United States Office of Water EPA 821 -R-95-032
Environmental Protection Engineering and Analysis Division (4303) April 1995
Agency Washington, DC 20460
v°/EPA Method 1639: Determination of Trace
Elements in Ambient Waters by
Stabilized Temperature Graphite
Furnace Atomic Absorption
U.8, Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevard, 12th Floor
Chicago, !L 60604-3590
> Printed on Recycled Paper
-------
Method 1639
Acknowledgments
Method 1639 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 Interface, Inc.
The following researchers in marine chemistry contributed to the philosophy behind this method. Their
contribution is gratefully acknowledged.
Shier Berman, National Research Council, Ottawa, Ontario, Canada
Nicholas Bloom, Frontier Geosciences, Inc., Seattle, Washington
Paul Boothe and Gary Steinmetz, Texas A&M University, College Station, Texas
Eric Crecelius, Battelle Marine Sciences Laboratory, Sequim, Washington
Russell Flegal, University of California at Santa Cruz, California
Gary Gill, Texas A&M University at Galveston, Texas
Carlton Hunt and Dion Lewis, Battelle Ocean Sciences, Duxbury, Massachusetts
Carl Watras, Wisconsin Department of Natural Resources, Boulder Junction, Wisconsin
Herb Windom and Ralph Smith, Skidaway Institute of Oceanography, Savannah, Georgia
In addition, J.T. Creed, L.B. Lobring, T.D. Martin, and J.W. O'Dell of the EPA Office of Research and
Development's Environmental Monitoring Systems Laboratory in Cincinnati, Ohio, are gratefully
acknowledged for developing the analytical procedures described in this method.
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: 202/260-7120
Fax: 202/260-7185
April 1995
-------
Method 1639
Introduction
This analytical method was designed to support 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 about the physical fate (e.g., concentration and dispersal) of
pollutants, and their effects on ecological and human health, and 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 their 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 those 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). This rule includes water quality criteria for 13 metals, on which the new sampling and
analysis methods are based. Method 1639 was specifically developed to provide reliable measurements
of six of these metals at EPA WQC levels using stabilized temperature graphite furnace atomic absorption
techniques.
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 the 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, so long as those procedures are demonstrated
to yield reliable results.
Requests for additional copies should be directed to
US EPA NCEPI
11029 Kenwood Road
Cincinnati, OH 45242
513/489-8190
April 1995
-------
Method 1639
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 that researchers in trace metals analysis have found certain procedures
essential in successfully analyzing samples and avoiding contamination; however, these procedures
can be modified or omitted if the laboratory can demonstrate that data quality is not affected.
iv April 1995
-------
Method 1639
Method 1639
Determination of Trace Elements in Ambient Waters
by Stabilized Temperature Graphite Furnace
Atomic Absorption
1.0 Scope and Application
1.1 This method provides procedures to determine dissolved elements in ambient waters at EPA
water quality criteria (WQC) levels using stabilized temperature graphite furnace atomic
absorption (GFAA). It may also be used to determine total recoverable element concentrations
in these waters. This method was developed by integrating the analytical procedures contained
in EPA Method 200.9 with the stringent quality control (QC) and sample handling procedures
necessary to avoid contamination and ensure the validity of analytical results during sampling
and analysis for metals at EPA WQC levels. This method contains QC procedures that will
ensure that contamination will be detected when blanks accompanying samples are analyzed.
This method is accompanied by Method 1669: Sampling Ambient Water for Determination of
Trace Metals at EPA Water Quality Criteria Levels (the "Sampling Method"). The Sampling
Method is necessary to ensure that contamination will not compromise trace metals
determinations during the sampling process.
1.2 This method is applicable to the following analytes:
Analyte
Antimony
Cadmium
Nickel
Selenium
Trivalent Chromium
Zinc
Symbol
(Sb)
(Cd)
(Ni)
(Se)
(Cr3*)
(Zn)
Chemical Abstract Services
Registry Number (CASRN)
7440-36-0
7440-43-9
7440-02-0
7782-49-2
16065-83-1
7440-66-6
Table 1 lists the EPA WQC levels, the Method Detection Limit (MDL) for each metal, and the
Minimum Level (ML) set for each metal in this method. Instrument operating conditions for
the applicable elements are listed in Table 3. They are intended as a guide and are typical of a
system optimized for the element employing commercial instrumentation. However, actual
linear working ranges will be dependent on the sample matrix, instrumentation, and selected
operating conditions.
April 1995
-------
Method 1639
1.3 This method is not intended to determine 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 mid to high part-per-billion
(ppb) range, whereas ambient metals concentrations are normally in the low part-per-trillion
(ppt) to low ppb range.
1.4 The ease of contaminating ambient water samples with the metal(s) of interest and interfering
substances cannot be overemphasized. This method includes suggestions for improvements in
facilities and analytical techniques that should maximize the ability of the laboratory to make
reliable trace metals determinations and minimize contamination. These suggestions are given
in Section 4.0, "Contamination and Interferences," and are based on findings of researchers
performing trace metals analyses (References 1-8). Additional suggestions for improving
existing facilities can 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.
1.5 Clean and ultraclean—The terms "clean" and "ultraclean" have been applied to the techniques
needed to reduce or eliminate contamination in trace metals determinations. These terms are
not used in this method, however, because they lack an exact definition. However, the
information provided in this method is consistent with and is copied from summary guidance
on clean and ultraclean techniques (Reference 9).
1.6 This method follows the EPA Environmental Methods Management Council's "Format for
Method Documentation" (Reference 10).
1.7 This method is "performance based"; i.e., an alternate procedure or technique may be used,
as long as the performance requirements in the method are met. Section 9.1.2 gives details of
the tests and documentation required to support equivalent performance.
1.8 For dissolved metal determinations, samples must be filtered through a 0.45-/zm capsule filter
at the field site. The filtering procedures are described in the Sampling Method. Except for
trivalent chromium, the filtered samples may be preserved in the field or transported to the
laboratory for preservation. Procedures for field preservation are detailed in the Sampling
Method; procedures for laboratory preservation are provided in this method. To determine
trivalent chromium, a field preparation step, which is described in the Sampling Method, is
used to isolate the trivalent chromium.
1.9 To determine total recoverable analytes in ambient water samples, a digestion/extraction is
required before analysis when the elements are not in solution (e.g., aqueous samples that
may contain particulate and suspended solids).
1.10 The sensitivity and limited linear dynamic range (LDR) of GFAA often implies the need to
dilute a sample prior to analysis. The actual magnitude of the dilution as well as the
cleanliness of the labware used to perform the dilution can dramatically influence the quality
of the analytical results. Therefore, sample types requiring large dilutions (> 50:1) should be
analyzed by an another approved test procedure that has a larger LDR or that is inherently
less sensitive than GFAA.
April 1995
-------
Method 1639
1.11 This method should be used by analysts experienced in the use of graphite furnace atomic
absorption spectroscopy, the interpretation of spectral and matrix interferences, and procedures
for their correction, and only by personnel thoroughly trained in handling and analyzing
samples to determine metals at EPA WQC levels. A minimum of six months' experience with
commercial instrumentation is recommended.
1.12 This method is accompanied by a data verification and validation guidance document titled
Guidance on the Documentation and Evaluation of Trace Metals Data Collected for CWA
Compliance Monitoring. Data users should state the data quality objectives (DQOs) required
for a project before using this method.
2.0 Summary of Method
2.1 An aliquot of a well-mixed, homogeneous aqueous sample is accurately measured for sample
processing. For total recoverable analysis of an aqueous sample containing undissolved
material, analytes are first solubilized by gentle refluxing with nitric and hydrochloric acids.
After cooling, the sample is made up to volume, mixed, and centrifuged or allowed to settle
overnight prior to analysis. To determine dissolved analytes in a filtered aqueous sample
aliquot, the sample is made ready for analysis by the appropriate addition of nitric acid, and
then diluted to a predetermined volume and mixed before analysis.
2.2 The analytes listed in this method are determined by stabilized temperature platform graphite
furnace atomic absorption (STPGFAA). In STPGFAA, the sample and the matrix modifier are
first pipeted onto the platform or a device that provides delayed atomization. The furnace
chamber is then purged with a continuous flow of a premixed gas (95% argon/5% hydrogen)
and the sample is dried at a relatively low temperature (about 120°C) to avoid spattering.
Once dried, the sample is pretreated in a char or ashing step, which is designed to minimize
the interference effects caused by the concomitant sample matrix. After the char step, the
furnace is allowed to cool before atomization. The atomization cycle is characterized by rapid
heating of the furnace to a temperature in which the metal (analyte) is atomized from the
pyrolytic graphite surface into a stopped gas flow atmosphere of argon containing 5%
hydrogen. (Only selenium is determined in an atmosphere of high-purity argon.) The
resulting atomic cloud absorbs the element-specific atomic emission produced by a hollow
cathode lamp (HCL) or an electrodeless discharge lamp (EDL). Following analysis, the
furnace is subjected to a cleanout period of high temperature and continuous argon flow.
Because the resulting absorbance usually has a nonspecific component associated with the
actual analyte absorbance, an instrumental background correction device is required to subtract
from the total signal the component that is nonspecific to the analyte. In the absence of
interferences, the background corrected absorbance is directly related to the concentration of
the analyte. Interferences relating to STPGFAA (Section 4.0) must be recognized and
corrected. Suppressions or enhancements of instrument response caused by the sample matrix
must be corrected by the method of standard addition (Section 12.5).
3.0 Definitions
3.1 Apparatus—Throughout this method, the sample containers, sampling devices, instrumentation,
and all other materials and devices used in sample collection, sample processing, and sample
analysis activities will be referred to collectively as the Apparatus.
April 1995
-------
Method 1639
3.2 Other definitions of terms are given in the glossary (Section 18) at the end of this method.
4.0 Contamination and Interferences
4.1 Preventing contamination of ambient water samples during the sampling and analytical process
constitutes one of the greatest difficulties encountered with trace metals determinations. Over
the last two decades, marine chemists have recognized that much of the historical data
regarding the concentrations of dissolved trace metals in seawater are erroneously high because
the concentrations reflect contamination from sampling and analysis rather than ambient levels.
