United States
Environmental Protection
Agency
C ff ice of Water
(-303!
EPA821-R-95-029
April 1995
v°/EPA Method 1636: Determination of
Hexavalent Chromium by Ion
Chromatography
Cr(vi)
Hexavalent
Chromium
51.996
Printed on Recycled Paper
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&EPA Method 1636: Determination of
Hexavaient Chromium by Ion
Chromatography
* Printed on Recycled Paper
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Method 1636
Acknowledgments
Method 1636 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 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/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, the following personnel at the EPA Office of Research and Development's Environmental
Monitoring Systems Laboratory in Cincinnati, Ohio, are gratefully acknowledged for the development of
the analytical procedures described in this method:
T.D. Martin
J.D. Pfaff
EJ. Arar (DynCorp, formerly Technology Applications, Inc.)
S.E. Long (DynCorp, formerly Technology Applications, Inc.)
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
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Method 1636
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, the effects of pollutants on ecological and human health, and the effect of pollutants on
biological community diversity, productivity, and stability.
Section 303 of the Clean Water Act requires states to set a water quality standard for each body of water
within its boundaries. A state water quality standard consists of a designated use or uses of a waterbody
or a segment of a waterbody, the water quality criteria that are necessary to protect the designated use or
uses, and an antidegradation policy. These water quality standards serve two purposes: (1) they establish
the water quality goals for a specific waterbody, and (2) they are the basis for establishing water quality-
based treatment controls and strategies beyond the technology-based controls required by Sections 301(b)
and 306 of the Clean Water Act.
In defining water quality standards, the state may use narrative criteria, numeric criteria, or both.
However, the 1987 amendments to the Clean Water Act required states to adopt numeric criteria for toxic
pollutants (designated in Section 307(a) of the Act) based on EPA Section 304(a) criteria or other
scientific data, when the discharge or presence of those toxic pollutants could reasonably be expected to
interfere with designated uses.
In some cases, these water quality criteria are as much as 280 times lower than those achievable using
existing EPA methods and required to support technology-based permits. Therefore, EPA developed new
sampling and analysis methods to specifically address state needs for measuring toxic metals at water
quality criteria levels, when such measurements are necessary to protect designated uses in state water
quality standards. The latest criteria published by EPA are those listed in the National Toxics Rule (57
FR 60848). This rule includes water quality criteria for 13 metals, and it is these criteria on which the
new sampling and analysis methods are based. Method 1636 was specifically developed to provide
reliable measurements of hexavalent chromium at EPA WQC levels using ion chromatography 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 Ken wood Road
Cincinnati, OH 45242
513/489-8190
April 1995
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Method 1636
Note: This method is intended to be performance based, and the laboratory is permitted to omit any
step or modify any procedure if 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
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Method 1636
Method 1636
Determination of Hexavalent Chromium by Ion
Chromatography
1.0 Scope and Application
1.1 This method is for the determination of dissolved hexavalent chromium (as CrO42) in ambient
waters at EPA water quality criteria (WQC) levels using ion chromatography (1C). This
method was developed by integrating the analytical procedures in EPA Method 218.6 with the
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.
Chemical Abstract Services
Analyte Registry Number (CASRN)
Hexavalent Chromium (as CrO42) 18540-29-9
1.2 Table 1 lists the EPA WQC level, the method detection limit (MDL), and the minimum level
(ML) for hexavalent chromium (Cr(VI)). Linear working ranges will be dependent on the
sample matrix, instrumentation, and selected operating conditions.
1.3 This method is not intended for determination of metals at concentrations normally found in
treated and untreated discharges from industrial facilities. Existing regulations (40 CFR Parts
400-500) typically limit concentrations in industrial discharges to the 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 and are based on findings of researchers performing trace metals analyses
(References 1-8). Additional suggestions for improvement of existing facilities may be found
in EPA's Guidance for Establishing Trace Metals Clean Rooms in Existing Facilities, which is
available from the National Center tor Environmental Publications and Information (NCEPI)
at the address listed in the introduction to this document.
April 1995
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Method 1636
1.5
not used in this method
1.6
1.7
1.8
and donation
samples should be preserved in the field
1.9
1.10
commercial instrumentation is recommended
1.11
Monitc
objectives (DQOs) required foa proc,
Management coundrs
or
"*"
°-45-
- The filtered
experience with
validation ui
CWA
*** the data
2.0 Summary of Method
2.1
introduced into the ion chromato/raph A
before the Cr(VI), as CrO is sted on h h
'
Postcolumn derivadzationof CrvD wi* dnhe
colored complex at 530 nm d,phenyl
fi,tra,e is adjusted to
°f "* Sample (50~250
from "
SeparatOr co'"mn-
,s followed by detection of the
April 1995
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Method 1636
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.
