies
       NOTE: 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, capped, and placed in a mercury-free class
                              100 clean bench until the outside of the bottle is dry. The caps are then
                             tightened with a wrench and the bottles are double-bagged in new
                             polyethylene zip-type bags. The capped bottles are  stored in wooden or
                             plastic boxes until use.

            To avoid long-term accumulation of Hg or CH3Hg on the bottle walls due
                             to trace organic coatings, used bottles are filled with reagent water
                             containing 0.02 N BrCl solution and allowed to stand over night. The
                             BrCl is neutralized with the addition of 0.2 mL of 20%NH2OH solution.
                             The bottles are then cleaned exactly as in Section, except that they
                             soak 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.

       6.1.3  Filtration Apparatus

            Filter—0.45-(jm, 15-mm diameter capsule filter (Gelman Supor 12175, or
                                                                               Draft, August, 1998

                                                                                     Method 1630
             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.  It is rinsed with
                              reagent water on a clean bench in a clean room and dried on 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

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

       NOTE: 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.

6.3    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 components.
Draft, August, 1998

 Method 1630
       6.3.1   Commercially available:  Tekran Model 2357 CVAFS, Brooks-Rand Model III CVAFS,
               or equivalent

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

            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., 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., or equivalent).

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

            Ultra high-purity argon (grade 5.0)

6.4    Equipment for CH3Hg 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   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
                                                                               Draft, August, 1998

                                                                                      Method 1630
               glass frit that extends to within 0.2 cm of the bubbler bottom (Frontier Geosciences, Inc.,
               or equivalent).

6.5    Equipment for the isothermal gas chromatography (GC) system.

       6.5.1   Figure 1 shows the schematic for the interface of the GC with the CVAFS detector
               (Reference 6).

       6.5.2  Figure 2b shows the orientation consideration for purging and desorbing CH3Hg from the
               Carbotrap® traps.

       6.5.3  Carbotrap® 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 30/45 mesh Carbotrap® graphitic carbon adsorbant (Supelco, Inc., or
               equivalent). The ends are plugged with silanized glass 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

             At least six traps are needed for efficient operation.

             Because the direction of flow is important in this analysis, the crimped end
                              of the Carbotrap® trap will be referred to as "side A," while the
                              uncrimped end will be referred to as "side B."

       6.5.4  Heating of Carbotrap® traps—To desorb CH3Hg collected on a trap, heat for 45 sec to
               45 0-5 00 °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 16-20 vac.  Potential is applied and
               finely adjusted with  an autotransformer.

       6.5.5  Timer—The heating interval is controlled by a timer-activated  120-V outlet, into which the
               heating coil autotransformer is plugged.

       6.5.6  Isothermal GC—Consists of two parts, a custom fabricated packed GC column, and a
               custom fabricated  constant temperature oven.

             The column is 1 m long, made from 0.25 inch OD by 4 mm ID
                              borosilicate glass GC column tubing.  The column is formed into  an 8 cm
                              diameter coil, with 15 cm straight extensions from each end. The column
                              is silanized, packed in the coiled portion with 60/80 mesh 15% OV-3 on
Draft, August, 1998

Method 1630
                             acid-washed Chromasorb W, and then conditioned under inert gas flow at
                             200°C. A column meeting these specifications may be custom fabricated
                             (Supelco Inc., or equivalent).

            The GC oven consists of a 500-watt aluminum jacketed heating mantle,
                             fitted with a custom machined fluoropolymer lid (14 cm OD by 1 cm
                             thick).  The lid is attached with stainless steel screws and contains three
                             threaded holes  (0.25 inch female NPT) in a triangular pattern in the top.
                             The spacing of the holes conforms exactly to the spacing between the two
                             15 cm glass extensions of the GC column.

            Fluoropolymer fittings, with 0.25-inch male NPT threads on the bottom
                             and 0.25-inch compression fittings on top, are placed into the threaded
                             holes. The GC column is secured into the oven by passing the glass
                             extensions through two of the fluoropolymer fittings, so that 3 cm of the
                             glass extensions protrude from the top, and tightening the compression
                             fittings.  The fluoropolymer lid holding the GC column is then screwed to
                             the top of the oven.

            Temperature feedback control (110 ± 2°C) is achieved through a
                             thermocouple temperature controller.  The oven is plugged into the
                             controller and the thermocouple probe is inserted through the third
                             fluoropolymer fitting in the lid, such that the sensor is located near the
                             center of the GC coil.

            Several research groups have successfully interfaced the
                             Carbotrap®/CVAFS system directly to a commercial gas chromatograph.
                             The use of capillary column GC will result  in better peak separation,
                             although at higher cost.

       6.5.7  Pyrolytic column—The output from the GC oven is connected directly to a high
              temperature column to decompose eluted organo-mercurial compounds to Hg°. The output
              of the pyrolytic column is connected to the inlet of the CVAFS system.

            The column consists of a 20-cm length of quartz tubing, packed over the
                             central 10 cm with quartz wool.

            The column is heated to orange heat (~ 700°C) by a  1 m length of 22
                             gauge Nichrome wire, tightly wrapped around the quartz wool packed
                             portion of the tube. The temperature of the coil is adjusted by visual
                             inspection of the color, using a 0-120 volt autotransformer.
                                                                               Draft, August, 1998

                                                                                       Method 1630
6.6     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.

6.7     Distillation unit—The distillation unit is a custom made temperature controlled aluminum block
        heater, as shown schematically in Figure 3 (Frontier Geosciences Inc., or equivalent).

        6.7.1  Heating block insulation—Each heating block is encased first in refractory spun rock
               insulation (1 inch thickness) and then an exterior wood shell for rigidity.

        6.7.2  Each heating block (10 cm wide x 20 cm long x 15 cm high) is bored with five 31 mm
               diameter holes (evenly spaced),  120 mm deep. A 3/8 inch diameter hole is bored to 90%
               of the block length, perpendicular to and behind the distillation tube holes, to accommodate
               a cylindrical heating element. A 2 mm diameter hole is bored parallel to the heating
               element hole, and 2 cm above it, to accommodate the temperature sensor.

        6.7.3  Heating element—Each heating block is equipped with a 750 watt cylindrical heating
               element, 6 inches long by 3/8 inch diameter (Omega Inc.), immobilized in its respective
               hole by a dab of silicone glue.

        6.7.4  Type J thermocouple probe—Each heating block is equipped with a type J thermocouple
               probe immobilized in  its respective hole by a dab of silicone glue.

        6.7.5  Digital temperature controller—The heating element and thermocouple are connected to a
               digital temperature controller.

        6.7.6  Fluoropolymer vials with caps—The distillation unit is designed to accommodate 60-mL
               fluoropolymer vials (part number 0202, Savillex, or equivalent). The original caps are
               used to close the vials when distillate is to be stored until analysis.

            For each distillation, two identical vials are needed: a distillation vessel
                              and a receiving vessel.  For convenience, each vial should be engraved
                              with a line  at 40.0 mL (obtained by weighing 40 g of water in the vial),
                              and a unique identification number, both on the vial and the cap.