More recently, historical trace metals data collected from freshwater rivers and streams have
been shown to be similarly biased because of contamination during sampling and analysis
(Reference 15). 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. For
example, it has been demonstrated that dental work (e.g., mercury amalgam fillings) in the
mouths of laboratory personnel can contaminate samples that are directly exposed to exhalation
(Reference 3).
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 cannot be compromised by contamination of
samples. Requirements and suggestions for control of sample contamination
are given in this method and in the Sampling Method.
4.3.1.2 Substances in a sample cannot be allowed to contaminate the laboratory work
area or instrumentation used for trace metals measurements. Requirements and
suggestions for protecting the laboratory are given in this method.
4.3.1.3 While contamination control is essential, personnel health and safety remain
the highest priority. Requirements and suggestions for personnel safety are
given in Section 5 of this method and in the Sampling Method.
4.3.2 Avoid contamination—The best way to control contamination is to completely avoid
exposure of the sample to contamination in the first place. Avoiding exposure means
performing operations in an area known or thought to be free from contamination.
Two of the most important factors in avoiding or 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.
April 1995
-------
Method 1639
4.3.3 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
must be performed in a class 100 clean bench or a nonmetal glove box fed by particle-
free air or nitrogen. Digestions must be performed in a nonmetal fume hood, ideally
situated in the clean room.
4.3.4 Minimize exposure—The Apparatus that will contact samples, blanks, or standard
solutions must only be opened or exposed 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 processing a given batch of samples, all work surfaces in
the hood, clean bench, or glove box in which the samples will be processed should be
cleaned by wiping with a lint-free cloth or wipe soaked with reagent water.
4.3.6 Wear gloves—Sampling personnel must wear clean, nontalc gloves (Section 6.9.7)
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 metals determinations at ambient
WQC levels must be nonmetallic and/or free of material that may contain metals.
4.3.7.1 Construction materials—Only the following materials should come in contact
with samples: fluoropolymer (FEP, PTFE), conventional or linear
polyethylene, polycarbonate, polypropylene, polysulfone, or ultrapure quartz.
PTFE is less desirable than FEP because the sintered material in PTFE may
contain contaminates and is susceptible to serious memory contamination
(Reference 6). Fluoropolymer or glass 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
(Reference 3). All materials, regardless of construction, that will directly or
indirectly contact the sample must be cleaned using the procedures described
in Section 11 and must be known to be clean and metal free before
proceeding.
4.3.7.2 The following materials have been found to contain trace metals and must not
be used to hold liquids that come in contact with the sample or must not
contact the sample itself, unless these materials have been shown to be free of
the metals of interest at the desired level: Pyrex, Kimax, methacrylate,
polyvinylchloride, nylon, and Vycor (Reference 6). In addition, highly colored
plastics, paper cap liners, pigments used to mark increments on plastics, and
rubber all contain trace levels of metals and must be avoided (Reference 12).
April 1995
-------
Method 1639
4.3.7.3 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.
4.3.7.4 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, 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. For samples containing high levels of metals, it may be necessary
to acid clean or replace the connecting tubing or inlet system to ensure that
contamination will not affect subsequent measurements. Samples known or
suspected to contain the lowest concentration of metals should be analyzed
first followed by samples containing higher levels. For instruments containing
autosamplers, the laboratory should keep track of which station is used for a
given sample. When an unusually high concentration of a metal is detected in
a sample, the station used for that sample should be cleaned more thoroughly
to prevent contamination of subsequent samples, and the results for subsequent
samples should be checked for evidence of the metal(s) that occurred in high
concentration.
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 inorganic substances are
processed and analyzed. As stated in Section 1.0, this method is not intended
for 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
April 1995
-------
Method 1639
bag and then subsequently transfer the contamination to the sample.
Therefore, it is imperative that every piece of the Apparatus that is directly or
indirectly used in collecting, processing, and analyzing 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, samples should be processed and
analyzed as far as possible from sources of airborne contamination.
4.4 Interferences—Several interference sources may cause inaccuracies in determining trace
elements by GFAA. These interferences can be classified into three major subdivisions,
namely spectral, matrix, and memory.
4.4.1 Spectral interferences are caused by the resulting absorbance of light by a molecule or
atom that is not the analyte of interest or emission from black body radiation.
4.4.1.1 Spectral interferences caused by an element only occur if there is a spectral
overlap between the wavelength of the interfering element and the analyte of
interest. Fortunately, this type of interference is relatively uncommon in
STPGFAA because of the narrow atomic line widths associated with
STPGFAA. In addition, the use of appropriate furnace temperature programs
and high spectral purity lamps as light sources can minimize the possibility of
this type of interference. However, molecular absorbances can span several
hundred nanometers, producing broadband spectral interferences. This type of
interference is far more common in STPGFAA. The use of matrix modifiers,
selective volatilization, and background correctors are all attempts to eliminate
unwanted nonspecific absorbance. The nonspecific component of the total
absorbance can vary considerably from sample type to sample type. Therefore,
the effectiveness of a particular background correction device may vary
depending on the actual analyte wavelength used as well as the nature and
magnitude of the interference. The background correction device to be used
with this method is not specified; however, it must provide an analytical
condition that is not subject to the occurring interelement spectral interferences
of palladium on copper, iron on selenium, and aluminum on arsenic.
4.4.1.2 Spectral interferences are also caused by the emissions from black body
radiation produced during the atomization furnace cycle. This black body
emission reaches the photomultiplier tube, producing erroneous results. The
magnitude of this interference can be minimized by proper furnace tube
alignment and monochromator design. In addition, atomization temperatures
that adequately volatilize the analyte of interest without producing unnecessary
black body radiation can help reduce unwanted background emission during
analysis.
4.4.2 Matrix interferences are caused by sample components that inhibit the formation of
free atomic analyte atoms during the atomization cycle.
April 1995
-------
Method 1639
4.4.2.1 Matrix interferences can be chemical or physical. In this method the use of a
delayed atomization device that provides stabilized temperatures is required.
These devices provide an environment that is more conducive to the formation
of free analyte atoms and thereby minimize this type of interference. This
type of interference can be detected by analyzing the sample plus a sample
aliquot fortified with a known concentration of the analyte. If the determined
concentration of the analyte addition is outside a designated range, a possible
matrix effect should be suspected (Section 9.3).
4.4.2.2 The use of nitric acid is preferred for GFAA analyses to minimize vapor state
anionic chemical interferences; however, in this method hydrochloric acid is
required to maintain stability in solutions containing antimony. When
hydrochloric acid is used, the chloride ion vapor state interferences must be
reduced using an appropriate matrix modifier. In this method a combination
modifier of palladium, magnesium nitrate, and a hydrogen (5%)/argon (95%)
gas mixture is used for this purpose. The effects and benefits of using this
modifier are discussed in detail in Reference 13 (Section 17.0). Listed in
Section 4.4.3 are some typical observed effects.
4.4.3 Specific element interferences
Antimony: Antimony suffers from an interference produced by K2SO4 (Reference 14).
In the absence of hydrogen in the char cycle (1300°C), K2SO4 produces a relatively
high (1.2 abs) background absorbance, which can produce a false signal, even with
Zeeman background correction. However, this background level can be dramatically
reduced (0.1 abs) by the use of a hydrogen/argon gas mixture in the char step. This
reduction in background is strongly influenced by the temperature of the char step.
Because the actual furnace temperature may vary from instrument to instrument, it
should be determined on an individual basis.
Cadmium: The HC1 present from the digestion procedure can influence the sensitivity
for Cd. The use of 20 uL of a 1% HC1 solution with Pd as a modifier results in a
80% loss in sensitivity relative to the analyte in a 1 % HNO3 solution. The use of
Pd/Mg/H2 as a matrix modifier reduces this suppression to less than 10% (Reference
13).
Selenium: Iron has been shown to suppress Se response with continuum background
correction (Reference 14). In addition, the use of hydrogen as a purge gas during the
dry and char steps can cause a suppression in Se response if not purged from the
furnace before atomization.
4.4.4 Memory interferences result from analyzing a sample containing a high concentration
of an element (typically a high atomization temperature element) that cannot be
removed quantitatively in one complete set of furnace steps. The analyte that remains
in the furnace can produ ce false positive signals on subsequent sample(s). Therefore,
the analyst should establish the analyte concentration that can be injected into the
furnace and adequately removed in one complete set of furnace cycles. If this
concentration is exceeded, the sample should be diluted and a blank analyzed to ensure
the memory effect has been eliminated before reanalyzing the diluted sample.
April 1995
-------
Method 1639
5.0 Safety
5.1 The toxicity or carcinogenicity of reagents used in this method have not been fully established.
Each chemical should be regarded as a potential health hazard and exposure to these
compounds should be as low as reasonably achievable.
5.1.1 Each laboratory is responsible for maintaining a current awareness file of OSHA
regulations regarding the safe handling of the chemicals specified in this method
(References 15-18). A reference file of material safety data sheets should also be
available to all personnel involved in the chemical analysis. It is also suggested that
the laboratory perform personal hygiene monitoring of each analyst who uses this
method and make the results available to the analyst. The references and bibliography
at the end of Reference 18 are particularly comprehensive in dealing with the general
subject of laboratory safety.
5.1.2 Concentrated nitric and hydrochloric acids present various hazards and are moderately
toxic and extremely irritating to skin and mucus membranes. These reagents should be
used in a fume hood whenever possible. If eyes or skin are touched, they must be
flushed with a large volume of water. Protective clothing should always be worn
along with safety glasses or a shield for eye protection, and proper mixing of these
reagents must be observed.
5.2 The acidification of samples containing reactive materials may result in the release of toxic
gases, such as cyanides or sulfides. Acidification of samples should be done in a fume hood.
5.3 All personnel handling environmental samples known to contain or to have been in contact
with human waste should be immunized against known disease-causing agents.
