SEPA
Method 1631: Mercury in Water by
Oxidation, Purge and Trap, and Cold
Vapor Atomic Fluorescence
Spectrometry
) Printed on Recycled Paper
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Method 1631
Acknowledgments
This method was prepared under the direction of William A. Telliard of the Engineering and Analysis
Division (HAD) within the U.S. Environmental Agency's (EPA's) Office of Science and Technology
COST) The method was prepared by Nicholas Bloom of Frontier GeoSciences under EPA Contract
68-C3-0337 with the DynCorp Environmental Programs Division. Additional assistance in preparing
the method was provided by Interface, Inc.
Disclaimer
This sampling method has been reviewed and approved for publication by the Analytical Methods
Staff within the Engineering and Analysis Division of the U.S. Environmental Protection Agency.
Mention of trade names or commercial products does not constitute endorsement or recommendation
for use.
Questions concerning this method or its application should be addressed to:
W.A. Telliard
Engineering and Analysis Division (4303)
U.S. Environmental Protection Agency
401 M Street SW
Washington, DC 20460
Phone: 202/260-7134
Fax: 202/260-7185
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Method 1631
Introduction
This analytical method supports water quality monitoring programs authorized under the Clean Water
Act Section 304(a) of the Clean Water Act requires EPA to publish water quality criteria that reflect
the latest scientific knowledge concerning the physical fate (e.g., concentration and dispersal) of
pollutants, the effects of pollutants on ecological and human health, and the effect of pollutants on
biological community diversity, productivity, and stability.
Section 303 of the Clean Water Act requires states to set a water quality standard for each body of
water within its boundaries. A state water quality standard consists of a designated use or uses of a
waterbody or a segment of a waterbody, the water quality criteria that are necessary to protect the
designated use or uses, and an antidegradation policy. These water quality standards serve two
purposes: (1) they establish the water quality goals for a specific waterbody, and (2) they are the basis
for establishing water quality-based treatment controls and strategies beyond the technology-based
controls required by Sections 301(b) .and 306 of the Clean Water Act.
In defining water quality standards, the state may use narrative criteria, numeric criteria or both
However, the 1987 amendments to the Clean Water Act required states to adopt numeric criteria for
toxic pollutants (designated in Section 307(a) of the Act) based on EPA Section 304(a) criteria or
other scientific data, when the discharge or presence of those toxic pollutants could reasonably be
expected to interfere with designated uses.
In some cases, these water quality criteria are as much as 280 times lower than those achievable using
existing EPA methods and required to support technology-based permits. Therefore, EPA developed
new sampling and analysis methods to specifically address state needs for measuring toxic metals at
water quality criteria levels, when such measurements are necessary to protect designated uses in state
water quality standards. The latest criteria published by EPA are those listed in the National Toxics
Rule (57 FR 60848) and the Stay of Federal Water Quality Criteria for Metals (60 FR 22228) These
rules include water quality criteria for 13 metals, and it is these criteria on which the new sampling
and analysis methods are based. Method 1631 was specifically developed to provide reliable
measurements of mercury at EPA WQC levels.
In developing these methods, EPA found that one of the greatest difficulties in measuring pollutants at
these levels was precluding sample contamination during collection, transport, and analysis The
degree of difficulty, however, is highly dependent on the metal and site-specific conditions This
analytical method, therefore, is designed to provide the level of protection necessary to preclude
contamination in nearly all situations. It is also designed to provide the procedures necessary to
produce reliable results at the lowest possible water quality criteria published by EPA. In recognition
of die variety of situations to which this method may be applied, and in recognition of continuing
technological advances, the method is performance based. Alternative procedures may be used as 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
11209 Kenwood Road
Cincinnati, OH 45242
513/489-8190
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Method 1631
Note: This method is intended to be performance based, and the laboratory is permitted to
omit "any step or modify any procedure provided that all performance requirements set forth in
this method are met. The laboratory is not allowed to omit any quality control analyses. The
terms "must," "may," and "should" are included throughout this method and are intended to
illustrate the' importance of the procedures in producing verifiable data at water quality criteria
levels. The term "must" is used to indicate the steps that are critical to production of reliable
results; however, these procedures may be modified or omitted if the laboratory can
demonstrate data quality is not affected.
iv
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Method 1631
Total Mercury in Water by Oxidation, Purge and Trap
and CVAFS
1.0 Scope and Application
1.1
1.2
1.3
1.4
1.5
1.6
This method is for determination of total mercury (Hg) in filtered and unfiltered water by
oxidation, purge and trap, desorption, and cold-vapor atomic fluorescence detection. This
method is for use in EPA's data gathering and monitoring programs associated with the Clean
Water Act, the Resource Conservation and Recovery Act, the Comprehensive Environmental
Response, Compensation and Liability Act, and the Safe Drinking Water Act. The method is
based on a contractor-developed method (Reference 1) and on peer-reviewed, published
procedures for the determination of mercury and in aqueous samples, ranging from sea water
to sewage effluent (References 2-5).
This method is accompanied by Method 1669: Sampling Ambient Water for Determination of
Trace Metals at EPA Water Quality Criteria Levels (Sampling Method). The Sampling
Method is necessary to ensure that contamination will not compromise trace metals
determinations during the sampling process.
This method is designed for measurement of total Hg in the range of 0.2-100 ng/L and may
be extended to higher levels by selection of a smaller sample size. This method is not
intended for determination of metals at concentrations normally found in treated and untreated
discharges from industrial facilities. Existing regulations (40 CFR Parts 400-500) typically
limit concentrations in industrial discharges to the part-per-billion (ppb) range, whereas
ambient mercury concentrations are normally in the low part-per-trillion (ppt) range.
The ease of contaminating ambient water samples with the metal(s) of interest and interfering
substances cannot be overemphasized. This method includes suggestions for improvements in
facilities and analytical techniques that should maximize the ability of the laboratory to make
reliable trace metals determinations and minimize contamination. Section 4.0 gives these
suggestions.
The detection limits and quantitation levels hi this method are usually dependent on the level
of background elements rather than instrumental limitations. The method detection limit
(MDL; 40 CFR 136, Appendix B) for total mercury has been estimated to be 0.05 ng/L when
no background elements or interferences are present. The minimum level (ML) has been
established as 0.2 ng/L.
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
Draft, January 1996
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Method 1631
not used in this method because they lack an exact definition. However, the information
provided hi this method is consistent with the summary guidance on clean and ultraclean
techniques.
1.7 This method follows the EPA Environmental Methods Management Council's "Format for
Method Documentation."
1 8 This method is "performance based." The analyst is permitted to modify the method to
overcome interferences or lower the cost of measurements if all performance criteria are met.
Section 9.1.2 gives the requirements for establishing method equivalency.
1 9 Any modification of this method, beyond those expressly permitted, shall be considered a
major modification subject to application and approval of alternate test procedures under 40
CFR 136.4 and 136.5.
1 10 This method should be used only by analysts who are experienced in the use of CVAF
' ' analysis and who are thoroughly trained hi the sample handling and instrumental techniques
described in this method. Each analyst who uses this method must demonstrate the ability to
generate acceptable results using the procedure hi Section 9.2.
1 11 This method is accompanied by a data verification and validation guidance document,
Guidance on the Documentation and Evaluation of Trace Metals Data Collected for CWA
Compliance Monitoring. Data users should state data quality objectives (DQOs) required for a
project before this method is used.
