EPA-821-R-05-001
February 2005
Method 245.7
Mercury in Water by Cold Vapor Atomic Fluorescence Spectrometry
Revision 2.0
February 2005
U.S. Environmental Protection Agency
Office of Water, Office of Science and Technology
Engineering and Analysis Division (4303)
Ariel Rios Building
1200 Pennsylvania Avenue, NW
Washington, DC 20460
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Method 245.7
Acknowledgments
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 CSC's Environmental Programs Group
and Interface, Inc.
Disclaimer
This method has been reviewed and approved for publication by the Statistics and Analytical Support
Branch within EPA's Engineering and Analysis Division. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use.
Questions concerning this method or its application should be addressed to:
W.A. Telliard
Statistics and Analytical Support Branch (4303T)
U.S. Environmental Protection Agency
Ariel Rios Building
1200 Pennsylvania Avenue, NW
Washington, DC 20460
Phone: 202/566-1061
Fax: 202/566-1053
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Method 245.7
Introduction
EPA Method 245.7, Mercury in Water by Cold Vapor Atomic Fluorescence Spectrometry, 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 version of the method specifically to 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.
Measurement of mercury by this method employs by cold-vapor atomic fluorescence spectrometry
(CVAFS), a brominating digestion, 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 Clean Water Act 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, one university laboratory, and an
interlaboratory validation study. 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 in reagent water among the laboratories in the interlaboratory study
was 1.8 ng/L.
In developing methods for determination of trace metals, EPA found that one of the greatest difficulties is
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:
EPA Sample Control Center (operated by CSC's Environmental Programs Group)
6101 Stevenson Avenue
Alexandria, VA 22304-3540
703/461-2100
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 must
not omit any quality control tests. The terms "shall" and "must" define procedures required for
producing reliable data. 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.
February 2005
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Method 245.7
Method 245.7
Mercury in Water by Cold Vapor Atomic Fluorescence Spectrometry
1.0 Scope and Application
1.1 Method 245.7 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 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 results from
single-laboratory and interlaboratory validation studies. The method contains procedures for
controlling contamination that are based on peer-reviewed, published procedures for the
determination of mercury in aqueous samples, ranging from marine waters to effluents
(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 (Reference 7). This sampling guidance is
recommended to preclude contamination during the sampling process.
1.3 The normal calibration range of this method is from 5 ng/L to 100 ng/L, and that range may be
extended by dilution of the sample.
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. Certain sections of this method contain
suggestions and other sections contain requirements to minimize contamination.
1.5 The method detection limit (MDL) and minimum level of quantitation (ML) using this procedure
usually are dependent on the level of interferences rather than instrumental limitations. The MDL
determined from single-laboratory and interlaboratory laboratory validation studies is 1.8 ng/L
and the ML has been established as 5.0 ng/L.
1.6 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 7-10).
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.
1.9 Any modification of this method, beyond those expressly permitted, shall be considered a major
modification subject to application and approval of alternate test procedures under 40 CFR 136.4
and 136.5.
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Method 245.7
1.10 This method should be used only by analysts experienced in the use of CVAFS techniques and
who are trained thoroughly in the sample handling and instrument techniques described in this
method. Each laboratory that uses this method must demonstrate the ability to generate
acceptable results using the procedures 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 10) 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 7).
2.2 For dissolved Hg, the sample is filtered through a 0.45-^m capsule filter prior to preservation.
2.3 The sample is preserved by adding 5 mL/L of pretested 12N HC1. If a sample also will be used
for the determination of methyl mercury, it should be preserved according to procedures in the
method that will be used for detection of methyl mercury.
2.4 Prior to analysis, all Hg in a sample is oxidized by a potassium bromate/potassium bromide
reagent.
2.5 After oxidation, the sample is sequentially pre-reduced 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 passing the sample through a gas/liquid separator and
purging with high purity argon gas (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
systems.
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-^m filter.
February 2005
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Method 245.7
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 (Section 17).
4.0 Contamination and Interferences
4.1 Preventing 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 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 11).
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.
4.3.1.1 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.
4.3.1.2 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.
4.3.1.3 Although contamination control is essential, personnel health and safety remain
the highest priority. The sampling guidance (Reference 7) 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.