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 ambient water samples from becoming contaminated during the sampling and
analytical process constitutes one of the greatest difficulties encountered in trace metals
determinations. Over the last two decades, marine chemists have come to recognize that much
of the historical data on the concentrations of dissolved trace metals in seawater are
erroneously high because the concentrations reflect contamination from sampling and analysis
rather than ambient levels. 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 11). 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
which 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 produced cannot be compromised by contamination
of samples. Requirements and suggestions for control of sample contamination
are given in this method and 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.
April 1995
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Method 1636
4.3.2
4.3.3
the most important factors in avoiding/reducin/^6] fr°m contaminati°n. Two of
awareness of potential sources X^^^^^"^011 ^ (1) an
done. Therefore it is imperative that to d attention to work being
carried out by well-trained ™~:. fJ" U™S described in this method
1S a class ,00
should be Performed a la
e an
4.3.4
4.3.5
4.3.6
4.3.7
box so that exposure to m
used, the AppLus shouTd
bench or in a plastic box o
- t,me betJen
samples- blanks- or
r°°m' C'ean bench' or «love
c e,'S minimiZed Whe" not
S"C Wrap' St0red in the
be deaned by wiping Wlh
isessed- a11 work
- nomaic
ot -
clean gloves may touch the AppTam If 1 » ^^ SampleS' 3nd blanks'
glove(s) must r/changed LforeT' in ha ndlin Th f" " ^^ " Wuched' the
that gloves have become con^inted wo"f m§u I Ed^h " " * ^ SUSPeC'e
=^1-^
work activity. q y Stllpped Wlth mmima^ disruption to the
metals, or both.
of metals at amMen,
"onmetamc, tree of material that may contain
-
// 7P95
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Method 1636
of the other materials, resulting either in contamination or low-biased results
(Reference 3). Stainless steel is a major source of chromium contamination.
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 should
not contact the sample or be used to hold liquids that contact the sample,
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).
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
April 1995
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Method 1636
°f
4.3.8.2 Contamination by samples-Significant laboratory or instrument contamination
may result when untreated effluents, in-process waters, landfillkachaTs atd
other samples containing high concentrations of inorganic sub ta^este
processed and ana.yzed. As stated in Section 1.0, thfs methodTn
Lu norrDe°nl r.'T'r' Td Samt"eS C°mainin« hi*h -ncentrad
should not be permitted into the clean room and laboratory dedicated for
processing trace metals samples. uiuirea ror
Therefore, it is imperative that every piece of the Apparatus that is
indirectly used in ,he collection, processing, and analysis of amtiem
samples be cleaned as specified in Section 11.
or
4.4
4.3.8.4 Contamination by airborne paniculate matter-Less obvious substances caoable
of contaminating samples include airborne particles. Samples mayl *
contaminated by airborne dust, dirt, particles, or vapors from unfiUered air
supplies; nearby corroded or rusted pipes, wires, or other fixture?or metal-
contaimng pamt. Whenever possible, sample processing and analysisThould
be done as far as possible from sources of airborne confamination
Interferences which affect the accurate determination of Cr(VI) may come from several
44-' fcfd^l^ ™ f~ » *e P£—e of reducing species in an
HK C3PaCity Wi* **h —trations of anionic
species, especially chlonde and sulphate, will cause a loss of Cr(VI) The column
5.0 Safety
5.1
April 1995
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Method 1636
5.2 Each laboratory is responsible for maintaining a current awareness file of OSHA regulations
for the safe handling of the chemicals specified in this method (References 14-17). A
reference file of material safety data sheets (MSDSs) 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 that the results of this
monitoring be made available to the analyst. The references and bibliography at the end of
Reference 17 are particularly comprehensive in dealing with the general subject of laboratory
safety.
5.3 Concentrated nitric and hydrochloric acids present various hazards and are moderately toxic
and extremely irritating to skin and mucus membranes. Use these reagents in a fume hood
whenever possible and if eye or skin contact occurs, flush with large volumes of water.
Always wear protective clothing and safety glasses or a shield for eye protection, and observe
proper mixing when working with these reagents.
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.
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 should 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 Ion Chromatograph
6.2.1 Instrument equipped with a pump capable of withstanding a minimum backpressure of
2000 psi and of delivering a constant flow in the range of 1-5 mL/min and containing
no metal parts in the sample, eluent, or reagent flow path
April 1995
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Method 1636
6.2.2 Helium gas supply (high purity, 99.995%)
6.2.3 Pressurized eluent container, plastic, 1- or 2-L size
6.2.4 Sample loops of various sizes (50-250uL)
6.2.5 A pressurized reagent deliver)' module with a mixing tee and beaded mixing coil
6.2.6 Guard Column-A column placed before the separator column and containing a
sorbent capable of removing strongly absorbing organics and particles that would
otherwise damage the separator column (Dionex lonPac NG1 or equivalent).