5.4 The graphite tube during atomization emits intense UV radiation. Suitable precautions should
be taken to protect personnel from such a hazard.
5.5 The use of the argon/hydrogen gas mixture during the dry and char steps may emit a
considerable amount of HC1 gas. Therefore, adequate ventilation is required.
6.0 Apparatus, Equipment, and Supplies
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 Facility
6.1.1 Clean room—Class 100, 200-ft2 minimum, with down-flow, positive-pressure
ventilation, air-lock entrances, and pass-through doors
April 1995
-------
Method 1639
6.1.1.1 Construction materials—Nonmetallic, preferably plastic sheeting attached
without metal fasteners. If painted, paints that do not contain the metal(s) of
interest must be used.
6.1.1.2 Adhesive mats, for use at entry points to control dust and dirt from shoes
6.1.2 Fume hoods, nonmetallic, two minimum, with one installed internal to the clean room
6.1.3 Clean benches, class 100, one installed in the clean room; the other adjacent to the
analytical instrument(s) for preparation of samples and standards
6.2 Graphite furnace atomic absorbance spectrophotometer
6.2.1 The GFAA spectrometer must be capable of programmed heating of the graphite tube
and the associated delayed atomization device. The instrument must be equipped with
an adequate background correction device capable of removing undesirable nonspecific
absorbance over the spectral region of interest and provide an analytical condition not
subject to the occurrence of interelement spectral overlap interferences. The furnace
device must be capable of using an alternate gas supply during specified cycles of the
analysis. The capability to record relatively fast (< 1 s) transient signals and evaluate
data on a peak area basis is preferred. In addition, a recirculating refrigeration bath is
recommended for improved reproducibility of furnace temperatures.
6.2.2 Single-element HDLs or single-element EDLs along with the associated power supplies
6.2.3 Argon gas supply (high-purity grade, 99.99%) for use during the atomization of
selenium, for sheathing the furnace tube when in operation, and during furnace
cleanout
6.2.4 Alternate gas mixture (hydrogen 5%/argon 95%) for use as a continuous gas flow
environment during the dry and char furnace cycles
6.2.5 Autosampler capable of adding matrix modifier solutions to the furnace, a single
addition of analyte, and completing methods of standard additions when required
6.3 Analytical balance, with capability to measure to 0.1 mg, to weigh solids and to prepare
standards
6.4 A temperature-adjustable hot plate capable of maintaining a temperature of 95°C
6.5 A centrifuge with guard bowl, electric timer, and brake (optional)
6.6 A gravity convection drying oven with thermostatic control capable of maintaining 105°C (±
5°C)
6.7 Alkaline detergent—Liquinox®, Alconox®, or equivalent
6.8 pH meter or pH paper
10 April 1995
-------
Method 1639
6.9 Labware—To determine trace levels of elements, contamination and loss are of prime
consideration. Potential contamination sources include improperly cleaned laboratory
apparatus and general contamination within the laboratory environment from dust and other
contaminants. A clean laboratory work area should be designated for trace element sample
handling. Sample containers can introduce positive and negative errors in determining trace
elements by contributing contaminants through surface desorption or leaching, and depleting
element concentrations through adsorption processes. All labware must be metal free.
Suitable construction materials are fluoropolymer (FEP, PTFE), conventional or linear
polyethylene, polycarbonate, and polypropylene. Fluoropolymer should be used when samples
are to be analyzed for mercury. All labware should be cleaned according to the procedure in
Section 11.4. Gloves, plastic wrap, storage bags, and filters may all be used new without
additional cleaning unless results of the equipment blank pinpoint any of these materials as a
source of contamination. In this case, either an alternate supplier must be obtained or the
materials must be cleaned.
NOTE: Chromic acid must not be used for cleaning glassware.
6.9.1 Volumetric flasks, graduated cylinders, funnels and centrifuge tubes
6.9.2 Assorted calibrated pipets
6.9.3 PTFE (or other suitable material) beakers, 250 mL with PTFE covers
6.9.4 Narrow-mouth storage bottles, FEP (fluorinated ethylene propylene) with ETFE
(ethylene tetrafluorethylene) screw closure, 125-mL to 250-mL capacities
6.9.5 One-piece stem FEP wash bottle with screw closure, 125-mL capacity
6.9.6 Tongs—For removal of Apparatus from acid baths. Coated metal tongs may not be
used.
6.9.7 Gloves—Clean, nontalc polyethylene, latex, or vinyl; various lengths. Heavy gloves
should be worn when working in acid baths as baths will contain hot, strong acids.
6.9.8 Buckets or basins—5-50 L capacity, for acid soaking of the Apparatus
6.9.9 Nonmetallic brushes for scrubbing Apparatus
6.9.10 Storage bags—Clean, zip-type, nonvented, colorless polyethylene (various sizes) for
storage of Apparatus
6.9.11 Plastic wrap—Clean, colorless polyethylene to store Apparatus
6.10 Sampling Equipment—The sampling team may contract with the laboratory or a cleaning
facility that is responsible for cleaning, storing, and shipping all sampling devices, sample
bottles, filtration equipment, and all other Apparatus used to collect ambient water samples.
Before shipping the equipment to the field site, the laboratory or facility must generate an
April 1995 11
-------
Method 1639
acceptable equipment blank (Section 9.5.3) to demonstrate that the sampling equipment is free
from contamination.
6.10.1 Sampling devices—Before ambient water samples are collected, consideration should
be given to the type of sample to be collected and the devices to be used (grab,
surface, or subsurface samplers). The laboratory or cleaning facility must clean all
devices used for sample collection. Various types of samplers are described in the
Sampling Method. Cleaned sampling devices should be stored in polyethylene bags or
wrap.
6.10.2 Sample bottles—Fluoropolymer (FEP, PTFE), conventional or linear polyethylene,
polycarbonate, or polypropylene; 500 mL with lids. Cleaned sample bottles should be
filled with 0.1% HC1 (v/v) until use.
NOTE: If mercury is a target analyte, fluoropolymer or glass bottles must be used.
6.10.3 Filtration apparatus
6.10.3.1 Filters, Gelman Supor 0.45-um, 15-mm diameter filter capsules
(German 12175), or equivalent
6.10.3.2 Peristaltic pump—115-V a.c., 12-V d.c., internal battery, variable
speed, single-head (Cole-Parmer, portable, "Masterflex L/S," Catalog
No. H-07570-10 drive with Quick Load pump head, Catalog No. H-
07021-24, or equivalent).
6.10.3.3 Tubing for use with peristaltic pump—Styrene/ethylene/butylene/
silicone (SEES) resin, approx 3/8-in i.d. by approximately 3 ft (Cole-
Parmer size 18, Catalog No. G-06464-18, or approximately 1/4-in i.d.,
Cole-Parmer size 17, Catalog No. G-06464-17, or equivalent). Tubing
is cleaned by soaking in 5-10% HC1 solution for 8-24 h, 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.
7.0 Reagents and Standards
Reagents may contain elemental impurities that might affect analytical data. Only high-purity
reagents should be used. If the purity of a reagent is in question, it should be analyzed for
contamination. All acids used for this method must be of ultra high-purity grade or
equivalent. Suitable acids are available from a number of manufacturers. Redistilled acids
prepared by subboiling distillation are acceptable.
7.1 Reagents for cleaning Apparatus, sample bottle storage, and sample preservation and
preparation
7.1.1 Nitric acid, concentrated (sp gr 1.41), Seastar or equivalent
12 April 1995
-------
Method 1639
7.1.2 Nitric acid (1+1)—Add 500 mL concentrated nitric acid to 400 mL of regent water
and dilute to 1 L.
7.1.3 Nitric acid (1+5)—Add 50 mL concentrated HNO3 to 250 mL reagent water.
7.1.4 Nitric acid (1+9)—Add 100 mL concentrated nitric acid to 400 mL of reagent water
and dilute to 1 L.
7.1.5 Hydrochloric acid, concentrated (sp gr 1.19)
7.1.6 Hydrochloric acid (1+1)—Add 500 mL concentrated hydrochloric acid to 400 mL of
reagent water and dilute to 1 L.
7.1.7 Hydrochloric acid (1+4)—Add 200 mL concentrated hydrochloric acid to 400 mL of
reagent water and dilute to 1 L.
7.1.8 Hydrochloric acid (HC1): IN trace metal grade
7.1.9 Hydrochloric acid (HC1): 10% wt, trace metal grade
7.1.10 Hydrochloric acid (HC1): 1% wt, trace metal grade
7.1.11 Hydrochloric acid (HC1): 0.5% (v/v), trace metal grade
7.1.12 Hydrochloric acid (HC1): 0.1% (v/v) ultrapure grade
7.1.13 Tartaric acid (CASRN 87-69-4)
7.2 Reagent water—Reagent water is demonstrably free of the metal(s) of interest and potentially
interfering substances at the MDL for that metal listed in Table 1. It is prepared by
distillation, deionization, reverse osmosis, anodic/cathodic stripping voltammetry, or other
technique that removes the metal(s) and potential interferent(s).
7.3 Matrix modifier—Dissolve 300 mg palladium (Pd) powder in concentrated HNO3 (1 mL of
HNO3, adding 0.1 mL of concentrated HC1, if necessary). Dissolve 200 mg of Mg(NO3)2 in
reagent water. Pour the two solutions together and dilute to 100 mL with reagent water.
NOTE: It is recommended that the matrix modifier be analyzed separately to assess
the contribution of the modifier to the absorbance of calibration and reagent blank
solutions.
7.4 Standard stock solutions—Stock standards may be purchased or prepared from ultra high-
purity grade chemicals (99.99% to 99.999% pure). All compounds must be dried for 1 h at
105°C, unless otherwise specified. It is recommended that stock solutions be stored in FEP
bottles. Replace stock standards when succeeding dilutions for preparation of calibration
standards can not be verified.
April 1995 13
-------
Method 1639
CAUTION: Many of these chemicals are extremely toxic if inhaled or swallowed
(Section 5.1). Wash hands thoroughly after handling.