2.0 Summary of Method
21 A 100-2000 mL sample is collected directly into specially cleaned, pretested, fiuoropolymer
botfle(s) using sample handling techniques specially designed for collection of mercury at trace
levels (Reference 6).
2.2 The sample is either field- or laboratory-preserved by the addition of 5 mL of pretested 12 N
HC1 per liter of sample, depending on the time between sample collection and arrival at the
laboratory.
2 3 Sample preparation and analysis are conducted laboratory facilities specially designed for
determination of mercury at 0.2-100 ng/L concentration. At this facility, a 100-mL sample
aliquot is placed hi a specially designed purge vessel.
2.4 Before analysis, 0.2 N BrCl solution is added to oxidize all Hg compounds to Hg(H).
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Method 1631
2.5
2.6
2.7
2.8
After oxidation, the sample is sequentially prereduced with NH2OH-HC1 to destroy the free
halogens, and then reduced with SnCl^ to convert Hg(II) to volatile Hg(0).
The Hg(0) is separated from solution by purging wira nitrogen onto a gold-coated sand trap.
The trapped Hg is thermally desorbed from the gold trap into an inert gas stream that carries
the released Hg(0) into the cell of a cold-vapor atomic fluorescence spectrometer (CVAFS) for
detection.
Quality is ensured through calibration and testing of the oxidation, purging, and detection
systems.
3.0 Definitions
3.1 -
3.2
4.1
4.2
Total mercury as defined by this method means all BrCl-oxidizable mercury forms and species
found in aqueous solution. This includes but is not limited to Hg(n), Hg(0), strongly
organocomplexed Hg(n) compounds, adsorbed paniculate Hg, and several tested covalently
bound organomercurials (i.e., CH3HgCl, (CH3)2Hg, and C6H5HgOOCCH3). The recovery of
Hg bound within microbial cells may require the additional step of UV photo-oxidation In
this context, "total" mercury refers to the forms and species of mercury, not to the total
recoverable or dissolved fraction normally determined in an unfiltered or filtered sample
respectively. In this method, the total recoverable fraction will be referred to as "total
recoverable" or "unfiltered."
Definitions of other terms used in this method are given in the glossary at the end of the
method.
4.0 Contamination and Interferences
Preventing ambient water samples from becoming contaminated during the sampling and
analytical process constitutes one of the greatest difficulties encountered in trace metals
determinations. Over the last two decades, marine chemists have come to recognize that much
or the historical data on the concentrations of dissolved trace metals in seawater are
erroneously high because the concentrations reflect contamination from sampling and analysis
rather than ambient levels. Therefore, it is imperative that extreme care be taken to avoid
contamination when collecting and analyzing ambient water samples for trace metals.
Samples may become contaminated by numerous routes. Potential sources of trace metals
contamination during sampling include: metallic or metal-containing labware (e.g talc gloves
that contain high levels of zinc), containers, sampling equipment, reagents, and reagent water-
improperly cleaned and stored equipment, labware, and reagents; and atmospheric inputs such
as dirt and dust. Even human contact can be a source of trace metals contamination For
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Method 1631
example it has been demonstrated that dental work (e.g., mercury amalgam fillings) in me
mouths of laboratory personnel can contaminate samples that are directly exposed to exhalation
(Reference 5).
4.3 Contamination Control
431 Philosophy—The philosophy behind contamination control is to ensure that any object
or substance that contacts the sample is metal free and free from any material that may
contain metals.
4.3.1.1 The integrity of the results produced cannot be compromised by contamination
of samples. This method and the Sampling Method give requirements and
suggestions for control of sample contamination.
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 Method and Section 5 of this method give
requirements and suggestions for personnel safety.
432 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.
433 Use a clean environment—The ideal environment for processing samples is a class 100
clean room (Section 6.1.1). If a clean room is not available, all sample preparation
should be performed in a class 100 clean bench or a nonmetal glove box fed by
mercury- and particle-free air or nitrogen. Digestions should be performed in a
nonmetal fume hood situated, ideally, in the clean room.
4.3.4 Minimize exposure—The Apparatus that will contact samples, blanks, or standard
solutions should be opened or exposed only in a clean room, clean bench, or glove
box so that exposure to an uncontrolled atmosphere is minimized. When not being
used, the Apparatus should be covered with clean plastic wrap, stored hi the clean
bench or hi a plastic box or glove box, or bagged in clean zip-type bags. Miriimizing
the time between cleaning and use will also minimize contamination.
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Method 1631
4.3.5
4.3.6
4.3.7
4.3.8
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.
Wear gloves—Sampling personnel must wear clean, nontalc gloves (Section 697)
during all operations involving handling of the Apparatus, samples, and blanks 'only
cean 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.
Use metal-free Apparatus—All Apparatus used for determination of metals at ambient
water quality criteria levels must be nonmetallic, free of material that may contain
metals, or both.
4.3,7.1 Construction materials—Only fluoropolymer containers should be used for
samples that will be analyzed for mercury because mercury vapors can diffuse
in or out of the other materials, resulting either in contamination or low-biased
results. 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 metal free before proceeding.
4.3.7.2 Serialization—It is recommended that serial numbers be indelibly marked or
etched on each piece of Apparatus so that contamination can be traced, and
logbooks should be maintained to track the sample from the container through
the labware to injection into the instrument. It may be useful to dedicate
separate sets of labware to different sample types; e.g., receiving waters vs.
effluents. However, the Apparatus used for processing blanks and standards
must be mixed with the Apparatus used to process samples so that
contamination of all labware can be detected.
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 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
facihty for proper cleaning before any sampling activity resumes.
Avoid sources of contamination—Avoid contamination by being aware of potential
sources and routes of contamination.
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Method 1631
4.3.8.1 Contamination by carryover—Contamination may occur when a sample
containing low concentrations of metals is processed immediately after a
sample containing relatively high concentrations of these metals. To reduce
carryover, the sample introduction system may be rinsed between samples with
dilute acid and reagent water. When an unusually concentrated sample is
encountered, it is followed by analysis of a laboratory blank to check for
carryover. Samples known or suspected to contain the lowest concentration of
metals should be analyzed first followed lay samples containing higher levels.
4382 Contamination by samples—Significant laboratory or instrument contamination
may result when untreated effluents, in-process waters, landfill leachates, and
other samples containing high concentrations of inorganic substances are
processed and analyzed. This method is not intended for application to these
samples, and samples containing high concentrations should not be permitted
into the clean room and laboratory dedicated for processing trace metals
samples.
4383 Contamination by indirect contact—Apparatus that may not directly come in
contact with the samples may still be a source of contamination. For example,
clean tubing placed in a dirty plastic bag may pick up contamination from the
bag and subsequently transfer the contamination to the sample. Therefore, it is
imperative that every piece of the Apparatus that is directly or indirectly used
in the collection, processing, and analysis of ambient water samples be cleaned
as specified in Section 11.
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.
4.4 Interferences
4.4.1 Because all forms of Hg are oxidized in the BrCl oxidation step, there are no observed
interferences with this method.
4.4.2 The potential exists for destruction of the gold trap if it is exposed to free halogens or
if the trap is overheated (> 500°C).
443 Water vapor may collect in the gold trap and subsequently condense in the
fluorescence cell upon desorption, giving a false peak due to scattering of the
excitation radiation. Condensation can be avoided by predrying the gold trap, and by
discarding those traps that tend to absorb large quantities of water vapor.