6.2.7 Separator Column-A column packed with a high capacity anion exchange resin
capable of separating CK)42 from other sample constituents (Dionex lonPac AST or
equivalent).
6.2.8 A low-volume flow-through cell, visible lamp detector containing no metal parts in
contact with the eluent flow path, Detection wavelength is at 530 nm.
6.2.9 Recorder, integrator, or computer for receiving analog or digital signals for recording
detector response (peak height or area) as a function of time §
6.3 Alkaline detergent— Liquinox®, Alconox®, or equivalent.
6.4 pH meter or pH paper
with capability to measure to ai mg- for - »
0' *termi"alion of trace lev^ of elements, contamination and loss are of prime
ation Potential contamination sources include improperly cleaned laboratory
apparatus and general contamination within the laboratory environment from dust, etc A
clean laboratory work area should be des,gnated for trace element sample handling Sample
lT iThT1 '" C P°SltiVe ^ "egatiVe 6IIOrS in *e Determination of trace elenZ by
(1) contributing contammams through surface desorption or leaching, and (2) depleting element
concentrates through adsorption processes. All labware must be Lai free SuU able
construcnon materials are fluoropolymer (PEP. PTFE), conventional or linear polyethylene
anlT^f ' P0l™lene' F'— polymer should be used when samples LTobe
analyzed for mercury. All labware should be cleaned according to the procedure in Section
11.4. Gloves, plasuc wrap, storage bags, and filters may all be used new without additional
685 * "* '' * °f these ™«<^ ™* sou™ of
USt "e °btained or the
NOTE: Chromic acid must not be used for cleaning glassware.
6.6.1 Glassware-Class A volumetric flasks and a graduated cylinder.
April 1995
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Method 1636
6.6.2 Assorted Class A calibrated pipets
6.6.3 10-mL male luer-lock disposable syringes
6.6.4 0.45-um syringe filters
6.6.5 Storage bottle—High density polypropylene, 1-L capacity.
6.6.6 Wash bottle—One-piece stem fluoropolymer, with screw closure, 125-mL capacity.
6.6.7 Tongs—For removal of Apparatus from acid baths. Coated metal tongs may not be
used.
6.6.8 Gloves—clean, nontalc polyethylene, latex, or vinyl; various lengths. Heavy gloves
should be worn when working in acid baths since baths will contain hot, strong acids.
6.6.9 Buckets or basins—5- to 50-L capacity, for acid soaking of the Apparatus.
6.6.10 Brushes—Nonmetallic, for scrubbing Apparatus.
6.6.11 Storage bags—Clean, zip-type, nonvented, colorless polyethylene (various sizes) to
store the Apparatus.
6.6.12 Plastic wrap—Clean, colorless polyethylene to store the Apparatus.
6.7 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 for the collection of ambient water
samples. Before the equipment is shipped to the field site, the laboratory or facility must
generate an acceptable equipment blank (Section 9.5.3) to demonstrate that the sampling
equipment is free from contamination.
6.7.1 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. The Sampling Method describes various types of
samplers. Cleaned sampling devices should be stored in polyethylene bags or wrap.
6.7.2 Sample bottles—Fluoropolymer, 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 ana/yte, fluoropolymer or glass bottles must be used.
6.7.3 Filtration Apparatus
6.7.3.1 Filter—Gelman Supor 0.45-um, 15-mm diameter capsule filter (Gelman 12175,
or equivalent).
April 1995
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Method 1636
6.7.3.2 Peristaltic pump-115-V a.c., 12-V d.c., internal battery, variable-speed
single-head (Cole Farmer, portable, "Masterflex US," Catalog No H-07570-10
drive with Quick Load pump head, Catalog No. H-07021-24, or equivalent).
ecc 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
?±g± G;°6464-17' or equivalent). Tubing is cleaned by soaking in '
5-0% HC1 solution for 8-24 h, rinsing with reagent water in a clean bench in
a clean room, and drying m 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 the integrity of analytical data
e reagent Srade salts' Since a concentrated
tes ed fo tnern, f T * adjUSt ^ PH °f SHmpeS' 6aCh W lot sho^ be
tested for the metals of interest by diluting and analyzing an aliquot from the lot using the
techniques and instrumentation to he used for analysis of samples. The lot will be acceptable
if the concentration of the metal of interes, is below the MDL listed in this method All acids
used for this method must be of ultra high-purity grade. Suitable acids are available from a
number of manufacturers or may be prepared by sub-boiling distillation.
