January 2001
                          Method 245.7

Mercury in Wafer by Cold Vapor Atomic Fluorescence Spectrometry
                           January 20Q1
                 U.S. Environmental Protection Agency
            Office of Water, Office of Science and Technology
                Engineering and Analysis Division (4303)
                         Ariel Rios Building
                   1200 Pennsylvania Avenue, N.W.
                        Washington, DC 20460

Draft Method 245.7 - do not cite or quote
This method was developed under the direction of William A. Telliard and Maria Gomez-Taylor of the
Engineering and Analysis Division (BAD) within the U.S. Environmental Protection Agency's (EPA's)
Office of Science and Technology (OST). The Method was developed by EPA's Human Exposure
Research and Environmental Services Divisions, in collaboration with Technology Applications, Inc.
Additional assistance in preparing the method was provided by DynCorp, Information and Enterprise
Technology and Interface, Inc.

This Method has been reviewed and approved for publication by the Analytical Methods Staff within
EPA's Engineering and Analysis Division. 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. Questions concerning this Method or its
application should be addressed to:

Maria Gomez-Taylor
Engineering and Analysis Division (4303)
U.S. Environmental Protection Agency
Ariel Rios Building
1200 Pennsylvania Avenue, N.W.
Washington, DC 20460
Phone: 202/260-1639
Fax:  202/260-7185

                                                               Draft Method 245.7 - do not cite or quote

EPA draft Method 245.7, Mercury in Water by Cold Vapor Atomic Fluorescence Spectrometry (the
"Method"), was developed through a collaboration between EPA's Environmental Monitoring Systems
Laboratory, EPA-Region 4, and Technology Applications, Inc. In developing this Method, EPA sought
to provide the environmental monitoring community with a rugged analytical protocol capable of
determining mercury (Hg) at the concentrations typically regulated under State water quality standards.

EPA developed this Method to specifically address State needs for measuring toxic metals at ambient
water quality criteria (WQC) levels, when such measurements are necessary to protect designated uses.
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), and codified at 40 CFR 131.36.
Method 245.7 was developed to provide reliable measurements of mercury at EPA WQC levels.

Measurement of mercury by this Method is by cold-vapor atomic fluorescence Spectrometry (CVAFS), a
brominating digestion which provides minimal interference, and the use of ultra-pure argon as carrier
gas.  The Method is similar to EPA Method 1631, Mercury in Water by Oxidation, Purge and Trap, and
CVAFS, which was promulgated for use in CWA programs on June 8,  1999 as a means for providing
reliable measurements at the lowest EPA ambient water quality criteria for mercury under the National
Toxics Rule and in the Great Lakes and Tribes (40 CFR 132.6).  Both methods require use of a CVAFS
detector to measure low levels of mercury. However, Method 245.7 uses liquid-gas separation and a
dryer tube for analyte isolation, while Method  1631 uses a purge and gold trap isolation procedure.

Method 245.7 has been validated in two EPA laboratories and one university laboratory, and results from
these studies indicate that the Method is capable of producing reliable measurements of mercury at toxic
criteria levels (40 CFR 136.6).  The highest method detection limit (MDL) determined by three
laboratories in reagent water was 1.8 ng/L. Following these studies, the Method was revised to conform
with recent EPA guidelines.

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. Method 245.7 is
designed to preclude contamination in nearly all situations.  In recognition of the variety of situations to
which this Method may be applied, and in recognition of continuing technological advances, Method
245.7 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:

U.S. EPA NCEPI      or     EPA Sample Control Center, DynCorp I&ET
11209 Kenwood Road         6101 Stevenson Avenue
Cincinnati, OH 45242         Alexandria, Virginia 22304-3540
513/489-8190                703/461-2100
Draft, January 2001

Draft Method 245.7 - do not cite or quote
    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 tests. The terms "shall" and "must" define procedures required
    for producing reliable data at water quality criteria levels.  The terms "should" and "may" indicate
    optional steps that may be modified or omitted if the laboratory can demonstrate that the modified
    method produces results equivalent or superior to results produced by this Method.
                                                                               Draft, January 2001

                                                             Draft Method 245.7 - do not cite or quote
                                     Method 245.7

Mercury in Water by Cold Vapor Atomic Fluorescence Spectrometry

1.0   Scope and Application

1.1     Method 245.7 (the "Method") is for determination of mercury (Hg) in filtered and unfiltered
       water by cold-vapor atomic fluorescence spectrometry (CVAFS). It is applicable to drinking
       water, surface and ground waters, marine water, and industrial and municipal wastewater. The
       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 method developed through a collaboration between EPA's Environmental Monitoring
       Systems Laboratory, EPA-Region 4, and Technology Applications, Inc. (Reference  1) and on
       peer-reviewed, published procedures for the determination of mercury in aqueous samples,
       ranging from marine water to effluent (References 2-6).

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

1.3     This Method may be used to determine Hg up to 200 ng/L and may be extended by dilution of
       the sample.  The normal calibration range for ambient water monitoring is 5 ng/L to 100 ng/L.

1.4     The ease of contaminating ambient water samples with mercury and interfering substances
       cannot be overemphasized. This Method includes suggestions for improvements in facilities and
       analytical techniques that should minimize contamination and maximize the ability of the
       laboratory to make reliable trace metals determinations. Section 4.0 gives these suggestions.

1.5     The method detection limit (MDL) and minimum level of quantitation (ML) in this Method
       usually are dependent on the  level of interferences rather than instrumental limitations.  The
       MDL has been determined from single laboratory validation studies as 1.8 ng/L and the ML has
       been established as 5.0 ng/L.

1.6     Clean and ultraclean—The terms "clean" and "ultraclean" have been applied to the techniques
       needed to reduce or eliminate contamination in trace metals determinations. These terms are not
       used in this Method because they lack an exact definition. However, the information provided in
       this Method is consistent with the summary guidance  on clean and ultraclean techniques
       (References 6-8).

1.7     This Method follows the EPA Environmental Methods Management Council's "Guidelines and
       Format for Methods to Be Proposed at 40 CFR, part 136 or part 141."

1.8     This Method is "performance based."  The laboratory 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.
Draft, January 2001

Draft Method 245.7 - do not cite or quote
1.9    Any modification of this Method, beyond those expressly permitted, shall be considered a maj or
       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 experienced in the use of CVAFS techniques, the
       handling of trace elements and clean laboratory practices and protocols.  Each laboratory that
       uses this Method must demonstrate the ability to generate acceptable results using the procedure
       in Section 9.1.1.

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 (Reference 9) that can be used for verification and validation of the data obtained.

2.0   Summary of Method

2.1    A 100- to 2000-mL sample is collected directly into a specially cleaned, pretested, fluoropolymer
       bottle using sample handling techniques  specially designed for collection of mercury at trace
       levels (Reference 10).

2.2    For dissolved Hg, the sample is filtered through a 0,45-^m capsule filter.

2.3    The sample is preserved by adding 5 mL/L of pretested 12N HC1.

2.4    Inorganic Hg compounds and organomercury species are oxidized by a potassium
       bromate/potassium bromide reagent,

2.5    After oxidation, the sample is sequentially prereduced with NH2OH-HC1 to destroy the excess
       bromine, then the ionic Hg is reduced with SnCl2 to convert Hg(II) to volatile Hg(0).

2.6    The Hg(0)  is separated from solution by purging with high purity argon  gas through a semi-
       permeable  dryer tube (Figure 1).