            Fluoropolymer vials are acid cleaned initially as described for other
                              fluoropolymer ware and stored filled with 0.5% HC1.  After use, receiving
                              vials  are rinsed with reagent water and filled with 0.5% HCL. The tubing
                              is looped around the cap as described in Section, and the vials are
                              placed in a 70°C (±  5°C) oven overnight.  Cleaning is the same for the
                              distillation  vials, with the exception that first the vials, caps, and tubing
Draft, August, 1998

Method 1630
                              are thoroughly scrubbed with an alkaline detergent and test tube brush to
                              remove any residues from the samples.

       6.7.7  Purge caps—The standard caps on the fluoropolymer vials are replaced with purge caps
              (part number 33-2-2, Savillex, or equivalent) for distillation purposes.

            Fluoropolymer tubing—each purge cap is threaded with a piece of 1/8
                              inch fluoropolymer tubing, approximately 30-40 cm long. One end is
                              pulled through one of the holes in the cap, down to a length that will allow
                              it to reach the bottom of the distillation vial when the vial is screwed onto
                              the cap.  The bottom end of this tubing is cut at a 45° angle. The outside
                              end of the tubing is cut perpendicularly and is looped around and inserted
                              into the second cap hole when not in use (to keep the system closed and

       6.7.8  Aluminum distillation cover—The  cover for the heating block consists of a 5 cm high
              aluminum block of the same cross section as the heating block (10 cm wide x 20 cm long),
              which has been milled out completely except for a 0.5 cm shell all around. In this lid is
              placed a series of 5 slots, 0.5 cm wide by 3 cm high, on each of the long sides, to allow
              passage of the distillation tubing in and out of the distillation vessels.

       NOTE:  It is very important that the heating block have an aluminum top covering the vessels,
       to avoid condensation and refluxing of the sample in the distillation vessels.	

       6.7.9  Polyethylene container—Distillate is received and cooled in a fluoropolymer receiving vial
              supported in an ice bath in a polyethylene container. A box approximately 15 cm wide x
              25  cm long x 10 cm high is a convenient container, and holes to accommodate the
              receiving vials can be cut into the lid of each box. Suitable boxes are generally available
              at sundries stores as storage containers.

       6.7.10        Rotometer/needle valve—Five needle valve/rotometer (0-300 mL/min N2)
                      assemblies are required,  one for each distillation vessel in the heating block.
                      These rotometers can be mounted in banks of 5 for each distillation block, with all
                      rotometers connected to  a common gas manifold.

           Fluoropolymer tubing-Inert gas (N2 or Ar at 0.5 -1 arm) is brought from
                              the regulator to the manifold and from the rotometer outlets to the
                              distillation vials by 1/8 inch fluoropolymer tubing.

       6.7.11        The entire distillation set-up can be mounted on a stepped structure or shelving
                      unit, such that the banks of rotometers are on the top and easily adjustable. Below
                                                                                 Draft, August, 1998

                                                                                     Method 1630
                      the rotometers are the distillation blocks, and lower still, the ice baths for the
                      receiving vessels.

6.8    Pipettors—All-plastic pneumatic fixed-volume and variable pipettors in the range of 10-uL to 5.0-

6.9    Analytical balance capable of weighing to the nearest 0.01 g.

7.0   Reagents and  Standards

7.1    Reagent water—18-MQ minimum, ultrapure deionized water starting from a prepurified (distilled,
       reverse osmosis, etc.) source. Water should be monitored for Hg, especially after ion exchange
       beds are changed.

7.2    Air—It is very important that the laboratory air be low in both particulate and gaseous Hg.
       Ideally, Hg 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 Hg by placing a
       gold-coated cloth prefilter over the intake.

       7.2.1  Gold-coated cloth filter: Soak 2 m2 of cotton gauze in 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 gold is precipitated.
               Allow the  mixture to set for several hours, then rinse with copious amounts of reagent
               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.

       NOTE:  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.  CH3Hg is
       not stable in concentrated acid, so the acid does not need to be tested for CH3Hg.

7.4    Sulfuric acid—Trace-metal purified reagent H2SO4 containing less than 5 pg/mL Hg.  CH3Hg is
       not stable in concentrated acid, so the acid does not need to be tested for CH3Hg.

7.5    1% APDC solution—To 100 mL of reagent water, add 1.0 g of reagent grade APDC (ammonium
       pyrrolidine dithiocarbamate), and shake to dissolve.  The solution is purified by extraction with
       three  10 mL aliquots of methylene  chloride.
Draft, August, 1998

 Method 1630
7.6    Glacial acetic acid—Reagent grade

7.7    2 M Acetate buffer—2 moles of reagent grade sodium acetate (272 g) and 2 moles of reagent grade
       glacial acetic acid (118 mL) dissolved in reagent water to give a final volume of 1.0 L.  To purify
       the buffer of traces of CH3Hg,  add 0.5 mL of 1% NaBEt4 and purge the solution overnight with
       Hg-free N2 or Ar.  This solution has an indefinite lifetime when stored in a fluoropolymer bottle at
       room temperature.

7.8    1% Sodium tetraethyl borate—This reagent is purchased in 1.0-g air-sealed bottles (Strem
       Chemical, or equivalent.  One hundred milliliters of 2% KOH in reagent water is prepared in a
       fluoropolymer bottle and chilled to 0°C. The bottle of NaBEt4 is rapidly opened and approximately
       5 mL of the KOH solution poured in. The reagent bottle is capped and shaken to dissolve the
       NaBEt4. This is poured into the 100 mL bottle of KOH solution, and shaken to mix. Immediately,
       the 1% NaBEt4 solution in 2% KOH is poured into fifteen (15) 7-mL fluoropolymer bottles, which
       are capped and placed in a low temperature freezer. For use, one of these bottles is removed and
       thawed until it starts to form a liquid layer. The reagent is then used until just before all of the ice
       is melted. Usually this lasts about 3 h if the bottle is placed in the refrigerator between uses.

       NOTE: It is imperative that this reagent be exposed to air a minimum length of time. Thus,
	when removing reagent,  open and close the lid quickly and tightly!	

       Frozen bottles of NaBEt4 will keep for at least one week. If any doubt arises about the quality of
       the ethylating reagent, make a new batch, as the old material often gives good results for reagent
       water spikes, but not for environmental samples. Do not use NaBEt4 solid or solutions if they have
       a yellow color.

       WARNING:  NaBEt4 is toxic, gives off toxic gases (triethylboron), and is  spontaneously
       combustible.  To discard unused portions of ethylating agent and empty bottles, place into a large
       beaker of 1NHCI in the  hood.  Triethylboron will bubble off to the air where it is eventually
       oxidized to harmless boric acid. Leave the acid beaker in the hood indefinitely, or boil down to '/2
	volume to destroy residues before discarding as any acid waste.	