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Method 1631
4.4.4
The fluorescence intensity is susceptible to the presence of foreign species in the
carrier gas, which may cause "quenching" of the excited Hg atoms. The dual-trap
technique in this method eliminates some quenching due to impurities in the carrier
gas, but it remains the analyst's responsibility to ensure high-purity inert carrier gas
and a leak-free analytical train.
5.0 Safety
5.1
5.2
5.3
The toxicity or carcinogemcity 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.
5.5.1.1 Chronic mercury exposure may cause kidney damage, muscle tremors, spasms,
personality changes, depression, irritability and nervousness. Organomercurials
may cause permanent brain damage. Because of the available lexicological
and physical properties of the Hg, pure standards should be handled only by
highly trained personnel thoroughly familiar with handling and cautionary
procedures and the associated risks.
5.5.1.2 It is recommended that the laboratory purchase a dilute standard solution of the
Hg in this method. If primary solutions are prepared, they shall be prepared in
a hood, and a NIOSH/MESA-approved toxic gas respirator shall be worn when
high concentrations are handled.
This method does not address all safety issues associated with its use. The laboratory is
responsible for maintaining a current awareness file of OSHA regulations for the safe handling
J,?™ C£dS specified "* *»* method- A reference file of material safety data sheets
(MSDSs) should also be made available to all personnel involved in these analyses It is also
suggested that the laboratory perform personal hygiene monitoring of each analyst who uses
this method and that the results of this monitoring be made available to the analyst
Additional information on laboratory safety can be found in References 7-10. The references
and bibliography at the end of Reference 10 are particularly comprehensive in dealing with the
general subject of laboratory safety.
Samples suspected to contain high concentrations of Hg are handled using essentially the same
techniques employed in handling radioactive or infectious materials. Well-ventilated
controlled access laboratories are required. Assistance in evaluating the health hazards of
particular laboratory conditions may be obtained from certain consulting laboratories and from
State Departments of Health or Labor, many of which have an industrial health service. Each
laboratory must develop a strict safety program for handling Hg.
5.3.1
Facility—When samples known or suspected of containing high concentrations of
mercury are handled, all operations (including removal of samples from sample
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Method 1631
containers, weighing, transferring, and mixing) should be performed in a glove box
demonstrated to be leaktight or in a fume hood demonstrated to have adequate airflow.
Gross losses to the laboratory ventilation system must not be allowed. Handling of the
dilute solutions normally used in analytical and animal work presents no inhalation-
hazards except in an accident.
5.3.2 Protective equipment—Disposable plastic gloves, apron or lab coat, safety glasses or
mask, and a glove box or fume hood adequate for radioactive work should be used. .
During analytical operations that may give rise to aerosols or dusts, personnel should
wear respirators equipped with activated carbon filters.
5.3.3 Training—Workers must be trained in the proper method of removing contaminated
gloves and clothing without contacting the exterior surfaces.
5.3.4 Personal hygiene—Hands and forearms should be washed thoroughly after each
manipulation and before breaks (coffee, lunch, and shift).
5.3.5 Confinement—Isolated work areas posted with signs, segregated glassware and tools,
and plastic absorbent paper on bench tops will 'aid in confining contamination.
5.3.6 Effluent vapors—The effluent from the CVAFS should pass through either a column
of activated charcoal or a trap containing gold or sulfur to amalgamate or react
mercury vapors.
5.3.7 Waste handling—Good technique includes minirriizing contaminated waste. Plastic
bag liners should be used in waste cans. Janitors and other personnel must be trained
in the safe handling of waste.
5.3.8 Decontamination
5.3.8.1 Decontamination of personnel—Use any 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.
539 Laundry—Clothing known to be contaminated should be collected in plastic bags.
Persons who convey the bags and launder the clothing should be advised of the hazard
and trained in proper handling. If the launderer knows of the potential problem, the
clothing may be put into a washer without contact. The washer should be run through
a cycle before being used again for other clothing.
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Method 1631
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 ug on a wipe constitutes an acute hazard and requires prompt cleaning
before further use of the equipment or work space, and indicates that unacceptable
work practices have been employed.
6.0 Apparatus and Materials
Disclaimer: The mention of trade names or commercial products in this method is for
illustrative purposes only and does not constitute endorsement or recommendation for use by
the Environmental Protection Agency. Equivalent performance may be achievable using
apparatus and materials other than those suggested here. The laboratory is responsible for
- demonstrating equivalent performance.
6.1 Sampling equipment
6.1.1
6.1.2
Sample collection botdes-Fluoropolymer, 125- to 1000-mL, with fluoropolymer or
fluoropolymer-lined cap.
Cleaning—New bottles are cleaned by heating to 65-75°C in 4 N HC1 for at least 48
h. The bottles are cooled, rinsed three times with reagent water, and filled with
reagent water containing 1% HC1. These bottles are capped and placed in a clean
oven at 60-70°C overnight. After cooling, they are rinsed three more times, filled with
reagent water plus 0.4% (v/v) HC1, and placed in a mercury-free class 100 clean bench
until dry. The bottles are then tightly capped (with a wrench) and double-bagged in
new polyethylene zip-type bags until needed. After the initial cleaning, bottles are
cleaned as above, except with only 6-12 h in the hot 4 N HC1 step.
6.1.3 Filtration Apparatus
6.1.3.1 Filter—Gehnan Supor 0.45-um, 15-mm diameter capsule filter (Gelman 12175
or equivalent)
6.1.3.2 Peristaltic pump—115-V a.c., 12-V d.c., internal battery, variable-speed,
single-head (Cole-Farmer, portable, "Masterflex L/S," Catalog No. H-07570-10
drive with Quick Load pump head, Catalog No. H-07021-24, or equivalent).
6.1.3.3 Tubing for use with peristaltic pump—styrene/ethylene/butylene/silicone
(SEES) resin, approx 3/8-in i.d. by approximately 3 ft (Cole-Farmer size 18,
Catalog No. G-06464-18, or approximately 1/4-in i.d., Cole-Farmer size 17,'
Catalog No. G-06464-17, or equivalent). Tubing is cleaned by soaking in '
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Method 1631
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 (HDP'E), half filled with 4 N HC1 hi
reagent water.
6.2.2 Panel immersion heater, 500-W, aU-fluoropolymer coated, 120 vac (Cole-Parmer H-
. 03053-04, or equivalent)
NOTE: Safety note: Read instructions carefully!! The heater will maintain steady
state, without temperature feedback control, of 60-75°C in a vat of the size described.
However, the equilibrium temperature will be higher (up to boiling) in a smaller vat.
Also, the heater plate MUST be maintained in a vertical position, completely
submerged and away from the vat walls to avoid melting the vat or burning out!
6.2.3 Laboratory sink in class 100 clean area, with high-flow reagent water (Section 7.1) for
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 used may either
be purchased from a supplier, or built in the laboratory from commercially available
components.
6.3.1 Commercially available: Tekran (Toronto, ON) Model 2357 CVAFS, or Brooks-Rand
(Seattle, WA) Model 3 CVAFS, or equivalent
6.3.2 Custom-built CVAFS (Reference 11). 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 cells or equivalent).
10
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Method 1631
6.4
6.5
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 reproducibly keeping the carrier gas
flow rate at 30 mL/min
6.3.2.7 Ultra high-purity argon (grade 5.0)
Equipment for Hg purging system—Figure 2a shows the schematic diagram for the purging
system. The system consists of the following:
6.4.1 Flow meter/needle valve—capable of controlling and measuring gas flow rate to the
purge vessel at 350 (± 50) mL/min.