2.7    The Hg passes into an inert gas stream that carries the released Hg(0) into the cell of a cold-vapor
       atomic fluorescence spectrometer (CVAFS) for detection. The concentration of Hg is
       determined by atomic fluorescence spectrometry at 253.7 nm.

2.8    Quality is assured through calibration and testing of the oxidation, purging, and detection

3.0   Definitions

3.1    Total mercury—all KBrO3/KBr-oxidizable mercury forms and species found in an unfiltered
       aqueous solution.  This includes, but is not limited to, Hg(II), Hg(0), strongly organo-complexed
       Hg(II) compounds, adsorbed particulate  Hg, and several tested covalently bound organo-
       mercurials  (e.g., CH3HgCl, (CH3)2Hg, and  C6H5HgOOCCH3).  The recovery of Hg bound within
       microbial cells may require the additional step of UV photo-oxidation. In this Method, total
       mercury and total recoverable mercury are synonymous.

3.2    Dissolved mercury—all  KBrO3/KBr-oxidizable mercury forms and species found in the filtrate
       of an aqueous solution that has been filtered through a 0.45  micron filter.
                                                                             Draft, January 2001

                                                                Draft Method 245.7 - do not cite or quote
3.3    Apparatus—Throughout this Method, 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.

3.4    Definitions of other terms used 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 constitutes one of the greatest
       difficulties encountered in trace metals determinations. Over the last two decades, chemists have
       come to recognize that much of the historical data on the concentrations of dissolved trace metals
       are erroneously high because the concentrations reflect contamination from sampling and
       analysis rather than ambient levels. Therefore, it is imperative that extreme care be taken to
       avoid contamination when collecting and analyzing ambient water samples for trace metals.

4.2    Samples may become contaminated by numerous routes.  Potential sources of trace metals
       contamination 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
       or stored equipment, labware, and reagents; and atmospheric inputs such as dirt and dust. Even
       human contact can be a source of trace metals contamination. For example, it has been
       demonstrated that dental work (e.g., mercury amalgam fillings) in the mouths of laboratory
       personnel can contaminate samples directly exposed to exhalation (Reference 5).

4.3    Contamination Control

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

      The integrity of the results produced cannot be compromised by contamination
                      of samples. This Method and the Sampling Guidance 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 Guidance and Section 5 of this Method give
                      suggestions and requirements for personnel safety.

       4.3.2   Avoiding contamination—The best way to control contamination is to completely avoid
               exposure of the sample to contamination in the first place. Avoiding exposure means
               performing operations in an area known to be free from contamination. Two of the most
               important factors in avoiding/reducing sample contamination are (1) an awareness of
               potential sources of contamination and (2) strict attention to work being done.
               Therefore, it is imperative that the procedures described in this Method be carried out by
               well-trained, experienced personnel.
Draft, January 2001

Draft Method 245.7 - do not cite or quote
       4.3.3   Use a clean environment—The ideal environment for processing samples is a class-100
               clean room.  If a clean room is not available, all sample preparation should be performed
               in a class-100 clean bench or a nonmetal glove box fed by mercury- and particle-free air
               or nitrogen.  Digestions should be performed in a nonmetal fume hood situated, ideally,
               in a clean room. Refer to EPA's Guidance on Establishing Trace Metal Clean Rooms in
               Existing Facilities for guidance (Reference 8).

       4.3.4   Minimize exposure—The Apparatus that will contact samples, blanks, or standard
               solutions should be opened or exposed only in a clean room, clean bench, or glove box
               so that exposure to an uncontrolled atmosphere is minimized. When not being used, the
               Apparatus should be covered with clean plastic wrap, stored in the clean bench or in a
               plastic box or glove box, or bagged in clean zip-type bags.  Minimizing the time between
               cleaning and use will also minimize contamination.

       4.3.5   Clean work surfaces—Before a given batch of samples is processed, all work surfaces in
               the hood, clean bench, or glove box in which the samples will be processed should be
               cleaned by wiping with a lint-free cloth or wipe soaked with reagent water.

       4.3.6   Wear gloves—Sampling personnel must wear clean, 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—Apparatus used for determination of mercury at ambient
               water quality criteria levels must be nonmetallic or free of materials that may contain

      Construction materials—Only fluoropolymer or borosilicate glass (if Hg is the
                      only target analyte) containers should be  used for samples that will be analyzed
                      for mercury because mercury vapors can diffuse in or out of other materials,
                      producing 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.
                      Logbooks should be maintained to track samples from containers through the
                      labware to 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 equipment can be

      The laboratory or cleaning facility is responsible for cleaning the Apparatus used
                      by the sampling team.  If there are any indications that the Apparatus is not clean
                      when received by the sampling team (e.g., ripped storage bags), an assessment of
                      the likelihood of contamination must be made. Sampling must not proceed if it
                                                                               Draft, January 2001

                                                                 Draft Method 245,7 - do not cite or quote
                      is possible that the Apparatus is contaminated. If the Apparatus is contaminated,
                      it must be returned to the laboratory or cleaning facility for proper cleaning
                      before any sampling activity resumes,

       4.3.8   Avoid sources of contamination—Avoid contamination by being aware of potential
               sources and routes of contamination,

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

      Contamination by samples—Significant laboratory or instrument contamination
                      may result when untreated effluents, in-process waters, landfill leachates, and
                      other undiluted samples containing concentrations of mercury greater than 100
                      ng/L are processed and analyzed.  Samples known or suspected to  contain Hg
                      concentrations greater than 100 ng/L should be diluted prior to bringing them
                      into the clean room or 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. It  is  imperative
                      that every piece of the Apparatus that is directly or indirectly used in the
                      collection, processing, and analysis of water samples be thoroughly cleaned
                      (Section 6).

      Contamination by airborne particulate matter—Less obvious substances capable
                      of contaminating samples include airborne particles. Samples may be
                      contaminated by airborne dust, dirt, particles, or vapors from unfiltered air
                      supplies; nearby corroded or rusted pipes, wires, or other fixtures; or metal-
                      containing paint.  Whenever possible, sample processing and analysis should
                      occur as far as possible from sources of airborne contamination.

      Contamination from reagents—Contamination can be  introduced into samples
                      from reagents used during processing and analysis. Reagent blanks must be
                      analyzed for contamination prior to use  (see Section 9.2.1). If reagent blanks are
                      contaminated, a new batch of reagents must be prepared (see Section

4.4    Interferences

       4.4.1   During development of this Method, gold, silver and iodide were known interferences.
               At a mercury concentration of 2.5 ng/L and at increasing iodide concentrations from 5 to
               100 mg/L, test data have shown that Hg recovery will be reduced from 100 to 0 percent
               (References 1 and 12).  At iodide concentrations greater than 3 mg/L, the sample should
               be pre-reduced with  SnCl2 (to clarify the brown color).  If samples containing iodide
               concentrations greater than 30 mg/L are analyzed, it may be necessary to clean the
               analytical system with 4N HC1 after the analysis (References 6 and 12).
Draft, January 2001

Draft Method 245.7 - do not cite or quote
       4.4.2   The use of a brominating digestion coupled with atomic fluorescence detection
               overcomes many of the chloride, sulfide and molecular absorption interferences. No
               interferences have been noted for sulfide concentrations below 24 mg/L (References 1
               and 6).

       4.4.3   High purity argon (99.998%) must be used as the carrier gas. Using nitrogen may reduce
               the sensitivity by a factor of eight fold, while the use of air may reduce the sensitivity
               thirty fold (Reference 1).