7.9    Methyl mercuric chloride(s)—A 5-g bottle of methyl mercuric chloride (s), reagent grade (Strem
       Chemical, or equivalent).

7.10  Stock methyl mercury standard—Either procure certified CH3Hg solution (Frontier Geosciences
       Inc., or equivalent) or prepare the stock solutions in the laboratory. Dissolve the contents of an
       entire 5-g bottle of methyl mercuric chloride in reagent water containing 0.5% (v/v) glacial acetic
       acid and 0.2% (v/v) HC1 in a fluoropolymer bottle.  This solution contains 4000-5000 mg/L
       CH3Hg as Hg. It does not have a specific titre because, due to the contamination danger, the
       methyl mercuric chloride is not weighed.  The stock solution has an indefinite lifetime when stored
                                                                                 Draft, August, 1998

                                                                                      Method 1630
       in an amber glass bottle with an fluoropolymer lid at room temperature.  Do not make or keep this
       concentrated stock solution in the trace mercury laboratory.

       NOTE: Making a CHflg standard rather than purchasing one requires the laboratory to have
       available the technology to perform analyses with Method 1631: Mercury in Water by Oxidation,
       Purge and Trap, and Cold Vapor Atomic Fluorescence Spectrometry. Total Hg and labile Hg
       (II) determinations, made with Method 1631, are necessary to accurately determine the CHflg
       concentration of the standards. Additionally, laboratories must be cautioned against assuming
       that purchased CHflg stock solution will remain constant in concentration. Purchased stock
	solution has been seen to degrade occasionally, in one case from 1000 mg/L to 4 mg/L.	

 7.11  Secondary methyl mercury standard—Dilute 1.00 mL of stock solution (B) to 1000.0 mL with
       reagent water containing 0.5% (v/v) glacial acetic acid and 0.2% (v/v) HC1.  This solution contains
       approximately 4-5 mg/L (5.00 ng/mL) CH3Hg as Hg.  The exact CH3Hg titre is determined as
       indicated in Sections 7.11.1-7.11.4. The secondary CH3Hg standard solution has been observed to
       maintain its titre over a year when stored in a fluoropolymer bottle in the refrigerator.

       7.11.1        Dilute the secondary standard 1:10 with concentrated BrCl solution (0.100 mL of
                      secondary stock solution added to 0.900 mL BrCl in a small FEP vial).  Allow the
                      solution to oxidize for at least 4 h. The total Hg in the dilution may then be
                      analyzed using dual amalgamation/CVAFS, by comparison to a dilution of NIST-
                      3133 (as in Method 1631). A mean of at least seven replicate analyses of the
                      secondary stock solution is necessary to accurately quantify  the total Hg
                      concentration of the solution.

       7.11.2        Analyze the secondary standard for labile Hg(II) using Method 1631 by directly
                      reducing an aliquot of standard solution with SnCl2, but without prior BrCl
                      oxidation as performed in Section 7.11.1. At least two determinations of labile
                      Hg(II) must be made of the stock solution.

       7.11.3        Calculate the CH3Hg in the secondary CH3Hg standard  solution by subtracting the
                      mean labile Hg(II) concentration from the mean total  Hg concentration.

       7.11.4        If the secondary CH3Hg stock solution drops below 98.0% CH3Hg, discard the
                      solution and make a fresh secondary solution.

7.12  Working methyl mercury standard—Prepare a dilution of the secondary  CH3Hg standard using
       reagent water containing 0.5% (v/v) glacial acetic acid and 0.2% (v/v) HC1.  A convenient
       concentration for this standard is 1.00 ng/mL CH3Hg as Hg. This solution will maintain its titre
       for more than one month when kept in a fluoropolymer bottle on the lab bench top.  Refrigeration
       is not necessary.
Draft, August, 1998

 Method 1630
7.13  IPR and OPR solutions—Using the working CH3Hg standard (Section 7.9), prepare IPR and OPR
       solutions at a concentration of 0.5 ng/L as Hg in reagent water.

7.14  Nitrogen—Grade 4.5 (standard laboratory grade) nitrogen that has been further purified by the
       removal of Hg using a gold-coated sand trap (Section 7.16).

7.15  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 (Section 7.16).

7.16  Gold-coated sand trap—The trap is made from  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., or
       equivalent).  The ends are plugged with quartz wool. Traps are fitted with 6.5-mm i.d.
       fluoropolymer friction-fit sleeves for connection to the system.

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 removing an aliquot for processing or
       direct analysis to ensure the sample has been properly preserved.

       NOTE: Do not dip pH paper or pH meter into the sample; remove a small aliquot with a clean
       pipet and test the aliquot pH.	

 8.2    Samples are  collected into rigorously cleaned fluoropolymer bottles with fluoropolymer or
       fluoropolymer-lined caps. Borosilicate glass bottles may be used if Hg and Hg species are the only
       target analytes. It is critical that the bottles have tightly sealing caps to avoid diffusion of
       atmospheric  Hg through the threads. Polyethylene sample bottles must not be used (Reference 13).

8.3    Collect samples using the Sampling Method (Reference 8). Procedures in the Sampling Method
       are based on rigorous protocols for collection of samples for Hg (Reference  13).

       NOTE: Discrete samplers have been found to contaminate samples with Hg at the ng/L level;
       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 CH3Hg, samples and field blanks are filtered through a 0.45-(jm
       capsule filter (Section The Sampling Method describes filtering procedures.
                                                                               Draft, August, 1998

                                                                                      Method 1630
8.5    Preservation—Samples are preserved by adding 4 mL/L of concentrated HCL (to allow both
       CH3Hg and total Hg determination).  Saline samples ([Cl~]>500 ppm) are preserved with 2 mL/L
       of 9 M H2SO4 solution.  Acid-preserved samples are stable for at least six months, if kept dark and

       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 of sampling.

       8.5.2  Handling of the samples in the laboratory should be undertaken on a mercury-free clean
               bench, after rinsing the outside of the bottles with reagent water and drying in the clean air

       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, 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. To
       maintain CH3Hg concentrations without degradation, it is necessary to keep acid-preserved
       samples dark and cool. If properly preserved, samples can be held up at least six months before

9.0   Quality Control

9.1    Each laboratory that uses this method is required to operate a formal quality assurance program
       (Reference 14). 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 (MSB) to assess accuracy and
       precision. Laboratory performance is compared to established performance criteria to determine
       whether 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 system, solvent extraction in place of distillation
Draft, August, 1998

Method 1630
              (Reference 2), direct electronic data acquisition, or changes in the detector (i.e., CVAAS,
              AES, ICP/MS).  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
              CH3Hg 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:

                  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
                                                                                 Draft, August, 1998

                                                                                      Method 1630
                                     (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 MSB 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 CH3Hg in water is controlled by an analytical batch. An analytical
               batch is a set of samples distilled 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 method blanks (Section 9.4), an OPR sample, and a
               QCS. In addition, there must be one MS and one MSB sample for every 10 samples (a
               frequency of 10%).