6.4.2 Fluoropolymer fittings—Connections between components and columns are made
using 6.4-mm o.d. fluoropolymer tubing and fluoropolymer friction-fit or threaded
tubing connectors. Connections between components requiring mobility are made with
3.2-mm o.d. fluoropolymer tubing because of its greater flexibility.
6.4.3 Acid fume pretrap—10-cm long x 0.9-cm i.d. fluoropolymer tube containing 2-3 g of
reagent grade, nonindicating, 8-14 mesh soda lime chunks, packed between wads of
silanized glass wool. This trap is cleaned of Hg by placing on the output of a bubbler
and purging for 1 h with N2 at 350 mL/min.
6.4.4 Bubbler—200-mL borosilicate glass (15 cm high x 5.0 cm diameter) with standard
taper 24/40 neck, fitted with a sparging stopper having a coarse glass frit that extends
to within 0.2 cm of the bubbler bottom.
Equipment for the dual-trap Hg(0) preconcentrating system
6.5.1 Figure 2b shows the schematic for the dual-trap amalgamation system (Reference 5).
6.5.2 Gold-coated sand trap—10-cm x 6.5-mm o.d. x 4-mm i.d. quartz tubing. The tube is
filled with 3.4 cm of gold-coated 45/60 mesh quartz sand (Frontier Geosciences Inc
Seattle, WA or equivalent). The ends are plugged with quartz wool.
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Method 1631
6.5.2.1 Traps are fitted with 6.5-mm i.d. fluoropolymer friction-fit sleeves for making
connection to the system. When traps are not in use, fluoropolymer end plugs
are inserted in trap ends to preclude contamination.
6.5.2.2 At least six traps are needed for efficient operation: one as the "analytical"
trap, and the others to sequentially collect samples on.
653 Heating of gold-coated sand traps—To blank trapiS and desorb Hg collected on the
traps heat for 3.0 min to 450-500°C (a barely visible red glow when the room is
darkened) with a coil consisting of 75 cm of 24-gauge Nichrome wire at a potential of
10 vac. Potential is applied and finely adjusted with an autotransformer.
6 5.4 Timers—The heating interval is controlled by a timer-activated 120-V outlet (Gralab or
equivalent), into which the healing coil autotransformer is plugged. Two timers are
required, one each for the "sample" trap and the "analytical" trap.
' 655 Air blowers—After heating, traps are cooled by blowing air from a small squirrel-cage
blower positioned immediately above the trap. Two blowers are required, one each for
the "sample" trap and the "analytical" trap.
6.6 Recorder/integrator—Any integrator with a range compatible with the CVAFS is acceptable.
6.7 Pipettors—All-plastic pneumatic fixed-volume and variable pipettors in the range of 10 uL to
5.0 mL.
6.8 Analytical balance capable of weighing to the nearest 0.01 g
7.0 Reagents and Standards
7.1 Reagent water—Water in which mercury is not detected by this method; 18-MQ ultrapure
deionized water starting from a prepurified (distilled, R.O., etc.) source.
7 2 Air—It is very important that the laboratory air be low in both paniculate and gaseous
mercury. Ideally, mercury work should be conducted in a new laboratory with mercury-free
paint on the walls. Outside air, which is very low hi Hg, should be brought directly into the
class 100 clean bench air intake. If this is impossible, air coming into the clean bench can be
cleaned for mercury by placing a gold-coated cloth prefilter over the intake.
721 Gold-coated cloth filter: Soak 2 m2 of cotton gauze hi 500 mL of 2% gold chloride
solution at pH 7. Li a hood, add 100 mL of 30% NHpH-HCl solution, and
homogenize into the cloth with gloved hands. As colloidal gold is precipitated, the
material will turn black. 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
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Method 1631
newspapers to air-dry. When dry, fold and place over the intake prefilter of your
laminar flow hood.
CAUTION: Great care should be taken to avoid contaminating the laboratory with
gold dust. This could cause interferences with the analysis if gold becomes
incorporated into the samples or equipment. The gilding procedure should be done in
a remote laboratory if at all possible.
7.3
7.4
7.5
7.6
7.7
7.8
7.9
7.10
Hydrochloric acid—trace-metal purified reagent HC1 containing less than 5 pg/mL Hg.
Hydroxykmine hydrochloride-Dissolve 300 g of NH2OH-HC1 in reagent water and bring to
1.0 L. This solution may be purified by the addition of 1.0 mL of SnCl2 solution and purging
overnight at 500 mL/min with Hg-free N2.
Stannous chloride—Bring 200 g of SnCl2-2H2Q and 100 mL concentrated HC1 to 1.0 L with
reagent water. Purge overnight with mercury-free N2 at 500 mL/min to remove all traces of
Hg. Store tightly capped.
Bromine monochloride (Brd)—Dissolve 27 g of reagent grade KBr in 2.5 L of low-Hg HC1
Place a clean magnetic stir bar in the bottle and stir for approximately 1 h in a fume hood
Slowly add 38 g reagent grade KBrO3 to the acid with stirring. When all of the KBrO, has
been added, the solution color should change from yellow to red to orange. Loosely cap the
bottle, and allow to stir another hour before tightening the lid.
CAUTION: This process generates copious quantities of free halogens (C12, Br2,
BrCl), which are released from the bottle. Add the KBrO3 SLOWLY in a fume hood!
Stock mercury standard—NIST-certified 10,000-ppm aqueous Hg solution (NBS-3133) This
solution is stable at least until the MIST expiration date.
Secondary Hg standard—Dilute 0.100 mL of the stock solution to 1.00 L of water containing
5 mL of BrCl This solution contains 1.00 ug/mL (1.00 ppm) Hg. Keep in a tightly closed
fluoropolymer bottle. This solution is stable indefinitely.
Working Hg standard—Dilute 5.00 mL of the secondary Hg standard to 1.00 L in a class A
volumetric flask with reagent water containing 0.5% by volume BrCl solution. This solution
contains 5.0 ng/mL and should be replaced monthly.
Calibration solutions—Using the secondary Hg standard (Section 7.8), prepare five calibration
solutions to contain Hg at a concentration of 0.2, 1.0, 5, 25, and 100 ng/L in reagent water
(section 7.1).
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Metlwd 1631
7.11 Nitrogen—Grade 4.5 (standard laboratory grade) nitrogen that has been further purified by the
removal of Hg using a gold-coated sand trap.
7.12 Argon—Grade 5.0 (ultra high-purity, GC grade) inert gas that has been further purified by-the
removal of Hg using a gold-coated sand trap.
8.0 Sample Collection, Preservation, and Storage
8 1 Before samples are collected, consideration should be given to the type of data required, (i.e.,
dissolved or total recoverable), so that appropriate preservation and pretreatment steps can be
taken. The pH of all aqueous samples must be tested immediately before aliquotting for
processing or direct analysis to ensure the sample has been properly preserved. If properly
acid-preserved, the sample can be held up to 6 months before analysis.
8 2 Samples are collected only into rigorously cleaned fiuoropolymer bottles with fluoropolymer or
fiuoropolymer-lined caps. It is critical that the bottles have tightly sealing caps to avoid
diffusion of atmospheric Hg through the threads (Reference 4). Clean bottles filled with high-
purity 0.4% (v/v) HC1 are dried, capped, and double bagged in new zip-type bags in the clean
room, and stored in wooden or plastic boxes until use.
83 Collect samples using the Sampling Method (Reference 6). Procedures in the Sampling
Method are based on rigorous protocols for collection of samples for mercury (References 4
and 11).
