ASTM D4309-02(2007)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D4309 − 02(Reapproved 2007)
Standard Practice for
Sample Digestion Using Closed Vessel Microwave Heating
Technique for the Determination of Total Metals in Water
This standard is issued under the fixed designation D4309; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D1192Guide for Equipment for Sampling Water and Steam
in Closed Conduits (Withdrawn 2003)
1.1 This practice covers the general considerations for
D1193Specification for Reagent Water
quantitative sample digestion for total metals in water using
D1687Test Methods for Chromium in Water
closed vessel microwave heating technique. This practice is
D1688Test Methods for Copper in Water
applicable to surface, saline, domestic, and industrial waste-
D1691Test Methods for Zinc in Water
water.
D1886Test Methods for Nickel in Water
1.2 Because of the differences among various makes and
D3370Practices for Sampling Water from Closed Conduits
models of satisfactory instruments, no detailed operating in-
D3557Test Methods for Cadmium in Water
structions can be provided. Instead, the analyst should follow
D3559Test Methods for Lead in Water
the instructions provided by the manufacturer of the particular
D3856Guide for Management Systems in Laboratories
instrument.
Engaged in Analysis of Water
1.3 This practice can be used with the following ASTM
D3919Practice for Measuring Trace Elements in Water by
standards, providing the user determines precision and bias Graphite Furnace Atomic Absorption Spectrophotometry
based on this digestion practice: Test Methods D857, Test
D4190TestMethodforElementsinWaterbyDirect-Current
Methods D858, Test Methods D1068, Specification D1192,
Plasma Atomic Emission Spectroscopy
Test Methods D1687, Test Methods D1688, Test Methods
D4453Practice for Handling of High Purity Water Samples
D1691, Test Methods D1886, Practices D3370, Test Methods
D4691Practice for Measuring Elements in Water by Flame
D3557, Test Methods D3559, Practice D3919, Test Methods
Atomic Absorption Spectrophotometry
D4190, Practice D4453, and Practice D4691.
2.2 U.S. Code of Federal Regulations:
1.4 This standard does not purport to address all of the
CFR 1.030.10Code of Federal Regulations, Volume 21
safety concerns, if any, associated with its use. It is the
2.3 Federal Communications Commission Standard:
responsibility of the user of this standard to establish appro-
Code of Federal Regulations,Volume 47, FCC Rule Part 18
priate safety and health practices and determine the applica-
2.4 U.S. EPA Method:
bility of regulatory limitations prior to use. For specific hazard
statements, see Section 9. U.S. EPAMethod:Methods for ChemicalAnalysis of Water
and Waste—March 1979, “Total Metals Digestion Proce-
2. Referenced Documents
dure” 4.1.3, page Metals 6
U.S. EPA Method: SW 846 Method 3015Microwave As-
2.1 ASTM Standards:
sisted Acid Digestion of Aqueous Samples and Extracts
D857Test Method for Aluminum in Water
D858Test Methods for Manganese in Water
D1068Test Methods for Iron in Water 3. Terminology
D1129Terminology Relating to Water
3.1 Definitions—For definitions of terms used in this
practice, refer to Terminology D1129.
This practice is under the jurisdiction ofASTM Committee D19 on Water and
is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents in
Water.
Current edition approved June 15, 2007. Published June 2007. Originally The last approved version of this historical standard is referenced on
approved in 1991. Last previous edition approved in 2002 as D4309–02. DOI: www.astm.org.
10.1520/D4309-02R07. Available from Office of the Federal Register, National Archives Records
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Administration, Superintendent of Documents, U.S. Government Printing Office,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Washington, DC 20401.
Standards volume information, refer to the standard’s Document Summary page on Available from National Technical Information Service (NTIS), 5285 Port
the ASTM website. Royal Rd., Springfield, VA 22161, http://www.ntis.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4309 − 02 (2007)
4. Summary of Practice pressure relief valve, rupture disc, pressure venting system or
beconnectedtoanexternalsafetyreliefvalvethatwillprevent
4.1 A representative aliquot of a homogeneous sample is
possible vessel rupture or ejection of the vessel cap.
digested with acid in a closed microwave transparent vessel,
using microwave heating. The digestate or a filtered digestate 7.3 Apparatus, to seal the vessel system to the manufactur-
is then analyzed by direct aspiration or injection by flame er’s specified requirement.