       4.4.3   Water vapor may collect in the fluorescence detector cell, resulting in a degradation of
               analytical signal or giving a false peak due to scattering of the excitation radiation.  The
               use of a membrane drying tube is required to remove any water vapor from the transfer
               tubing that can contaminate the detector (References 1 and 6).

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.

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

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

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. OSHA rules require that a reference file of material
       safety data sheets (MSDSs) must be made available to all personnel involved in these analyses
       (29 CFR 1917.28, appendix E). It is also suggested that the laboratory perform personal hygiene
       monitoring of each analyst who uses this Method  and that the results of this monitoring be made
       available to the analyst. Personal hygiene monitoring should be performed using OSHA or
       NIOSH approved personal hygiene monitoring methods.  Additional information on laboratory
       safety can be found in References 15-18. The references and bibliography at the end of
       Reference 18 are particularly comprehensive in dealing with the general  subject of laboratory

5.3    Samples suspected to contain concentrations of Hg at ug/L or higher levels 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 safety program for handling Hg.

       5.3.1   Facility—When handling samples known or suspected of containing high concentrations
               of mercury, all operations (including removal of samples from sample containers,

6                                                                              Draft, January 2001

                                                                 Draft Method 245.7 - do not cite or quote
               weighing, transferring, and mixing) should be performed in a glove box demonstrated to
               be leak-tight 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 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.

       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 CVAFS effluent should pass through either a column of activated
               charcoal or a trap containing gold or sulfur to amalgamate or react mercury vapors.

       5.3.7   Waste handling—Good technique includes minimizing contaminated waste. Plastic bag
               liners should be used in waste cans. Trash removers and other personnel must be trained
               in the safe handling of contaminated waste,

       5.3.8   Decontamination

       Decontamination of personnel—Use mild soap with plenty of scrubbing action.

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

       5.3.9   Laundry—Clothing known to be contaminated should be collected in plastic bags.
               Persons that 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 ug per wipe
               indicates acceptable cleanliness; anything higher warrants further cleaning. More than
               10 \ig constitutes an acute hazard, requires prompt cleaning before further use of the
               equipment or work space, and indicates that unacceptable work practices have been
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Draft Method 245.7 - do not cite or quote
6.0   Apparatus and Materials
       Disclaimer:  The mention of trade names or commercial products in this Method is for
       illustrative purposes only and does not constitute endorsement or recommendation for use by the
       Environmental Protection Agency  Equivalent performance may be achievable using apparatus,
       materials, or cleaning procedures other than those suggested here.  The laboratory is
	responsible for demonstrating equivalent performance.	

6.1    Sampling Equipment

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

      New bottles are cleaned by heating to 65-75 °C in 4N HC1 for at least 48 h. The
                      bottles are cooled, rinsed three times with reagent water, and filled with reagent
                      water containing 1% HC1.  These bottles are capped and placed in a clean oven
                      at 60-70 °C overnight. After cooling, they are rinsed three more times with
                      reagent water, filled with reagent water containing 0.4% (v/v) HC1, and placed in
                      a mercury-free class-100 clean bench until the outside surfaces are dry. The
                      bottles are tightly capped (with a wrench), double-bagged in new polyethylene
                      zip-type bags, and stored in wooden or plastic boxes until use. See Section 6.2
                      for equipment needed for bottle and glassware cleaning.

      Used bottles known not to have contained mercury at high (> 100 ng/L) levels are
                      cleaned as above, except for only 6-12 h  in hot 4N HC1.

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

       6.1.2   Filtration Apparatus

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

      Peristaltic pump—115-V a.c., 12-V d.c.,  internal battery, variable-speed, single-
                      head (Cole-Parmer, portable, "Masterflex L/S,"  Catalog No. H-07570-10 drive
                      with Quick Load pump head, Catalog No. H-07021-24, or equivalent).

      Tubing—styrene/ethylene/butylene/silicone (SEBS) resin for use with peristaltic
                      pump, approximately 3/8-in ID by approximately 3 ft (Cole-Parmer size 18,
                      Catalog No. G-06424-18), or approximately 1/4-in OD (Cole-Parmer size 17,
                      Catalog No. G-06424-17, or equivalent).  Tubing is cleaned by soaking in 5-10%
                      HC1 solution for 8-24 h, rinsing with reagent water in a clean bench in a clean
                      room, and drying in the clean bench by purging  with metal-free air or nitrogen.
                      After drying, the tubing is double-bagged in clear polyethylene bags, serialized
                      with a unique number, and stored until use.

6.2    Equipment for bottle and glassware cleaning

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

8                                                                              Draft, January 2001

                                                                Draft Method 245.7 - do not cite or quote
       6.2.2   Panel immersion heater, 500-W, all-fluoropolymer coated, 120 vac (Cole-Parmer H-
               03053-04, or equivalent).

       WARNING: Read instructions carefully!! The heater will maintain a 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 be
       purchased either from a supplier or built in the laboratory from commercially available

       6.3.1   Commercially available CVAFS—Tekran (Toronto, ON) Model 2500 CVAFS, or
               Brooks-Rand (Seattle, WA) Model III CVAFS, or equivalent.

       6.3.2   Custom-built CVAFS.  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 or Starna Cell, or equivalent).

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

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

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

      Flowmeter—with needle valve capable of stabilizing gas flow rate.

6.4    Analytical System—Semi-automated mercury atomic fluorescence analytical system (Figure 1).
       The system consists of the following:

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

Draft, January 2001                                                                               <

Draft Method 245.7 - do not cite or quote
       6.4.2   Peristaltic Pump and pump tubing—three-channel peristaltic pump capable of flow rates
               up to 10 mL/min. Silicone pump tubing for the tin(II), reagent water flush and sample
               solutions. For the tin(II) solution: Watson-Marlow, Product Code 910, 0005-016, 0.5
               mm ID,  1.6 mm wall thickness (w.t.), or equivalent. For the system blank and sample
               solutions: Watson-Marlow, Product Code 910, 0008-016, 0.8 mm ID, 1.6 mm w.t. or

       6.4.3   Solenoid switching valve box—Dual, two-way valves activated by timed events.

       6.4.4   Argon gas regulator—low pressure regulator with flow controller.  Used for maximum
               stability of gas flow rates through the analytical system.

       6.4.5   Gas liquid separator—used to sparge argon gas through the flowing mixture of sample
               liquid and tin(II) solution to liberate the mercury vapor.

       6.4.6   Membrane dryer tube—used for the removal of moisture from the argon gas carrier flow.
               Perma-Pure, Inc. (Model number MD-070-24F)

       6.4.7   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.

6.5    Laboratory equipment

       6.5.1   Pipettors—all-plastic, pneumatic, fixed-volume and variable pipettors in the range  of 5
               \jiL to 2500 uL.

       6.5.2   Analytical balance capable of accurately weighing to the nearest 0.001 g.

       6.5.3   Centrifuge vials—polypropylene 50 mL conical vials with screw-cap lids, Falcon, Blue
               Max, Catalogue #2098 or equivalent.

       6.5.4   Mercury wipes—Merconwipes towelettes,  EPS Chemical Inc,. Fisher Catalogue #17-
               976-8 or equivalent.

