&EPA
Method 1632: Inorganic Arsenic in
Water by Hydride Generation Quartz
Furnace Atomic Absorption
> Printed on Recycled Paper
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Method 1632
Acknowledgments
Method 1632 was prepared under the direction of William A. Telliard of the U.S. Environmental
Protection Agency's (EPA's) Office of Water (OW), Engineering and Analysis Division (BAD). The
method was prepared under EPA Contract 68-C3-0337 by the DynCorp Environmental Programs Division
with assistance from Quality Works, Inc. and Interface, Inc. The method is based on procedures
developed by Eric Crecelius of the Battelle Marine Sciences Laboratory in Sequim, Washington.
Disclaimer
This method has been reviewed and approved for publication by 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
USEPA Office of Water
Analytical Methods Staff
Mail Code 4303
401 M Street, SW
Washington, DC 20460
Phone: 202/260-7134
Fax: 202/260-7185
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Method 1632
introduction
This analytical method supports water quality monitoring programs authorized under the Clean Water Act
(CWA, the "Act"). CWA Section 304(a) requires EPA to publish water quality criteria that reflect the
latest scientific knowledge concerning the physical fate (e.g., concentration and dispersal) of pollutants,
the effects of pollutants on ecological and human health, and the effect of pollutants on biological
community diversity, productivity, and stability.
CWA Section 303 requires each state to set a water quality standard for each body of water within its
boundaries. A state water quality standard consists of a designated use or uses of a waterbody or a
segment of a waterbody, the water quality criteria that are necessary to protect the designated use or uses,
and an antidegradation policy. These water quality standards serve two purposes: (1) they establish the '
water quality goals for a specific waterbody, and (2) they are the basis for establishing water quality-based
treatment controls and strategies beyond the technology-based controls required by CWA Sections 301(b)
and 306.
In defining water quality standards, the state may use narrative criteria, numeric criteria, or both.
However, the 1987 amendments to CWA required states to adopt numeric criteria for toxic pollutants
(designated in Section 307(a) of the Act) based on EPA Section 304(a) criteria or other scientific data,
when the discharge or presence of those toxic pollutants could reasonably be expected to interfere with
designated uses.
In some cases, these water quality criteria are as much as 280 times lower than those achievable using
existing EPA methods and required to support technology-based permits. Therefore, EPA developed new
sampling and analysis methods to specifically address state needs for measuring toxic metals at water
quality criteria levels, when such measurements are necessary to protect designated uses in state water
quality standards. The latest criteria published by EPA are those listed in the National Toxics Rule (58 FR
60848) and the Stay of Federal Water Quality Criteria for Metals (60 FR 22228). These rules include
water quality criteria for 13 metals, and it is these criteria on which the new sampling and analysis
methods are based. Method 1632 was specifically developed to provide reliable measurements of
inorganic arsenic at EPA WQC levels using hydride generation quartz furnace atomic absorption
techniques.
In developing methods for determination of trace metals, EPA found that one of the greatest difficulties
was precluding sample contamination during collection, transport, and analysis. The degree of difficulty,
however, is highly dependent on the metal and site-specific conditions. This method is designed to
preclude contamination in nearly all situations. It also contains procedures necessary to produce reliable
results at the lowest ambient water quality criteria published by EPA. In recognition of the variety of
situations to which this method may be applied, and in recognition of continuing technological advances,
Method 1632 is performance based. Alternative procedures may be used so long as those procedures are
demonstrated to yield reliable results.
Requests for additional copies of this method should be directed to-
U.S.EPANCEPI
11209 Kenwood Road
Cincinnati, OH 45242
513/489-8190
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Method 1632
Note: This method is performance based. The laboratory is permitted to omit any step or modify
any procedure provided that all performance requirements in this method are met. The laboratory
may not omit any quality control analyses. The terms "shall" and "must" define procedures
required for producing reliable data at water quality criteria levels. The terms "should" and "may"
indicate optional steps that may be modified or omitted if the laboratory can demonstrate that the
modified method produces results equivalent or superior to results produced by this method.
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Method 1632
Method 1632
Inorganic Arsenic in Water by
Hydride Generation Quartz Furnace AA
1.0 Scope and Application
1.1 This method is for determination of total inorganic arsenic (As) in filtered and unfiltered water by
hydride generation and quartz furnace atomic absorption detection. The method is for use in
EPA's data gathering and monitoring programs associated with the Clean Water Act. The method
is based on a contractor-developed method (Reference 16.1) and on peer-reviewed, published
procedures for the determination of arsenic in aqueous samples (Reference 16.2).
1.2 This method is accompanied by Method 1669: Sampling Ambient Water for Determination of
Trace Metals at EPA Water Quality Criteria Levels (Sampling Method). The Sampling Method is
necessary to preclude contamination during the sampling process.
1.3 This method is designed for measurement of dissolved and total arsenic in the range of 10-200
ng/L. This method is not intended for determination of arsenic 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 arsenic concentrations are normally in the low part-per-trillion (ppt) range.
1.4 The detection limits and quantitation levels in this method are usually dependent on the level of
background elements rather than instrumental limitations. The method detection limit (MDL; 40
CFR 136, Appendix B) for total inorganic arsenic has been determined to be 3 ng/L when no
background elements or interferences are present. The minimum level (ML) has been established
at 10 ng/L.
1.5 The ease of contaminating 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.
Additional suggestions for improvement of existing facilities may be found in EPA's Guidance for
Establishing Trace Metals Clean Rooms in Existing Facilities, which is available from the
National Center for Environmental Publications and Information (NCEPI) at the address listed in
the introduction to this document.
1.6 Clean and ultraclean—The terms "clean" and "ultraclean" have been applied to the techniques
needed to reduce or eliminate contamination in trace metals determinations. These terms are not
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Method 1632
used in this method because they lack an exact definition. However, the information provided in
this method is consistent with EPA's 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 at 40 CFR 136.4 and
136.5.
1.10 Each analyst who uses this method must demonstrate the ability to generate acceptable results
using the procedure in Section 9.2.
1.11 This method is accompanied by a data verification and validation guidance document, Guidance
on the Documentation and Evaluation of Trace Metals Data Collected for CWA Compliance
Monitoring. Before this method is used, data users should state data quality objectives (DQOs)
required for a project
2.0 Summary of Method
2.1 A 100-2000 mL sample is collected directly into a specially cleaned, pretested, fluoropolymer,
conventional or linear polyethylene, polycarbonate, or polypropylene bottle using sample
handling techniques specially designed for collection of metals at trace levels (Reference 16.3).