Below are typical stock solution preparation procedures for 1 L quantities, but for the purpose
of pollution prevention, the analyst is encouraged to prepare smaller quantities when possible.
Concentrations are calculated based upon the weight of the pure element or upon the weight of
the compound multiplied by the fraction of the analyte in the compound.
From pure element,
Concentration = we*ht
volume (L)
From pure compound,
Concentration = weight (mg) x gravimetric factor
volume (L)
Where:
gravimetric factor = the weight fraction of the analyte in the compound
7.4.1 Antimony solution, stock, 1 mL = 1000 ug Sb: Dissolve 1.000 g of antimony powder,
weighed accurately to at least four significant figures, in 20.0 mL (1+1) HNO3 and
10.0 mL concentrated HC1. Add 100 mL reagent water and 1.50 g tartaric acid.
Warm solution slightly to effect complete dissolution. Cool solution and add reagent
water to volume in a 1-L volumetric flask.
7.4.2 Cadmium solution, stock, 1 mL = 1000 ug Cd: Dissolve 1.000 g Cd metal, acid
cleaned with (1+9) HNO3, weighed accurately to at least four significant figures, in 50
mL (1+1) HNO3 with heating to effect dissolution. Let solution cool and dilute with
reagent water in a 1-L volumetric flask.
7.4.3 Chromium solution, stock, 1 mL = 1000 ug Cr: Dissolve 1.923 g CrO3 (Cr fraction =
0.5200), weighed accurately to at least four significant figures, in 120 mL (1+5)
HNO3. When solution is complete, dilute to volume in a 1-L volumetric flask with
reagent water.
7.4.4 Nickel solution, stock, 1 mL = 1000 pg Ni: Dissolve 1.000 g of nickel metal, weighed
accurately to at least four significant figures, in 20.0 mL hot concentrated HNO3, cool,
and dilute to volume in a 1-L volumetric flask with reagent water.
7.4.5 Selenium solution, stock, 1 mL = 1000 ug Se: Dissolve 1.405 g SeO2 (Se fraction =
0.7116), weighed accurately to at least four significant figures, in 200 mL reagent
water and dilute to volume in a 1-L volumetric flask with reagent water.
14 April 1995
-------
Method 1639
7.4.6 Zinc solution, stock 1 mL = 1000 pg Zn: Pickle zinc metal in (1+9) nitric acid to an
exact weight of 0.100 g. Dissolve in 5 mL (1+1) nitric acid, heating to effect
solution. Cool and dilute to 100 mL with reagent water.
7.5 Preparation of calibration standards—Fresh calibration standards should be prepared every 2
weeks, or as needed. Dilute each of the stock standard solutions to levels appropriate to the
operating range of the instrument using the appropriate acid diluent (see note). Calibration
standards should be prepared at a minimum of three concentrations, one of which must be at
the ML (Table 1), and another of which must be near the upper end of the linear dynamic
range. Calibration standards should be initially verified using a quality control sample
(Section 7.7).
NOTE: The appropriate acid diluent for the determination of dissolved elements is 1%
HNO3. For total recoverable elements in waters, the appropriate acid diluent is 2%
HNO3 and 1% HCl. The reason for these different diluents is to match the types of
acids and the acid concentrations of the samples with the acid present in the standards
and blanks.
7.6 Blanks—The laboratory should prepare the following types of blanks. A calibration blank is
used to establish the analytical calibration curve; the laboratory (method) blank is used to
assess possible contamination from the sample preparation procedure and to assess spectral
background; and the rinse blank is used to flush the instrument autosampler uptake system.
All diluent acids should be made from concentrated acids (Section 7.1) and reagent water
(Section 7.2). In addition to these blanks, the laboratory may be required to analyze field
blanks (Section 9.5.2) and equipment blanks (Section 9.5.3).
7.6.1 Calibration blank—The calibration blank consists of the appropriate acid diluent
(Section 7.5 note) (HC1/HNO3) in reagent water. The calibration blank should be
stored hi a FEP bottle.
7.6.2 Laboratory blank—The laboratory blank must contain all the reagents in the same
volumes as used in processing the samples. The laboratory blank must be carried
through the same entire preparation scheme as the samples including digestion, when
applicable (Section 9.5.1).
7.6.3 The rinse blank is prepared as needed by adding 1.0 mL of concentrated HNO3 and
1.0 mL of concentrated HCl to 1 L of reagent water.
7.7 Quality control sample (QCS)—The QCS must be obtained from an outside source different
from the standard stock solutions and prepared in the same acid mixture as the calibration
standards (Section 7.5 note). The concentration of the analytes hi the QCS solution should be
such that the resulting solution will provide an absorbance reading of approximately 0.1. The
QCS solution should be stored in a FEP bottle and analyzed as needed to meet data quality
needs. A fresh solution should be prepared quarterly or more frequently as needed.
7.8 Ongoing precision and recovery (OPR) sample—The OPR should be prepared in the same acid
mixture as the calibration standards (Section 7.5 note) by combining method analytes at
April 1995 75
-------
Method 1639
appropriate concentrations. The OPR must be carried through the same entire preparation
scheme as the samples including sample digestion, when applicable (Section 9.6).
8.0 Sample Collection, Filtration, Preservation, and Storage
8.1 Before an aqueous sample is 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
aliquoting 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 Sample collection—Samples are collected as described in the Sampling Method.
8.3 Sample filtration—For dissolved metals, samples and field blanks are filtered through a 0.45-
um capsule filter at the field site. Filtering procedures are described in the Sampling Method.
For the determination of total recoverable elements, samples are not filtered but should be
preserved according to the procedures in Section 8.4.
8.4 Sample preservation—Preservation of samples and field blanks for both dissolved and total
recoverable elements may be performed in the field at time of collection or in the laboratory.
However, to avoid the hazards of strong acids in the field and transport restrictions, to
minimize the potential for sample contamination, and to expedite field operations, the sampling
team may prefer to ship the samples to the laboratory within 2 weeks of collection. Samples
and field blanks should be preserved at the laboratory immediately upon receipt. For all
metals, preservation involves the addition of 10% HNO3 (Section 7.1.3) to bring the sample to
pH < 2. For samples received at neutral pH, approximately 5 mL of 10% HNO3 per liter will
be required.
8.4.1 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 clean 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. When the nature of the sample is either
unknown or known to be hazardous, acidification should be done in a fume hood
(Section 5.2).
8.4.2 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. The sample should
then verified to be pH < 2 just before withdrawing an aliquot for processing or direct
analysis. If for some reason such as high alkalinity the sample pH is verified to be
> 2, more acid must be added and the sample held for 16 h until verified to be pH < 2
(Section 8.1).
8.4.3 With each sample set, preserve a method blank and an OPR sample in the same way
as the sample(s).
16 April 1995
-------
Method 1639
8.4.4 Store sample bottles in polyethylene bags at 0-4°C until analysis.
8.5 Samples collected to determine trivalent chromium
8.5.1 Samples to determine trivalent chromium are prepared at the field site by isolating the
trivalent chromium using a iron hydroxide coprecipitation technique. These
procedures are described in the Sampling Method.
8.5.2 The sampling team is also responsible for the preparation of laboratory blanks, OPRs,
and MS/MSD samples for trivalent chromium as described in the Sampling Method.
9.0 Quality Assurance/Quality Control
9.1 Each laboratory that uses this method is required to operate a formal quality assurance
program (Reference 19). The minimum requirements of this program consist of an initial
demonstration of laboratory capability, analysis of samples spiked with metals of interest to
evaluate and document data quality, and analysis of standards and blanks as tests of continued
performance. Laboratory performance is compared with established performance criteria to
determine that results of the analysis meet the performance characteristics of the method.
9.1.1 The analyst will demonstrate the ability to generate acceptable accuracy and precision
with this method. This ability is established as described in Section 9.2.
9.1.2 In recognition of advances that are occurring in analytical technology, the analyst is
permitted 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 substituting a colorimetric technique or changes that degrade method performance,
are not allowed. If an analytical technique other than the techniques specified in the
method is used, then 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 a modification is made to the method, the analyst is required to
repeat the procedure in Section 9.2. If the detection limit of the method will
be affected by the change, the laboratory is required to demonstrate that the
MDL (40 CFR Part 136, Appendix B) is lower than the MDL for that analyte
in this method, or one-third the regulatory compliance level, whichever is
higher. If calibration will be affected by the change, 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:
9.1.2.2.1 The names, titles, addresses, and telephone numbers of the
analyst(s) who performed the analyses and modification, and of
the quality control officer who witnessed and will verify the
analyses and modification
April 1995 77
-------
Method 1639
9.1.2.2.2 A listing of metals measured, by name and CAS Registry
number
9.1.2.2.3 A narrative stating reason(s) for the modification(s)
9.1.2.2.4 Results from all quality control (QC) tests comparing the
modified method with this method, including the following:
(a) Calibration
(b) Calibration verification
(c) Initial precision and recovery (Section 9.2)
(d) Analysis of blanks
(e) Accuracy assessment
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, the following:
(a) Sample numbers and other identifiers
(b) Digestion/preparation or extraction dates
(c) Analysis dates and times
(d) Analysis sequence/run chronology
(e) Sample weight or volume
(f) Volume before extraction/concentration step
(g) Volume after each extraction/concentration step
(h) Final volume before analysis
(i) Injection volume
(j) Dilution data, differentiating between dilution of a
sample or extract
(k) Instrument and operating conditions (make, model,
revision, modifications)
(1) Sample introduction system (auto sampler, flow
injection system, etc.)
(m) Operating conditions (background corrections,
temperature program, flow rates, etc.)
(n) Detector (type, operating conditions, etc.)
(o) Mass spectra, printer tapes, and other recordings of raw
data
(p) Quantitation reports, data system outputs, and other
data to link raw data to results reported
9.1.3 Analyses of blanks are required to demonstrate freedom from contamination. The
required types, procedures, and criteria for analysis of blanks are described in Section
9.5.
9.1.4 The laboratory will spike at least 10% of the samples with the metal(s) of interest to
monitor method performance. This test is described in Section 9.3 of this method.