7.1 Reagents for cleaning Apparatus, sample bottle storage, and sample preservation and analysis
7.1.1 Nitric acid-concentrated (sp gr 1 .41 ), Seastar or equivalent
7.1.2 Nitric acid (l + l)_Add 500 mL concentrated nitric acid to 400 mL of regent water
and dilute to 1 L.
7.1.3 Nitric acid ( 1 +9)-Add 1 00 mL concentrated nitric add to 400 mL of reagent water
and dilute to 1 L.
7.1.4 Hydrochloric acid — concentrated (sp gr 1.19).
7. 1 .5 Hydrochloric acid (1 + 1 )_ Add 500 mL concentrated hydrochloric acid to 400 mL of
reagent water and dilute to i L.
7. 1 .6 Hydrochloric acid ( 1 +4)-Add 200 mL concentrated hydrochloric acid to 400 mL of
reagent water and dilute to I L.
7. 1 .7 Hydrochloric acid (HC1)— I N trace metal grade
7.1.8 Hydrochloric acid (HC1)— 10% wt, trace metal grade
7.1.9 Hydrochloric acid (HC1)— J
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Method 1636
7.1.10 Hydrochloric acid (HC1)—0.5% (v/v), trace metal grade
7.1.11 Hydrochloric acid (HCD—0.1% (v/v) ultrapure grade
7.1.12 Ammonium hydroxide, NH,OH, (sp gr 0.902), (CASRN 1336-21-6)
7.1.13 Ammonium sulphate, (NH4.2SO4, (CASRN 7783-20-2)
7.1.14 1,5-Diphenylcarbazide, (CASRN 140-22-7)
7.1.15 Methanol, HPLC grade
7.1.16 Sulfuric acid, concentrated (sp gr 1.84)
7.2 Reagent water—Water demonstrated to be free from the metal(s) of interest and potentially
interfering substances at the MDL for that metal listed in Table 1. Prepared by distillation,
deionization, reverse osmosis, anodic/cathodic stripping voltammetry, or other technique that
removes the metal(s) and potential interferent(s).
7.3 Cr(VI) Stock Standard Solution—To prepare a 1000 mg/L solution, dissolve 4.501 g of
Na2CrO4.4H2O in reagent water and dilute to 1 L. Transfer to a polypropylene storage
container.
7.3.1 Preparation of calibration standards—Fresh calibration standards should be prepared
every 2 weeks or as needed. Dilute the siock standard solution to levels appropriate to
the operating range of the instrument using reagent water. Before final dilution, the
standards should be adjusted to pH 9-9.5 with the buffer solution (Section 7.6).
Calibration standards should be prepared at a minimum of three 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. Calibration standards should be verified initially using a
quality control sample (Section 7.8).
7.4 Eluent—Dissolve 33 g of ammonium sulphate in 500 mL of reagent water and add 6.5 mL of
ammonium hydroxide. Dilute to 1 L with reagent water.
7.5 Postcolumn Reagent—Dissolve 0.5 g of 1.5-diphenylcarbazide in 100 mL of HPLC grade
methanol. Add to about 500 mL of reagent water containing 28 mL of 98% sulfuric acid
while stirring. Dilute with reagent water to 1 L in a volumetric flask. Reagent is stable for 4
or 5 days but should be prepared only as needed.
7.6 Buffer Solution—Dissolve 33 g of ammonium sulphate in 75 mL of reagent water and add 6.5
mL of ammonium hydroxide. Dilute to 100 mL with reagent water.
7.7 Blanks The laboratory should prepare the following types of blanks. A calibration blank is
used to establish the analytical calibration curve; and the laboratory (method) blank is used to
assess possible contamination from the sample preparation procedure. 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).
April 1995 ll
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Method 1636
7
<- .00 ug/L in reagen
The QCS should be analyzed a. neerie i ,n
be prepared quarterly or n^re fte.uentt as
Ongoing precision and recovery (OPR) Samnle Tn ^
from the stock standard (Section 5 L prelreTh^ °OTR
the same entire preparation scheme as the Lmples
bfT- '° '
b"ffer S°lutlon (Section 7-6>
****• ^ " ^ S°lu«°"
'"'
8.0 Sample Collection, Filtration, Preservation, and Storage
, pe.or.ed at the ,, of sample
<*** -uired so that
Sample coHecuon-Samples are ,,,llec,ed as described in the Samphng
Method
o
™st be analyzed w.thin 24 h of
.6 Samples should be stored in polyethylene bags a, 0-4°C until analysis
9.0 Quality Assurance/Quality Control
demonstration
and document da
assurance
C°nSist °f an initial
Y 7995
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Method 1636
performance. To determine that results of the analysis meet the performance characteristics of
the method, laboratory performance is compared to established performance criteria.