       6.5.5   Muffle furnace—Not required if commercially available pre-mixed brominating solution
               is used.  The muffle furnace is used to volatilize Hg contamination from potassium
               bromate and potassium bromide reagent. It is  important that the furnace be Hg free and
               located in a clean, Hg-free laboratory. The furnace should be vented to a fume hood to
               avoid laboratory Hg contamination,

       6.5.6   Volumetric flasks—clean, glass volumetric flasks at 100, 500, and 1000 mL.
10                                                                            Draft, January 2001

                                                               Draft Method 245.7 - do not cite or quote
7.0   Reagents and Standards

7.1     Reagent water—18-Mii minimum, ultra-pure 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 laboratory air be low in both particulate and gaseous mercury.
       Ideally, mercury work should be conducted in a 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 not possible, air coming into the clean bench can be cleaned 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 deionized water. Squeeze-dry the rinsed cloth, and spread flat on newspapers to
              air-dry. When dry, fold and place over the intake prefilter of the laminar flow hood.
              Great care should be taken to avoid contaminating the laboratory with gold dust.  This
              could cause analytical interference if gold becomes incorporated into the samples or
              equipment. The gilding procedure should be done in a remote laboratory if at all

7.3     Argon Gas (Ar)—high-purity grade (99.998%), with two stage regulator or gas from liquid
       argon. Use of a gas purifier cartridge for removing mercury,  oxygen and organic compounds is

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

7.5     Nitric acid—concentrated, trace-metal  purified reagent-grade HNO3 containing less than 5 pg/mL
       Hg. The HNO3 should be preanalyzed before use,

7.6     Reagents

       7.6.1   Hydroxylamine hydrochloride  (NH2OH-HC1), CASRN 5470-11-1.

       7.6.2   Mercuric chloride (HgCl2) CASRN 7487-94-7, 99.99% pure with assay.

       7.6.3   Methyl mercury chloride (CH3HgCl), CASRN 115-09-3, 95% pure with assay.

       7.6.4   Potassium bromate (KBrO3), CASRN 7758-01 -2—volatilize trace mercury impurities by
              heating in a muffle furnace at 250 °C  for a minimum of 8 hours. The compound is then
              placed in a desiccator for cooling.

       7.6.5   Potassium bromide (KBr) CASRN 7758-02-3—volatilize trace mercury impurities by
              heating in a muffle furnace at 250°C  for a minimum of 8 hours. The compound is then
              placed in a desiccator for cooling.

       7.6.6   Stannous chloride (SnCl2-2H2O), CASRN 10025-69-1—assayed mercury level not
              exceeding 0.05 ppm.

Draft, January 2001                                                                             11

Draft Method 245.7 - do not cite or quote
       7.6.7   Stock mercury standard—NIST-certified 10,000 ppm aqueous Hg solution (NIST-3133).
               This solution is stable at least until the NIST expiration date.

7.7    Reagent and Standards

       7.7.1   Hydrochloric acid solution—add concentrated HC1 (Section 7.4) to reagent water in the
               ratio of 1:1 (v/v). Prepare 500 mL weekly, or as needed.

       7.7.2   Hydroxylamine solution—Dissolve 12.0 g of NH2OH-HC1 in 100 mL reagent water.
               Prepare weekly or as needed. This solution may be purified by the addition of 0.1 mL of
               SnCl2 solution and purging overnight at 500 mL/min with Hg-free Ar.

       7.7.3   Stannous chloride solution, 2% (w/v) in 10% (v/v) HC1—add 100 mL concentrated HC1
               to 400 mL of reagent water to a 1L volumetric flask. To this solution, add 20.0 g
               stannous chloride (Section 7.6.6) and swirl until dissolved. Bring to 1 L with reagent
               water. To remove traces of Hg, purge the solution with Ar at a flow rate of
               approximately 2 L/min for 30 minutes in a fume hood. Store tightly capped.

       7.7.4   Bromate/bromide solution—In a fume hood, dissolve 2.78 g KBrO3 (Section 7.6.4) and
               11.90 g KBr (Section 7.6.5) in 500 mL reagent water. It is recommended that 0. IN
               potassium bromate/bromide solution (Alfa Chemicals, Catalogue #35593, or equivalent)
               be used. Prepare weekly or as needed.

       WARNING:  This process generates copious quantities of free halogens, which are released
       from the bottle. Add the KBrO3 slowly in a fume hood!

       7.7.5   Secondary Hg standard—Add approximately 0.5 L of reagent water and 5 mL bromate/
               bromide solution (Section 7.7.4) to a 1L Class A volumetric flask.  Add 0.100 mL stock
               mercury standard (Section 7.6.7) and dilute to 1.00 L with reagent water.  This  solution
               contains 1.00 (jg/mL (1.00 ppm) Hg. Transfer the solution to a fluoropolymer bottle and
               cap tightly.  This solution is considered stable until the NIST expiration date.

       7.7.6   Working Hg standard—Dilute 1.00 mL of the secondary Hg standard (Section 7.7.5) to
               100 mL in a Class A volumetric flask with reagent water containing 0.5% by volume
               bromate/bromide solution (Section 1.1 A). This solution contains 10.0 ng/mL Hg and
               should be replaced monthly.

       7.7.7   IPR and OPR solutions—Using the working Hg standard solution (Section 7.7.6),
               prepare IPR and OPR solutions at a concentration of 10 ng/L Hg in reagent water.

8.0   Sample Collection, Preservation, and Storage

8.1    Before samples are collected, consideration should be given  to the type  of data required (i.e.,
       dissolved or total) so that appropriate preservation and pretreatment steps can be taken. The pH
       of all aqueous samples must be tested immediately before aliquotting or direct analysis  to ensure
       the sample has been properly preserved,

8.2    Samples are collected into rigorously cleaned fluoropolymer bottles with fluoropolymer or
       fluoropolymer-lined caps. Borosilicate glass bottles may be  used if Hg  is the only target analyte.
       It is critical that the  bottles have tightly sealed caps to avoid  diffusion of atmospheric Hg through
       the threads (Reference 4). Polyethylene sample bottles must not be used (Reference 12).

12                                                                           Draft, January 2001

                                                                Draft Method 245.7 - do not cite or quote
8.3    Collect samples using procedures in the Sampling Guidance (Reference 10). These procedures
       are based on rigorous protocols for collection of samples for mercury (References 4 and 12).
       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. It may be
       necessary for the sampling team to use other means of sample collection if samples are
	found to be contaminated using the discrete sampler.	

8.4    Sample filtration—For dissolved Hg, samples and field blanks are filtered through a 0.45-um
       capsule filter (Section The Sampling Guidance gives the filtering procedures.

8.5    Preservation—Samples are preserved by adding 5 mL/L of pretested 12 N HC1.  Acid-preserved
       samples are stable for a period of 28 days.

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

       8.5.2   Samples that are acid-preserved may lose Hg to coagulated organic materials in the water
               or condensed on the walls (Reference 13).  The best approach is to add KBrO3/KBr
               directly to the sample bottle at least 24 hours before analysis. If other Hg species are to
               be analyzed, aliquots must be removed prior to addition of KBrO3/KBr. If KBrO3/KBr
               cannot be added directly to the sample bottle, the bottle must be shaken vigorously prior
               to  sub-sampling.

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

Note: Due to the potential for contamination, sample filtration and preservation should be performed in
a clean room in the laboratory. However, if circumstances prevent overnight shipment of samples,
samples should be filtered and preserved in a designated clean area in the field in accordance with the
procedures given in the Sampling Guidance (Reference 10).	