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Method 245.7
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 equipped with
HEPA filtration and situated, ideally, in a clean room. Refer to EPA's Guidance on
Establishing Trace Metal Clean Rooms in Existing Facilities for more information
(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, free of materials that may contain metals, or
both.
4.3.7.1 Construction materials - Only fluoropolymer or glass containers must 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.
Polyethylene and/or polypropylene labware may be used for digestion and other
purposes because the time of sample exposure to these materials is relatively
short. All materials, regardless of construction, that will directly or indirectly
contact the sample must be known to be clean and free of Hg at the levels
specified in this method before proceeding.
4.3.7.2 Serialization - It is recommended that serial numbers be indelibly marked or
etched on each piece of reusable 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
detected.
4.3.7.3 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
February 2005
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Method 245.7
the likelihood of contamination must be made. Sampling must not proceed if it is
possible that the apparatus is contaminated. If the apparatus is contaminated, it
must be returned to the laboratory or cleaning facility for proper cleaning before
any sampling activity resumes.
4.3.8 Avoid sources of contamination - Avoid contamination by being aware of potential
sources and routes of contamination.
4.3.8.1 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 must 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.
4.3.8.2 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.
4.3.8.3 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).
4.3.8.4 Contamination by airborne particulate matter - Less obvious substances capable
of contaminating samples include airborne particles. Samples may be
contaminated by airborne dust, dirt, particles, or vapors from unfiltered air
supplies; nearby corroded or rusted pipes, wires, or other fixtures; or metal-
containing paint. Whenever possible, sample processing and analysis should
occur as far as possible from sources of airborne contamination.
4.3.8.5 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 9.2.1.3).
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 30
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 remove the brown color) and additional or more
concentrated SnCl2 should be added. To preclude loss of Hg, the additional SnCl2 should
be added in a closed vessel or analysis should proceed immediately. If samples
February 2005
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Method 245.7
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).
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).
4.4.4 Water vapor may collect in the fluorescence detector cell, resulting in a degradation of
the analytical signal or giving a false peak due to scattering of the excitation radiation.
The use of a membrane drying tube is required to reduce quenching and to remove any
water vapor from the transfer tubing that can contaminate the detector (Reference 1).
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 also is 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 13-16. The references and bibliography at the end of
Reference 16 are particularly comprehensive in dealing with the general subject of laboratory
safety.
5.3 Samples suspected to contain concentrations of Hg at ^ig/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.
6 February 2005
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Method 245.7
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,
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
5.3.8.1 Decontamination of personnel - Use mild soap with plenty of scrubbing action.
5.3.8.2 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 ^g per wipe
indicates acceptable cleanliness; anything higher warrants further cleaning. More than 10
l^g constitutes an acute hazard, requires prompt cleaning before further use of the
equipment or work space, and indicates that unacceptable work practices have been
employed.
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Method 245.7
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 glass, 125- to 1000-mL, with
fluoropolymer or fluoropolymer-lined cap.
6.1.1.1 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. The bottles may
be shipped to the sampling site containing dilute HC1 solution (e.g., 0.04%),
containing reagent water, or empty. See Section 6.2 for equipment needed for
bottle and glassware cleaning.
6.1.1.2 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.
6.1.1.3 Bottle blanks must be analyzed as described in Section 9.2.4 to verify the
effectiveness of the cleaning procedures.
6.1.1.4 As an alternative to cleaning by the laboratory, bottles may be purchased from a
commercial supplier and each lot certified to be clean. Bottles from the lot must
be tested as bottle blanks (Section 9.4.2) and demonstrated to be free of mercury
at the ML of this method. If mercury is present above this level in any bottle,
either the lot must be rejected or the bottles must be recleaned.
6.1.2 Filtration apparatus
6.1.2.1 Filter - 0.45-^m, 15-mm diameter capsule filter (Gelman Supor 12175, or
equivalent).
6.1.2.2 Peristaltic pump - 115-V AC., 12-V DC., 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).
6.1.2.3 Tubing - Styrene/ethylene/butylene/silicone (SEES) 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.
8 February 2005
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Method 245.7
After drying, the tubing is double-bagged in clear polyethylene bags, serialized
with a unique number, and stored until use.