9.1.1 The analyst shall make an initial demonstration of the ability to generate acceptable
accuracy and precision with this method. This ability is established as described in
Section 9.2.
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 the substitution of a colonmetric technique or changes that degrade method
performance, are not allowed. If an analytical technique other than the techniques
specified in the method is used, that technique must have a specificity equal to or
better than the specificity of the techniques in the method for the analytes of interest.
9.1.2.1 Each time the method is modified, the analyst is required to repeat the
procedure in Section 9.2. If the change will affect the detection limit of the
method, the laboratory is required to demonstrate that the MDL (40 CFR Part
136, Appendix B) is lower than the MDL for that analyte in this method, or
one-third the regulatory compliance level, whichever is higher. If the change
will affect calibration, the analyst must recalibrate the instrument according to
Section 10.
9.1.2.2 The laboratory is required to maintain records of modifications made to this
method. These records include the following, at a minimum:
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
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 to this method, including:
(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,
April 1995 13
-------
Method 1636
area, or other signal) to the final result. These data are to
include, where possible:
(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
(0 Volume before each 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) Columns (type, resin, etc.)
(m) Operating conditions (background corrections,
temperature program, flow rates, etc.)
(n) Detector (type, operating conditions, etc.)
(o) 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. Section
¥.:> describes the required types, procedures, and criteria for analysis of blanks.
9.1.4 The laboratory shall spike at least 10% of the samples with the metal 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
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.
The laboratory shall, on an ongoing basis, demonstrate through calibration verification
and through analysis of the ongoing precision and recovery aliquot that the analytical
system is in control. Sect.ons 10.4 and 9.6 describe these procedures.
9.1.6 The laboratory shall maintain records to define the quality of data that are generated
Section 9.3.4 describes the development of accuracy statements.
9.2 Initial demonstration of laboratory capability
9.2.1 Method detection limit-To establish the ability to detect hexavalent chromium the
analyst shall determine the MDL for Cr(VI) according to the procedure in 40 CFR
136, Appendix B using the apparatus, reagents, and standards that will be used in the
practice of this method. The laboratory must produce an MDL that is less than or
equal to the MDL listed in Table ], or one-third the regulatory compliance limit
14 ' -—
April 1995
9.1.5
-------
Method 1636
whichever is greater. MDLs should be determined when a new operator begins work
or whenever, in the judgement 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 shall perform the following operations.
9.2.2.1 Analyze four aliquots of reagent water spiked with Cr(VI) at 2-3 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, compute the average percent recovery
(X) for the Cr(VI) in each aliquot and the standard deviation of the recovery
(s) for each metal.
9.2.2.3 Compare s and X with the corresponding limits for initial precision and
recovery in Table 2. If s and X meet the acceptance criteria, system
performance is acceptable and analysis of blanks and samples may begin. If,
however, s exceeds the precision limit or X falls outside the range for
accuracy, system performance is unacceptable. Correct the problem and repeat
the test (Section 9.2.2.1).
9.2.3 Linear dynamic range (LDR)-- The LDR should be determined by analyzing a
minimum of 7 calibration standards ranging in concentration from 1 ug/L to 5,000
ug/L across all sensitivity settings of the spectrophotometer. To normalize responses,
divide the response by the sensitivity setting multiplier. Perform the linear regression
of normalized response vs. concentration and obtain the constants m and b, where m is
the slope of the line and b is the y-mtercept. Incrementally analyze standards of
higher concentration until the measured absorbance response, /?, of a standard no
longer yields a calculated concentration, Cc, that is ± 10% of the known concentration,
C, where Cc = (R - b)/m. That concentration defines the upper limit of the LDR for
that instrument and analytical operating conditions. Samples having a concentration
that is :> 90% of the upper limit of the LDR must be diluted to fall within the bounds
of the current calibration curve concentration range and reanalyzed.