2.2 The sample is either field or laboratory preserved by the addition of 5 mL of pretested 10% HNO3
per liter of sample, depending on the time between sample collection and arrival at the laboratory.
2.3 An aliquot of sample is placed in a specially designed reaction vessel and 6 M HC1 is added.
2.4
Before analysis, 4% NaBH4 solution is added to convert organic and inorganic arsenic to volatile
arsines.
2.5 The arsines are purged from the sample onto a cooled glass trap packed with 15% OV-3 on
Chromasorb® WAW-DMCSO. or equivalent.
2.6 The trapped arsines are thermally desorbed, in order of increasing boiling points, into an inert gas
stream that carries them into the quartz furnace of an atomic absorption spectrophotometer for
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Method 1632
detection. The first arsine to be desorbed will be AsH3, which represents total inorganic arsenic in
the sample.
2.7 Quality is ensured through calibration and testing of the hydride generation, purging, and
detection systems.
3.0 Definitions
3.1 Total inorganic arsenic—all NaBH4-reducible inorganic arsenic compounds found in aqueous
solution. This method can be extended to measure organic arsenic as well. Organic arsenic
includes, but is not limited to, monomethylarsonate and dimethylarsonate. In this method, total
arsenic and total recoverable arsenic are synonymous.
3.2 Dissolved inorganic arsenic—all NaBH4-reducible inorganic arsenic compounds found in aqueous
solution filtrate after passing the sample through a 0.45- uM capsule filter.
3.3 Apparatus—Throughout this method, the sample containers, sampling devices, instrumentation,
and all other materials and devices used in sample collection, sample processing, and sample
analysis that come in contact with the sample and therefore require careful cleaning will be
referred to collectively as the Apparatus.
3.4 Definitions of other terms used in this method are given in the glossary at the end of the method.
4.0 Contamination and Interferences
4.1 Preventing ambient water samples from becoming contaminated during the sampling and
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 of
the historical data on the concentrations of dissolved trace metals in seawater are erroneously high
because the concentrations reflect contamination from sampling and analysis rather than ambient
levels. Therefore, it is imperative that extreme care be taken to avoid contamination when
collecting and analyzing ambient water samples for trace metals.
4.2 Samples may become contaminated by numerous routes. Potential sources of trace metals
contamination during sampling include: metallic or metal-containing labware (e.g., talc gloves
that contain high levels of zinc), containers, sampling equipment, reagents, and reagent water;
improperly cleaned and stored equipment, labware, and reagents; and atmospheric inputs such as
dirt and dust. Even human contact can be a source of trace metals contamination.
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Method 1632
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 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.
4.3.2 Avoiding contamination—The best way to control contamination is to completely avoid
exposure of the sample to contamination in the first place. Avoiding exposure means
performing operations in an area known to be free from contamination. Two of the most
important factors in avoiding/reducing sample contamination are (1) an awareness of
potential sources of contamination and (2) strict attention to work being done. Therefore,
it is imperative that the procedures described in this method be carried out by well-trained,
experienced personnel.
4.3.3 Use a clean envkonment—The ideal environment for processing samples is a class 100
clean room (Section 1.5). 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 arsenic- and
particle-free air or nitrogen. Digestions should be performed in a nonmetal fume hood
situated, ideally, in the clean room.
4.3.4 Minimize exposure—The apparatus that will contact samples, blanks, or standard
solutions should be opened or exposed only in a clean room, clean bench, or glove box so
that exposure to an uncontrolled atmosphere is minimized. When not being used, the
apparatus should be covered with clean plastic wrap, stored in the clean bench or in a
plastic box or glove box, or bagged in clean zip-type bags. Minimizing the time between
cleaning and use will also minimize contamination.
4.3.5 Clean work surfaces—Before a given batch of samples is processed, all work surfaces in
the hood, clean bench, or glove box in which the samples will be processed should be
cleaned by wiping with a lint-free cloth or wipe soaked with reagent water.
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Method 1632
4.3.6 Wear gloves—Sampling personnel must wear clean, nontalc gloves during all operations
involving handling of the apparatus, samples, and blanks. Only clean gloves may touch
the apparatus. If another object or substance is touched, the glove(s) must be changed
before again handling the apparatus. If it is even suspected that gloves have become
contaminated, work must be halted, the contaminated gloves removed, and a new pair of
clean gloves put on. Wearing multiple layers of clean gloves will allow the old pair to be
quickly stripped with minimal disruption to the work activity.
4.3.7 Use metal-free apparatus—All apparatus used for determination of arsenic 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 (FEP, PTFE), conventional or linear
polyethylene, polycarbonate, or polypropylene containers should be used for
samples mat will be analyzed for arsenic. PTFE is less desirable than FEP
because the sintered material in PTFE may contain contaminants and is
susceptible to serious memory effects (Reference 16.4). All materials, regardless
of construction, that will directly or indirectly contact the sample must be cleaned
using the procedures given 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 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 low concentrations of metals is processed immediately after a sample
containing relatively high concentrations of these metals. To reduce carryover,
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Method 1632
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 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 samples containing high concentrations of arsenic 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.
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. Therefore, it is
imperative that every piece of the apparatus that is directly or indirectly used in
the collection, processing, and analysis of ambient water samples be thoroughly
cleaned (see Section 6.1.2).
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 If the transfer line between the cold trap and the atomizer is not well heated, water vapor
may condense in the line. Such condensation can interfere with the determination of
dimethylarsine.
5.0 Safety
5.1 The toxicity or carcinogenicity of each chemical used in this method has not been precisely
determined; however, each compound should be treated as a potential health hazard. Exposure to
these compounds should be reduced to the lowest possible level. It is recommended that the
laboratory purchase a dilute standard solution of the As 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.
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Method 1632
5.2
5.3
This method does not address all safety issues associated with its use. The laboratory is
responsible for maintaining a current awareness file of OSHA regulations for the safe handling of
the chemicals specified in this method. A reference file of material safety data sheets (MSDSs)
should also be made available to all personnel involved in these analyses. 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 16.5-16.8. The references and bibliography at the
end of Reference 16.8 are particularly comprehensive in dealing with the general subject of
laboratory safety.