6.2 Equipment for bottle and glassware cleaning
6.2.1 Vat, 100-200 L, high-density polyethylene (HOPE), half filled with 4N HC1 in reagent
water.
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 a Class-100 clean area, with high-flow reagent water (Section 7.1)
for rinsing.
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 either may be
purchased from a supplier or built in the laboratory from commercially available components.
6.3.1 Commercially available CVAFS - Tekran (Toronto, ON) Model 2500 CVAFS; Brooks-
Rand (Seattle, WA) Model III CVAFS; Leeman Labs (Hudson, NH) Hydra AF/Hydra AF
Gold Plus; PS Analytical (Kent, UK) Millennium Merlin Systems; or equivalent.
6.3.2 Custom-built CVAFS. Figure 1 shows the schematic diagram. The system consists of
the following:
6.3.2.1 Low-pressure 4-W mercury vapor lamp
6.3.2.2 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).
6.3.2.3 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).
6.3.2.4 Photometer and PMT power supply (Oriel Corp. or equivalent) to convert PMT
output (nanoamp) to millivolts.
6.3.2.5 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).
6.3.2.6 Flowmeter - With needle valve capable of stabilizing gas flow rate.
February 2005 9
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Method 245.7
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.
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. Forthe tin(II) solution: Watson-Marlow, Product Code 910, 0005-016, 0.5
mm ID, 1.6 mm wall thickness (w.t), or equivalent. Forthe system blank and sample
solutions: Watson-Marlow, Product Code 910, 0008-016, 0.8 mm ID, 1.6 mm w.t. or
equivalent.
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
[iL to 2500 [iL.
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 February 2005
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Method 245.7
7.0 Reagents and Standards
Note: The quantities of reagents and the preparation procedures in this section are for
illustrative purposes. Equivalent performance may be achievable using quantities of
reagents and procedures other than those suggested here. The laboratory is responsible
for demonstrating equivalent performance.
7.1 Reagent water - 18-MQ 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.
A source of air that 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. Gold-coated cloth filter: Soak a 2-m2 piece 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.
Caution: 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 possible.
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
recommended.
7.4 Hydrochloric acid - Concentrated, trace-metal purified reagent-grade HC1 containing less than 5
pg/mL Hg. The HC1 should be analyzed for Hg before use.
Note: In order to create bromine monochloride (BrCl) to fully oxidize substances in
samples and standards, an aliquot ofHCl solution and bromate/bromide solution
(Section 7.6.4) must be added to all samples and standards (see, e.g., Section 11.1.4).
7.5 Reagents
7.5.1 Hydroxylamine hydrochloride (NH2OH-HC1), CASRN 5470-11-1.
7.5.2 Mercuric chloride (HgCl2) CASRN 7487-94-7, 99.99% pure with assay.
7.5.3 Methyl mercury chloride (CH3HgCl), CASRN 115-09-3, 95% pure with assay.
7.5.4 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.
February 2005 11
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Method 245.7
7.5.5 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.
7.5.6 Stannous chloride (SnCl2-2H2O), CASRN 10025-69-1 - Assayed mercury level not
exceeding 0.05 ppm.
7.5.7 Stock mercury standard - NIST-certified 10,000 ppm aqueous Hg solution (NIST-3133).
This solution is stable at least until the NIST expiration date.
7.6 Reagent and Standards
7.6.1 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.
7.6.2 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.
7.6.3 Stannous chloride solution, 2% (w/v) in 10% (v/v) HC1 - Add 10 mL HC1 (Section 7.4)
to 400 mL of reagent water in a 1-L volumetric flask. To this solution, add 20.0 g
Stannous chloride (Section 7.5.6) and swirl until dissolved. Bring to 1 L with reagent
water. To remove traces of Hg, purge the solution with argon at a flow rate of
approximately 2 L/min for 30 minutes in a fume hood. Store tightly capped.
7.6.4 Bromate/bromide solution - In a fume hood, dissolve 2.78 g KBrO3 (Section 7.5.4) and
11.90 g KBr (Section 7.5.5) in 500 mL reagent water. Prepare weekly or as needed.