9.2.4 Quality control sample (QCS)—When beginning the use of this method, quarterly or
as required to meet data quality needs, verify the calibration standards and acceptable
instrument performance with the preparation and analyses of a QCS (Section 7.8). To
verify the calibration standards the determined mean concentration from 3 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, acceptable instrument
performance, or both 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
April 1995 15
-------
Method 1636
batch
B,anks (e.,, fie,d
9.3. 1 TT,e concentration of the MS and MSD is determined as follows-
9.3.2 Assessing spike recover
9.3.2.4 Calculate each percent recovery (P) as lOOfA RVT u ^P •
true value of the spike. ( " B)/T' Where T ls the
9.3.3 Compare the percent recovery (P) for CrfVn
criteria found in Table 2. If P fa 1 outside
acceptance criteria have no, been met
QC acceptance
f°r recovery' the
9.3.3.1 If the acceptance criteria were not met anal™ ^
recovery standard (Section 9 6) Hhe OPR ,1 ^"^ PreC1Si°n and
2), the analytical system is in ont ol and th ^ " '"^ ^ Cr(VI) (Table
sample matrix. ^ the pr°blem can be a«nbuted to the
9.3.4 Recovery for samples should be as
assessed and records maintained
V 7995
-------
Method 1636
average percent recovery (R) and the standard deviation of the percent
recovery (SR). Express the accuracy assessment as a percent recovery interval
from R - 2SR to R + 2SR for each matrix. For example, if R - 90% and SR
- 10% for five analyses of river water, the accuracy interval is expressed as
70-110%.
9.3.4.2 Update the accuracy assessment for Cr(VI) in each matrix on a regular basis
(e.g., after each five to ten new measurements).
9.4 Precision of matrix spike and duplicate
9.4.1 Calculate the relative percent difference (RPD) between the MS and MSD per 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.
RPD = 100(|D7-D2)
(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 matrix spike and the matrix spike duplicate
must be less than 20%. If this criterion is not met, the analytical system is be 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 Cr(VI) 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.
April 1995 17
-------
Method 1636
9.5.1.4 If the result for a single blank remains above the MDL or if the result for the
average concentrat.on plus two standard deviations of three or rrTre blanks
A^W *7 re8ulatol> compliance level, results for samples associatec
Aose blanks may not be reported for regulatory compliance purposes Sfc
another way results for all initial precision and recovery tests Section 92
tefore Zf" T* * IT*"'6'1 Wi* M ^ntamirlted method Wank
before these results may be reported for regulatory compliance purposes
9.5.2 Field blank
With each « of san>P'es
from u ^Pe
from the same site at the same time, to a maximum of 10 sampled)
the blank immediately before analyzing the samples in the batch
9.5.2.2 If Cr(VI) or any potentially interfering substance is found in the field blank at
a c°ncemra.,on e<,uai to or greater man me ML (Table 1), or grealer thaHne
fifth the level m the associated sample, whichever is greater, results for
associated samples may be the result of contamination and may nm te reported
for regulatory compliance purposes. reported
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 averageTonc^ntration
plus two standard deviations must be less than the regulatory compU»cetveT
or less than one-half the level in the associated sampfe, whkhev™ is^eater
9.5.2.4 If contamination of the field blanks and associated samples is known or
suspected, the laboratory should communicate this to the san^UngT™ so that
° identified and
9.5.3
Equipment Blanks-Before any sampling equipment is used at
a given site the
blanks are required: bottle blanks and sampler check blanks.
9.5.3.1
undergoing appropriate cleaning procedures (Section
, bottles should be subjected to conditions of use to verify the
h.^™ °] theucleanin8 Pr°<*d«res. A representative set of sample bottles
shou d be filled with reagent water adjusted to a pH 9-9.5 with the buffer
solution (Section 7.6) and allowed to stand for a minimum of 24 h Ideally
*e IT fr K60"'68 "* aU°Wed l° Stand Should >» - <*<** as possible"^
the actual time that sample will be in contact with the bottle. After standing
U* > water should be analyzed for any signs of contamination. If any "
shows signs of contammation, me problem must be identified, the deanng
° °r deanin SOlU and a"
9.5.3.2 Sampler check blanks-Sampler check blanks are generated in the laboratory
or at the equipment cleamng contractor's facility by processing reagent wato
April 1995
-------
Method 1636
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 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 Cr(VI) or any potentially
interfering substance is detected in the blank, the source of
contamination or interference must be identified, and the
problem corrected. The equipment must be demonstrated to be
free from Cr(VI) 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 analysis of the method blank and samples from the
same batch.
9.6.3 Compute the percent recovery of Cr(VI) in the OPR sample.
9.6.4 Compare the concentration to the limits for ongoing recovery in Table 2. If the
acceptance criteria are met, system performance is acceptable and analysis of blanks
and samples may proceed. If, however, the recovery falls outside of the range given,
the analytical processes are not being performed properly. Correct the problem,
reprepare the sample batch, and repeat the ongoing precision and recovery test (Section
9.6).
April 1995 79
-------
Method 1636
9.6.5
10.0 Calibration and Standardization
io.:
detector is 2.0 mL/min Thi reire m |POSCOumn reagent (Se«ion 7.5) from the
based on anticipated sample
// 7PP5
-------
Method 1636
10.4 Calibration verification—Immediately following calibration, an initial calibration verification
should be performed. Adjustment of the instrument is performed until verification criteria are
met. Only after these criteria are met may blanks and samples be analyzed.