9.2    Initial demonstration of laboratory capability

       9.2.1  Method detection limit—To establish the ability to detect CH3Hg, the analyst shall
               determine the MBL 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 MBL that is less than or equal to the MBL listed in Section
               1.5 or one-third the regulatory compliance limit, whichever is greater. The MBL 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
               MBL 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:
Draft, August, 1998

 Method 1630
             Analyze four replicates of the IPR solution (0.5 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

             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    Method accuracy—To assess the performance of the method on a given sample matrix, the
       laboratory must perform either matrix spike (MS) and matrix spike duplicate (MSB) sample
       analyses on 10% of the samples from each site being  monitored, or at least one MS/MSD sample
       analysis for each sample set, whichever is more frequent.

       9.3.1   The concentration of the CH3Hg in the sample shall be determined as follows:

             If, as in compliance monitoring, the concentration of CH3Hg 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 CH3Hg  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.

       9.3.2  Assessing spike recovery

             Determine the background concentration (B) by analyzing 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 spiking solution to produce an appropriate level in
                              the sample (Section 9.3.1).
                                                                                Draft, August, 1998

                                                                                      Method 1630
             Spike two sample aliquots with the spiking solution and analyze these
                              aliquots as described in Section 11.1.2 to determine the concentration after
                              spiking (A).

             Calculate the percent recovery (P) in each aliquot using Equation 1:

                                           Equation 1
                      A =Measured concentration ofanalyte after spiking
                      B=Measured concentration ofanalyte before spiking
                      P=Percent recovery
              	T=True concentration of the spike
       9.3.3  Compare the percent recovery (P) with the QC acceptance criteria in Table 2.

             If P falls outside the designated range for recovery in Table 2, the CH3Hg
                              analysis has failed to meet the established performance criteria. If P is
                              unacceptable, analyze the OPR standard (Section 9.5). If the OPR is
                              within established performance criteria (Table 2), the analytical system is
                              within specification and the problem can be attributed to interference by
                              the sample matrix.

             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 CH3Hg 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 outside specified limits. The
                              analyst must identify and correct the problem and reanalyze the sample

       9.3.4  Relative percent difference between duplicates—Compute the relative percent difference
               (RPD) between the MS and MSB results according to Equation 2 using the CH3Hg
               concentrations found in the MS and MSB. Bo not use the recoveries calculated in Section
Draft, August, 1998

 Method 1630
      for this calculation because the RPD is inflated when the background concentration
               is near the spike concentration.

                                           Equation 2

                                   RPD =200*
                                                   A + A

                      RPD=Relative percent difference
                      D ^Concentration ofCHflg in the MS sample
              	D2=Concentration ofCHflg in the MSP sample
       9.3.5  The RPD for the MS/MSD pair must not exceed the acceptance criterion in Table 2. If
               the criterion is not met, the system performance is unacceptable.  The problem must
               immediately be identified and corrected, and the analytical batch reanalyzed.

       9.3.6  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 9.3.2, 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).

9.4    Blanks—Blanks are critical to the reliable determination of CH3Hg 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  Ethylation blanks—Reagent water typically contains no CH3Hg. The reagent (ethylation)
               blank may conveniently be determined by adding 0.3 mL of acetate buffer and 0.040 mL
               of 1% NaBEt4 solution to 50 mL of reagent water in the reaction vessel.

       NOTE: Do not ever use a previously ethylated water sample, as a build-up of the gas triethyl
	boron will occur,  which results in a negative interference and poor chromatography.	
                                                                                Draft, August, 1998

                                                                                      Method 1630
             A single ethylation blank is analyzed with each analytical run, as part of
                              the calibration sequence. This value is used to blank correct the standard

             The presence of more than 2 pg of CH3Hg indicates aproblem with the
                              reagent water or one of the reagent solutions. An investigation of the
                              cause of the high blank can be made by varying, one at a time, the
                              amounts of buffer, reagent water, and NaBEt4.  Because NaBEt4 cannot
                              be purified, a new batch should be made from different reagents and
                              should be tested for Hg levels if the level of CH3Hg is too high.  If the
                              reagent water is found high, this can be remedied by replacing the
                              purification cartridges.

       9.4.2  Method blanks—The method blanks  (distillation blanks) are prepared by the distillation
               and analysis of 45 mL aliquots of 0.4% HC1 acidified reagent water, exactly as if they
               were samples.
Three method blanks should accompany each analytical batch. The mean
blank value should be less than 0.045 ng/L of CH3Hg, and the variability
should be less than 0.015 ng/L of CH3Hg. A mean blank value greater
than 0.045 ng/L CH3Hg or a variability greater than 0.015 ng/L of
CH3Hg is unacceptable for low level ambient analysis.
       9.4.3  Field blanks
             Analyze the field blank(s) shipped with each sample set. Analyze the
                              blank immediately before analyzing the samples in the batch.

             If CH3Hg or any potentially interfering substance is found in the field
                              blank at a concentration equal to or greater than the ML (Table 1), or
                              greater than one-fifth the level in the associated sample, whichever is
                              greater, results for associated samples may be the result of contamination
                              and may not be reported for regulatory compliance purposes.

             Alternatively, if a sufficient number of field blanks (three minimum) are
                              analyzed to characterize the nature of the field blanks, 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 blank(s)  and associated samples is known or
                              suspected, the laboratory should communicate this to the  sampling team
Draft, August, 1998

Method 1630
                             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  0.4% HCL 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 cleaned

           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
                                     (Section 7.17) 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 CH3Hg or any potentially interfering substance
                                     is detected in the blank, the source of contamination or
                                     interference must be identified,  and the problem corrected. The
                                                                                Draft, August, 1998

                                                                                     Method 1630
                                     equipment must be demonstrated to be free from CH3Hg 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

9.5    Ongoing precision and recovery (OPR)—To demonstrate that the analysis system is within
       specified limits 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 (0.5 ng/L, Section 7.10) followed by a ethylation blank prior to
               the analysis of each analytical batch according to the procedure 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 ethlyation blank from the peak height (or
               area) for the OPR and compute the concentration for the blank-subtracted OPR.

       9.5.2  Compare the computed  OPR concentration with the limits in Table 2.  If the concentration
               is in the range specified, the analysis system is within specification and analysis of samples
               and blanks may proceed. If, however, the concentration is not in the specified range, the
               analytical process is not within the specified limits. Correct the problem and repeat the
               OPR test.

       9.5.3  The laboratory should add results that pass the specification in Section 9.5.2 to IPR 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-

9.6    Quality control sample (QCS)—The laboratory must obtain a QCS from a source different from
       the CH3Hg 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). Good QCS samples may be made by KOH/methanol digestion (Reference 2) of CH3Hg
       certified tissue CRMs.  CH3Hg certified CRMs are available through the National Institute of
       Standards Technology (NIST), National Research Council  of Canada (NRCC), and International
       Atomic Energy Agency (IAEA).
Draft, August, 1998

 Method 1630
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 35%. If the RPD of the field duplicates exceeds 35%, the laboratory
       should communicate this to the sampling team so that the source of error can be identified and
       corrective measures taken before the next sampling event.