Note: Formation ofBrCl oxidizing agent is indicated by a pale yellow color
when KBr/KBrO3 solution contacts HCl in samples, standards, and blanks. This
color must persist throughout sample digestion, or additional reagent must be
added. (See e. g., Sections 11.1.5 - 11.1.6).
7.6.5 Secondary Hg standard - To approximately 0.5 L of reagent water (Section 7.1) in a
clean 1-L Class A volumetric flask, add 0.100 mL stock mercury standard (Section 7.5.7,
5 mL bromate/bromide solution (Section 7.6.4), and 2.5 mL of HCl solution (Section
7.6.1). Bring to 1.0 L with reagent water. This solution contains 1.00 ^g/rnL (1 ppm)
Hg. Transfer the solution to a glass or fluoropolymer bottle and cap tightly. This
solution is considered stable until the NIST expiration date.
7.6.6 Working Hg standard - To approximately 50 mL of reagent water (Section 7.1) in a
clean 100-mL volumetric flask, add 1.00 mL of the secondary Hg standard (Section
7.6.5), 0.5 mL of bromate/bromide solution (Section 7.6.4), and 2.5 mL of HCl solution
(Section 7.6.1). Bring to 100 mL with reagent water. This solution contains 10.0 ng/mL
Hg, and should be replaced monthly, or longer if extended stability is demonstrated.
7.6.7 IPR and OPR solution - To approximately 50 mL of reagent water (Section 7.1) in a
clean 100-mL volumetric flask, add 0.100 mL of the working Hg standard solution
(Section 7.6.6), 0.5 mL bromate/bromide solution (Section 7.6.4), and 2.5 mL of HCl
solution (Section 7.4). Bring to 100 mL with reagent water. This solution contains 10.0
ng/L (10 ppt) Hg. A more concentrated or dilute solution may be used for a
commensurately higher or lower working range.
12 February 2005
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Method 245.7
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. An
excess of KBr/KBrO3 should be confirmed either visually (presence of a yellow color) or with
starch iodide indicating paper, using a separate sample aliquot, prior to sample processing or
direct analysis to ensure the sample has been properly preserved.
8.2 Samples are collected into rigorously cleaned fluoropolymer bottles with fluoropolymer or
fluoropolymer-lined caps. 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).
8.3 Collect samples using procedures in the sampling guidance (Reference 7). 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 are filtered through a 0.45-^m capsule filter
(Section 6.1.2.1) in a mercury-free clean area prior to preservation. If the sample is filtered, it
must be accompanied by a blank that has been filtered under the same conditions. The sampling
guidance (Reference 7) gives the filtering procedures.
8.5 Preservation - Samples are preserved by adding 5 mL/L of pretested 12 N HC1. If a sample also
will be used for the determination of methyl mercury, it should be collected and preserved
according to procedures in the method that will be used for determination of methyl mercury
(e.g., HC1 or H2SO4 solution). 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 collected in
fluoropolymer or glass bottles and capped tightly. The samples must be acid-preserved
within 48 h of collection. Samples for dissolved Hg must be filtered before preservation.
8.5.2 Samples that are acid-preserved may lose Hg to coagulated organic materials in the water
or condensed on the bottle 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: Because of the potential for contamination, it is recommended that
filtration and preservation of samples be performed in the clean room in the
laboratory. However, if circumstances 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 Method 1669 (Reference 7). If
filtered in the field, samples ideally should be filtered into the sample bottle.
February 2005 13
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Method 245.7
8.6 Storage - Sample bottles should be stored in clean (new) polyethylene bags until analysis.
8.7 Sample storage, preservation, and holding time requirements also are given at 40 CFR 136.3(e)
Table II.
9.0 Quality Control
9.1 Each laboratory that uses this method is required to operate a formal quality assurance program
(Reference 14). The minimum requirements of this program consist of an initial demonstration of
laboratory capability, ongoing analysis of standards and blanks as a test of continued
performance, and the analysis of matrix spikes (MS) and matrix spike duplicates (MSB) to assess
accuracy and precision. Laboratory performance is compared to established performance criteria
to determine that the results of analyses meet the performance characteristics of the method.
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.
9.1.1.1 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 only, and should be determined when a
new operator begins work or whenever, in the judgement of the laboratory, a
change in instrument hardware or operating conditions would dictate
reevaluation of capability.