10.4.1 Analyze the mid-point calibration standard (Section 10.3).
10.4.2 Compute the percent recovery of Cr(VI) using the calibration curve obtained in the
initial calibration.
10.4.3 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 the value falls outside the range given, system performance is
unacceptable. Locate and correct the problem and/or prepare a new calibration check
standard and repeat the test (Sections 10.4.1-10.4.3), or recalibrate the system
according to Section 10.3.
10.4.4 Calibration must be verified following every ten samples by analyzing the mid-point
calibration standard. If the recovery does not meet the acceptance criteria specified in
Table 2, analysis must be halted, the problem corrected, and the instrument
recalibrated. All samples after the last acceptable calibration verification must be
reanalyzed.
10.5 A calibration blank must be analyzed following every calibration verification to demonstrate
that there is no carryover of Cr(VI) 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 10.4), and repeat the analysis of the calibration blank.
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 6.6.8), storage bags (Section 6.6.11), and plastic wrap
(Section 6.6.12) 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, those cleaning steps that do not eliminate these artifacts may be
omitted if all performance criteria outlined in Section 9 are met.
April 1995 21
-------
Method 1636
11.3.1 Bottles, labware, and sampling equipment
11.3.1.1 RH a precleaned basin (Section 6.6.9) with a sufficient quantity of
^fr 1 'f'd.^ge" (Secti°" "X and compete./
11.3.1.2
11.3.1.3
11.3.1.4
11.3.1.5
Using a pair of clean gloves (Section 6.6.8) and clean
nonmetallic
"
the
Place the scrubbed materials in a precleaned basin. Change gloves.
Thoroughly rinse the inside and outside of each piece with reagent
no sign of detergent
Change gloves, immerse the rinsed equipment in a hot
reagent
HNO
hart,
"AU iztt^ttzzzzr-Md
"AI-7 |»~S"^
IIM* s^t^TSrand b°"ies with reagent—
Proceed with Section 11.3.3 fc
11.3.2 Labware and sampling equipment
11.3.2.1 After cleaning, air-dry in a class 100 clean air bench.
'3'2'2 each piece of warc
11.3.3 Fh^ropolymer samp.e bott.es-These bottles should be used if mercury is a Urge,
1 1 O O 1 ...
*«inpie Dottles with 0.1% (v/v) ultra.Diirp Hr^l
(Section 7.1.11) and cap tightly. To ensure a tight seal, it may be
necessary to use a strap wrench. y
11.3.3.2 After capping, double-bag each bottle in polyethylene zip-type bags
Store at room temperature until sample collection. §
-------
Method 1636
11.3.4 Bottles, labware, and sampling equipment (polyethylene or material other than
fluoropolymer)
11.3.4.1 Apply the steps outlined in Sections 11.3.1.1-11.3.1.8 to all bottles,
labware, and sampling equipment. Proceed with 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
7.1.11). 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 or 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 for vapors to
diffuse 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).
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 7.1.8) and flushing with water from the site before sample collection.
11.3.6 Extension pole—Because of its length, it is impractical to submerse the 2-m
polyethylene extension pole (used in with the optional grab sampling device) in acid
solutions as described above. If such an extension pole is used, a nonmetallic brush
(Section 6.6.10) should be used to scrub the pole with reagent water and the pole
wiped down with acids described in Section 11.3.4. 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
April 1995 23
-------
Method 1636
12.0 Procedures for Sample Preparation and Analysis
e br°Ught '° amb-< '-P-ature before
Initiate .nstrument operat.ng configurat.cn and caHbrate the .nstrument as described in Section
123
range should bracket
correction (r) for the
(peak height or area) vs-
6 °' '"" "" °f mag"«ude- The calibration
12-4
exceed the calibration
13.0 Data Analysis and Calculations
13J
Report al, resuHs for metals found
14.0 Method Performance
K1
chromium.
15.0 Pollution Prevention
in .borato, operate. e
°f
3 mL °f sam"k- ^« «*
C°nCentrati°nS that
c-
"
n
21) for dissolved hexavalent
the quan«ity or
April 1995
-------
Method 1636
management techniques that places pollution prevention as the management option of first
choice. Whenever feasible, laboratory personnel should use pollution prevention techniques to
address their waste generation. When wastes cannot be feasibly reduced at the source, the
Agency recommends recycling as the next best option. The acids used in this method should
be reused as practicable by purifying by electrochemical techniques. The only other chemicals
used in this method are the neat materials used in preparing standards. These standards are
used in extremely small amounts and pose little threat to the environment when managed
properly. To minimize the volume of expired standards to be disposed, standards should be
prepared in volumes consistent with laboratory use.