8.6    Storage—Sample bottles should be stored in clean (new) polyethylene bags until sample
       analysis. If properly preserved, samples can be held up to 28 days before analysis. Sample
       storage and holding time requirements are given at 40 CFR 136.3(e) Table EL

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 (MSD)  to assess
       bias (as recovery) and precision.  Laboratory performance is compared to performance criteria to
       determine  that the results of analyses meet the performance characteristics of the Method.
Draft, January 2001                                                                               13

Draft Method 245.7 - do not cite or quote
        9.1.1   Initial Demonstration of Performance—The laboratory shall make an initial
               demonstration of the ability to generate acceptable recovery and precision with this

       Method detection limit—To establish the ability to detect Hg, the laboratory
                       shall achieve an MDL that is less than or equal to the MDL listed in Section 1.5
                       or one-third the regulatory compliance limit, whichever is greater. The MDL
                       shall be determined according to the procedure at 40 CFR 136, appendix B using
                       the apparatus, reagents, and standards used in this Method. This MDL shall be
                       used for determination of laboratory capability, and should be determined when
                       a new operator begins work or whenever there is a change in instrument
                       hardware or  operating conditions,

       Initial demonstration of freedom from contamination—The analysis of ultra-
                       trace Hg concentrations require extreme care in minimizing the contamination
                       during sample preparation prior to and including the analysis. Given the
                       inherent skill and unique laboratory facilities required to control contamination
                       at these concentrations, it is required that the laboratory initially demonstrate
                       that the analytical system is free from contamination. This demonstration
                       consists of analysis of a blank along with the precision and recovery samples
                       (Section The level of mercury in the blank shall be less than the MDL
                       specified in Section 1.5 of this Method or, if the mercury measurements will be
                       used for compliance monitoring, less than one-third the regulatory compliance
                       limit, whichever is greater.  If mercury is found in a blank above these levels, the
                       source of contamination must  be identified and corrected prior to the analysis of

       Initial precision and recovery  (IPR)—To establish the ability to generate
                       acceptable precision and recovery, the laboratory shall perform the following

                     Analyze four  replicates of the IPR solution (10 ng/L, Section
                                      7.7.7) according to the procedure beginning in Section 11.

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

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

        9.1.2   Method modifications—In recognition of advances that are occurring in analytical
               technology, the laboratory is permitted certain options to improve results or lower the
               cost of measurements.  These options  include direct electronic data acquisition,
               calibration using gas-phase elemental  Hg standards, changes in the gas-liquid separator
               or dryer tube design, or changes in the detector (i.e., CVAAS) when less sensitivity is
14                                                                              Draft, January 2001

                                                                 Draft Method 245.7 - do not cite or quote
               acceptable or desired.  Changes in the principle of the determinative technique, such as
               the use of colorimetry, are not allowed. If a technique other than the CVAFS technique
               specified in this Method is used, that technique must have a specificity for mercury equal
               to or better than the specificity of the technique in this Method.

      Each time this Method is modified, the laboratory is required to repeat the
                      procedure in Section 9.1.1 to demonstrate that an MDL (40 CFR part 136,
                      appendix B) less than or equal to one-third the regulatory compliance level or
                      less than or equal to the MDL of this Method, whichever is greater, can be
                      achieved.  If the change will affect calibration, the instrument must be
                      recalibrated 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
                                     (c)     Analysis of blanks (Section 9.2)
                                     (d)     Matrix spike/matrix spike duplicate  (Section 9.5)
                                     (e)     Ongoing precision and recovery (Section 9.4)
                                     (f)     Quality control sample (Section 9.3)
                                     (g)     Method detection limit (Section

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

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

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

        9.2.1   Reagent blanks—The Hg concentration in reagent blanks must be determined on
               solutions of reagents by adding these reagents to reagent water in the same amounts at
               which they are added to a sample(s).

Draft, January 2001                                                                                15

Draft Method 245.7 - do not cite or quote
      Reagent blanks are required when the batch of reagents are prepared, with
                      verification in triplicate each month until a new batch of reagents is needed.
                      Reagent blank analysis also is required with each set of 20 samples.

      Add aliquots of KBrO3/KBr, NH2OH and SnCl2 to reagent water and analyze as
                      though analyzing a sample.  In order to evaluate the reagents as a potential
                      source of contamination, the amount of reagent added to the reagent blank(s)
                      must be the same as the amount of reagent added to the sample(s). Samples high
                      in organic materials may require additional KBrO3/KBr.

      The presence of Hg at a level greater than the MDL indicates a problem with the
                      reagent solution. The purging of reagent solutions, such as SnCl2 or NH2OH,
                      with mercury-free argon can reduce Hg to acceptable levels.  Because the
                      KBrO3/KBr solution cannot be purified, a new batch should be made from
                      different reagents and should be tested for Hg levels if the level of Hg in the
                      KBrO3/KBr solution is too high.

        9.2.2   Field blanks

      Analyze the field blank(s) shipped with each set of samples (samples collected
                      from the same site at the same time). Analyze the blank immediately before
                      analyzing the samples in the batch.

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

      Alternatively, if a sufficient number of field blanks (three minimum) are
                      analyzed to characterize the nature of the field blank, the  average concentration
                      plus two standard deviations must be less than the regulatory compliance limit or
                      less than one-half the level in the associated sample, whichever is greater. If this
                      criteria is not met, the results for the associated samples may not be reported or
                      otherwise used for regulatory compliance purposes.

      If contamination of the field blank(s) and associated samples is known or
                      suspected, the laboratory should communicate this to the  sampling team so that
                      the source of contamination can be identified and corrective measures taken
                      before the next sampling  event.

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

      Bottle blanks—After undergoing the cleaning procedures in this Method, bottles
                      should be subjected to conditions of use  to verify the effectiveness of the
                      cleaning procedures.  A representative set of sample bottles should be filled with
                      reagent water, acidified to pH <2, and allowed to stand for a minimum of 24 h.
                      Ideally, the time that the bottles are allowed to stand should be as close as
16                                                                             Draft, January 2001

                                                                Draft Method 245.7 - do not cite or Quote
                      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 a
                      bottle shows contamination at or above the level specified for the field blank
                      (Section the problem must be identified, the cleaning procedures
                      corrected or cleaning solutions changed, and all affected bottles recleaned.

      Sampler check blanks—Sampler check blanks are generated in the laboratory or
                      at the equipment cleaning facility by processing reagent water through the
                      sampling devices using the same procedures that are used in the field (see
                      Sampling Guidance). 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 carboy or other
                                     container with reagent water (Section 7.1) and processing the
                                     reagent water through the equipment using the same procedures
                                     that are used in the field (see Sampling Guidance, Reference
                                     10). Manual grab sample 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 a submersible pump or intake tubing into the water
                                     and pumping water into a sample container.

                   The sampler check blank must be analyzed using the procedures
                                     in this Method. If mercury or any potentially interfering
                                     substance is detected in the blank at or above the level specified
                                     for the field blank (Section, the source of contamination
                                     or interference must be identified, and the problem corrected.
                                     The equipment must be demonstrated to be free from mercury
                                     and interferences before the equipment may be used in the field.

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

9.3    Quality Control Sample (QCS)—The laboratory must obtain a QCS from a source different from
       the Hg source used to produce the standards used routinely in this Method (Section 7.7). The
       QCS should be analyzed as an independent check of system performance.

9.4    Ongoing precision and recovery (OPR)—To demonstrate that acceptable precision and recovery
       is being maintained within each analytical batch, the laboratory shall perform the following

       9.4.1   Analyze the OPR solution (10 ng/L, Section 7.7.7) prior to the analysis of each analytical
               batch according to the procedure beginning in Section 11. An  OPR also must be
               analyzed at the end of each analytical batch or at the end of each 12-hour shift,
               whichever occurs first.  Calculate the percent recovery for the OPR.