9.1.1.2 Initial demonstration of freedom from contamination - The analysis of low-level
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
9.1.1.3). The level of mercury in the blank shall be less than the ML 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
samples.
9.1.1.3 Initial precision and recovery (IPR) - To establish the ability to generate
acceptable precision and recovery, the laboratory shall perform the following
operations:
9.1.1.3.1 Analyze four replicates of the IPR solution (10 ng/L, Section 7.6.7)
according to the procedure beginning in Section 11.
14 February 2005
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Method 245.7
9.1.1.3.2 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.
9.1.1.3.3 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 9.1.1.3).
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
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.
9.1.2.1 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 CFRpart 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.
9.1.2.2 The laboratory is required to maintain records of modifications made to this
method. These records include the following, at a minimum:
9.1.2.2.1 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
9.1.2.2.2 A narrative stating the reason(s) for the modification(s)
9.1.2.2.3 Results from all quality control (QC) tests comparing the modified
method to this method, including the following:
(a) Calibration (Section 10)
(b) Initial precision and recovery (Section 9.1.1.3)
(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 9.1.1.1)
February 2005 15
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Method 245.7
9.1.2.2.4 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. Analysis of additional blanks is
recommended as necessary to pinpoint sources of contamination in, and external to, the
laboratory.
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.
9.2.1.1 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.
9.2.1.2 Analyze reagent water 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
solution.
9.2.1.3 The presence of Hg at a level greater than the ML indicates a problem with the
reagent solution. The purging of reagent solutions, such as SnCl2 orNH2OH,
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 - Field blanks are used to demonstrate that samples have not been
contaminated by the sample collection and transport activities.
9.2.2.1 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.
9.2.2.2 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.
16 February 2005
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Method 245.7
9.2.2.3 Alternatively, if a sufficient number of field blanks (three minimum) are
collected, if the average concentration (of the multiple field blanks) plus two
standard deviations is equal to or greater than the regulatory compliance limit, or
equal to or greater than one-half of the level in the associated sample, results for
associated samples may be the result of contamination and may not be reported
or otherwise used for regulatory compliance purposes.
9.2.2.4 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.
9.2.3.1 Equipment 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 Method). Therefore, the
"clean hands/dirty hands" technique used during field sampling should be
followed when preparing equipment blanks at the laboratory or cleaning facility
for low level mercury measurements. If grab samples are to be collected using
any ancillary equipment, e.g., an extension pole or a dipper, an equipment blank
is generated by submersing this equipment into the reagent water and analyzing
the resulting reagent water collected.
9.2.3.2 The equipment 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 9.2.2), 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.
9.2.4 Bottle blanks - Bottles must be subjected to conditions of use to verify the effectiveness
of the cleaning procedures. A representative set of sample bottles (Section 6.1.1) should
be filled with reagent water acidified to pH <2 and allowed to stand for a minimum of 24
hours. At least 5% of the bottles from a given lot should be tested, and the time that the
bottles are allowed to stand should be as close as possible to the actual time that the
sample will be in contact with the bottle. After standing, the water must be analyzed for
any signs of contamination. If a bottle shows contamination at or above the level
specified for the field blank (Section 9.2.2), the problem must be identified, the cleaning
procedures corrected or cleaning solutions changed, and all affected bottles re-cleaned.
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 (Sections 7.5 and 7.6).
The QCS should be analyzed as an independent check of system performance.
9.4 Ongoing precision and recovery (OPR) - To demonstrate that the analytical system is within the
performance criteria of this method and that acceptable precision and recovery is being
maintained within each analytical batch, the laboratory shall perform the following operations:
February 2005 17
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Method 245.7
9.4.1 Analyze the OPR solution (10 ng/L, Section 7.6.7) 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
range, the analytical process is not in control. Correct the problem and repeat the
ongoing precision and recovery 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 (RJ and the standard deviation
of the percent recovery (sr). Express the accuracy as a recovery interval from R,, - 2sr to
R, + 2sr. For example, if R, = 95% and sr = 5%, the accuracy is 85-105%.