10.0  Calibration and Standardization

10.1   Establish the operating conditions necessary to purge Hg species from the bubbler and to desorb
       Hg species from the traps so that sharp peaks are given. The system is calibrated using CH3Hg
       standards ultimately traceable to NIST standard total Hg reference material, as follows:

       10.1.1        Calibration

           The calibration must contain five or more non-zero points and the results
                             of analysis of one ethylation blank.  The lowest calibration point must be
                             at the minimum level (ML).

           Standards are analyzed by the addition of aliquots of the CH3Hg working
                             standard (Section 7.9) directly into the bubblers (Section 6.4.3).  Add  50
                             mL of fresh reagent water, a 0.005 ng aliquot of the standard,  0.3 mL  of
                             acetate buffer, and 0.04 mL of NaBEt4 to the bubbler, swirling to mix.
                             Allow to react for 17 min, and then purge and analyze as below (Section
                             11). Sequentially follow with aliquots of 0.05, 0.1, 0.2, and 0.01 ng
                             CH3Hg in separate bubblers.

           For each point, correct the standard peak height or area by subtracting the
                             peak height or area of the ethylation blank for the analytical batch.
                             Calculate the calibration  factor (CF) for CH3Hg for each of the five
                             standards using the mean ethylation-blank-corrected peak height or area
                             (Equation 3).
                                                                                Draft, August, 1998

                                                                                    Method 1630
                                           Equation 3
                      Rs=Peak height or area of the standard
                      Re=Peak height or area of the ethylation blank
              _ C '^Concentration of the standard (ng/L) _
           Calculate the mean calibration factor (CFm), the standard deviation of the
                             CFm (SD), and the relative standard deviation (RSD) of the calibration,
                             where RSD = 100 x SD/CFm. If the RSD is < 15%, the CFm may be used
                             to calculate sample concentrations. If RSD > 15%, recalibrate the
                             analytical system and repeat the test.

           The net concentration recovery (minus ethylation blank) for the lowest
                             standard must be in the range of 65-135% 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.

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-up.	

11.1  Sample Distillation

       11.1.1        Weigh a 45-mL aliquot from a thoroughly shaken, acidified sample, into a 60-mL
                      fluoropolymer distillation vial. Add 200 \\L of 1% APDC solution, and replace
                      the distillation cap, such that the tubing extends to the bottom of the vial.
Repeat this procedure for all samples to be distilled in a set, including
three reagent water blanks and spiked samples.
           Matrix spikes and matrix spike duplicates—For every 10 or fewer
                             samples, pour two additional 45-mL aliquots from a randomly selected
Draft, August, 1998

Method 1630
                              sample. Spike the aliquots at the level specified in Section 9.3 and process
                              them in the same manner as the samples. There should be two MS/MSD
                              pairs for each analytical batch of 20 samples.

            For each sample, prepare a 60-mL distillate receiving vial. Add 5.0 mL
                              reagent water to each receiving vial and replace the cap so that the tubing
                              extends into the water layer.

            Record the sample ID associated with each distillation and receiving vial.
                              It is important to develop an unambiguous tracking system, such as the
                              use of engraved vial numbers, because the distillation vials themselves
                              cannot be labeled (due to the heat).

       11.1.2        Place each prepared distillation vial into one of the holes in the heating block and
                      attach the fluoropolymer tubing to the incoming gas supply from the rotometer
                      manifold. Adjust the gas flow rate through the bubbler to 60 ± 20 mL/min.

       11.1.3        As each distillation vial with sample is placed into the heating block, place the
                      corresponding labeled distillation vial into the ice bath immediately adjacent to the
                      heating block. Attach the tubing from the receiving vessel to the port of the
                      distillation vessel.

       11.1.4        Once all the holes in a heating block are filled, place the aluminum lid over the
                      vessel caps in such a way that all tubing is passing without crimps through the
                      slots, and the lid is making metal-to-metal contact with the block (to provide
                      proper heating of the lid).

       11.1.5        Turn on the temperature controllers to the heating blocks to a pre-set block
                      temperature of 125 ± 3°C.

       11.1.6        Distill the samples until each receiving vial fills to the engraved 40 mL line.  This
                      time period will be approximately 2.5 h to 4 h depending upon exact temperatures,
                      gas flow rates, and water characteristics.

            Different samples and locations on the block will distill at somewhat
                              different rates, so after about 2 h, all of the tubes should be monitored
                              frequently to avoid over-distillation. As the individual samples fill to the
                              line, they should be removed from the distillation unit.

            Over-distillation is the greatest potential risk for poor recoveries by this
                              method. If more than the prescribed amount of sample distills over, the
                                                                                 Draft, August, 1998

                                                                                       Method 1630
                              risk of HC1 fumes co-distilling increases.  Chloride and low pH are
                              interferences with the ethylation procedure.

           If any samples are suspected of over-distillation, they should be checked
                              with pH paper.  If the distillate has a pH of less than 3.5, it should be
                              discarded, rather than analyzed.

        11.1.7         Once all of the vials are distilled, the distillates may be stored at room temperature
                       and in the dark for up to 48 h before analysis (loop the fluoropolymer tube around
                       to close off the second port on the receiving vial).  Do not refrigerate or store
                       longer than 48 h.

        11.1.8         The distillation-side (dirty) vials must be scrubbed thoroughly with a test-tube
                       brush and alkaline detergent, then rinsed in reagent water, to remove organics
                       prior to acid cleaning. To acid-clean between uses, the vials are filled with 10%
                       HC1, recapped with the tubing looped around to close off the port, and placed in
                       an oven at 80°C overnight.

11.2   Ethylation and purging of the distillates

        11.2.1         Immediately before analysis, add 0.3 mL of acetate buffer to the sample in the
                       receiving vial, and then  add another 10 mL of reagent water to the vial (so that the
                       total sample volume is > 50 mL; the vial is almost full).

        11.2.2         Pour the buffered sample into the  reaction vessel/bubbler, and add  0.04 mL of
                       freshly thawed 1% NaBEt4 solution.  Close the reaction vessel with the bubbler
                       cap, and swirl gently to  mix.

        11.2.3         If standards,  ethylation blanks, or QCS are being analyzed, pour 50 mL of reagent
                       water into the bubbler, add 0.3 mL of acetate buffer, the appropriate spike, etc.,
                       and 0.04 mL 1% NaBEt4 solution.

        11.2.4         Allow the contents of the bubbler to react for 17 min. All CH3Hg in the sample is
                       converted to volatile methylethyl mercury.

        11.2.5         After reaction, attach a  Carbotrap® trap to each bubbler with the 1/4"
                       fluoropolymer fitting, and purge the sample with N2 (200 mL/min) for  17 min.