When results of these spikes indicate atypical method performance for samples, an
18 April 1995
-------
Method 1639
alternative extraction or cleanup technique must be used to bring method performance
within acceptable limits. If method performance for spikes 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 will, 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. These procedures are described in Sections 10.7 and 9.6 of this
method.
9.1.6 The laboratory shall maintain records to define the quality of data that are generated.
Development of accuracy statements is described in Section 9.3.4.
9.2 Initial demonstration of laboratory capability
9.2.1 Method detection limit—To establish the ability to detect the trace metals of interest,
the analyst shall determine the MDL for each analyte acceding 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 Table 1, or one-third the regulatory compliance limit,
whichever is greater. MDLs 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 they be redetermined.
9.2.2 Initial precision and recovery (IPR)—To establish the ability to generate acceptable
precision and recovery, the analyst will perform the following operations.
9.2.2.1 Analysis of four aliquots of reagent water spiked with the metal(s) of interest
at two to three times the ML (Table 1), according to the procedures in Section
12. 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, computation of the average percent
recovery (X) for the metal(s) in each aliquot and the standard deviation of the
recovery (s) for each metal.
9.2.2.3 For each metal, comparison of s and X with the corresponding limits for initial
precision and recovery in Table 2. If s and X for all metal(s) meet the
acceptance criteria, system performance is acceptable and analysis of blanks
and samples may begin. If, however, any individual s exceeds the precision
limit or any individual X falls outside the range for accuracy, system
performance is unacceptable for that metal. The problem must be corrected
and the test repreated (Section 9.2.2.1).
9.2.3 Linear dynamic range (LDR)—The upper limit of the LDR must be established for the
wavelength used for each analyte by determining the signal responses from a minimum
of six different concentration standards across the range, two of which are close to the
upper limit of the LDR. Determined LDRs must be documented and kept on file. The
linear calibration range that may be used for the analysis of samples should be judged
April 1995 19
-------
Method 1639
by the analyst from the resulting data. The upper LDR limit should be an observed
signal no more than 10% below the level extrapolated from the four lower standards.
The LDRs should be verified whenever, in the judgment of the analyst, a change in
analytical performance caused by either a change in instrument hardware or operating
conditions dictates that they be redetermined.
NOTE: Multiple deanout furnace cycles may be necessary to fully define or use the
LDR for certain elements such as chromium. For this reason the upper limit of the
linear calibration range may not correspond to the upper LDR limit.
Determined sample analyte concentrations that exceed the upper limit of the linear calibration
range must either be diluted and reanalyzed with concern for memory effects (Section 4.4) or
analyzed by another approved method.
9.2.4 Quality control sample (QCS)—When beginning the use of this method, on a quarterly
basis or as required to meet data quality needs, the calibration standards and acceptable
instrument performance must be verified with the preparation and analyses of a QCS
(Section 7.7). To verify the calibration standards, the determined mean concentration
from three analyses of the QCS must be within ± 10% of the stated QCS value. If the
QCS is not within the required limits, an immediate second analysis of the QCS is
recommended to confirm unacceptable performance. If the calibration standards and/or
acceptable instrument performance cannot be verified, the source of the problem must
be identified and corrected before proceeding with further analyses.
9.3 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 batch (samples collected
from the same site at the same time, to a maximum of 10 samples), whichever is more
frequent. Blanks (e.g., field blanks) may not be used for MS/MSD analysis.
9.3.1 Determine the concentration of the MS and MSD as follows:
9.3.1.1 If, as in compliance monitoring, the concentration of a specific metal in the
sample is being checked against a regulatory concentration limit, the spike
must be at that limit or at one to five 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 one to five times the background concentration or at
one to five times the ML in Table 1, whichever is greater.
9.3.2 Assess spike recovery
9.3.2.1 Determine the background concentration (B) of each metal by analyzing one
sample aliquot according to the procedure in Section 12.
20 April 1995
-------
Method 1639
9.3.2.2 If necessary, prepare a QC check sample concentrate that will produce the
appropriate level (Section 9.3.1) in the sample when the concentrate is added.
9.3.2.3 Spike a second sample aliquot with the QC check sample concentrate and
analyze it to determine the concentration after spiking (A) of each metal.
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) for each metal with the corresponding QC
acceptance criteria found in Table 2. If any individual P falls outside the designated
range for recovery, that metal has failed the acceptance criteria.
9.3.3.1 For a metal that has failed the acceptance criteria, analyze the ongoing
precision and recovery standard (Section 9.6). If the OPR is within its
respective limit for the metal(s) that failed (Table 2), the analytical system is in
control and the problem is attributable to the sample matrix.
9.3.3.2 For samples that exhibit matrix problems, further isolate the metal(s) from the
sample matrix using dilution, 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 the metal remains outside the acceptance criteria, the
analytical result for that metal in the unspiked sample is suspect and may not
be reported for regulatory compliance purposes.
9.3.4 Assess recovery for samples and maintain records.
9.3.4.1 After the analysis of five samples of a given matrix type (river water, lake
water, etc.) for which the metal(s) pass the tests in Section 9.3.3, compute the
average percent recovery (R) and the standard deviation of the percent
recovery (SR) for the metal(s). 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 70-110%.
9.3.4.2 Update the accuracy assessment for each metal in each matrix on a regular
basis (e.g., after each 5-10 new measurements).
9.4 Precision of MS and MSD
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 is
inflated when the background concentration is near the spike concentration.
April 1995 21
-------
Method 1639
RPD -
(Dl+D2)/2
Where:
Dl = concentration of the analyte in the MS sample
D2 = concentration of the analyte in the MSD sample
9.4.2 The relative percent difference between the MS and the MSD must be less than 20
percent. If this criterion is not met, the analytical system is judged to be out of
control. Correct the problem and reanalyze all samples in the sample batch associated
with the MS/MSD that failed the RPD test.
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 sample preparation process (Section 12) on the same 12-
hour shift, to a maximum of 10 samples). To demonstrate freedom from
contamination, analyze the blank immediately after analysis of the OPR
(Section 9.6).
9.5.1.2 If the metal of interest 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
samples and a new method blank prepared, and the sample batch and fresh
method blank reanalyzed.
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). Analyze
the blank immediately before analyzing the samples in the batch.
9.5.2.2 If the metal of interest 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,
22 April 1995
-------
Method 1639
then 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 using any sampling equipment 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
11.4), 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 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 Sampler check blanks are generated by filling a large carboy or
other container with reagent water (Section 7.2) 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.
9.5.3.2.2 The sampler check blank must be analyzed using the
procedures given in this method. If any metal of interest or
any potentially interfering substance is detected in the blank,
April 1995 23
-------
Method 1639
the source of contamination/ 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.
9.5.3.2.3 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.
9.6 Ongoing precision and recovery
9.6.1 Prepare an ongoing 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 sample preparation process
(Section 12) on the same 12-hour shift, to a maximum of 10 samples) by spiking an
aliquot of reagent water with the metal(s) of interest.
9.6.2 Analyze the OPR sample before analyzing the method blank and samples from the
same batch.
9.6.3 Compute the percent recovery of each metal in the OPR sample.
9.6.4 For each metal, compare the concentration with the limits for ongoing recovery in
Table 2. If all metals meet the acceptance criteria, system performance is acceptable
and analysis of blanks and samples may proceed. If, however, any individual recovery
falls outside of the range given, the analytical processes are not being performed
properly for that metal. Correct the problem, prepare the sample batch again, and
repeat the ongoing precision and recovery 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 each metal in each matrix. Update QC charts to form a graphic representation
of continued laboratory performance. Develop a statement of laboratory accuracy for
each metal 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 contained 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
metals by this method.
9.8 Depending on specific program requirements, the laboratory may be required to analyze field
duplicates collected to determine the precision of the sampling technique. The RPD between
field duplicates should be less than 20%. If the RPD of the field duplicates exceeds 20%, the
laboratory should communicate it to the sampling team so that the source of error can be
identified and corrective measures taken before the next sampling event.
24 April 1995
-------
Method 1639
10.0 Calibration and Standardization
10.1 Recommended wavelengths and instrument operating conditions are listed in Table 3.
However, because of differences between makes and models of spectrophotometers and
electrothermal furnace devices, the actual instrument conditions selected may vary from those
listed.
10.2 Before using this method, optimize the instrument operating conditions. The analyst should
follow the instructions provided by the manufacturer while using the conditions listed in Table
3 as a guide. Of particular importance is the determination of the charring temperature limit
for each analyte. This limit is the furnace temperature setting where a loss in analyte will
occur before atomization. This limit should be determined by conducting char temperature
profiles for each analyte and when necessary, in the matrix of question. The charring
temperature selected should minimize background absorbance while providing some furnace
temperature variation without loss of analyte. For routine analytical operation the charring
temperature is usually set at least 100°C below this limit. The optimum conditions selected
should provide the lowest reliable MDLs and be similar to those listed in Table 3. Once the
optimum operating conditions are determined, they should be recorded and available for daily
reference.
10.3 Before an initial calibration, determine the linear dynamic range of the analyte (Section 9.2.3)
using the optimized instrument operating conditions (Section 10.2). For all determinations,
allow an instrument and hollow cathode lamp warm-up period of not less than 15 minutes. If
an EDL is to be used, allow 30 minutes for warm-up.
10.4 Before daily calibrating the instrument, inspect the graphite furnace, the sample uptake system,
and the autosampler injector for any change in the system that would affect instrument
performance. Clean the system and replace the graphite tube and/or platform when needed or
daily.
10.5 After the warm-up period but before calibration, demonstrate instrument stability by analyzing
a standard solution with a concentration three times the ML a minimum of five times. The
resulting relative standard deviation (RSD) of absorbance signals must be < 5%. If the RSD is
> 5%, determine and correct the cause before calibrating the instrument.
10.6 For initial and daily operation, calibrate the instrument according to the instrument
manufacturer's recommended procedures using the calibration blank (Section 7.6.1) and
calibration standards (Section 7.5) prepared at three or more concentrations, one of which must
be at the ML (Table 1), and another that must be near the upper end of the linear dynamic
range.