8 4 Sample filtration—For dissolved Hg, samples and field blanks are filtered through a 0.45-um
capsule filter at the field site. The Sampling Method describes filtering procedures. For the
determination of total recoverable Hg, samples are filtered before preservation.
8 5 Preservation—Samples may be preserved by adding 5 mL/L of concentrated HC1 (to allow
both total and methyl Hg determination) or 5 mL/L BrCl solution, if total mercury only is to
be determined. Acid- and Bra-preserved samples are stabile for a mhiimum of 6 months.
8 5.1 Samples may be shipped to the laboratory unpreserved if they are (1) coUected 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.
852 Samples that are acid-preserved may lose Hg to coagulated organic materials hi the
water or the Hg may be condensed on the walls (Reference 12). Add BrCl directly to
the sample bottle at least 24 h before analysis to prevent coagulation, condensation, or
both. Aliquots for determination of other Hg species must be removed before BrCl is
added. If BrCl cannot be added directly to the sample bottle, the bottle should be
vigorously shaken before subsampling.
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Method 1631
8.6
8.5.3 All handling of the samples in the laboratory should be undertaken in a mercury-free
clean bench, after rinsing the outside of the bottles with reagent water and drying in
the clean air hood.
8.5.4 If preserved in the laboratory, preserve a blank and OPR with each sample batch.
Storage—Sample bottles should be stored in polyethylene bags at 0-4°C until analysis.
9.0 Quality Control
9.1
Each laboratory that uses this method is required to operate a formal quality assurance
program (Reference 13). The minimum requirements of this program consist of an initial
demonstration of laboratory capability, ongoing analysis of standards and blanks as a test of
iSST* perfonnance' and me ^sis of matrix spikes (MS) and matrix spike duplicates
(MSD) to assess accuracy and precision. Laboratory performance is compared to established
performance criteria to determine that the results of analyses meet the performance
characteristics of the method.
9.1.1
9.1.2
The analyst shall make an initial demonstration of the ability to generate acceptable
accuracy and precision with this method. This ability is established as described in
Section 9.2.
In recognition of advances that are occurring in analytical technology, the analyst is
permitted certain options to improve results or lower the cost of measurements. These
options include automation of the dual-amalgamation system, direct electronic data
acquisition, changes in the bubbler design (including substitution of a flow-injection
system) to maximize throughput, and changes in the detector (i.e., CVAAS), where
less sensitivity is acceptable or desired. Changes in the principle of the determinative
technique, such as the use of colorimetry, are not allowed. If an analytical technique
other than the techniques specified in the method is used, that technique must have a
specificity equal to or better than the specificity of the techniques in the method for
the analytes of interest.
9.1.2.1 Each time this method is modified, the analyst is required to repeat the
procedure hi Section 9.2. If the change will affect the detection limit of the
method, the laboratory is required to demonstrate that the MDL (40 CFR Part
136, Appendix B) is lower than one-third the regulatory compliance level or
lower than the MDL of this method, whichever is higher. If the change will
affect calibration, the analyst must recalibrate the instrument according to
Section 10.
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:
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Method 1631
9.1.2.2.1 The names, titles, addresses, and telephone numbers of the
analyses) 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 modifications)
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) Calibration verification (Section 9.5)
(c) Initial precision and recovery (Section 9.2)
(d) Analysis of blanks (Section 9.4)
(e) Accuracy assessment (Section 9.3)
(f) Ongoing precision and recovery (Section 9.6)
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 o:r volume
(f) Copies of logbooks, chart recorder, or other raw data
output
(g) Calculations linking raw data to the results reported
9.1.3 Analyses of MS and MSD samples are required to demonstrate the accuracy and
precision and to monitor matrix interferences. Section 9.3 describes the procedure and
QC criteria for spiking.
9.1.4 Analyses of laboratory blanks are required to demonstrate acceptable levels of
contamination. Section 9.4 describes the procedures and criteria for analyzing a blank.
9.1.5 The laboratory shall, on an ongoing basis, demonstrate through analysis of the ongoing
precision and recovery (OPR) sample and the quality control sample (QCS) that the
system is in control. Sections 9.5 and 9.6 describe these procedures respectively.
9.1.6 The laboratory shall maintain records to define the quality of the data that are
generated. Sections 9.3.7 and 9.6.3 describe the development of accuracy statements.
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Method 1631
9.1.7 The determination of total 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 10
samples. Each batch must be accompanied by at least three bubbler blanks (Section
9.4), an OPR sample, and one MS and one MSD. If more than 10 samples are run
during one 12-hour shift, an additional bubbler blank, OPR sample, and MS/MSD
must be analyzed for each additional 10 or fewer additional samples. Reagent blanks
for this determination are required when the batch of reagents (bromine monochloride
plus hydroxylamine hydrochloride) are made, with verification in triplicate each month
until a new batch of reagents is needed.
9.2 Initial demonstration of laboratory capability
9.2.1 Method detection limit—To establish the ability to detect Hg, the analyst shall
determine the MDL determined according to the procedure in 40 CFR 136, Appendix
B using the apparatus, reagents, and standards that will be used in the practice of this
method. The laboratory must produce an MDL that is less than or equal to the MDL
listed in Section 1.3 or one-third the regulatory compliance limit, whichever is greater.
The MDL should be determined when a new operator begins work or whenever, in the
judgment of the analyst, a change in instrument hardware or operating conditions
would dictate that the MDL be redetermined.
9.2.2 Initial precision and recovery (IPR)—To establish the ability to generate acceptable
precision and accuracy, the analyst shall perform the following operations:
9.2.2.1 Analyze four replicates of the working Hg standard (Section 7.9) according to
the procedure beginning in Section 11.
9.2.2.2 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 total
Hg.
9.2.2.3 Compare s and X with the corresponding limits for initial precision and
recovery in Table 1. 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
9.2.2.1).
9.3 Matrix spike (MS) and matrix spike duplicate (MSD)—To assess the performance of the
method on a given sample matrix, the laboratory must spike, in duplicate, a minimum of 10%
(1 sample in 10) from a given sampling site or, if for compliance monitoring, from a given
discharge. Blanks (e.g., field blanks) may not be used for MS/MSD analysis.
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Method 1631
9.3.1 The concentration of the spike in the sample shall be determined as follows:
9.3.1.1 If, as in compliance monitoring, the concentration of total Hg in the sample is
being checked against a regulatory concentration limit, the spiking level shall
be at that limit or at 1-5 times higher than the background concentration of the
sample (determined in Section 9.3.2), whichever concentration is higher.
9.3.1.2 If the concentration of total Hg hi a sample is not being checked against a
limit, the spike shall be at the concentration of the low-level working standard
(Section 7.9) or at 1-5 times the background concentration, whichever
concentration is higher.
9.3.2 To determine the background concentration (B), analyze 1 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.
9.3.2.1 If necessary, prepare a standard solution appropriate to produce a level in the
sample at the regulatory compliance limit or at 1-5 times the background
concentration (Section 9.3.1).
9.3.2.2 Spike two additional sample aliquots with the spiking solution and analyze
these aliquots to determine the concentration after spiking (A).