        NOTE:  The Carbotrap® trap must be  attached such that the gas from the bubbler enters the
	trap on side A.	
Draft, August, 1998

Method 1630
       11.2.6        Once the sample has been purged for 17 min, any adsorbed water must be dried
                      from the Carbotrap® trap. Disconnect the Carbotrap® trap from the bubbler and
                      attach the N2 flow directly to the trap. Use the same orientation (i.e., N2 entering
                      from side A), and purge the trap for 7 min.

       11.2.7        The sample is now ready for analysis. The methylethyl mercury collected on the
                      trap is quantitatively stable for up to 6 h and must be analyzed within that period.

11.3  Desorption of methylethyl mercury from the Carbotrap® trap

       11.3.1        Close the argon stopcock on the GC, and allow 30 sec for the pressure in the
                      system to dissipate.  Remove the previous Carbotrap® trap from the GC.

       11.3.2        Attach the Carbotrap® trap containing the new sample to the GC column using a
                      1/4" fluoropolymer friction fit connector, such that side A is facing toward the
                      GC column.

       11.3.3        Place the Nichrome wire heating coil around the Carbotrap® trap, centered over,
                      and extending beyond the packing material on side A. Re-connect the argon gas to
                      side B of the Carbotrap® trap.

       11.3.4        Open the argon stopcock, and allow gas to  flow for 30 sec prior to heating the
                      column.  Make sure that the post GC pyrolytic column is on and red-hot (~700°C).

       11.3.5        Apply power to the coil around the sample trap for 45 sec (using an automatic
                      timer) to thermally desorb the ethylated species from the sample trap into the GC

       11.3.6        Turn on the chart recorder or other data acquisition device to start data collection.

       11.3.7        Three peaks should emerge during the analytical run. The first peak (~1 min) is
                      Hg°, which is residual, and non-quantitative. This peak signifies the start of the
                      peak set. Usually, the second peak to emerge (-2.5 min) is methylethyl mercury,
                      the peak of interest.  Following this (~4 min) is the peak for diethyl mercury
                      ((CH3CH2)2Hg), which is the ethylation product of Hg(II). If (CH3)2Hg were
                      present in the sample, it would appear as a  second peak between Hg° and
                      methylethyl mercury-not fully resolved from the Hg°. See appendix for advice on
                      the quantitation of (CH3)2Hg.
                                                                                Draft, August, 1998

                                                                                     Method 1630
       11.3.8        Allow the GC run to proceed at least 1 min beyond the point that the diethyl
                      mercury (Hg(II)) peak returns to base line. Place the next sample Carbotrap® trap
                      in line and proceed with analysis of the next sample.

11.4  Peaks generated using this technique should be very sharp and almost symmetrical. Methylethyl
       mercury elutes at approximately 2.5 min and has a width at half-height of about 10 sec. Earlier
       peaks (Hg°, (CH3)2Hg) are sharper, while later peaks (diethyl mercury) are broader.

       11.4.1        The appearance of only one peak (Hg°) usually signifies either that the pyrolytic
                      column is not turned on, or that NaBEt4 was not added to the sample.

       11.4.2        Normally the Hg° peak is quite small.  However, some Hg° is generated by thermal
                      degradation of diethyl mercury during the desorption step. Thus, when samples
                      contain a high concentration of Hg(II), both the Hg° and the diethyl mercury peaks
                      will be bigger.  The ratio of the two peaks is indicative of the quality of the
                      Carbotrap® trap. As the  Carbotrap® trap degrades, the  amount of thermal
                      breakdown of organo-mercurials increases. Since the diethyl mercury is much
                      more sensitive to thermal breakdown than the methylethyl mercury, monitoring the
                      latter peak can serve as an early warning for Carbotrap® trap replacement.
                      Generally, the Carbotrap® traps should be replaced any time the Hg° peak grows
                      to be as large as the diethyl mercury peak. As a rule of thumb for samples with
                      significant Hg(II), use 1.0 ng Hg(II) from a non-acidified solution deliberately
                      added to the  reaction vessel as a trap check. For samples very low in Hg(II), such
                      as blanks, the Hg° peak is generally higher than the diethyl mercury peak, due to
                      residual sources.

       11.4.3        In the event that samples with large Hg(II) content are analyzed, some of the
                      diethyl mercury generated breaks down to monoethyl mercury (CH3CH2Hg)
                      during thermal desorption.  If this occurs, a very broad peak (width of several
                      minutes)  will appear at some long time after the run is over (5-20 min). Such
                      occurrences result in a confusing and messy increase and then decrease  in the
                      baseline.  Such peaks can be hurried through the system by turning the GC column
                      to 140°C  until the peak emerges, and then reducing the temperature back to 110°C
                      before resuming analysis.

12.0  Data Analysis and Calculations

12.1   Calculate the following parameters for each analytical batch:

       12.1.1  Ethylation blank (n = 1) or the mean ethylation blank (n > 1)
Draft, August, 1998

Method 1630
       12.1.2 Ethylation-blank subtracted calibration factor for each standard (Cfx, Section 10.1.3) and
              peak measurement for each sample (RJ

       12.1.3 The mean calibration factor (Cfm), standard deviation of the calibration factor (SD), and
              relative standard deviation (RSD) of the calibration factor (Section

12.2   Compute the concentration of CH3Hg in ng/L (parts-per-trillion; ppt; Equation 4).

                                          Equation 4

                                                     R, — RCD
                                  [CH3Hg](ng/L) =

                      Rs=gross peak height (or area) of signal for CHflg in sample
                      Re=peak height (or area) of signal for CHflg in ethylation blank (n = 1) or
                      mean ethylation blank (n > 1)
                      CFm=mean calibration factor
              	V=Sample volume (L)	
1 2.3   The CH3Hg concentration of the mean (n=3 or more) method blank (ng/L, Equation 4) should be
       subtracted from the sample concentration calculated above to obtain the net in situ CH3Hg
       concentration (Equation 5).

                                          Equation 5
                                                           MB      s
                      RMB=gross peak height (or area) of signal for CHflg in the mean method blank
                      REB=gross peak height (or area) of signal for CHflg in the ethylation blank (n
                      = 1) or the mean ethylation blank (n > 1)
                      CFm=Mean calibration factor
                      VMB=Volume of the method blank
                      V=Volume of the sample _
                                                                               Draft, August, 1998

                                                                                    Method 1630
                                          Equation 6

                        fCH.Hgl   = fCH.Hgl      - fCH.Hgl
                        L    3  &Jnet    L    3   &Jsample   L    3  &JMB
                      [CHflg]net=net in situ CHBHg concentration (ng/L)
                      [CHflg]sample=ethylation-blank corrected concentration ofCHSHg in the sample
                      (ng/L, Equation 3)
                      [CH3HgJMB=concentration ofCHSHg in the mean method blank (ng/L, Equation
12.4  Reporting

       12.4.1        All results are reported after subtraction of mean method blanks (Equation 6).

       12.4.2        Under the conditions described here, the distillation procedure not 100% efficient
                      in recovering CH3 Hg because not all of the sample volume can be distilled, to
                      avoid co-distillation of HC1. Laboratories should calculate the efficiency of the
                      distillation for their laboratory. This calculation is done by keeping a running
                      mean of the last 30 recoveries calculated for precision and recovery samples (IPR
                      and OPR), excluding all values that are more than two standard deviations from
                      the mean.  Since the distillation technique is inherently and reproducibly non-
                      quantitative, all results should be recovery corrected by an empirically derived
                      factor (Equation 7).