Samples suspected to contain high concentrations of As are handled using essentially the same
techniques used 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 As.
5.3.1 Facility—When samples known or suspected of containing high concentrations of arsenic
are handled, all operations (including removal of samples from sample containers,
weighing, transferring, and mixing) should be performed in a glove box demonstrated to
be leaktight or in a fume hood demonstrated to have adequate air flow. 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 laboratory 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 AAS should pass through either a column of
activated charcoal or a trap designed to remove As.
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Method 1632
5.3.7 Waste handling—Good technique includes minimizing contaminated waste. Plastic bag
liners should be used in waste cans. Janitors and other personnel must be trained in the
safe handling of waste.
5.3.8 Decontamination
5.3.8.1 Decontamination of personnel—Use any mild soap with plenty of scrubbing
action.
5.3.8.2 Glassware, tools, and surfaces—Satisfactory cleaning may be accomplished by
washing with any detergent and water.
5.3.9 Laundry—Clothing known to be contaminated should be collected in plastic bags.
Persons who convey the bags and launder the clothing should be advised of the hazard
and trained in proper handling. If the launderer knows of the potential problem, the
clothing may be put into a washer without contact. The washer should be run through a
cycle before being used again for other clothing.
5.3.10 Wipe tests—A useful method of determining cleanliness of work surfaces and tools is to
wipe the surface with a piece of filter paper. Extraction and .analysis by this method can
achieve a limit of detection of less than 1 ng per wipe. Less than 0.1 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,
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, conventional or linear polyethylene,
polycarbonate, or polypropylene, 500-1000 mL
6.1.2 Cleaning—Bottles are cleaned with liquid detergent and thoroughly rinsed with reagent
water. The bottles are then immersed in a hot (50-60°) bath of IN trace metal grade HC1
for at least 48 h. The bottles are then thoroughly rinsed with reagent water and filled with
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Method 1632
0.1% (v/v) ultrapure HC1 and double-bagged in new polyethylene zip-type bags until
needed.
6.2 Equipment for bottle and glassware cleaning
6.2.1 Vats, up to 200-L capacity, constructed of high-density polyethylene (HDPE) or other
nonmetallic, noncontaminating material suitable for holding concentrated HNO3 and
dilute HC1
6.2.2 Panel immersion heater, all-fluoropolymer coated, capable of maintaining a temperature
of 60-75 °C in a vat of the size used (Cole-Parmer H-03053-04, or equivalent)
Note: Caution: Read instructions carefully!! The heater will maintain steady state,
without temperature feedback control, of 60-75 °C in a vat of the size described.
However, the equilibrium temperature will be higher (up to boiling) in a smaller vat.
Also, the heater plate MUST be maintained in a vertical position, completely submerged
and away from the vat walls to avoid melting the vat or burning out!
6.2.3 Laboratory sink in class 100 clean area, with high-flow reagent water for rinsing
6.2.4 Clean bench, class 100, for drying rinsed bottles.
6.3
6.4
Atomic absorption spectrophotometer (AAS)—Any atomic absorption spectrophotometer may
serve as a detector. A bracket is required to hold the quartz atomizer in the optical path of the
instrument. Table 3 gives typical conditions for the spectrophotometer.
6.3.1 Electrodeless discharge lamp for measuring arsenic at 193.7 nm
6.3.2 Quartz cuvette burner tube (Reference 16.2), 70 mm long and 9 mm in diameter with two
6-mm o.d.- side tubes, each 25 mm long. Figure la shows a schematic of the tube and
bracket.
Equipment for reaction vessel—Figure Ib shows the schematic diagram for the vessel used for the
reaction of the sample with sodium borohydride. The system consists of the following:
6.4.1 125-mL gas wash bottle (Coming # 1760-125 or equivalent) onto which an 8-mm o.d.
sidearm inlet tube 2 cm long has been grafted
6.4.2 Silicone rubber stopper septum (Ace Glass #9096-32 or equivalent)
6.4.3 Four-way Teflon stopcock valve capable of switching of the helium from the purge to the
analysis mode of operation
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Method 1632
6.4.4 Flow meter/needle valve capable of controlling and measuring gas flow rate to the
reaction vessel at 150 (± 30) mL/min
6.4.5 Silicone tubing—All glass-to-glass connections are made with silicone rubber sleeves.
6.5 Equipment for cryogenic trap—Figure Ic shows the schematic diagram for the trap. It consists of
the following:
6.5.1 Nichrome wire (22-gauge)
6.5.2 Variacs for controlling Nichrome wire
6.5.3 A 6-mm o.d. borosilicate glass U-tube about 30 cm long with a 2-cm radius of bend (or
similar dimensions to fit into a tall widemouth Dewar flask), which has been silanized and
half-packed with 15% OV-3 on Chromasorb® WAW-DMCS (45-60 mesh), and the ends
of which have been packed with silanized glass wool.
6.5.3.1 Conditioning the trap—The input side of the trap (the side that is not packed) is
connected with silicone rubber tubing to He at a flow rate of 40 mL/min, and the
trap is placed in an oven at 175°C for 2 h. At the end of this time, inject two 25-
|jL aliquots of GC column conditioner (Silyl-8®, Supelco, Inc., or equivalent)
through the silicone tubing into the glass trap. Return the trap to the oven, with
the He still flowing, for 24 h.
6.5.3.2 After conditioning, the trap is wrapped with approximately 1.8 m of 22-gauge
Nichrome wire, the ends of which are affixed to crimp-on electrical contacts.
6.5.3.3 The trap is connected by silicone rubber tubing to the output of the reaction
vessel. The output side of the trap is connected by 6-mm diameter borosilicate
tubing that has been wrapped by Nichrome wire to the input of the flame
atomizer.
6.5.4 Dewar flask capable of containing the trap described in Section 6.5.3.
6.6 Recorder/integrator—Any integrator with a range compatible with the AAS 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 gram
10
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Method 1632
7.0 Reagents and Standards
7.1 Reagent water—Water demonstrated to be free from As and potentially interfering substances at
the MDL. Prepared by distillation, deionization, reverse osmosis, anodic/cathodic stripping
voltammetry, or other technique mat removes As and potential interferant(s).
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
Hydrochloric acid—Trace-metal purified reagent HC1.