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

Draft, January 2001                                                                               17

Draft Method 245.7 - do not cite or quote
               range, the analytical process is not in control. Correct the problem and repeat the
               ongoing precision and recover}' test. All reported results must be associated with an
               OPR that meets the Table 2 performance criteria at the beginning and end of each batch.

        9.4.3   The laboratory should add results that pass the specification in Section 9.4.2 to IPR and
               previous OPR data and update QC charts to form a graphic representation of continued
               laboratory performance. The laboratory also should develop a statement of laboratory
               data quality by calculating the average percent recovery (Ra) and the standard deviation
               of the percent recovery (sr). Express the accuracy as a recovery interval from R., - 2sr to
               Ra + 2sr.  For example, if Ra = 95% and  sr = 5%, the accuracy is  85-105%.

9.5     Matrix spike (MS) and matrix spike duplicate (MSD) — To assess the performance of the Method
        on a given matrix, the laboratory must spike, in duplicate, a minimum of 10% of the samples
        collected from a given sampling site or, if for compliance monitoring, from a given discharge.
        Analysis of 20 samples would require two pairs of MS/MSD samples (four spiked samples total).

        9.5. 1   The concentration of the spike in the sample shall be determined as follows:

      If, as in compliance monitoring, the  concentration of Hg in the sample is being
                      checked against a regulatory compliance limit, the spike level shall be at that
                      limit or at 1-5 times the background concentration of the sample, whichever is

      If the concentration of Hg in a sample is not being checked against a limit, the
                      spike shall be at 1-5 times the background concentration or at the concentration
                      in the IPR/OPR solution (Section  7.7.7).

        9.5.2   To  determine the background concentration  (B), analyze one sample aliquot from each
               set  of 10 samples from each site or discharge according to the procedure in Section 1 1.
               If the expected background concentration  is known from previous experience or other
               knowledge, the spiking level may be established a priori.

               9.5.2. 1 If necessary, prepare a standard solution to produce an appropriate level in the
                      sample (Section 9.5.1).

       Spike two additional sample aliquots with the spiking solution and analyze  as
                      described in Section 1 1  to determine the concentration after spiking (A).

9.5.3   Calculate the percent recovery (R) in each aliquot using the following equation:

                                           Equation 1

                                         (R) =  100 Mi*>
                   A  =  Measured concentration of analyte after spiking
                   B  =  Measured concentration (background) of analyte before spiking
                   T  =  True concentration of the spike
                   R  =  Recovery (%)
18                                                                              Draft, January 2001

                                                                 Draft Method 245.7 - do not cite or quote
       9.5.4   Compare percent recovery (R) with the QC acceptance criteria in Table 2.

      If results of the MS/MSD are similar and fail the acceptance criteria, and
                      recovery for the OPR standard (Section 9.4) for the analytical batch is within the
                      acceptance criteria in Table 2, an interference is present and the results may not
                      be reported or otherwise used  for permitting or regulatory compliance purposes.
                      If the interference can be attributed to sampling, the site or discharge should be
                      resampled. If the interference can be attributed to a method deficiency, the
                      laboratory must modify the method, repeat the test required in Section 9.1.1, and
                      repeat analysis of the sample and MS/MSD. However, during the development
                      of Method 245.7, very few interferences have been noted in the determination of
                      Hg using this Method. (See Section 4 for information on interferences.)

      If the results of both the  MS/MSD and the OPR test fall outside the acceptance
                      criteria, the analytical system is judged to be out of control. Analyses must be
                      halted and the laboratory must identify and correct the problem and reanalyze all
                      samples in the sample batch.

       9.5.5   Relative percent difference between duplicates — Compute the relative percent difference
               (RPD) between the MS and MSD results according to the following equation using the
               concentrations found in the MS and MSD, Do not use the recoveries calculated in
               Section 9.5.3 for this calculation because the RPD is inflated when the background
               concentration is near the spike concentration.

                                           Equation 2

                                    RPD  , 200
                            Dl - concentration  of Hg in the MS sample
                            D2 = concentration  of Hg in the MSD sample
        9.5.6   The RPD for the MS/MSD pair must not exceed the acceptance criterion in Table 2. If
               the criterion is not met, the system is judged to be out of control.  The problem must be
               identified and corrected immediately, and the analytical batch reanalyzed.

        9.5.7   As part of the QC program for the laboratory, method precision and accuracy for samples
               should be assessed and records maintained. After analyzing five samples in which the
               recovery performance criteria in Table 2 have been met, compute the average percent
               recovery (RJ and the standard deviation of the percent recovery (sr). Express the
               accuracy assessment as a percent recovery interval from Ra - 2sr to Ra + 2sr. For example,
               if R.J = 90% and sr = 10% for five analyses, the accuracy interval is expressed as
               70-1 10%. Update the accuracy assessment regularly (e.g., after every five to ten new
               accuracy measurements).

9.6     The laboratory shall, on an ongoing basis, demonstrate through analysis of the quality control
        sample (QCS) and the ongoing precision and recovery (OPR) sample that the system is in
        control. Sections 9.3 and 9.4 describe these procedures, respectively.

9.7     The laboratory shall maintain records to define the quality of the data that are  generated.
        Sections 9.4.3 and 9.5.7 describe the  development of accuracy statements.

Draft, January 2001                                                                               19

Draft Method 245.7 - do not cite or quote
9.8    The determination of Hg in water is controlled by an analytical batch. An analytical batch is a
       set of samples oxidized with the same batch of reagents, and analyzed during the same 12-hour
       shift. A batch may be from 1 to as many as 20 samples. Each batch must be accompanied by at
       least one reagent blank (Section 9.2.1), an OPR sample, and a QCS.  In addition, there must be at
       least one MS and one MSD sample for every  10 samples (a frequency of 10%).

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

10.0 Calibration and Standardization

10.1   Establish the operating conditions necessary to purge Hg from the  gas-liquid separator and dryer
       tube and produce a clear detection peak. Further details for operating the analytical system are
       given in Section 11.  The entire system is calibrated using standards traceable to NIST standard
       reference material, as follows:

        10.1.1  Calibration

       The calibration must contain five or more non-zero standards. The lowest
                        calibration standard must be at the minimum level (ML) of 5 ng/L.

      Calibration standards are prepared by the addition of aliquots of the Hg
                        working standard solution (Section 7.7.6) to 50 mL conical vials containing
                        25-30 mL reagent water. To  each vial,  add 20-30 mL reagent water. Except
                        for the calibration blanks, dispense into each of  5 vials the following volumes
                        of working standard solution (Section 7.7.6): 25.0 uL, 50.0 ^L,  125.0 uL,
                        250.0 uL, 500.0 jiL.  Dilute each calibration standard and calibration blank to
                        the 50 mL vial mark with reagent water, cap vials and invert to mix. The
                        concentrations in these vials will be 5.0 ng/L,  10.0 ng/L, 25.0 ng/L, 50.0 ng/L
                        and 100.0 ng/L respectively.

      Remove caps and add 50 )iL of the hydroxylamine solution (Section 7.7.2).
                        Recap and invert once to mix and allow to stand until the yellow color
                        disappears. Remove all caps and place vials into the analysis rack.

      each calibration standard, determine the peak  height or area. Calculate the
                       calibration factor (CFJ for Hg in each of the five standards using the following
20                                                                            Draft, January 2001

                                                                 Draft Method 245.7 - do not cite or quote
                                           Equation 3

                                              '    (Q
                           AX  = peak height or area for Hg in standard
                           C  - concentration of standard analyzed (ng/L)
       Calculate the mean calibration factor (CFm), the standard deviation of the
                        calibration factor (SD), and the relative standard deviation (RSD) of the
                        calibration factor, where RSD = 100 x SD/CFm.