April 1995 25
-------
Method 1639
10.6.1 Calculate the response factor (RF) for each metal in each CAL solution using the
following equation and the height or area produced by the metal.
Where:
Rx = height or area of the signal for the metal
Cx = concentration of compound injected
10.6.2 For each metal, calculate the mean RF (M), the standard deviation (SD) of the RF, and
the relative standard deviation (RSD) of the mean, where RSD = 100 x SD/M.
10.6.3 Linearity-If the RSD of the mean RF for any metal is less than 25% over the
calibration range, an averaged RF may be used for that analyte. Otherwise, a
calibration curve for that metal must be used over the calibration range.
10.7 Calibration verification—Immediately following calibration, perform an initial calibration
verification. Adjustment of the instrument is performed until verification criteria are met.
Only after these criteria are met may blanks and samples be analyzed.
10.7.1 Analyze the midpoint calibration standard (Section 10.6).
10.7.2 Compute the percent recovery of each metal using the average RF or the calibration
curve obtained in the initial calibration.
10.7.3 For each metal, compare the recovery with the corresponding limit for calibration
verification in Table 2. If all metals meet the acceptance criteria, system performance
is acceptable and analysis of blanks and samples may continue using the response from
the initial calibration. If any individual value falls outside the range given, system
performance is unacceptable for that compound. Locate and correct the problem
and/or prepare a new calibration check standard and repeat the test (Sections
10.7.1-10.7.3), or recalibrate the system according to Section 10.6.
10.7.4 Verify calibration following every 10 samples by analyzing the midpoint 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 the last acceptable calibration verification must be reanalyzed.
10.8 Analyze a calibration blank following every calibration verification to demonstrate that there is
no carryover of the analytes of interest and that the analytical system is free from
contamination. If the concentration of an analyte in the blank result exceeds the MDL, correct
the problem, verify the calibration (Section 10.7), and repeat the analysis of the calibration
blank.
26 April 1995
-------
Method 1639
11.0 Procedures for Cleaning the Apparatus
11.1 All sampling equipment, sample containers, and labware should be cleaned in a designated
cleaning area that has been demonstrated to be free of trace element contaminants. Such areas
may include class 100 clean rooms as described by Moody (Reference 20), labware cleaning
areas as described by Patterson and Settle (Reference 6), or clean benches.
11.2 Materials, such as gloves (Section 6.9.7), storage bags (Section 6.9.10), and plastic wrap
(Section 6.9.11) may be used new without additional cleaning unless the results of the
equipment blank pinpoint any of these materials as a source of contamination. In this case,
either an alternate supplier must be obtained or the materials must be cleaned.
11.3 Cleaning procedures—Proper cleaning of the Apparatus is extremely important, because the
Apparatus may not only contaminate the samples but may also remove the analytes of interest
by adsorption onto the container surface.
NOTE: If laboratory, field, and equipment blanks (Section 9.5) from Apparatus
cleaned with fewer cleaning steps than those detailed below show no levels of analytes
above the MDL, than those cleaning steps that do not eliminate these artifacts may be
omitted provided all performance criteria outlined in Section 9 are met.
11.3.1 Bottles, labware, and sampling equipment
11.3.1.1 Fill a clean basin (Section 6.9.8) with a sufficient quantity of a 0.5%
solution of liquid detergent (Section 6.7), and completely immerse each
piece of ware. Allow to soak in the detergent for at least 30 minutes.
11.3.1.2 Using a parr of clean gloves (Section 6.9.7) and clean nonmetallic
brushes (Section 6.9.9), thoroughly scrub down all materials with the
detergent.
11.3.1.3 Place the scrubbed materials in a clean basin. Change gloves.
11.3.1.4 Thoroughly rinse the inside and outside of each piece with reagent
water until there is no sign of detergent residue (e.g., until all soap
bubbles disappear).
11.3.1.5 Change gloves, immerse the rinsed equipment in a hot (50-60°C) bath
of concentrated reagent grade HNO3 (Section 7.1.1) and allow to soak
for at least 2 h.
11.3.1.6 After soaking, use clean gloves and tongs to remove the Apparatus and
thoroughly rinse with distilled, deionized water (Section 7.2).
11.3.1.7 Change gloves and immerse the Apparatus in a hot (50-60°C) bath of
IN trace metal grade HC1 (Section 7.1.8), and allow to soak for at
least 48 h.
April 1995 27
-------
Method 1639
11.3.1.8 Thoroughly rinse all equipment and bottles with reagent water.
Proceed to Section 11.3.2 for labware and sampling equipment.
Proceed to Section 11.3.3 for sample bottles.
11.3.2 Labware and sampling equipment
11.3.2.1 After cleaning, air-dry in a class 100 clean air bench.
11.3.2.2 After drying, wrap each piece of ware/equipment in two layers of
polyethylene film.
11.3.3 Fluoropolymer sample bottles—These bottles should be used if mercury is a target
analyte.
11.3.3.1 After cleaning, fill sample bottles with 0.1% (v/v) ultrapure HC1
(Section 7.1.11) and cap tightly. It may be necessary to use a strap
wrench to ensure a tight seal.
11.3.3.2 After capping, double-bag each bottle in polyethylene zip-type bags.
Store at room temperature until sample collection.
11.3.4 Bottles, labware, and sampling equipment (polyethylene or material other than
fluoropolymer)
11.3.4.1 Apply the steps outlined above in Section 11.3.1.1-11.3.1.8 to all
bottles, labware, and sampling equipment. Proceed to Section 11.3.4.2
for bottles or Section 11.3.4.3 for labware and sampling equipment.
11.3.4.2 After cleaning, fill each bottle with 0.1% (v/v) ultrapure HC1 (Section
7.1.12). Double-bag each bottle in a polyethylene bag to prevent
contamination of the surfaces with dust and dirt. Store at room
temperature until sample collection.
11.3.4.3 After rinsing labware and sampling equipment, air-dry in a class 100
clean air bench. After drying, wrap each piece of ware/equipment in
two layers of polyethylene film.
NOTE: Polyethylene bottles cannot be used to collect samples that will be analyzed
for mercury at trace (e.g., 0.012 ug/L) levels because of the potential of vapors
diffusing through the polyethylene.
11.3.4.4 Polyethylene bags—If polyethylene bags need to be cleaned, clean
according to the following procedure:
11.3.4.4.1 Partially fill with cold, (1+1) HNO3 (Section 7.1.2) and rinse
with distilled deionized water (Section 7.2).
28 April 1995
-------
Method 1639
11.3.4.4.2 Dry by hanging upside down from a plastic line with a plastic
clip.
11.3.5 Silicone tubing, fluoropolymer tubing, and other sampling apparatus—Clean any
silicone, fluoropolymer, or other tubing used to collect samples by rinsing with 10%
HC1 (Section 7.1.9) and flushing with water from the site before sample collection.
11.3.6 Extension pole—Submerging the 2-m polyethylene extension pole (used in with the
optional grab sampling device) in acid solutions as described above is impractical
because of its length. If such an extension pole is used, a nonmetallic brush (Section
6.9.9) should be used to scrub the pole with reagent water and the pole wiped down
with acids as described in Section 11.3.4 above. After cleaning, the pole should be
wrapped in polyethylene film.
11.4 Storage—Store each piece or assembly of the Apparatus in a clean, single polyethylene zip-
type bag. If shipment is required, place the bagged apparatus in a second polyethylene zip-
type bag.
11.5 All cleaning solutions and acid baths should be periodically monitored for accumulation of
metals that could lead to contamination. When levels of metals in the solutions become too
high, the solutions and baths should be changed and the old solutions neutralized and
discarded in compliance with state and federal regulations.
12.0 Procedures for Sample Preparation and Analysis
12.1 Aqueous sample preparation—dissolved analytes (except trivalent chromium)
12.1.1 To determine dissolved analytes in ground and surface waters, pipet an aliquot (> 20
mL) of the filtered, acid-preserved sample into a clean 50-mL polypropylene centrifuge
tube. Add an appropriate volume of (1+1) nitric acid to adjust the acid concentration
of the aliquot to approximate a 1% (v/v) nitric acid solution (e.g., add 0.4 mL (1+1)
HNO3 to a 20-mL aliquot of sample). Cap the tube and mix. The sample is now
ready for analysis. Allowance for sample dilution should be made in the calculations.
12.2 Aqueous sample preparation—total recoverable analytes (except trivalent chromium)
NOTE: To preclude contamination during sample digestion, it may be necessary to
perform the open-beaker, total-recoverable digestion procedure described in Sections
12.2.1-12.2.6 in a fume hood that is located in a clean room. An alternate digestion
procedure is provided in Section 12.2.7; however, this procedure has not undergone
interlaboratory testing.
12.2.1 To determine total recoverable analytes in ambient water samples, transfer a 100-mL
(± 1 mL) aliquot from a well-mixed, acid-preserved sample to a 250-mL Griffin
beaker (Section 6.9.3). If appropriate, a smaller sample volume may be used.
April 1995 29
-------
Method 1639
12.2.2 Add 2 mL (1+1) nitric acid and 1.0 mL of (1+1) hydrochloric acid to the beaker and
place the beaker on the hot plate for digestion. The hot plate should be located in a
fume hood and previously adjusted to provide evaporation at a temperature of
approximately but not higher than 85 °C. (See the following note.) Cover the beaker
or take other necessary steps to prevent sample contamination from the fume hood
environment.
NOTE: For proper heating, adjust the temperature control of the hot plate so that an
uncovered Griffin beaker containing 50 mL of water placed in the center of the hot
plate can be maintained at a temperature of approximately but not higher than 85°C.
(Once the beaker is covered with a watch glass, the temperature of the water will rise
to approximately 95°C.)
12.2.3 Reduce the volume of the sample aliquot to about 20 mL by gentle heating at 85°C.
Do not boil. This step takes about 2 h for a 100-mL aliquot with the rate of
evaporation rapidly increasing as the sample volume approaches 20 mL. (A spare
beaker containing 20 mL of water can be used as a gauge.)