6M hydrochloric acid—Equal volumes of trace metal grade concentrated HC1 (Section 7.2) and
reagent water (Section 7.1) are combined to give a solution approximately 6M in HC1.
Nitric acid—Trace-metal purified reagent HNO3
10% nitric acid—Nitric acid (HNO3): 10% wt, Seastar, or equivalent
Sodium borohydride solution-4 g of >98% NaBH4 (previously analyzed and shown to be free of
measurable arsenic) are dissolved in 100 mL of 0.02 M NaOH solution. This solution is stable for
only 8-10 h, and must be made fresh daily.
Liquid nitrogen for cooling the cryogenic trap
Helium—Grade 4.5 (standard laboratory grade) helium.
Hydrogen—Grade 4.5 (standard laboratory grade) hydrogen.
7.10 Air—Grade 4.5 (standard laboratory grade) air.
7.11 QC sample concentrate—From a source different than the one used to prepare calibration
standards, prepare a QC sample concentrate containing 1.50 ug/L As in reagent water (Section
7.1) preserved with sufficient HNO3 to bring the pH to <2.
7.12 Arsenic Standards
7.12.1 Stock standard solution (1000 mg/L)—Either procure NIST-certified aqueous standards
from a supplier and verify by comparison to a second standard from a separate source, or
dissolve 1.320 g of arsenic trioxide (As2O3) in 100 mL of reagent water (Section 7.1)
containing 4 g NaOH. Acidify the solution with 20 mL concentrated HNO3 and dilute to
1.0 liter.
7.12.2 Primary dilution standard (1.0 mg/L)—-Pipet 1.0 mL arsenic stock solution (Section
7.12.1) into a 1000-mL volumetric flask and bring to volume with reagent water (Section
7.1) containing 1.5 mL concentrated HNO3 per liter.
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Method 1632
7.12.3 Standard arsenic solution (10 ug/L)—Pipet 10.0 mL primary dilution arsenic standard
(Section 7.12.2) into a 1000-mL volumetric flask and bring to volume with reagent water
(Section 7.1) containing 1.5 mL concentrated HNO3/liter (1 mL = 0.01 ug As).
7.12.4 Calibration solutions—Using the standard arsenic solution (Section 7.12.3), prepare
calibration solutions in reagent water, one of which contains As at a concentration of 10
ng/L and at least two others that fall within the calibration range of the instrument.
8.0 Sample Collection, Preservation, and Storage
8.1 Sample collection—Samples are collected as described in the Sampling Method (Reference 16.3).
8.2 Sample filtration—For dissolved metals, samples and field blanks are filtered through a 0.45-uM
capsule filter at the field site. The Sampling Method describes the filtering procedures.
8.3 Sample preservation—Preservation of samples may be performed in the field or in the laboratory.
The sampling team may prefer to use laboratory preservation of samples to expedite field
operations and to minimize the potential for sample contamination. Samples and field blanks
should be preserved at the laboratory immediately when received. Preservation involves the
addition of 10% HNO3 (Section 7.5) to bring the sample to pH <2. For samples received at
neutral pH, approximately 5 mL of 10% HNO3 per liter will be required.
8.3.1 Wearing clean gloves, remove the cap from the sample bottle, add the volume of reagent
grade acid that will bring the pH to <2, and recap the bottle immediately. If the bottle is
full, withdraw the necessary volume using a precleaned pipet and then add the acid.
Record the volume withdrawn and the amount of acid used.
Note: Do not dip pH paper or a pH meter into the sample; remove a small aliquot with
a clean pipet and test the aliquot.
8.3.2 Store the preserved sample for a minimum of 48 h at 0-4°C to allow the acid to
completely dissolve the metal(s) adsorbed on the container walls.
8.3.3 With each sample set, preserve a method blank and an OPR sample in the same way as
the sample(s).
8.3.4 Sample bottles should be stored in polyethylene bags at 0-4°C until analysis.
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Method 1632
9.0 Quality Control/Quality Assurance
9.1
Each laboratory that uses this method is required to operate a formal quality assurance program
(Reference 16.3). The minimum requirements of this program consist of an initial demonstration
of laboratory capability, analysis of samples spiked with As to evaluate and document data
quality, and analysis of standards and blanks as tests of continued performance. To determine if
the results of analyses meet the performance characteristics of the method, laboratory performance
is compared to established performance criteria.
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 to exercise certain options to eliminate interferences or lower the costs of
measurements. These options include alternate digestion, concentration, and cleanup
procedures, and changes in instrumentation. Alternate determinative techniques such as
the substitution of a colorimetric technique or changes that degrade method performance
are not allowed. If an analytical technique other than the techniques specified in this
method is used, that technique must have a specificity equal to or better than the
specificity of the techniques in the referenced method for the analytes of interest.
9.1.2.1 Each time this method is modified, the analyst is required to repeat the procedure
in Section 9.2. If the change will afreet the detection limit of the method, the
laboratory is required to demonstrate that the MDL (40 CFR Part 136, Appendix
B) is lower than the MDL for this method or one-third of the regulatory
compliance level, whichever is higher. If the change will affect calibration, the
analyst must recalibrate the instrument according to Section 10 of this method.
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
analyses) who performed the analyses and modification, and of
the quality control officer who witnessed and will verify the
analyses and modification
9.1.2.2.2 A listing of metal measured (As), by name and CAS Registry
number
9.1.2.2.3 A narrative stating reason(s) for the modification(s)
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Method 1632
9.1.3
9.1.4
9.1.2.2.4 Results from all quality control (QC) tests comparing the
modified method to this method, including:
(a) Calibration (Section 10)
(b) Calibration verification (Section 10.2)
(c) Initial precision and recovery (Section 9.2)
(d) Analysis of blanks (Section 9.5)
(e) Matrix spike/matrix spike duplicate analysis (Section
9.3)
(f) Ongoing precision and recovery (Section 9.6)
9.1.2.2.5 Data that will allow an independent reviewer to validate each
determination by tracing the instrument output (peak height, area,
or other signal) to the final result. These data are to include,
where possible:
(a) Sample numbers and other identifiers
(b) Preparation dates
(c) Analysis dates and times
(d) Analysis sequence/run chronology
(e) Sample volume
(f) Volume before each preparation step
(g) Volume after each preparation step
(h) Final volume before analysis
(i) Dilution data
(j) Instrument and operating conditions (make, model, revision,
modifications)
(k) Sample introduction system (ultrasonic nebulizer, hydride
generator, flow injection system, etc.)