9.5 Matrix spike (MS) and matrix spike duplicate (MSB) - 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:
9.5.1.1 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 (as determined
in Section 9.5.2), whichever is greater.
9.5.1.2 If the concentration of Hg in a sample is not being checked against a limit, the
spike shall be at 1-5 times the background concentration, or at 1-5 times the ML
in Table 1, whichever is greater.
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 11. 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).
9.5.2.2 Spike two additional sample aliquots with the spiking solution and analyze as
described in Section 11 to determine the concentration after spiking (A).
18 February 2005
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Method 245.7
9.5.3 Calculate the percent recovery (R) in each aliquot using the following equation:
R = 100
where:
A =
B =
T =
R =
measured concentration of the analyte after spiking
measured concentration (background) of the analyte before spiking
true concentration of the spike
recovery (%)
9.5.4 Compare the percent recovery (R) with the QC acceptance criteria in Table 2.
9.5.4.1 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, then 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. See Section 4 for information
on interferences.
9.5.4.2 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, and the results may
not be reported or used for permitting or regulatory compliance purposes. 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.
RPD = 200
D2)
where:
D] = 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, and the MS/MSD and corresponding samples reanalyzed.
9.5.7 As part of the QC program for the laboratory, method precision and recovery for samples
should be assessed and records maintained. After analyzing five samples in which the
February 2005
19
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Method 245.7
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 R, - 2sr to R,,+ 2sr. For example,
if Rj = 90% and sr = 10% for five analyses, the accuracy interval is expressed as
70-110%. Update the accuracy assessment regularly (e.g., after every five to ten new
accuracy measurements).
9.6 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.
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 MSB 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 Calibration - 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 The calibration must contain five or more non-zero standards. The lowest calibration
standard must be at, or below, the minimum level (ML) of 5 ng/L.
10.1.2 Calibration standards are prepared by the addition of aliquots of the Hg working standard
solution (Section 7.6.6) to 50-mL conical vials containing 25-30 mL reagent water. To
each vial, add 20-30 mL reagent water followed by 5 mL (1:1) HC1 (Section 7.6.1) and 1
mL KBr/KBrO3 solution (Section 7.6.4). Except for the calibration blanks, dispense into
each of 5 vials the following volumes of working standard solution (Section 7.6.6): 25.0
I^L, 50.0 |^L, 125.0 |^L, 250.0 |^L, 500.0 |^L. 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.
10.1.3 Cap all vials and allow the blanks and standards to oxidize for approximately 30 minutes.
20 February 2005
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Method 245.7
10.1.4 Remove caps and add 50 [iL of the hydroxylamine solution (Section 7.6.2) to each vial to
eliminate the excess bromine. Recap and invert the vials once to mix and allow to stand
until the yellow color disappears. Remove all caps and place vials into the analysis rack.
10.1.5 For each calibration standard, determine the peak height or area. Calculate the
calibration factor (CFX) for Hg in each of the five standards using the following equation:
where:
Ax = peak height (or area) for Hg in the standard
Cx = concentration of the standard analyzed in ng/L
10.1.6 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 = 100xSD/CFm.
10.1.7 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.
10.1.8 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 greater than the ML,
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 anew IPR/OPR solution (Section 7.6.7) 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 10.1.7) or
on which calibration has been verified (Section 10.2).
February 2005 21
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Method 245.7
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-^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 an appropriate volume of HC1
solution (Section 7.6.1) and KBrO3/KBr solution (Section 7.6.4) to each vial. For clear
water and filtered samples, add 0.25 mL of KBrO3/KBr solution; for brown or turbid
samples, add 0.5 mL of KBrO3/KBr solution.
Note: Formation of the BrCl oxidizing agent is indicated by a pale yellow color
when KBr/KBrO3 solution contacts HCl in samples, standards, and blanks. This
color must persist throughout sample digestion, or additional reagent must be
added. (See e. g., Sections 11.1.5 - 11.1.6).