15.2 For information about pollution prevention that may be applied to laboratories and research
institutions, consult Less is Better: Laboratory Chemical Management for Waste Reduction,
available from the American Chemical Society's Department of Government Relations and
Science Policy, 1155 16th Street NW, Washington DC 20036, 202/872-4477.
16.0 Waste Management
16.1 The Environmental Protection Agency 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 by 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, 76, 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, VA, 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, 79, 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.
April 1995 25
-------
Method 1636
10
11
12
13
14
15
16
17
18
19
20
21
Fi.zge.ld, W.F, Watras, C.J. Science oflhe Total Environment 1989, 87,88, 223.
Gill, G.A.; Fitzgerald, W.F. Deep Sea Res. 1985, 32, 287.
Manage^ and Environmema,
EPA Envi™
Contro1 m Trace Metals
Dionex Technical Note No. 26, May 1990.
and Health, Publication No. 77-206 i ST, 977 AV^ Tl '"T for OccuPati°nal Safety
Information Service (NTIS) as PB-277256. Nati°nal Teclffii
"OSHA Safety and Health Standards, General Industry"- 29 CFK loin r>
and Health Administration, OSHA 2206 (revisedCary 197™ ' °CCUPatIonal
Laboratories'' American
La—ories, Occupational Safety and Hea,th
Grohse, P. Research Triangle Zns.Hute, Tnstitute Drive, Building 6, Research Triangle Park, NC
CIean
OynCorp), 300 N. e .
EPA
Quality
// 7995
-------
Method 1636
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 7.7.1).
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.
April 1995 27
-------
Method 1636
1810 Initial Precision and
establish the ability to
P™ i
** °PR Standard
to
18.11 Instrument Detection Limit
» equal ,o three ,imes the
18.12
e
cahbrauon blank signal a, the selected analytical wavelength
are used with samples. ^ la™^ '
- Present in the labora^
. "» «"^ sig»<" *hich
meaSUrcments <* «*
' Qr ^^ ^ ^ ^.^
18.22 Method Blank-See Laboratory Blank.
18.23 Method Detection Limit (MDL)—Th
identified, measured, and reported with yy%, ,
greater than zero (Section 9.2.1 and Table 1)
* - "»** ** ca« »
* ** ***** Concentration is
April 1995
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Method 1636
18.24 Minimum Level (ML)—The lowest level at which the entire analytical system gives a
recognizable signal and acceptable calibration point (Reference 9).
18.25 Must—This action, activity, or procedural step is required.
18.26 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 assure that the results produced by
the laboratory remain within the method-specified limits for precision and accuracy (Sections
7.9 and 9.6).
18.27 Preparation Blank—See Laboratory Blank.
18.28 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.
18.29 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 external to the laboratory or is
prepared from a source of standards different from the source of calibration standards. It is
used to check laboratory performance with test materials prepared external to the normal
preparation process.
18.30 Reagent Water—Water demonstrated to be free from the method analytes and potentially
interfering substances at the MDL for that metal in the method.
18.31 Should—This action, activity, or procedural step is suggested but not required.
18.32 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.
April 1995 29
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Method 1636
Table 1
,„„„„„,
Metal
Hexavalent Chromium
Lowest Ambitnt Water
Quality Criterion (ug/L)1
Method Detection Limit (MDL)
and Minimum Level (ML); ug/L
Notes:
EPA
Method Detection Limit as determined by 40 CFR Pan 156, Appendix B.
cvei ^IV1L_) calculated bv multinlvino ioK^.^oi.^_. j_»-.. • . .
Table 2
QuaUty Control Acceptance Criteria for Performance Tests in EPA Method ,636'
Metal
Hexavalent Chromium
Initial Precision and
Recovery (Section 9.2)
Calibration Verification
(Section 10.4)
Ongoing Precision and
Recovery (Section 9.6)
All specifications expressed as percent.
Spike Recovery
(Section 9.3)
April 1995
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Method 1636
Table 3: Recommended Ion Chromatographic Conditions
Columns:
Eluent:
Postcolumn Reagent:
Detector:
Retention Time:
Guard Column—Dionex lonPac NG1
Separator Column—Dionex lonPac AS7
250 mM (NH4)2SO4
100 mM NH4OH
Flow rate =1.5 mL/min
2mM Diphenylcarbohydrazide
10% v/v CH3OH
IN H2S04
Flow rate = 0.5 mL/min
Visible 530 nm
3.8 min
April 1995
31
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