(1) Operating conditions (ashing temperature, temperature
program, flow rates, etc.)
(m) Detector (type, operating conditions, etc.)
(n) Printer tapes and other recordings of raw data
(o) Quantitation reports, data system outputs, and other data to
link the raw data to the results reported
Analyses of blanks are required to demonstrate freedom from contamination. Section 9.5
describes the required types, procedures, and criteria for analysis of blanks.
The laboratory shall spike at least 10% of the samples with As to monitor method
performance. Section 9.3 describes this test. When results of these spikes indicate
atypical method performance for samples, an alternative extraction or cleanup technique
must be used to bring method performance within acceptable limits. If method
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Method 1632
performance for splices cannot be brought within the limits given in this method, the result
may not be reported for regulatory compliance purposes.
9.1.5 The laboratory shall, on an ongoing basis, demonstrate through calibration verification
and through analysis of the ongoing precision and recovery aliquot that the analytical
system is in control. Sections 10.2 and 9.6 describe these procedures, respectively.
9.1.6 The laboratory shall maintain records to define the quality of data that are generated.
Section 9.3.4 describes the development of accuracy statements.
9.2 Initial demonstration of laboratory capability
9.2.1 Method detection limit—To establish the ability to detect As, the analyst shall determine
the MDL per 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 no more than one-tenth the regulatory compliance level or that is
less than the MDL listed in Table 1, whichever is greater.
9.2.2 Initial precision and recovery (IPR)—To establish the ability to generate acceptable
precision and recovery, the analyst shall perform the following operations.
9.2.2.1 Analyze four aliquots of reagent water spiked with As at 0.015 jag/L according to
the procedures in this method. Prepare these by diluting each of four 1.0-mL
aliquots of the QC Sample Concentrate (Section 7.11) to 100 mL. All digestion,
extraction, and concentration steps, and the containers, labware, and reagents that
will be used with samples must be used in this test.
9.2.2.2 Using results of the set of four analyses, compute the average percent recovery
(X) in each aliquot and the standard deviation(s) of the recovery.
9.2.2.3 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 blanks and samples may begin. If, however, s exceeds
the precision limit or X falls outside the range for accuracy, system performance
is unacceptable for As. Correct the problem and repeat the test (Section 9.2.2.1).
Method accuracy—To assess the performance of the method on a given sample matrix, the
laboratory must perform matrix spike (MS) and matrix spike duplicate (MSD) sample analyses on
10% of the samples from each site being monitored, or at least one MS sample analysis and one
MSD sample analysis must be performed for each sample set (samples collected from the same
site at the same time, to a maximum of 10 samples), whichever is more frequent.
9.3
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Method 1632
9.3.1 The concentration of the MS and MSD is determined as follows:
9.3.1.1 If, as in compliance monitoring, the concentration of As in the sample is being
checked against a regulatory concentration limit, the spike must be at that limit or
at 1-5 times the background concentration, whichever is greater.
9.3.1.2 If the concentration is not being checked against a regulatory limit, the
concentration must be at 1-5 times the background concentration or at 1-5 times
the ML in Table 1, whichever is greater.
9.3.2 Assessing spike recovery
9.3.2.1 Determine the background concentration (B) of As by analyzing one sample
aliquot according to the procedures in Section 11.
9.3.2.2 If necessary, prepare a matrix spiking concentrate that will produce the
appropriate level (Section 9.3.1) in the sample when the concentrate is added.
9.3.2.3 Spike two additional aliquots with the QC check sample concentrate (or, if
necessary, with the matrix spiking concentrate) and analyze these aliquots to
determine the concentration after spiking (A).
9.3.2.4 Calculate each percent recovery (P) as 100(A - B)/T, where T is the known true
value of the spike.
9.3.3 Compare the percent recovery (P) with the corresponding QC acceptance criteria in Table
2. If P falls outside the designated range for recovery, the As result has failed the
acceptance criteria.
9.3.3.1 If the As result has failed the acceptance criteria, analyze the ongoing precision
and recovery standard (Section 9.6). If the OPR is within acceptance criteria
(Table 2), the analytical system is in control and the problem can be attributed to
the sample matrix.
9.3.3.2 For samples that exhibit matrix problems, further isolate As from the sample
matrix using chelation, extraction, concentration, hydride generation, or other
means, and repeat the accuracy test (Section 9.3.2).
9.3.3.3 If the recovery for As remains outside the acceptance criteria, the analytical result
in the unspiked sample is suspect and may not be reported for regulatory
compliance purposes.
9.3.4 Recovery for samples should be assessed and records maintained.
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Method 1632
9.3.4. 1 After the analysis of five samples of a given matrix type (river water, lake water,
etc.) for which As passes the tests in Section 9.3.3, compute the average percent
recovery (R) 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
each matrix. For example, if R = 90% and SR = 10% for five analyses of river
water, the accuracy interval is expressed as 70-1 10%.
9.3.4.2 Update the accuracy assessment in each matrix regularly (e.g., after each five to
ten new measurements).
9.4 Precision of matrix spike duplicates
9.4.1
Calculate the relative percent difference (RPD) between the MS and MSD according to
the equation below using the concentrations found in the MS and MSD. Do not use the
recoveries calculated in Section 9.3.2.4 for this calculation because the RPD of recoveries
is inflated when the background concentration is near the spike concentration.
RPD -
Where:
Dl = concentration of the analyte in the MS sample
D2 = concentration of the analyte in the MSD sample
9.4.2
Compare the RPD with the limits in Table 2. If the criteria are not met, the analytical
system is judged to be out of control. Correct the problem and reanalyze all samples in
the sample set associated with the MS/MSD that failed the RPD test.
1 9.5 Blanks—Blanks are analyzed to demonstrate freedom from contamination.
9.5.1 Laboratory (method) blank
9.5.1.1 Prepare a method blank with each sample batch (samples of the same matrix
started through the preparation process on the same 12-hour shift, to a maximum
of 10 samples). Analyze the blank immediately after analysis of the OPR
(Section 9.6) to demonstrate freedom from contamination.
9.5.1.2 If As or any potentially interfering substance is found in the blank at a
concentration equal to or greater than the MDL (Table 1), sample analysis must
be halted, the source of the contamination determined, the problem corrected, and
the sample batch and fresh method blank reanalyzed.