9.3.3 Calculate the percent recovery (P) in each aliquot using the following equation:
where:
A = Measured concentration of analyte after spiking
B - Measured concentration of analyte before spiking
T - True concentration of the spike
9.3.4 Compare the percent recovery (P) with the QC acceptance criteria in Table 1.
9.3.4.1 If the results of spike fail the acceptance criteria, and recovery for the
OPR standard (Section 9.6) for ithe analytical batch is within the
acceptance criteria in Table 1, an interference may be present. The
result may not be reported for regulatory compliance purposes. If the
interference can be attributed to sampling, the site or discharge should
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Method 1631
9.3.5
be resampled. If the interference can be attributed to a method
deficiency, the analyst must modify the method, repeat the test
required in Section 9.1.2, and repeat analysis of the sample and
MS/MSD. However, when this method was written, there were no-
known interferences in the determination of total Hg using this
method. If such a result is observed, the analyst should investigate it
thoroughly.
9.3.4.2 If the results of both the spike and the OPR test fail the acceptance criteria, the
analytical system is judged to be out of control. The analyst must identify and
correct the problem and reanalyze the sample batch.
Relative percent difference between duplicates—Compute the relative percent
difference (RPD) between the MS and MSD according to the following equation using
the concentrations found in the MS and MSD. Do not use the recoveries calculated in
Section 9.3.3 for this calculation because the RPD is inflated when the background
concentration is near the spike concentration.
RPD = 200 x
(D1+D2)
Where:
Dl = concentration of Hg in the MS sample
D2 = concentration of Hg in the MSD sample
9.4
9.3.6 The RPD for the MS/MSD pair shall meet the acceptance criterion in Table 1. If the
criterion is not met, the system is judged to be out of control. The problem must
immediately be identified and corrected, and the analytical batch reanalyzed.
9.3.7 As part of the QC program for the laboratory, method precision and accuracy for
samples should be assessed and records maintained. After analyzing five samples in
which the recovery passes the test in Section 9.3.4, compute the average percent
recovery (Pa) and the standard deviation of the percent recovery (sp). Express the
accuracy assessment as a percent recovery interval from Pa - 2sp to Pa+ 2s . For
example, if Pa = 90% and sp = 10% for five analyses, the accuracy interval is
expressed as 70-110%. Update the accuracy assessment regularly (e.g., after every
five to ten new accuracy measurements).
Blanks—Blanks are critical to the reliable determination of Hg at low levels. The sections
below give the minimum requirements for analysis of blanks. However, it is suggested that
additional blanks be analyzed as necessary to pinpoint sources of contamination in, and
external to, the laboratory.
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Method 1631
9.4.1 Bubbler blanks—Bubbler blanks are analyzed to demonstrate freedom from system
contamination.
9.4.1.1 Immediately after analyzing a sample for total Hg, place a clean gold trap en
the bubbler, analyze the sample a second time using the procedure in Section
11, and determine the amount of Hg remiiining in the system.
9.4.1.2 If the bubbler blank is found to contain more than 50 pg Hg, the system is out.
of control. The problem must be investigated and remedied, and the samples
run on that bubbler must be reanalyzed. The remedy for a contaminated
bubbler usually involves cleaning the bubbler, changing the soda lime trap on
the affected bubbler, or both. If the blank from another bubbler contains less
than 50 pg Hg, the data associated with that bubbler remain valid.
9.4.1.3 The mean result for all bubbler blanks (from bubblers passing the specification
in Section 9.4.2) in an analytical batch (a;t least three bubbler blanks) is
calculated at the end of the batch. The mean result must be < 25 pg with a
standard deviation of < 10 pg for the batch to be considered valid. If the
mean is < 25 pg, the value is subtracted from all raw data before results are
calculated.
9.4.2 Reagent blanks—Since even reagent water often contains measurable Hg, blanks must
be determined on solutions of reagents by adding these reagents to previously purged
reagent water in the bubbler.
9.4.2.1 Add aliquots of BrCl (0.5 mL), NH2OH (0.2 mL) and SnClj (0.5 mL)
individually to previously purged reagent water in the bubbler.
9.4.2.2 The presence of more than 25 pg of Hg indicates a problem with the reagent
solution. The purging of reagent solutions with mercury-free nitrogen or argon
can reduce Hg to acceptable levels.
9.4.3 Field blanks
9.4.3.1 Analyze the field blank(s) shipped with each set of samples (samples collected
from the same site at the same time, to a maximum of 10 samples). Analyze
the blank immediately before analyzing the samples in the batch.
9.4.3.2 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 sample, whichever is greater, results for
associated samples may be the result of contamination and may not be reported
for regulatory compliance purposes.
20 Draft, January 1996
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Method 1631
9.4.4
9.4.3.3 Alternatively, if a sufficient number of field blanks (three minimum) are
analyzed to characterize the nature of the field blank, the average concentration
plus two standard deviations must be less than the regulatory compliance level
or less than one-half the level in the associated sample, whichever is greater.
9.4.3.4 If contamination of the field blanks and associated samples is known or
suspected, the laboratory should communicate this to the sampling team so that
the source of contamination can be identified and corrective measures taken
before the next sampling event.
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.
9.4.4.1 Bottle blanks—After undergoing the cleaning procedures in this method,
bottles should be subjected to conditions of use to verify the effectiveness of
the cleaning procedures. A representative set of sample bottles should be filled
with reagent water acidified to pH < 2 and allowed to stand for a minimum of
24 h. Ideally, the time that the bottles are allowed to stand should be as close
as possible to the actual time that the sample will be in contact with the bottle.
After standing, the water should be analyzed for any signs of contamination.
If any bottle shows signs of contamination, the problem must be identified, the
cleaning procedures corrected or cleaning solutions changed, and all affected
bottles recleaned.
9.4.4.2 Sampler check blanks—Sampler check blanks are generated in the laboratory
or at the equipment cleaning contractor's facility by processing reagent water
through the sampling devices using the same procedures that are used in the
field (see Sampling Method). Therefore, the "clean hands/dirty hands"
technique used during field sampling should be followed when preparing
sampler check blanks at the laboratory or cleaning facility.
9.4.4.2.1
Sampler check blanks are generated by filling a large carboy or
other container with reagent water (Section 7.1) and processing
the reagent water through the equipment using the same
procedures that are used in the field (see Sampling Method).
For example, manual grab sampler check blanks are collected
by directly submerging a sample bottle into the water, filling
the bottle, and capping. Subsurface sampler check blanks are
collected by immersing the sampler into the water and
pumping water into a sample container.
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Method 1631
9.4.42.2 The sampler check blank must be analyzed using the
procedures in this method. If any metal of interest or any
potentially interfering substance is detected in the blank, the
source of contamination or interference must be identified, and
the problem corrected. The equipment must be demonstrated
to be free from the metal(s) of interest before the equipment
may be used in the field.
9.4.4.2.3 Sampler check blanks must be run on all equipment that will
be used in the field. If, for example, samples are to be
collected using both a grab sampling device and a subsurface
sampling device, a sampler check blank must be run on both
pieces of equipment.
9 5 Ongoing precision and recovery (OPR)—To demonstrate that the analysis system is in control
and that acceptable precision and accuracy is being maintained within each analytical batch,
the analyst shall perform the following operations:
9.5.1 Analyze the low-level Hg working standard (Section 7.9) and a bubbler blank before
analysis of each analytical batch according to the procedure beginning in Section 11.
Subtract the peak area of the bubbler blank from the area for the standard and compute
the concentration for the blank-subtracted standard.
9 5.2 Compare the concentration with the limits for ongoing precision and recovery in Table
1. If the concentration is in the range specified, the analysis system is hi control and
analysis of samples and blanks may proceed. If, however, the concentration is not in
the specified range, the analytical process is not ha control. Correct the problem and
repeat the ongoing precision and recovery test.