11.1.5 Transfer samples to corresponding vials and fill to the 50-mL mark. Immediately cap the
vials, invert, and check each for a complete seal. Discard any leaking vials, and
reprocess those samples. 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
and HCl 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 and HCl solution (i.e., 5 mL/100 mL of sample) and longer oxidation times
or elevated temperatures (i.e., place sealed bottles in an oven or a water bath at 50 °C for
6 hours). The amount of reagent added to the reagent blank must be the same as the
amount added to the sample (see Section 9.2.1.2) and therefore separate reagent blanks
may be required for such highly organic matrices. 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 |^L of hydroxylamine
solution (Section 7.6.2) 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
22 February 2005
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Method 245.7
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.
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 Hg.
11.2.3 Allow sufficient time for the system to equilibrate before beginning 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 10.1.7). If the reagent blank contains Hg at greater than the MDL
listed 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 ng/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.
February 2005 23
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Method 245.7
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:
[Hg] (ng/L) =
IB sample
where:
s = peak height (or area) for Hg in the sample
CFm = mean calibration factor (Section 10.1.6)
Vstd = volume (mL) of reagent water used to prepare the standard minus the volume (mL) of
reagent used in the standard (Section 10. 1.2)
Vsampie = volume (mL) of sample minus the volume (mL) of reagent used in the sample (Section
11.1.4)
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 (C^), correct the
concentration of Hg in the reagent blank for the volume of KBrO3/KBr solution used for the
particular sample (Section 11.1) using the following equation:
where:
VBS = volume of KBrO3/KBr solution used in the sample (Section 11.1.4)
VERB = volume of KBrO3/KBr solution used in the reagent blank (Section 9.2.1.2)
12.4 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 or field 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. 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, and report the corrected result in addition to reporting the
separate sample, field blank, and reagent blank results.
24 February 2005
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Method 245.7
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 reporting timely results.
13.0 Method Performance
13.1 This method was tested in three laboratories using reagent water, freshwater, marine water, marsh
water and effluent, and in an interlaboratory validation study (Reference 19) involving eight
laboratories using reagent water, marine water, freshwater, and effluent. The quality control
acceptance criteria listed in Table 2 and the MDL given in Section 1.5 and Table 1 were
determined from data gathered in these studies.
13.2 Precision and recovery data for reagent water, freshwater, marine water, and effluents 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 feasiblely 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
February 2005 25
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Method 245.7
Reduction, both available from the American Chemical Society's Department of Government
Relations and Science Policy, 1155 16th Street NW, Washington, DC 20036.
16.0 References
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,
15, 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. Ada. 1988, 208, 151.
6. Method 163 IE: 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, September
2002.
7. 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.
8. 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-
96-001.
9. 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.
10. 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.
11. Bloom, N.S. "Ultra-Clean Sampling, Storage, and Analytical Strategies for the Accurate
Determination of Trace Metals in Natural Waters." Proceeding of the 16th Annual EPA
Conference on the Analysis of Pollutants in the Environment, Norfolk, VA, May 5, 1993. EPA
821-R-94-001.
12. Bloom, N.S. "Trace Metals & Ultra-Clean Sample Handling," Environ. Lab. 1995, 7, 20.
26 February 2005
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Method 245.7
13. "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.
14. "OSHA Safety and Health Standards, General Industry," OSHA 2206, 29 CFR 1910.
15. "Safety in Academic Chemistry Laboratories," ACS Committee on Chemical Safety, 1979.
16. "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. 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.
18. "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.
19. Results of the Interlaboratory Validation Study of EPA Method 245.7, US Environmental
Protection Agency, March 2002.
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 Equipment Blank - Reagent water that has been processed through the sampling device at a
laboratory or other equipment cleaning facility prior to shipment of the sampling equipment to
the sampling site. The equipment blank is used to demonstrate that the sampling equipment is
free from contamination prior to use. Where appropriate, the "clean hands/dirty hands" technique
used during field sampling should be followed when preparing equipment blanks at the laboratory
or cleaning facility.
17.4 Field Blank - Reagent water that has been transported to the sampling site and exposed to the
same equipment and operations as a sample at the sampling site. The field blank is used to
demonstrate that the sample has not been contaminated by the sampling and sample transport
systems.
17.5 Matrix Spike (MS) and Matrix Spike Duplicate (MSD) - Aliquots of an environmental sample
to which known quantities of the analyte(s) of interest is added in the laboratory. The MS and
MSD are analyzed exactly like a sample. Their purpose is to quantify the bias and precision
caused by the sample matrix. The background concentrations of the analytes in the sample matrix
February 2005 27
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Method 245.7
must be determined in a separate aliquot and the measured values in the MS and MSB corrected
for these background concentrations.