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Method 1632
9.5.1.3 Alternatively, if a sufficient number of blanks (three minimum) are analyzed to
characterize the nature of a blank, the average concentration plus two standard
deviations must be less than the regulatory compliance level.
9.5.1.4 If the result for a single blank remains above the MDL or if the result for the
average concentration plus two standard deviations of three or more blanks
exceeds the regulatory compliance level, results for samples associated with those
blanks may not be reported for regulatory compliance purposes. Stated another
way, results for all initial precision and recovery tests (Section 9.2) and all
samples must be associated with an uncontaminated method blank before these
results may be reported for regulatory compliance purposes.
9.5.2 Field blank
9.5.2.1 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). If the samples
are filtered for the determination of dissolved As, the field blank shall be filtered
as well. Analyze the blank immediately before analyzing the samples in the
batch.
9.5.2.2 If As or any potentially interfering substance is found in the field blank at a
concentration equal to or greater than the MDL (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.
9.5.2.3 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.
9.5.2.4 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.
9.5.3
Equipment blanks—Before any sampling equipment is used at a given site, the laboratory
or cleaning facility is required to generate equipment blanks to demonstrate that the
sampling equipment is free from contamination. Two types of equipment blanks are
required: bottle blanks and sampler check blanks.
9.5.3.1 Bottle blanks—After undergoing appropriate cleaning procedures (Section 6.1.2),
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
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Method 1632
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 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.
9.5.3.2 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.
9.5.3.2.1
9.5.3.2.2
9.5.3.2.3
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. "Clean hands/dirty hands"
techniques must be used.
The sampler check blank must be analyzed using the procedures
in this method. If As 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 As before the equipment
may be used in the field.
Sampler check blanks must be run on all equipment that will be
used in the field. If, for example, samples are to be collected
using both a grab sampling device and a subsurface sampling
device, a sampler check blank must be run on both pieces of
equipment.
9.6 Ongoing precision and recovery
9.6.1
Prepare a precision and recovery sample (laboratory-fortified method blank) identical to
the initial precision and recovery aliquots (Section 9.2) with each sample batch (samples
of the same matrix started through the extraction process on the same 12-hour shift, to a
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Method 1632
maximum of 10 samples) by diluting a 1.0-mL aliquot of QC check sample concentrate to
100 mL with reagent water.
9.6.2 Analyze the OPR aliquot before analyzing the method blank and samples from the same
batch.
9.6.3 Compute the percent recovery of As in the OPR aliquot using the procedure given in this
method.
9.6.4 Compare the concentration to the limits for ongoing recovery in Table 2. If the
acceptance criteria are met, system performance is acceptable and analysis of blanks and
samples may proceed. If, however, recovery falls outside of the range given, the
analytical processes are not being performed properly. Correct the problem, reprepare the
sample batch, and repeat the OPR test (Section 9.6).
9.6.5 Add results that pass the specifications in Section 9.6.4 to initial and previous ongoing
data for As in each matrix. Update QC charts to form a graphic representation of
continued laboratory performance. Develop a statement of laboratory accuracy in each
matrix type by calculating the average percent recovery (R) and the standard deviation of
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%.
9.7 The specifications in this method can be met if the instrument used is calibrated properly and then
maintained in a calibrated state. A given instrument will provide the most reproducible results if
dedicated to the settings and conditions required for the analyses of As by this method.
9.8 Depending on specific program requirements, field duplicates may be collected to determine the
precision of the sampling technique. The relative percent difference (RPD) between field
duplicates should be less than 20%.
10.0 Calibration and Standardization
10.1 Calibration—Calibrate at a minimum of three points, one of which must be the ML (Table 1), and
another that must be near the upper end of the linear dynamic range. Calibration is required
before any samples or blanks are analyzed.
10.1.1 External standard calibration
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Method 1632
10.1.1.1
Calculate the response factor (RF) for As in each CAL solution using the
following equation and the height or area produced.
RF =
Where:
10.1.1.2
10.1.1.3
Rx = height or area of the signal for As
Cx = concentration of arsenic standard (ng/L)
Calculate the mean response factor (RFJ, the standard deviation of the
RFm (SD), and the relative standard deviation (RSD) of the mean, where
RSD = 100 x SD/RFm.
Linearity—If .the RSD of RFm is less than 25% over the calibration range,
the RFm may be used to calculate sample concentrations.
10.2 Calibration verification—Immediately after calibration, an initial calibration verification should be
performed. Adjustment of the instrument is performed until verification criteria are met. Only
after these criteria are met may blanks and samples be analyzed.
10.2.1 Verify the specificity of the instrument for As and adjust the wavelength or tuning until
the resolving power specified in this method is met.
10.2.2 Inject the mid-point calibration standard (Section 10.1) or a dilution of the QC check
sample concentrate with a concentration near the midpoint of the calibration range.
10.2.3 Compute the percent recovery, of As using the mean response or calibration curve
obtained in the initial calibration.
10.2.4 Compare the recovery with the corresponding limit for calibration verification in Table 2.
If acceptance criteria are met, system performance is acceptable and analysis of blanks
and samples may continue using the response from the initial calibration. If acceptance
criteria are not met, system performance is unacceptable. Locate and correct the problem
and/or prepare a new calibration check standard and repeat the test (Sections
10.2.2-10.2.4), or recalibrate the system according to this method and Section 10.1.
10.2.5 Calibration should be verified following every ten samples by analyzing the mid-point
calibration standard. If the recovery does not meet the acceptance criteria specified in
Table 2, analysis must be halted, the problem corrected, and the instrument recalibrated.
All samples after die last acceptable calibration verification must be reanalyzed.
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Method 1632
11.0 Procedure
11.1 Set the AA system up according to manufacturer's instructions. The settings in Tables 3 and 4 can
be used as a guide. Calibrate the instrument according to Section 10.
Note: Precision and sensitivity are affected by gas flow rates and these must be
individually optimized for each system, using the figures in Table 4 as an initial guide.
11.2 To light the flame, turn on all gases and expose the end of the quartz cuvette to a flame. At this
point, a flame will be burning out the ends of the tube. Allow the tube to heat for approximately 5
min, then place a flat metal spatula over each end of the tube in sequence. An invisible
air/hydrogen flame should now be burning in the center of the cuvette. To check for the flame,
place a mirror near the end of the tube and observe condensation of water vapor or turn-off the
room light to observe the flame.