12.2.4 Gently reflux the sample for 30 minutes. (Slight boiling may occur, but vigorous
boiling must be avoided to prevent loss of the HC1-H2O azeotrope.)
12.2.5 Allow the beaker to cool. Quantitatively transfer the sample solution to a 50-mL
volumetric flask or 50-mL class A stoppered graduated cylinder, make to volume with
reagent water, stopper, and mix.
12.2.6 Allow any undissolved material to settle overnight, or centrifuge a portion of the
prepared sample until clear. (If, after centrifuging or standing overnight, the sample
contains suspended solids that would clog the nebulizer, a portion of the sample may
be filtered to remove the solids before analysis. However, care should be exercised to
avoid potential contamination from filtration.) The sample is now ready for analysis.
Because the effects of various matrices on the stability of diluted samples cannot be
characterized, all analyses should be performed as soon as possible after the completed
preparation.
12.2.7 Alternate total recoverable digestion procedure
12.2.7.1 Open the preserved sample under clean conditions. Add ultrapure
nitric and hydrochloric acid at the rate of 10 mL/L and 5 mL/L,
respectively. Remove the cap from the original container only long
enough to add each aliquot of acid. The sample container should not
be filled to the lip by the addition of the acids. However, only
minimal headspace is needed to avoid leakage during heating.
12.2.7.2 Tightly recap the container and shake thoroughly. Place the container
in an oven preheated to 85 °C. The container should be placed on an
insulating piece of material such as wood rather than directly on the
typical metal grating. After the samples have reached 85°C, heat for
two hours. (Total time will be 2.5-3 h depending on the sample size).
30 April 1995
-------
Method 1639
Temperature can be monitored using an identical sample container with
distilled water and a thermocouple to standardize heating time.
12.2.7.3 Allow the sample to cool. The sample is now ready for analysis.
Remove aliquots for analysis under clean conditions.
12.3 Sample preparation for trivalent chromium
12.3.1 When the samples are received at the laboratory, shake the vial until the precipitate on
the filter dissolves.
12.3.2 After the precipitate dissolves, add 4 mL of reagent water.
12.3.3 Samples are now ready for analysis according to Section 12.4.
12.4 Sample Analysis
12.4.1 Initiate instrument operating configuration. Tune and calibrate the instrument for the
analytes of interest (Section 10.0).
12.4.2 Use an autosampler to introduce all solutions into the graphite furnace. Once the
standard, sample or QC solution plus the matrix modifier is injected, the furnace
controller completes furnace cycles and cleanout period as programmed. Analyte
signals must be integrated and collected as peak area measurements. Background
absorbances, background corrected analyte signals, and determined analyte
concentrations on all solutions must be able to be displayed on a CRT for immediate
review by the analyst and be available as hard copy for documentation to be kept on
file. Rush the autosampler solution uptake system with the rinse blank (Section 7.6.3)
between each solution injected.
12.4.3 Analyze samples in the same operational manner used in the calibration routine.
12.4.4 During the analysis of samples, the laboratory must comply with the required quality
control described in Sections 9 and 10.
12.4.5 For every new or unusual matrix, when practical, it is highly recommended that an
inductively coupled plasma atomic emission spectrometer be used to screen for high
element concentration. Information gained from this screening may be used to prevent
potential damage to the instrument and to better estimate which elements may require
analysis by graphite furnace.
12.4.6 Determined sample analyte concentrations that are 90% or more of the upper limit of
calibration must either be diluted with acidified reagent water and reanalyzed with
concern for memory effects (Section 4.4.4), or determined by another approved test
procedure.
12.4.7 When it is necessary to assess an operative matrix interference (e.g., signal reduction
due to high dissolved solids), the MSA described in Section 12.5 is recommended.
April 1995 31
-------
Method 1639
12.4.8 Report data as directed in Section 13.
12.5 Standard Additions—If the MSA is required, the following procedure is recommended:
12.5.1 The MSA (Reference 21) involves preparing new standards in the sample matrix by
adding known amounts of standard to one or more aliquots of the processed sample
solution. This technique compensates for a sample constituent that enhances or
depresses the analyte signal, thus producing a different slope from that of the
calibration standards. It will not correct for additive interference, which causes a
baseline shift. The simplest version of this technique is the single-addition method.
The procedure is as follows: Two identical aliquots of the sample solution, each of
volume Vx, are taken. To the first (labeled A) is added a small volume Vs of a
standard analyte solution of concentration Cs. To the second (labeled B) is added the
same volume Vs of the solvent. The analytical signals of A and B are measured and
corrected for nonanalyte signals. The unknown sample concentration Cx is calculated:
c = -*v*Cs
where SA and SB are the analytical signals (corrected for the blank) of solutions A and
B, respectively. Vs and Cs should be chosen so that SA is roughly twice SB on the
average. It is best if Vs is made much less than Vx, and thus Cs is much greater than
Cx, to avoid excess dilution of the sample matrix. If a separation or concentration step
is used, the additions are best made first and carried through the entire procedure. For
the results from this technique to be valid, the following limitations must be taken into
consideration:
1. The response vs amount must be linear.
2. The chemical form of the analyte added must respond in the same manner as
the analyte in the sample.
3. The interference effect must be constant over the working range of concern.
4. The signal must be corrected for any additive interference.
13.0 Data Analysis and Calculations
13.1 Sample data should be reported in units of pg/L (parts-per-billion; ppb). Report results at or
above the ML for metals found in samples and determined in standards. Report all results for
metals found in blanks, regardless of level.
13.2 Compute the concentration of each analyte in the sample using the averaged RF determined
from the calibration data (Section 10.6) according to the following equation:
32 April 1995
-------
Method 1639
where the terms are defined in Section 10.6.1.
13.3 For total recoverable aqueous analytes (Sections 12.2.1-12.2.6), multiply solution analyte
concentrations by the dilution factor 0.5, when 100-mL aliquot is used to produce the 50-mL
final solution. If a different aliquot volume other than 100 mL is used for sample preparation,
adjust the dilution factor accordingly. Also, account for any additional dilution of the prepared
sample solution needed to complete the determination of analytes exceeding the upper limit of
the calibration curve. Do not report data below the determined analyte MDL concentration or
below an adjusted detection limit reflecting smaller sample aliquots used in processing or
additional dilutions required to complete the analysis.
13.4 For data values less than the ML, two significant figures should be used for reporting element
concentrations. For data values greater than or equal to the ML, three significant figures
should be used.
13.5 The QC data obtained during the analyses provide an indication of the quality of the sample
data and should be provided with the sample results.
14.0 Method Performance
14.1 The MDLs listed in Table 1 and the quality control acceptance criteria listed in Table 2 were
validated in three laboratories (Reference 22) for all dissolved analytes except trivalent
chromium.
15.0 Pollution Prevention
15.1 Pollution prevention encompasses any technique that reduces or eliminates the quantity or
toxicity of waste at the point of generation. Numerous opportunities for pollution prevention
exist in laboratory operation. EPA has established a preferred hierarchy of environmental
management techniques that place 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, EPA
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
volume of expired standards to be disposed.
15.2 For information about pollution prevention that may be applicable to laboratories and research
institutions, consult Less is Better: Laboratory Chemical Management for Waste Reduction,
available from the American Chemical Society's Department of Government Relations and
Science Policy, 1155 16th Street NW, Washington DC 20036, 202/872-4477.
April 1995 33
-------
Method 1639
16.0 Waste Management
16.1 EPA requires that laboratory waste management practices be conducted consistent with all
applicable rules and regulations. The Agency urges laboratories to protect the air, water, and
land by minimizing and controlling all releases from hoods and bench operations, complying
with the letter and spirit of any sewer discharge permits and regulations, and complying with
all solid and hazardous waste regulations, particularly the hazardous waste identification rules
and land disposal restrictions. For further information on waste management, consult The
Waste Management Manual for Laboratory Personnel, available from the American Chemical
Society at the address listed in Section 15.2.
17.0 References
1 Adeloju, S.B.; Bond, A.M. "Influence of Laboratory Environment on the Precision and
Accuracy of Trace Element Analysis," Anal Chem. 1985, 57, 1728.
2 Herman, S.S.; Yeats, P.A. "Sampling of Seawater for Trace Metals," CRC Reviews in
Analytical Chemistry 1985, 16, 1.
3 Bloom, N.S. "Ultra-Clean Sampling, Storage, and Analytical Strategies for the Accurate
Determination of Trace Metals in Natural Waters," presented at the 16th Annual EPA
Conference on the Analysis of Pollutants in the Environment, Norfolk, Virginia, May 5, 1993.
4 Bruland, K.W. 'Trace Elements in Seawater," Chemical Oceanography 1983, 8, 157.
5 Nriagu, J.O.; Larson, G.; Wong, H.K.T.; Azcue, J.M. "A Protocol for Minimizing
Contamination in the Analysis of Trace Metals in Great Lakes Waters," J. Great Lakes
Research 1993, 19, 175.
6 Patterson, C.C.; Settle, D.M. "Accuracy in Trace Analysis," in National Bureau of Standards
Special Publication 422; LaFleur, P.D., Ed., U.S. Government Printing Office: Washington,
DC, 1976.
7 Fitzgerald, W.F.; Watras, C.J. Science of the Total Environment 1989, 87/88, 223.
8 Gill, G.A.; Fitzgerald, W.F. Deep Sea Res. 1985, 32, 287.
9 Prothro, M.G. "Office of Water Policy and Technical Guidance on Interpretation and
Implementation of Aquatic Life Metals Criteria," EPA Memorandum to Regional Water
Management and Environmental Services Division Directors, Oct. 1, 1993.
10 "Format for Method Documentation," distributed by the EPA Environmental Monitoring
Management Council, Washington, DC, Nov. 18, 1993.
11 Windom, H.L; Byrd, J.T.; Smith, R.G., Jr.; Huan, F. "Inadequacy of NASQAN Data for
Assessing Metal Trends in the Nation's Rivers," Environ. Sci. Technol 1991, 25, 1137.