17.6 May - This action, activity, or procedural step is allowed but not required.
17.7 May not - This action, activity, or procedural step is prohibited.
17.8 Minimum Level (ML) - The lowest level at which the entire analytical system must give a
recognizable signal and acceptable calibration point for the analyte. It is equivalent to the
concentration of the lowest calibration standard, assuming that all method-specified sample
weights, volumes, and cleanup procedures have been employed.
17.9 Must - This action, activity, or procedural step is required.
17.10 Quality Control Sample (QCS) - A sample containing Hg at known concentrations. The QCS is
obtained from a source external to the laboratory, or is prepared from a source of standards
different from the source of the calibration standards. It is used as an independent check of
instrument calibration.
17.11 Reagent Blank - Reagent blanks are used to determine the concentration of mercury in the
reagent that are used to prepare and analyze the samples. In this method, reagent blanks are
required when each batch of reagents are prepared (with verification in triplicate each month),
and with each set of 20 samples.
17.12 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
reagents.
17.13 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.
17.14 Shall - This action, activity, or procedure is required.
17.15 Should - This action, activity, or procedure is suggested, but not required.
17.16 Stock Solution - A solution containing an analyte that is prepared from a reference material
traceable to EPA, NIST, or a source that will attest to the purity and authenticity of the reference
material.
28 February 2005
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Method 245.7
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 Water Quality Criterion1
1.3 ng/L
Method Detection Limit 2
1.8 ng/L
Minimum Level 3
5.0 ng/L
1 The lowest water quality criterion is for the Great Lakes System (Table 4, 40 CFR 132). The lowest criterion that is
applicable nationwide (e.g., outside of the Great Lakes) is 12 ng/L (40 CFR 131.36).
2 Method detection limit (MDL 40 CFR 136, Appendix B)
3 Minimum level (ML) of quantitation (see Glossary)
Table 2
Quality Control Acceptance Criteria for Performance Tests
Performance Test
Initial Precision and Recovery (IPR)
Ongoing Precision and Recovery (OPR)
Matrix Spike/Matrix Spike Duplicate (MS/MSD)
Acceptance Criterion
Recovery (%)
78 - 108
76-113
63-111
RSD (%)
16
—
—
RPD (%)
—
—
18
Table 3
Example Fluorescence Instrument and Gas Flow Settings
Instrument Parameter
Delay Time
Rise Time
Analysis Time
Memory Time
Argon Gas Control
Gas Regulator
Carrier Flow
Drier Tube Flow
Sheath Flow
Example Range of Settings PSA Merlin Series AFS
5 to 15 seconds
20 to 30 seconds
30 seconds
60 seconds
Range of Settings
20 to 30 psi
150 to 450 mL/minute
2.5to3.5L/minute
150 to 250 mL/minute
February 2005
29
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Method 245.7
Table 4
Precision and Recovery for Reagent Water, Fresh Water, Marine Water, and Effluent
Matrix
Reagent Water
Marine Water (Filtered)
Marine Water (Unfiltered)
Freshwater (Filtered)
Municipal Effluent (Filtered)
Municipal Effluent (Unfiltered)
Industrial Effluent (Filtered)
Industrial Effluent (Unfiltered)
Mean Recovery (%)
87.6
86.5
84.6
70.5
87.0
79.9
64.6
57.1
Precision (% RSD)
17.2
20.1
12.9
27.4
25.2
24.0
30.3
28.7
Mean recoveries and RSDs are based on expected Hg concentrations in blind duplicate samples analyzed by
laboratories during EPA's interlaboratory validation study (Reference 19).
Figure 1: Automated Mercury Fluorescence System
Peristaltic Valve
Pump Box
Data
Acquisition
Flourescence
Detector
Carbon
Filter
Gas/
Liquid
Separator
Liquid Waste
Collection
(Vent to Hood)
Argon Gas
***, — ff •
Ha+2
L Dryer \
"f 1
Vent
to
Hood
Sheath
30
February 2005
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