11.3 Place a known volume of aqueous sample (up to 70 mL) into the reaction vessel. If less than 70
mL of sample is used, add sufficient reagent water to result in a total volume of 70 mL. Add 5.0
mL of 6M HC1. Set the four-way valve on the reaction vessel to pass the flow of He through the
sample and onto the trap and begin purging the vessel with He.
11.4 Lower the trap into a Dewar flask containing liquid nitrogen (LN^ and top the flask off with LN2
to a constant level.
11.5 Add 10 mL of NaBH4 solution slowly (over a period of approximately 2 min) through the rubber
septum with a disposable hypodermic syringe and begin timing the reaction. After 7 min, turn the
stopcock on the four-way valve to bypass the reaction vessel and pass helium directly to the trap.
11.6 Quickly remove the trap from the LN2, activate the heating coils to heat the trap and begin
recording output from the AA system. The transfer line is maintained at 80 °C.
11.7 To ensure that all organic reduction products have been desorbed from the trap, maintain the trap
temperature at 80°C and keep He flowing through the trap for at least 3 min between samples.
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Method 1632
12.0 Data Analysis and Calculations
12.1 Compute the concentration of As in ng/L (parts-per-trillion; ppt) using the calibration data
(Section 10.1) according to the following equation:
[As] (ng/L) =
_£*_
RF
•where:
Rx = height or area of signal for As in sample
RFm = mean response factor
12.2 If the concentration exceeds the linear dynamic range of the instrument, dilute the sample by
successive factors of 10 until the concentration is within the linear dynamic range.
12.3 Report results at or above the ML for As found in samples and determined in standards. Report
all results for As found in blanks, regardless of level.
12.4 Report results to one significant figure at or below the MDL, two significant figures between the
MDL and ML, and three significant figures at or above the ML.
12.5 Do not perform blank subtraction on the sample results.
13.0 Method Performance
13.1
The method detection limit (MDL) listed in Table 1 and the quality control acceptance criteria
listed in Table 2 were validated in two laboratories (Reference 16.9).
14.0 Pollution Prevention
14.1
Pollution prevention encompasses any technique that reduces or eliminates the quantity or toxicity
of waste at the point of generation. Many opportunities for pollution prevention exist in
laboratory operation. EPA has established a preferred hierarchy of environmental management
techniques that places pollution prevention as the management option of first choice. Whenever
feasible, laboratory personnel should use pollution prevention techniques to address their waste
generation. When wastes cannot be feasibly reduced at the source, the Agency recommends
recycling as the next best option. The acids used in this method should be reused as practicable by
purifying by electrochemical techniques. The only other chemicals used in this method are the
neat materials used in preparing standards. These standards are used in extremely small amounts
and pose little threat to the environment when managed properly. Standards should be prepared in
volumes consistent with laboratory use to minimize the disposal of excess volumes of expired
standards.
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Method 1632
14.2 For information about pollution prevention that may be applied to laboratories and research
institutions, consult Lew 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.
15.2 Acids and samples at pH <2 must be neutralized before being disposed, or must be handled as
hazardous waste.
15.3 For further information on waste management, consult The Waste Management Manual for
Laboratory Personnel and Less is Better: Laboratory Chemical Management for Waste
Reduction, both available from the American Chemical Society's Department of Government
Relations and Science Policy, 1155 16th Street NW, Washington, DC 20036.
16.0 References
16.1 Crecelius, E.A.; Bloom, N.S.; Cowan, C.E.; Jenne, E.A. Speciation of Selenium and Arsenic in
Natural Waters and Sediments, Volume 2: Arsenic Speciation. Final Report. Prepared for
Electric Power Research Institute, Palo Alto, CA by Battelle, Pacific Northwest Laboratories,
Richland, WA. 1986.
16.2 Andreae, M.O. "Determination of Arsenic Species in Natural Waters," Anal Chem. 1977,49,
820.
16.3 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 St SW, Washington,
DC 20460 (January 1996).
16.4 Patterson, C.C.; Settle, D.M. "Accuracy in Trace Analysis"; In National Bureau of Standards
Special Publication 422; LaFleur, P.O., Ed., U.S. Government Printing Office, Washington, DC,
1976.
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Method 1632
16.5 "Working with Carcinogens," Department of Health, Education, and Welfare, Public Health
Service, Centers for Disease Control, NIOSH, Publication 77-206, Aug. 1977, NTIS PB-277256.
16.6 "OSHA Safety and Health Standards, General Industry," OSHA 2206,29 CFR 1910.
16.7 "Safety in Academic Chemistry Laboratories," ACS Committee on Chemical Safety, 1979.
16.8 "Standard Methods for the Examination of Water and Wastewater," 18th ed. and later revisions,
American Public Health Association, 1015 15th Street NW, Washington DC 20005, 1-35: Section
1090 (Safety), 1992.
16.9 "Results of the EPA Method 1632 Validation Study," July 1996. Available from the EPA Sample
Control Center, 300 N. Lee St., Alexandria, VA, 22314; 703/519-1140.
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 the 12-hour periods 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 Calibration Standard (CAL)—A solution prepared from a dilute mixed standard and/or stock
solutions and used to calibrate the response of the instrument with respect to analyte
concentration.
17.4 Equipment Blank—An aliquot of reagent water that is subjected in the laboratory to all aspects
of sample collection and analysis, including contact with all sampling devices and apparatus. The
purpose of the equipment blank is to determine if the sampling devices and apparatus for sample
collection have been adequately cleaned before shipment to the field site. An acceptable
equipment blank must be achieved before the sampling devices and apparatus are used for sample
collection. In addition, equipment blanks should be run on random, representative sets of gloves,
storage bags, and plastic wrap for each lot to determine if these materials are free from
contamination before use.
17.5 Field Blank—An aliquot of reagent water that is placed in a sample container in the laboratory,
shipped to the field, and treated as a sample in all respects, including contact with the sampling
devices and exposure to sampling site conditions, storage, preservation, and all analytical
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Method 1632
procedures, which may include filtration. The purpose of the field blank is to determine if the
field or sample transporting procedures and environments have contaminated the sample.
17.6 Field Duplicates (FD1 and FD2)—Two separate samples collected in separate sample bottles at
the same time and place under identical circumstances and treated exactly the same throughout
field and laboratory procedures. Analyses of FD1 and FD2 give a measure of the precision
associated with sample collection, preservation, and storage, as well as with laboratory
procedures.