9.5.3 The laboratory should add results that pass the specification hi Section 9.5.2 to IPR
and previous OPR data and update QC charts to form a graphic representation of
continued laboratory performance. The laboratory should also develop a statement of
laboratory data quality for each analyte by calculating the average percent recovery (R)
and the standard deviation of the percent recovery (sr). Express the accuracy as a
recovery interval from R - 2sr to R + 2st. For example, if R - 95% and sr = 5%, the
accuracy is 85-105%.
9 6 Quality control sample (QCS)—It is suggested that the laboratory obtain a QCS from a source
different from the Hg used to produce the standards used routinely in this method (Sections
7.7-7.10), and that the QCS be analyzed periodically to verify the concentration of these
standards.
9.7 Depending on specific program requirements, the laboratory may be required to analyze field
duplicates and field spikes collected to assess the precision and accuracy of the sampling,
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Method 1631
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
10.2
Establish me operating conditions necessary to purge Hg from the bubbler and to desorb Hg
from the trap in a sharp peak. The system is calibrated using the external standard technique
as follows:
10.1.1 Initial calibration—Analyze each calibration standard (Section 7.10) according to the
procedure in Section 11. After the analysis of each standard, analyze a bubbler blank
(Section 9.4.1) on the same bubbler used for the standard. Subtract the peak area of
the bubbler blank from the area of each respective standard. Tabulate the resulting
peak area against the respective concentration of each solution to form five calibration
factors. Calculate the relative standard deviation (RSD) of the calibration factor over
the five-point range.
10.1.2 Linearity—If the calibration factor is constant (< 20% RSD) over the five-point
calibration range, linearity through the origin can be assumed and the average
calibration factor can be used; otherwise, a complete calibration curve must be used
over the five-point range.
Calibration verification and ongoing precision and recovery—The ongoing precision and
recovery standard (Section 9.5) is used to verify the working calibration curve or calibration
factor at the beginning of each 12-hour working shift on which samples are analyzed
11.0 Procedure
11.1 Sample Preparation
11.1.1 Pour a 100-mL aliquot from a thoroughly shaken, acidified sample, into a 125-mL
fluoropolymer bottle. Add bromine monochloride (BrCl), cap the bottle, and digest at
room temperature for 12 hs minimum.
11.1.1.1
For clear water and filtered samples, add 0.5 mL of BrCl; for brown
water and turbid samples, add 1.0 mL of BrCl. If the yellow color
disappears because of consumption by organic matter or sulfides, more
BrCl should be added until a permanent (12-h) yellow color is
obtained.
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Method 1631
11.1.1.2 Some highly organic matrices, such as sewage effluent, will require
high levels of BrCl (i.e., 5 mL/100 mL of sample), and longer
oxidation times, or elevated temperatures (i.e.; place sealed bottles in
oven at 50°C for 6 h). The oxidation always must be continued until a
permanent yellow color remains.
11.1.2 Matrix spikes and matrix spike duplicates— For each 10' or fewer samples, pour two
additional 100-mL aliquots from a randomly selected sample, spike at the level
specified in Section 9.3, and process in the same manner as the samples.
11.2 Hg reduction and purging— Place 100 mL of reagent water in each bubbler, add 1.0 mL of
SnCl2, and purge with Hg-free N2 for 20 min at 300-400 mL/min.
11.2.1 Connect a gold/sand trap to the output of the soda lime pretrap, and purge the water
another 20 min to obtain a bubbler blank. Discard the water in the bubbler.
11.2.2 Add 0.2 mL of 30% NH2OH to the BrCl-oxidized sample in the 125-mL
fluoropolymer bottle. Cap the bottle and swirl the sample. The yellow color will
disappear, indicating the destruction of the BrCl. Allow the sample to react for 5 min
with periodic swirling to be sure that no traces of halogens remain.
NOTE: Purging of halogens onto the gold trap
irreproducible results.
result in damage and low or
1 1.2.3 Connect a fresh trap to the bubbler, pour the reduced sample into the bubbler, add 0.5
mL of 20% SnCl2 solution, and purge the sample with N2 for 20 min.
1 1.3 Desorption of Hg from the gold trap
11.3.1 Remove the gold (sample) trap from the bubbler, place the Nichrome wire coil around
the sample trap and connect the sample trap into the analyzer train between the
incoming Hg-free argon and the second gold-coated (analytical) sand trap (Figure la).
11.3.2 Pass argon through the sample and analytical traps at a flow rate of approximately 30
mL/min for approximately 2 min to drive off condensed water vapor.
11.3.3 Apply electrical current to the coil around the sample trap for 3 minutes to thermally
desorb the Hg (as Hg(0)) from the sample trap onto the analytical gold trap.
11.3.4 After the 3-min desorption time, turn off the current to the Nichrome coil, and cool the
sample trap using the cooling fan.
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Method 1631
11.3.5 Apply electrical current to the Nichrome wire coil around the analytical trap and begin
data collection. Heat the analytical trap for 3 min or for 1 min beyond the point at
which the peak returns to baseline, whichever is greater
11.3.6 Stop data collection, turn off the current to the Nichrome coil/and cool the analytical
trap to room temperature using the cooling fan.
11.3.7 Place the next sample trap in line and proceed with analysis of the next sample.
NOTE: The analytical trap must be at or near room temperature -when the sample
fa? is heated; otherwise, Hg may be lost by passing through the analytical trap.
11.4 Peaks generated using this technique should be very sharp and almost symmetrical. Mercury
elutes at approximately 1 min and has a width at half-height of about 5 seconds.
- 11.4.1 Broad or asymmetrical peaks indicate a problem with the desorption train, such as low
gas flow rate, water vapor on the trap(s), or an analytical column damaged by
chemical fumes or overheating.
11.4.2 Damage to an analytical trap is also indicated by a sharp peak, followed by a small,
broad peak.
11.4.3 If the analytical trap has been damaged, it and the fluoropolymer tubing downstream
from it should be discarded because of the possibility of gold migration on
downstream surfaces.
11.4.4 Gold-coated sand traps should be tracked by unique identifiers so that any trap
producing poor results can be quickly recognized and discarded.
12.0 Data Analysis and Calculations
12.1 Subtract the peak area of the mean of a minimum of three bubbler blanks (Section 9.4.1.3)
from the peak area of each sample.
12.2 Using the blank-subtracted area, calculate the concentration of Hg hi each sample directly from
the mean calibration factor if a linear calibration is used, or from the calibration curve if the
calibration factor does not meet the criterion in Section 10.1.2.
12.3 Reporting—Report results for samples in ng/L to three significant figures for total Hg found
above the ML (Section 1.3). Report results below the ML as < 0.2 ng/L, or as required by the
permitting authority or in the permit.
Draft, January 1996
25
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Method 1631
13.0 Method Performance
The data in Table 2 give an example the performance of the method under actual operating conditions
by several different analysts over a period of 1 year. In addition to such data, this methodology has
been intercompared with other techniques for low-level mercury determination in water under a variety
of studies, including ICES-5 (Reference 14) and the Internationa] Mercury Speciation Intercomparison
Exercise (Reference 15).