                                          Equation 7
                      F=Empirically derived correction factor
	R=Recovery (the running mean of the last 30 IPR and OPR samples)	

       12.4.3        Report all values in ng/L to three significant figures. Report results below the  ML
                      as <0.06 ng/L, or as required by the permitting authority or in the permit.  If the
                      laboratory achieved an MDL lower than 0.02 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
Draft, August, 1998

Method 1630
                      Below Analytical Detection/Quantitation 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. In addition, the techniques in this method have
       been intercompared with other techniques for low-level CH3Hg determination in water in the
       International Mercury Speciation Intercomparison Exercise (Reference 15).

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, 202/872-4477.

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

15.2   Acids, samples at pH <2, and BrCl  solutions must be neutralized before being disposed of, or must
       be handled as hazardous waste.
                                                                               Draft, August, 1998

                                                                                  Method 1630
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.

16.0  References

16.1   Frontier Geosciences, Inc., Purchase Order 97-1-003 from DynCorp Viar, Inc., January, 1997.

16.2   Bloom, N.S "Determination of Picogram Levels of Methylmercury by Aqueous Phase Ethylation,
       Followed by Cryogenic Gas Chromatography with Cold Vapor Atomic Fluorescence Detection."
       Can. J. FishAq. Sci. 1989, 46: 1131.

16.3   Bloom, N.S and Fitzgerald, W.F. "Determination of Volatile Mercury Species at the Picogram
       Level by Low Temperature Gas Chromatography With Cold Vapor Atomic Fluorescence
       Detection." ,4«a/.  Chim. Acta.  1988, 208: 151.

16.4   Horvat, M., Bloom, N.S., and Liang, L. "A Comparison of Distillation with other Current Isolation
       Methods for the Determination of Methyl Mercury Compounds in Low Level Environmental
       Samples Part 2, Water" Anal. Chim. Acta, 1993, 282: 153.

16.5   Bloom, N.S. and von der Geest, E.J. "Matrix Modification to Improve Recovery of CH3Hg from
       Clear Waters using the Acid/Chloride Distillation Procedure," Wat Air Soil Pollut  1995, 80:

16.6   Liang, L., Horvat, M., and Bloom, N.S. 1994. "An Improved Speciation Method for Mercury by
       GC/CVAFS After Aqueous Phase Ethylation and Room Temperature Precollection," Talanta

16.7   Bloom, N.S., Coleman, J.A., and Barber, L. "Artifact Formation of Methyl Mercury During
       Extraction of Environmental Samples by Distillation." Fres. Anal.  Chem. 1997, (in press).

16.8   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.

16.9   "Working with  Carcinogens," Department of Health, Education, and Welfare, Public Health
       Service. Centers for Disease Control. NIOSH Publication 77-206, Aug.  1977, NTIS PB-277256.

16.10 "OSHA Safety  and Health Standards, General  Industry," OSHA 2206, 29 CFR 1910.
Draft, August, 1998

Method 1630
16.11  "Safety in Academic Chemistry Laboratories," ACS Committee on Chemical Safety, 1979.

16.12 "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.

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

16.14 "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.

16.15 Bloom, N.S.; Horvat, M.; Watras, C.J.  "Results of the International Mercury Speciation
       Intercomparison Exercise," Wat. Air. SoilPollut., 1995, 80, 1257.
                                                                              Draft, August, 1998

                                                                              Method 1630
17.0  Tables and Diagrams

Table 1        Methyl Mercury Analysis Using Method 1630: Lowest Water Quality Criterion, Method
              Detection Limit, and Minimum Level
Methyl Mercury
Lowest Ambient
Water Quality
Method Detection Limit (MDL) and Minimum
Level (ML)
0.02 ng/L
0.06 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 1630
IPR (Section 9.2)
(Section 9.5)
Method Blanks
(Section 9.4)
< 0.1 ng/L
(Section 9.3)
              1.      Recovery corrected
Draft, August, 1998

 Method 1630
                                Flow Meter •   -
           Oven with
           GC Column
                                                                            0-1000 Volt DC
                                                                             Power Supply
Figure 1       Schematic Diagram of the Cold Vapor Atomic Fluorescence Spectrometer (CVAFS)
              Detector interfaced with the isothermal GC and pyrolytic decomposition column.
                                                                             Draft, August, 1998

                                                                               Method 1630
              a. Purge
                                      Aqueous Sample + NaBEt4
               b. Analyze
                  Hg Free
                  Ar Hg Free Ar
Figure 2       Schematic Diagram of Bubbler Setup (a), and Carbotrap® trap orientation (b).
Draft, August, 1998

 Method 1630
    Hg free .
    N2 or Ar
    Sample +
  heating block
     125° C
                                                               Fluoropolymer vials
                                                                    Ice bath
Figure 3      Schematic diagram showing the CH3Hg distillation set-up.
                                                                        Draft, August, 1998

                                                                                      Method 1630
18.0   Glossary

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

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

18.2   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 an OPR and
        a QCS. MS/MSD samples must be prepared at a frequency of 10% per analytical batch (one
        MS/MSD for every 10 samples).

18.3   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.

18.4   Matrix Spike (MS) and Matrix Spike Duplicate (MSP): Aliquots of an environmental sample to
        which known quantities of the analyte(s) of interest is added in the laboratory. The MS and MSB
        are analyzed exactly like a sample.  Their purpose is to quantify the bias and precision caused by
        the sample matrix. The background concentration(s) of the analyte(s) in the sample matrix must be
        determined in a separate aliquot and the measured values in the MS and MSB corrected for these
        background concentrations.

18.5   May: This action, activity, or procedural step is  allowed but not required.

18.6   May not:  This action, activity, or procedural step is prohibited.

18.7   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
        weights, volumes, and cleanup procedures have been employed.  The ML is calculated by
        multiplying the MBL by 3.18 and rounding the result to the number nearest to (1, 2, or 5) x  1 On,
        where n is an integer.

18.8   Must: This action, activity, or procedural step is  required.

18.9   Quality Control Sample (QCS): A sample containing CH3Hg  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

Draft, August, 1998


Method 1630
18.10 Reagent Water:  Prepared from 18 MQ ultrapure deionized water starting from a prepurified
       source. Reagent water is used to wash bottles, as source water for trip and field blanks, and in the
       preparation of standards and reagents.

18.11 Sample set: Samples collected from the same site or, if for compliance monitoring, from a given
       discharge. This term applies to samples collected at the same time, to a maximum often samples.