       If RSD < 15%, calculate the recovery for the lowest standard (5.0 ng/L) using
                        CFm.  If the RSD < 15% and the recovery of the lowest standard is in the range
                        of 75-125%, the calibration is acceptable and CFm may be used to calculate the
                        concentration of Hg in samples. If RSD >  15% or if the recovery of the lowest
                        standard is not in the range of 75-125%, recalibrate the analytical system and
                        repeat the test.

       Determine the concentration in at least two calibration blanks using the
                        equation 4 in Section 12.2. If either calibration blank has a concentration of
                        Hg > MDL, the analytical system and reagents should be checked for
                        contamination, the problem remediated, and the system recalibrated.

10.2    Ongoing precision and recovery (OPR)

        10.2.1  Perform the ongoing precision  and recovery test (Section 9.4) to verify calibration prior
               to and after analysis of samples in each analytical batch.

        10.2.2  The CF for the OPR must fall within ± 15% of CFm.

        10.2.3  If the CF is not within this range, calibration has not  been verified. In this event prepare
               and analyze a new IPR/OPR solution (Section 7.7.7)  and repeat the test (Section 10.2.1).
               If calibration is not verified (Section 10.2.2), recalibrate the system (Section 10.1).  All
               analyses must be run on a system that has met the calibration criteria (Section
               or on which calibration has been verified (Section 10.2).
Draft, January 2001                                                                                21

Draft Method 245.7 - do not cite or quote
11.0  Procedure
       NOTE: The following procedures for analysis of samples are provided as guidelines.
       Laboratories may find it necessary to optimize the procedures, such as drying time or
	gas flow rates, for the laboratory s specific instrumental set-up.   	

11.1   Sample Preparation

       11.1.1  The following procedure should be conducted within a class 100-clean hood, glove box/
               dry-box or glove bag to prevent contamination of reagents, samples, and equipment.
               Reagents should be stored within the clean hood, glove box or glove bag until use.

       11.1.2  Transfer samples to a class-100 clean fume hood or a disposable glove bag filled with
               argon.  Care should be taken to isolate samples from reagents and other solutions.  Label
               sample vials and corresponding lids to assure that vials and caps are not interchanged.

       11.1.3  For determination of dissolved mercury using samples not filtered or preserved during
               sampling or upon receipt by the laboratory, use a disposable syringe with an attached
               0.45 p.m filter. Remove the syringe plunger and pour the sample into the syringe to
               overflowing.  Replace the plunger and press the sample through the filter into the
               corresponding sample vial, filling to the 50 mL mark.
       11.1.4  Prepare the conical vials for sample digestion by adding 5 mL (1:1) HC1 solution
               (Section 7.7.1) and 1.0 mL KBrO3/KBr solution (Section 7.7.4). For clear water and
               filtered samples, add 1.0 mL of KBrO3/KBr solution; for brown or turbid samples, add
               2.0 mL of KBrO3/KBr solution.

       11.1.5  Transfer samples to corresponding vials and fill to the 50 mL mark. Immediately cap the
               vials and check each for a complete seal. Discard any leaking vials, and reprocess that
               sample. Allow samples to digest for at least 30 minutes. If the yellow color disappears
               because of consumption by organic matter or sulfides, more KBrO3/KBr solution should
               be added until a permanent yellow color is obtained.

       11.1.6  Some highly organic matrices, such as sewage effluent, will require high levels of
               KBrO3/KBr solution (i.e., 5 mL/100 mL of sample) and longer oxidation times or
               elevated temperatures (i.e., place sealed bottles in oven at 50 °C for 6 hours). The
               amount of reagent added to a sample must be the same as the amount added to the
               reagent blank to detect contamination in the reagents (see Section  The
               oxidation must be continued until it is complete. Complete oxidation can be determined
               either by observation of a permanent yellow color remaining in the sample or the use of
               starch iodide indicating paper to test for residual free oxidizer.

       11.1.7  After oxidation is complete, remove each vial cap and add 50 )j,L of hydroxylamine
               solution (Section 7.7.2) to eliminate excess bromine.  Recap and invert once to mix.
               Allow to stand for a few seconds. The yellow color will disappear, indicating the
               destruction of the KBrO3/KBr. Allow the sample to react for 5 minutes with periodic
               swirling to be sure that no traces  of halogens  remain. Remove all caps and place vials
               into the analysis rack.

11.2   Instrument set up and operation—The automated mercury analytical system is usually configured
       as shown in Figure 1.
22                                                                            Draft, January 2001

                                                                 Draft Method 245.7 - do not cite or quote
       11.2.1  Initiate operation of the atomic fluorescence instrument and data collection system.
               Follow the instrument manufacturer's recommendations for settings as the setting may
               vary between manufacturers and upgrades,  Typical instrument settings for the PSA
               Automated Mercury Analyzer are listed in Table 3,

       11.2.2  Adjust the gain on the detector to produce a peak height of 35% full scale for 50 ng/L

       11.2.3  Allow sufficient time for the system to equilibrate before initiating sample analysis.  It is
               recommended that this time be coordinated with the completion of sample oxidation and
               the addition of hydroxylamine hydrochloride solution (Section 11.1.7).

11.3   Sample analysis

       11.3.1  After instrument calibration and before sample analysis, at least two reagent blanks must
               be analyzed (Section  10.1.1,7).  If the reagent blank contains Hg at greater than MDL
               given in Section 1.5 of this Method, blank control has not been demonstrated, and the
               source of contamination must be identified and corrected.

       11.3.2  If an autosampler is used, set up a reagent water wash solution, or place a vial containing
               reagent water between each vial to be analyzed. The purpose of this solution is to wash
               mercury from the sample probe and the sample tubing.

       11.3.3  If the analytical system is operated manually, the sample line should be inserted into a
               reagent water wash solution between analysis of samples. Insert the sample tubing or
               sample probe at the time the "delay" cycle starts, and withdraw when the "analysis"
               cycle ends.  During the  "memory" cycle, return the sample tubing or probe to the wash
               solution. Repeat this operation until all samples have been analyzed.

       11.3.4  Any sample indicating a Hg concentration greater than 100 ug/L must be diluted and re-
               analyzed. Do not dilute the digested sample. Instead, dilute the  original sample with
               reagent water to bring the concentration within the calibration range.