34 April 1995
-------
Method 1639
12 Zief, M.; Mitchell, J.W. "Contamination Control in Trace Metals Analysis," Chemical
Analysis 1976, 47, Chapter 6.
13 Creed, J.T.; Martin, T.D.; Lobring, L.B.; O'Dell, J.W. Environ. Sci. TechnoL, 1992, 26, 102-
106.
14 Waltz, B.; Schlemmar, G.; Mudakavi, J.R. JAAS, 1988, 3, 695.
15 Carcinogens—Working with Carcinogens; Department of Health, Education, and Welfare,
Public Health Service, Center for Disease Control, National Institute for Occupational Safety
and Health, Publication No. 77-206, August 1977. Available from the National Technical
Information Service (NTIS) as PB-277256.
16 OSHA Safety and Health Standards, General Industry, (29 CFR 1910); Occupational Safety
and Health Administration, OSHA 2206 (revised January 1976).
17 Safety in Academic Chemistry Laboratories; American Chemical Society Publication,
Committee on Chemical Safety, 3rd ed., 1979.
18 Proposed OSHA Safety and Health Standards; Laboratories, Occupational Safety and Health
Administration, Federal Register, July 24, 1986.
19 Handbook of Analytical Quality Control in Water and Waste-water Laboratories; U.S.
Environmental Protection Agency. EMSL-Cincinnati, OH, March 1979; EPA-600/4-79-019.
20 Moody, J.R. "NBS Clean Laboratories for Trace Element Analysis," Anal. Chem. 1982, 54,
1358A.
21 Winefordner, J.D. Trace Analysis: Spectroscopic Methods for Elements; in Chemical Analysis,
Vol. 46, pp. 41-42.
22 "Results of the Validation Study for Determination of Trace Metals at EPA Water Quality
Criteria Levels," April 1995. Available from the Sample Control Center (operated by
DynCorp), 300 N. Lee Street, Alexandria, VA 22314, 703/519-1140.
April 1995 35
-------
Method 1639
18.0 Glossary
Many of the terms and definitions listed below are used in the EPA 1600-series methods, but
terms have been cross-referenced to terms commonly used in other methods where possible.
18.1 Ambient Water—Waters in the natural environment (e.g., rivers, lakes, streams, and other
receiving waters), as opposed to effluent discharges.
18.2 Analyte—A metal tested for by the methods referenced in this method. The analytes are
listed in Table 1.
18.3 Apparatus—The sample container and other containers, filters, filter holders, labware, tubing,
pipets, and other materials and devices used for sample collection or sample preparation, and
that will contact samples, blanks, or analytical standards.
18.4 Calibration Blank—A volume of reagent water acidified with the same acid matrix as in the
calibration standards. The calibration blank is a zero standard and is used to calibrate the ICP
instrument (Section 7.6.1).
18.5 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.
18.6 Dissolved Analyte—The concentration of analyte in an aqueous sample that will pass through
a 0.45-um membrane filter assembly before sample acidification (Section 8.3).
18.7 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.
18.8 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 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.
18.9 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.
36 April 1995
-------
Method 1639
18.10 Initial Precision and Recovery (EPR)—Four aliquots of the OPR standard analyzed to
establish the ability to generate acceptable precision and accuracy. IPRs are performed before
the first time a method is used and any time the method or instrumentation is modified.
18.11 Instrument Detection Limit (IDL)—The concentration equivalent to the analyte signal which
is equal to three times the standard deviation of a series of 10 replicate measurements of the
calibration blank signal at the selected analytical wavelength.
18.12 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 method analytes or
interferences are present in the laboratory environment, the reagents, or the apparatus.
(Sections 7.6.2 and 9.5.1).
18.13 Laboratory Control Sample (LCS)—See Ongoing Precision and Recovery (OPR) Standard.
18.14 Laboratory Duplicates (LD1 and LD2)—Two aliquots of the same sample taken in the
laboratory and analyzed separately with identical procedures. Analyses of LD1 and LD2
indicates precision associated with laboratory procedures, but not with sample collection,
preservation, or storage procedures.
18.15 Laboratory Fortified Blank (LFB)—See Ongoing Precision and Recovery (OPR) Standard.
18.16 Laboratory Fortified Sample Matrix (LFM)—See Matrix Spike and Matrix Spike Duplicate.
18.17 Laboratory Reagent Blank (LRB)—See Laboratory Blank.
18.18 Linear Dynamic Range (LDR)—The concentration range over which the instrument response
to an analyte is linear (Section 9.2.3).
18.19 Matrix Modifier—A substance added to the graphite furnace along with the sample to
minimize the interference effects by selective volatilization of either analyte or matrix
components.
18.20 Matrix Spike (MS) and Matrix Spike Duplicate (MSD)—Aliquots of an environmental
sample to which known quantities of the method 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 hi the MS
and MSD corrected for background concentrations (Section 9.3).
18.21 May—This action, activity, or procedural step is optional.
18.22 May Not—This action, activity, or procedural step is prohibited.
18.23 Method Blank—See Laboratory Blank.
April 1995 37
-------
Method 1639
18.24 Method Detection Limit (MDL)—The minimum concentration of an analyte that can be
identified, measured, and reported with 99% confidence that the analyte concentration is
greater than zero (Section 9.2.1 and Table 1).
18.25 Minimum Level (ML)—The lowest level at which the entire analytical system gives a
recognizable signal and acceptable calibration point (Reference 9).
18.26 Must—This action, activity, or procedural step is required.
18.27 Ongoing Precision and Recovery (OPR) Standard—A laboratory blank spiked with known
quantities of the method analytes. The OPR is analyzed exactly like a sample. Its purpose is
to determine whether the methodology is in control and to ensure that the results produced by
the laboratory remain within the method-specified limits for precision and accuracy.
18.28 Preparation Blank—See Laboratory Blank.
18.29 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.
18.30 Quality Control Sample (QCS)—A sample containing all or a subset of the method analytes
at known concentrations. The QCS is obtained from a source outside of 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 outside of the normal
preparation process.
18.31 Reagent Water—Water demonstrated to be free from the method analytes and potentially
interfering substances at the MDL for that metal in the method.
18.32 Should—This action, activity, or procedural step is suggested but not required.
18.33 Standard Addition—The addition of a known amount of analyte to the sample to determine
the relative response of the detector to an analyte within the sample matrix. The relative
response is then used to assess either an operative matrix effect or the sample analyte
concentration.
18.34 Stock Standard Solution—A solution containing one or more method analytes 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.
18.35 Total Recoverable Analyte—The concentration of analyte determined by analysis of the
solution extract of an unfiltered aqueous sample following digestion by refluxing with hot
dilute mineral acid(s) as specified in the method (Section 12.2).
38 April 1995
-------
Method 1639
Table 1
List of Analytes Amenable to Analysis Using Method 1639: Lowest Water Quality Criterion
for Each Metal Species, Method Detection Limits, and Minimum Levels
Metal
Antimony
Cadmium
Chromium (III)
Nickel
Selenium
Zinc
Lowest EPA
Water
Quality
Criterion
ML)1
14
0.32
57
7.1
5
28
Method Detection
Limit (MDL) and
Minimum Level (ML);
V9/L
MDL2
1.9
0.023
0.1
0.65
0.83
0.14
ML3
5
0.05
0.2
2
2
0.5
Notes:
1.
2.
3.
Lowest of the freshwater, marine, and human health WQC promulgated by EPA for 14 states at 40 CFR Part 131 (57 FR 60848), with
hardness-dependent freshwater aquatic life criteria adjusted in accordance with 57 FR 60848 to reflect the worst case hardness of 25
mg/L CaCO3 and all aquatic life criteria adjusted in accordance with the Oct. 1, 1993 Office of Water guidance to reflect dissolved
metals criteria.
Method Detection Limit (MDL) as determined by 40 CFR Part 136, Appendix B.
Minimum Level (ML) calculated by multiplying laboratory-determined MDL by 3.18 and rounding result to nearest multiple of 1, 2,
5,10, 20, 50, etc. in accordance with procedures used by BAD and described in the EPA Draft National Guidance for the Permitting,
Monitoring, and Enforcement of Water Quality-Based Effluent Limitations Set Below Analytical Detection/Quantitation Levels, March
22, 1994.
April 1995
39
-------
Method 1639
Table 2
Quality Control Acceptance Criteria for Performance Tests'
Method
200.9
Metal
Antimony
Cadmium
Chromium
Nickel
Selenium
Zinc
Initial Precision and
Recovery (Section
9.2)
s X
60 24-144
11 67-142
26 76-129
36 69-141
31 60-128
19 67-142
Calibration
Verification
(Section 10.7)
54-114
86-123
89-116
87-123
77-111
86-123
Ongoing Precision
and
Recovery (Section
9.6)
18-150
64-145
74-131
65-145
56-131
67-142
Spike
Recovery
(Section 9.3)
18-150
64-145
74-131
65-145
56-131
67-142
All specifications expressed as percent.
40
April 1995
-------
Method 1639
TABLE 3
RECOMMENDED GRAPHITE FURNACE OPERATING CONDITIONS AND RECOMMENDED
MATRIX MODIFIER1'3
Element
Sb6
Cd
Cr
Ni
Se6
Wavelength
217.6
228.8
357.9
232.0
196.0
Slit
0.7
0.7
0.7
0.2
2.0
Temperature '
Char
1100
800
1650
1400
1000
Atom
2000
1600
26005
2500
2000
1 Matrix Modifier = 0.015 mg Pd + 0.01 mg Mg(NO3)2.
2 A 5% H2 in Ar gas mix is used during the dry and char steps at 300 mL/min for all elements.
3 A cool-down step between the char and atomization is recommended.
4 Actual char and atomization temperatures may vary from instrument to instrument and are best determined on
an individual basis. The actual drying temperature may vary depending on the temperature of the water used
to cool the furnace.
5 A 7-s atomization is necessary to quantitatively remove the analyte from the graphite furnace.
6 An electrodeless discharge lamp was used for this element.
April 1995 41
------- |