18.12 Shall:  This action, activity, or procedure is required.

18.13 Should: This action, activity, or procedure is suggested, but not required.

18.14 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

18.15 Ultraclean Handling: A series of established procedures designed to ensure that samples are not
       contaminated for CH3Hg during sample collection, storage, or analysis.
                                                                                 Draft, August, 1998

                                                                                 Method 1630
                                   Appendix A  :

                    Determination of Dimethyl Mercury

1.0   Scope and Application

1.1    This method is for determination of dimethyl mercury ((CH3)2Hg) in unfiltered water by direct
       purge and trap, isothermal GC separation, and CVAFS detection.

1.2    The method described in this appendix is not supportable by the full range of QC samples, so the
       method is to be considered for research purposes only.

1.3    The method described in this appendix is subsidiary to Method 1630 (Methyl Mercury in Aqueous
       Samples by Aqueous Phase Ethylation, Purge and Trap,  and CVAFS). As such, only the major
       differences between the (CH3)2Hg method and the CH3Hg method will be described.

1.4    This method is designed for the determination of in the range of 0.0002 to 0.1 ng/L, and may be
       extended to higher levels by  selection of a smaller sample size.

1.5    Since no reagents are added to the sample, the MDL is not ethylation blank limited, but is only
       limited by the instrumental noise. With the Tekran analyzer, the MDL for a 1 L sample volume is
       approximately 0.0002 ng/L as Hg (based on 7 replicates of a 0.0015 ng/L solution).

2.0   Summary of Method Changes

2.1    The analysis is performed using fresh, unfiltered, unpreserved samples. To minimize analyte
       losses, all efforts must be extended to speed the time between sample collection and sample
       analysis, and to minimize the contact of the sample with  the atmosphere prior to purging.

2.2    Samples should be purged and analyzed in the field, but  if this is not possible, samples may be
       collected directly into headspace-free 1-L glass bottles with fluoropolymer-lined caps, and sent via
       express to the laboratory for analysis. If kept unpreserved, dark, and cool, the (CH3)2Hg present in
       the sample is found to be stable for up to 48 h from the time of collection.

2.3    Under no circumstances can plastic bottles of any kind (including fluoropolymer) be used for the
       collection of samples for the determination of (CH3)2Hg.  The half-life of dissolved (CH3)2Hg in
       fluoropolymer bottles is only about 6 h.

2.4    The entire  1 L sample is purged directly onto a Carbotrap® trap, using N2 at a flow rate of 300
       mL/min for 30 min. A specially constructed 1 L bottle with 24/40 ground glass fitting and fritted

Draft, August, 1998


 Method 1630
       bubbler cap must be utilized for this purpose.  After purging, the trap must be dried with N2 and
       analyzed within 6 h, as described in method 1630.

2.5    The analyzer set-up for (CH3)2Hg is exactly as in Method 1630, with the exception that the GC
       oven must be set at 80°C rather than 110°C, to facilitate separation of Hg° from (CH3)2Hg.

2.6    Upon desorption of the Carbotrap® trap into the GC column, up to two peaks will appear. The
       first is usually Hg°, which appears at approximately 1.0 min.  The second is (CH3)2Hg, which
       appears approximately at 1.5 min.

       NOTE:  Because  these peaks are so  close to each other, and either one or the other, or neither
       may be present, it is imperative that an event marker be triggered to signal the start of the GC
	run, so that the peak may be positively identified by its retention time.	

2.7    Calibration is performed by spiking appropriate aliquots of a (CH3)2Hg standard into the same
       volume of reagent water as the samples, and purging onto Carbotrap® traps.  A good calibration
       range is from 1 to 100 pg as Hg.

2.8    The stock solution  for (CH3)2Hg is a 1.0 parts per million solution in methanol, custom prepared
       by Strem Chemical (Newburyport, MA).  A working stock (1 ng/mL) is prepared by 1:1000
       dilution of the stock solution with methanol. These solutions have been found to be stable for over
       4 years, when kept refrigerated, and dark, in glass bottles.

2.9    The stock solution  as supplied by Strem is only approximate in its concentration.  To exactly
       calibrate the solution, an aliquot of the working stock equal to approximately 1 ng is spiked into a
       bubbler of pre-purged reagent water, and then purged onto a gold coated sand trap.  The trap is
       analyzed for total Hg according to EPA Method 1631. In this case, total Hg purged onto the trap
       equals (CH3)2Hg. Pre-calibrated working standards of (CH3)2Hg in methanol are available for
       purchase (Frontier Geosciences Inc., or equivalent).

3.0   QC  Measures

3.1    Not all QC measures available for method 1630 are available for use with the (CH3)2Hg technique.

       3.1.1  For each set of samples (or batch of 20),  three method blanks, and two MS/MSD pairs
               should be measured. Since (CH3)2Hg is rarely detected in the environment, matrix spikes
               should be low (i.e.,  1-5 pg), to assure  the ability to measure near the MDL.

       3.1.2  No certified reference materials (CRMs)  or second source LCSWs are available for
                                                                                Draft, August, 1998

                                                                                   Method 1630
3.2    No interferences have been observed for this method, although volatile organic compounds, as
       might be present in waste waters and effluents could diminish the observed (CH3)2Hg signal by co-
       eluting, and quenching the atomic fluorescence.

3.3    Separate field samples should be collected for replicates, and matrix spikes, since once the sample
       is opened, (CH3)2Hg will rapidly be lost from solution by diffusion to the air.

3.4    Samples must not be filtered prior to analysis, or (CH3)2Hg will be lost to the air.

3.5    Samples must not be stored acidified, or (CH3)2Hg will decompose to CH3Hg. Samples may be
       acidified just prior to analysis, if Hg° and (CH3)2Hg are to be both purged simultaneously (as in
       Method 1631 Appendix).

3.6    Samples should be kept out of light, or (CH3)2Hg will decompose to CH3Hg.

3.7    Samples must not be stored in plastic containers, or (CH3)2Hg will rapidly be lost by diffusion into
       the plastic matrix.

4.0   Performance

4.1    This method is not often used, and so has not been rigorously tested. However, experience
       indicates that the following QC objectives can be met in ambient water samples, when using 1 L
Draft, August, 1998


 Method 1630
5.0   Tables

Table 1       Dimethyl Mercury Analysis Using Method 1630 Appendix: Lowest Water Quality
              Criterion, Method Detection Limit, and Minimum Level
Dimethyl Mercury
Lowest Ambient
Water Quality
Method Detection Limit (MDL) and Minimum
Level (ML)
0.0002 ng/L
0.0006 ng/L

1.      Lowest of the freshwater, marine, and human health ambient water quality criteria promulgated by
       EPA for nine States and the District of Colubia at 40 CFR Part 136 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 Levels (ML).

Table 2       Quality Control Acceptance Criteria for Performance Tests In EPA Method 1630
(Section 9.2)
(Section 9.5)
Method Blanks
(Section 9.4)
Max Mean
< 0.0001 ng/L
(Section 9.3)
Recovery corrected.
                                                                           Draft, August, 1998

                                                                                         Method 1630
Draft, August, 1998