14.0 Pollution Prevention
14.1 Pollution prevention encompasses any technique that reduces or eliminates the quantity or
toxicity of waste at the point of generation. Many opportunities for pollution prevention exist
in laboratory operation. EPA has established a preferred hierarchy of environmental
• management techniques that places pollution prevention as the management option of first
choice. Whenever feasible, laboratory personnel should use pollution prevention techniques to
address their waste generation. When wastes cannot be feasibly reduced at the source, the
Agency recommends recycling as the next best option. The acids used hi 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 hi preparing standards. These standards are
used hi extremely small amounts and pose little threat to the environment when managed
properly. Standards should be prepared hi 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, slate, and local regulations
governing waste management, particularly hazardous waste identification rules and land
disposal restrictions, and for protecting the air, water, and land by rruiiirnizing and controlling
all releases from fume hoods and bench operations. Compliance with all sewage discharge
permits and regulations is also required.
15.2 Acids, samples at pH < 2, and BrCl solutions must be neutralized before being disposed of, or
must be handled as hazardous waste.
26
Draft, January 1996
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Method 1631
15.3 For further information on waste management, consult The Waste Management Manual for
Laboratory Personnel and Less is Better: Laboratory Chemical Management for Waste
Reduction, both available from the American Chemical Society's Department of Government
Relations and Science Policy, 1155 16th Street NW, Washington, DC 20036
16.0 References
8
9
10
Frontier Geosciences, Inc., Purchase Order 8762 from DynCorp Viar, Inc., August 22,
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.
Bloom, N.S; Crecelius, E.A. "Determination of Mercury hi Sea water at Subnanogram
per Liter Levels," Mar. Chem. 1983,14, 49.
GUI, G.A.; Fitzgerald, W.F. "Mercury Sampling of Open Ocean Waters at the
Picogram Level," Deep Sea Res 1985, 32, 287.
Bloom, N.S; Fitzgerald, W.F. "Determination of Volatile Mercury Species at the
Picogram Level by Low-Temperature Gas Chromatography with Cold-Vapor Atomic
Fluorescence Detection," Anal. Chim. Acta. 1988, 208, 151.
Method 1669, "Method for Sampling Ambient Water for Determination of Metals at
EPA Ambient Criteria Levels," U.S. Environmental Protection Agency, Office of
Water, Office of Science and Technology, Engineering and Analysis Division (4303)
401 M Street SW, Washington, DC 20460, April 1995 with January 1996 revisions. '
"Working with Carcinogens," Department of Health, Education, and Welfare, Public
Health Service. Centers for Disease Control. NIOSH Publication 77-206 Aue 1977
NTIS PB-277256.
"OSHA Safety and Health Standards, General Industry," OSHA 2206, 29 CFR 1910.
"Safety in Academic Chemistry Laboratories," ACS Committee on Chemical Safety,
"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. '
Draft, January 1996
27
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Method 1631
11 Bloom, N.S. "Trace Metals & Ultra-Clean Sample Handling," Environ. Lab. 1995, 7,
20.
12 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, CJ., Eds.; Lewis Publishers, Ann Arbor, ML 1994.
13 "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.
14 Cossa, D.; Couran, P. "An International Intercomparison Exercise for Total Mercury in
Sea Water," App. Organomet. Chem. 1990, 4, 49.
15 Bloom, N.S.; Horvat, M.; Watras, CJ. "Results of the International Mercury Speciation
Intercomparison Exercise," Wat. Air. SoilPollut., in-press.
17.0 Glossary
The definitions and purposes below are specific to this method, but have been conformed to common
usage as much as possible.
17.1 Ambient Water—Waters in the natural environment (e.g., rivers, lakes, streams, and other
receiving waters), as opposed to effluent discharges.
17 2 Analytical Shift—All of the 12-hour period during which analyses are performed. The period
begins with the purging of the OPR standard and ends exactly 12 hours later. All analyses
both started and completed within this 12-hour period are valid.
17.3 Bubbler Blank—The process of analyzing water in the bubbler, including purging Hg from
the water, trapping the Hg purged on a sample trap, desorbing the Hg onto an analytical trap,
desorbing the Hg from the analytical trap, and determining the amount of Hg present. The .
blank is somewhat different between days, and the average of a minimum of the results from
three bubbler blanks must be subtracted from all standards and samples before reporting the
results for these standards and samples.
17.4 Xntercomparison Study—An exercise hi which samples are prepared and split by a reference
laboratory, then analyzed by one or more testing laboratories and the reference laboratory.
The intercomparison, with a reputable laboratory as the reference laboratory, serves as the best
test of the precision and accuracy of the analyses at natural environmental levels.
17.5 Matrix Spike (MS) and Matrix Spike Duplicate (MSB)—Aliquots of an environmental
sample to which known quantities of the analyte(s) of interest is added in the laboratory. The
28
Draft, January 1996
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Method 1631
17.6
17.7
17.8
17.9
17.10
17.11
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.
Must—This action, activity, or procedural step is required.
Quality Control Sample (QCS)—A sample containing Hg at known concentrations The QCS
is obtained from a source external to the laboratory, or is prepared from a source of standards
different from the source of calibration standards. It is used to check laboratory performance
with test materials prepared external to the usual preparation process.
Reagent Water—Water known not to contain the analyte(s) of interest at the detection limit
of this method. For this method, the Hg level is made as low as possible in mercury usually
by double deionization. The reagent water is used to wash bottles and as trip and field blanks.
Should—This action, activity, or procedure is suggested, but not required.
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.
Ultraclean Handling—A series of established procedures designed to ensure that samples are
not contaminated for Hg during sample collection, storage, or analysis.
Draft, January 1996
29
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Method 1631
TABLE 1
Acceptance Criteria For Performance Test
Acceptance Criterion
Method Detection Limit
Initial Precision and Recovery
Precision (s)
•Recovery (X)
Interlaboratory Intercomparison
Matrix Spike/Matrix Spike Duplicate
Recovery
Relative Percent Difference
Bubbler Blanks
Maximum
Mean
Ongoing Precision and Recovery
Section
9.2.1
9.9.2
9.2.2.3
9.2.2.3
9.2.2.2
9.3
9.3.4
9.3.6
9.4
9.4.1.2
9.4.1.3
9.5
Limits
<0.2 ng/L
± 21%
79-121%
75-125%
75-125%
±24%
<50pg
<25pg
77-123%
30
Draft, January 1996
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Method 1631
TABLE 2
Typical QC Results for Routine Water Analysis
(Frontier Geosciences Inc., February-August 1993)
Parameter
Reagent Blanks
Matrix Spike Recoveries
Laboratory Duplicates
Field Duplicates
Intercomparison Exercise
Units
ng/L
%
RPD
RPD
%Diff
Mean
0.14
99.6
4.9
13.3
0.0
SD
0.04
6.3
6.6
14.6
13.3
N
36
60
49
33
18 labs
Draft, January 1996
31
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Method 1631
Figure 1. Schematic diagram of the Cold Vapor Atomic Fluorescence Spectrometer
(CVAFS) detector
Helium
in
350'C
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Trap
• Carbo
; Trap
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Cell
0-1000 volt DC
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HOTI
32
Draft, January 1996
-------
Method 1631
Figure 2. Schematic diagram of bubbler setup (a), and dual-amalgamation system (b)
showing proper orientation of gold traps and soda lime pretraps
He Gas
r • \ ouua inline n
r~D^^^^^
Soda Lime Pre-Trap Gold Sample Trap
Aqueous Sample + SnCl2
He Gas
Gas Phase Syringe Injection Port
\
Gold Sample Trap
Hg Free
He Gas
Quartz Detection
Cell x Photomulriplier Tube
NichromeCoil / Nichrome Coil
Gold Analysis Trap
Hg Lamp
He Gas
Draft, January 1996
33
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