17.7 Initial Precision and Recovery (DPR)—Four aliquots of the ongoing precision and recovery
standard analyzed to establish the ability to generate acceptable precision and accuracy. IPRs are
performed before a method is used for the first time and any time the method or instrumentation is
modified.
17.8 Intercomparison Study—An exercise in which samples are prepared and split by a reference
laboratory, then analyzed by one or more testing laboratories and the reference laboratory. The
intercomparison, with a reputable laboratory as the reference laboratory, serves as the best test of
the precision and accuracy of the analyses at natural environmental levels.
17.9 Laboratory Blank—An aliquot of reagent water that is treated exactly as a sample including
exposure to all glassware, equipment, solvents, reagents, internal standards, and surrogates that are
used with samples. The laboratory blank is used to determine if analytes or interferences are
present in the laboratory environment, the reagents, or the apparatus.
17.10 Laboratory Control Sample (LCS)—See Ongoing Precision and Recovery (OPR) Standard.
17.11 Laboratory Duplicates (LD1 and LD2)—Two aliquots of the same sample taken in the
laboratory from the same sample bottle and analyzed separately using the referenced method.
Analyses of LD1 and LD2 indicate precision associated with laboratory procedures, but not with
sample collection, preservation, transportation, or storage procedures.
17.12 Laboratory Fortified Blank—See Ongoing Precision and Recovery (OPR) Standard.
17.13 Laboratory Fortified Sample Matrix—See Matrix Spike (MS) and Matrix Spike Duplicate
(MSD).
17.14 Laboratory Reagent Blank—See Laboratory Blank.
17.15 Matrix Spike (MS).and Matrix Spike Duplicate (MSD)—Aliquots of an environmental sample
to which known quantities of the analytes are added in the laboratory. The MS and MSD are
analyzed exactly like a sample. Their purpose is to quantify the bias and precision caused by the
sample matrix. The background concentrations of the analytes in the sample matrix must be
determined in a separate aliquot and the measured values in the MS and MSD corrected for
background concentrations.
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Method 1632
17.16
17.17
17.18
17.19
17.20
17.21
17.22
17.23
17.24
17.25
17.26
17.27
May—This action, activity, or procedural step is optional.
May Not—This action, activity, or procedural step is prohibited.
Method Blank—See Laboratory Blank.
Minimum Level (ML)—The lowest level at which the entire analytical system must give a
recognizable signal and acceptable calibration point for the analyte. It is equivalent to the
concentration of the lowest calibration standard, assuming that all method-specified sample
weights, volumes, and cleanup procedures have been employed. The ML is calculated by
multiplying the MDL by 3.18 and rounding the result to the number nearest to (1, 2, or 5) x 10°,
where n is an integer.
Must—This action, activity, or procedural step is required.
Ongoing Precision and Recovery (OPR) Standard - A laboratory blank spiked with known
quantities of analytes. The OPR is analyzed exactly like a sample. Its purpose is to assure that the
results produced by the laboratory remain within the limits specified in the referenced methods for
precision and accuracy.
Preparation Blank—See Laboratory Blank.
Primary Dilution Standard—A solution containing the analytes that is purchased or prepared
from stock solutions and diluted as needed to prepare calibration solutions and other solutions.
Quality Control Sample (QCS)—A sample containing all or a subset of the analytes 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 normal preparation process.
Reagent Water—Water demonstrated to be free from the metal(s) of interest and potentially
interfering substances at the MDL for that metal in the referenced method.
Should—This action, activity, or procedural step is suggested but not required.
Stock Solution—A solution containing an analyte that is prepared using a reference material
traceable to EPA, the National Institute of Science and Technology (NIST), or a source that will
attest to the purity and authenticity of the reference material.
Draft, July 1996
27
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Method 1632
Table 1
Arsenic Analysis Using Method 1632: Lowest Water Quality Criterion,
Method Detection Limit, and Minimum Level
Metal
Arsenic (As)
Lowest Ambient Water
Quality Criterion1
18ng/L
Method Detection Limit (MDL) and
Minimum Level (ML)
MDL<2>
3ng/L
ML(3)
lOng/L
1. Lowest of the freshwater, marine, and human health ambient water quality criteria promulgated by EPA for 9 States and the District of
Columbiaat40CFRPartl31 onMay4, 1995 (60 FR 22229)
2. Method Detection Limit as determined by the procedure in 40 CFR Part 136, Appendix B.
3. Minimum Level (ML)
Table 2
Quality Control Acceptance Criteria for Performance Tests In EPA Method 1632
Metal
As
IPR (Section 9.2)
s X
<42% 59-143%
OPR
(Section 9.6)
55-146%
CALVER
(Section 10.2)
76-116%
MS/MSD
(Section 9.3)
%R RPD
55-146% <20%
28
Draft, July 1996
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Method 1632
TABLE 3: TYPICAL SPECTROPHOTOMETER
SETTINGS
Parameter
EDL energy
EDL power
Wavelength
Slit width
Typical Setting
59
8W
193.7 nm
0.7 nm
TABLE 4: TYPICAL FLOWS AND PRESSURES FOR GASES IN THE HYDRIDE
GENERATION SYSTEM
Gas
Flow Rate (mL/min)
Pressure (lb/in2)
He
H2
Air
150
350
180
10
20
20
Draft, July 1996
29
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Method 1632
Figure 1. Arsenic Speciation Apparatus: (a) Quartz Cuvette Burner Tube, (b) Reaction Vessel, and (c) Schematic
Diagram
1B
REACTION VESSEL
-J, JflL %wMv 4-Way Valve
UgWPath
H, Input
From Trap
1C
SCHEMATIC DIAGRAM
Arsenic
i E.D.L
ao B H ToVariac •
jogftl — -^ivr^'O i ; -iTr" *\ r
1
{
!)
1 1
i
1
i 4-
;
'
9
XX ) j
Connector I 1
From Trap LJ
To Burner t"
80= C |
Hz
Wire-wound
Pyrex U-Tube
—Half-packed with
15% OV-3 on
Chromasorb "W
^
«^;
f?
i
Atomic
Absorpti
Detector
1
jC—
r
Air
Quartz
Cuvette
Burner Tube
Chart Recorder Output
'30
Draft, July 1996
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