12.0 Data Analysis and Calculations

12.1   Measure the peak height or area for each sample.

12.2   Calculate the concentration of Hg in ng/L (parts-per-trillion; ppt) in each sample according to the
       following equation:

                                          Equation 4

                                     [Hg] (ng/L)  , -A-  x -^-
                             As = peak height (or urea) for Hg in sample
                             CFm = mean calibration jactor (Section
                             Vsld - 50 ml  - mL reagent used in standards
                             ^sample  ~ ^0 "^ ~ '"^ ''eagent used in sample
Draft, January 2001                                                                               23

Draft Method 245.7 - do not cite or quote
12.3    To determine the concentration of Hg in the reagent blank, use the equation in Section 12.2 and
        substitute the peak height or area resulting from the reagent blank for As.  To determine the
        amount of Hg in the reagent blank that may have been introduced into a sample (CRB), correct the
        concentration of Hg in the reagent blank by the volume of KBrO3/KBr solution used for the
        particular sample (Section 11.1) using the following equation:

                                           Equation 5
                  Vgs - volume of KBrOj/KBr solution used in sample (Section 11.1.3)
                  VBKB = volume of KBrOj/KBr solution used in reagent  blank (Section
12 A    Reporting
        12.4.1  Report results for Hg at or above the ML, in ng/L to three significant figures. Report
               results for Hg in samples below the ML as <5.0 ng/L, or as required by the regulatory
               authority or in the permit. Report results for Hg in reagent blanks and field blanks at or
               above the ML, in ng/L to three significant figures. Report results for Hg in reagent
               blanks or field blanks below the ML but at or  above the MDL to two significant figures.
               Report results for Hg not detected in reagent blanks  as < 1.8 ng/L, or as required by the
               regulatory authority or in the permit.

        12.4.2  Report results for Hg in samples, reagent blanks and field blanks separately, unless
               otherwise requested or required by a regulatory authority or in a permit.  If blank
               correction is requested or required, subtract the concentration of Hg in either the reagent
               blank or the field blank from the concentration of Hg in the sample to obtain the net
               sample Hg concentration.

        12.4.3  Results from tests performed with an analytical system that is not in control must not be
               reported or otherwise used for permitting or regulatory compliance purposes but do not
               relieve a discharger or permittee of timely reporting.
24                                                                               Draft, January 2001

                                                               Draft Method 245.7 - do not cite or Quote
13.0  Method Performance

13.1    This method was tested in 3 laboratories using reagent water, freshwater, marine water, marsh
       water and effluent.  The quality control acceptance criteria listed in Table 2 and the MDL given
       in Section 1.5 and Table 1 were determined by data gathered in these studies.

13.2    Precision and recovery data for reagent water, freshwater, marine water, marsh water and
       effluent are given in Table 4.

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 waste
       generation. When wastes cannot be reduced feasibly 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 required. An overview of requirements can be found in Environmental
       Management Guide for Small Laboratories (EPA 233-B-98-001).

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

15.3    For further information on waste management, consult The Waste Management Manual for
       Laboratory Personnel and Less is Better: Laboratory Chemical Management for Waste
       Reduction, both available from the American Chemical Society's Department of Government
       Relations and Science Policy, 1155 16th Street NW, Washington, DC  20036.
Draft, January 2001                                                                            25

Draft Method 245.7 - do not cite or quote
16.0  References

1      Method 245.7, Revision 1.1: "Determination" of Ultra-Trace Level (ng Hg/L) Total Mercury in
       Water by Cold Vapor Atomic Fluorescence Spectrometry", U.S. EPA, National Exposure
       Research Laboratory, Research Triangle Park. Office of Research and Development, May 1996.

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

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

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

5      Bloom, N.S.; Fitzgerald, W.F. "Determination of Volatile Mercury Species at the Picogram
       Level by Low-Temperature Gas Chromatography with Cold-Vapor Atomic Fluorescence
       Detection," Anal. Chim. Acta. 1988,203, 151.

6      Method 1631: Mercury in Water by Oxidation, Purge and Trap, and CVAFS, U.S. EPA Office of
       Water, Office of Science and Technology, Engineering and Analysis Division, March 1998.

7      Guidance  on Establishing Trace Metal Clean Rooms in Existing Facilities, 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, January 1996, EPA 821-B-

8      Trace Metal Cleanroom, prepared by Research Triangle Institute for U.S. Environmental
       Protection Agency, 26 W. Martin Luther King Dr., Cincinnati,  OH 45268, RTI/6302/04-02 F.

9      Guidance  on the Documentation and Evaluation of Trace Metals Data Collected for Clean Water
       Act Compliance Monitoring, 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, July 1996. EPA 821-B-96-004.

10     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.

11     Correspondence from Nicolas Bloom, Frontier Geosciences, Inc. to Dale Rushneck, Interface,
       Inc., December 31, 1998.
12     Bloom, N.S. "Trace Metals & Ultra-Clean Sample Handling," Environ. Lab.  1995, 7, 20.

13     Bloom, N.S. "Influence of Analytical Conditions on the Observed 'Reactive Mercury,'
       Concentrations in Natural Fresh Waters." In Mercury as a Global Pollutant; Huckabee, J. and
       Watras, C.J., Eds.; Lewis Publishers, Ann Arbor, MI:  1994.
26                                                                          Draft, January 2001

                                                               Draft Method 245.7 - do not cite or quote
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.

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

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

18     "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.

17.0  Glossary

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

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

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

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

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

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

17.6   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 MDL by 3.18 and rounding  the result to the number nearest to (1, 2, or 5) x 10",
       where n is an integer.

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

17.8    Quality Control Sample (QCS)—A sample containing Hg at known concentrations. The QCS
       is obtained from a source external to the laboratory, or is prepared from a source of standards
Draft, January 2001                                                                             27

Draft Method 245.7 - do not cite or quote
        different from the source of calibration standards,  It is used as an independent check of
        instrument calibration.

17.9    Reagent Water—Water demonstrated to be free of mercury at the MDL of this Method. It is
        prepared from 18 MQ ultra-pure deionized water starting from a prepurified source. Reagent
        water is used to wash bottles, as trip and field blanks, and in the preparation of standards and

17.10   Regulatory Compliance Limit—A limit on the concentration or amount of a pollutant or
        contaminant specified in a nationwide standard, in a permit, or otherwise established by a
        regulatory authority.

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

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

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

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

18.0  Tables and  Figures

                                             Table 1

    Lowest Ambient Water Quality Criterion for Mercury and the Method Detection Limit and
                      Minimum Level of Quantitation for EPA Method 245.7
Mercury (Hg)
Lowest Nationwide
Water Quality
12 ng/L
Method Detection Limit (MDL)
and Minimum Level (ML)
1.8 ng/L
5.0 ng/L
1.       The lowest Nationwide criterion is 12 ng/L (40 CFR 131.36).
2.       Method detection limit (40 CFR 136, Appendix B)
3.       Minimum level of quantitation (sec Glossary)
Draft, January 2001

                                                             Draft Method 245.7 - do not cite or quote
                                          Table 2

        Quality Control Acceptance Criteria for Performance Tests in EPA Method 245.7
Mercury (Hg)
% Recovery
% Recovery
                                          Table 3

                          Instrument Control and Gas Flow Settings
Fluorescence Instrument
Delay Time
Rise Time
Analysis Time
Memory Time
Argon Gas Control
Gas Regulator
Carrier Flow
Drier Tube Flow
Sheath Flow
PSA Merlin Series AFS
Range of Settings
5 to 1 5 seconds
20 to 30 seconds
30 seconds
60 seconds
Range of Settings
20 to 30 psi.
2.5 to 3.5 L/minute
Draft, January 2001

Draft Method 245.7 - do not cite or quote
                                            Table 4

   Precision and Recovery for Reagent Water, Fresh Water, Marine Water, and Effluent Water
                                      Using Method 245.1
Drinking Water
Drinking / groundwater
Artificial Marine Water
Municipal Effluent
Marsh Water
(% RSD)
                *Mean percent recoveries and RSDs are based on expected Hg concentrations.
Draft, January 2001

                                                         Draft Method 245.7 - do not cite or quote
              Figure 1: Automated Mercury Fluorescence System
                                                     Liquid Waste
                                                     (Vent to Hood)
             Argon Gas
Draft, January 2001