atomic absorption spectrophotometry (FAAS), inductively
coupled plasma emission techniques (ICP), direct current 8. Reagents
plasma emission techniques (DCP), or graphite furnace atomic
8.1 Purity of Reagents—Reagent grade chemicals shall be
absorption spectrophotometry (GFAAS), or a combination of
used in this practice. Unless otherwise indicated, it is intended
methods.
that all reagents shall conform to the specifications for the
Committee onAnalytical Reagents of theAmerican Chemical
5. Significance and Use
Society,wheresuchspecificationsareavailable. Othergrades
5.1 The analysis of many types of water for metals using
may be used, provided it is first ascertained that the reagent is
flame atomic absorption spectrophotometry, inductively
of sufficiently high purity to permit its use without lessening
coupled plasma emission spectrophotometry, direct current
the accuracy of the determination.
plasma emission spectrophotometry, or graphite furnace
8.2 Purity of Water—Unless otherwise indicated, references
atomic absorption spectrophotometry necessitates the use of a
towatershallbeunderstoodtomeanreagentwaterconforming
digestion practice in order to ensure the proper statistical
to Specification D1193,Type I. Other reagent water types may
recovery of the metals from the sample matrix. The use of
be used provided it is first ascertained that the water is of
closed vessel microwave techniques will speed the complete
sufficiently high purity to permit its use without adversely
recovery of metals from the water matrices and eliminate
affecting the bias and precision of the method. Type II water
sample contamination from external sources.
was used for the data shown in Appendix X1.
6. Interferences 8.3 Hydrochloric Acid (sp gr 1.19) (HCl).
6.1 No interferences have been observed using microwave
8.4 Nitric Acid (sp gr 1.42) (HNO ).
heating.
8.5 Nitric Acid (1 + 1) —Add 1 volume of HNO (sp gr
6.2 Precautions should be exercised to avoid those interfer-
1.42) to 1 volume of water.
encesnormallyassociatedwiththeparticularanalyticalmethod
for metals determination. 9. Hazards
6.3 This practice will not totally solubilize solid silicates
9.1 The microwave unit should be operated in accordance
that are suspended in or settle out of the water sample. with the manufacturer’s recommended operating and safety
precautions. Caution—It is not recommended to place a
7. Apparatus
microwaveunitinafumehood,whereitissurroundedbyacid
fumes, which can cause corrosion of the equipment. Acid
7.1 Laboratory Microwave Heating System, capable of de-
fumes generated inside the oven cavity should be air swept
livering 575 to 1000 W of power. The unit should be capable
away from the oven cavity to a hood.
of 1% power adjustment and 1 s time adjustment. The oven
cavity should be fluorocarbon-coated or coated with a material
9.2 Precaution—The closed vessel should be operated in
that has equivalent acid resistance and microwave properties
accordance with the manufacturer’s recommended operating
and be equipped with exhaust ventilation at 2.8 m /min (100
and safety instructions.
ft /min)foracidvaporprotectionoftheunitandoperator.The
unit must have a rotating or alternating turntable, capable of
10. Procedure
holding 1 to 14 digestion vessels, to ensure even sample
10.1 Power Temperature Control—procedure for 7 to 12
heating. Safety interlocks, to shut off magnetron power output,
vessel digestions:
must be contained in the oven door opening mechanism. The
unit may contain a temperature control device capable of NOTE 1—For fewer than seven samples, see 10.2.
controlling vessel temperatures to 200°C and/or a pressure
10.1.1 Perform an instrument power check as outlined in
control device capable of controlling vessel pressures to a
Annex A1.
minimum 100 psig.
10.1.2 Refer to ASTM test methods for sampling and
7.1.1 The unit must comply with U.S. Health and Human
analysis (such as Guide D3856) to determine any sample
Services Standards under CFR Part 1030.10, sub parts (C) (1),
preservation requirements.
(C) (2), and (C) (3), for microwave leakage. The unit should
have FCC-type approval for operations under FCC Rule Part
18.
Reagent Chemicals, American Chemical Society Specifications , American
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
7.2 Closed Vessel, capable of holding 100 mL of solution.
listed by the American Chemical Society, see Analar Standards for Laboratory
The vessel must be transparent to microwave energy and
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
capable of withstanding internal pressures of 100 psig and
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
temperatures of 200°C. The vessel must contain a safety MD.
D4309 − 02 (2007)
10.1.3 Transfer 50.0 mL of a representative aliquot of the match the heating rates in Fig. 1. Depress the start key and
well-mixed sample into a clean vessel (see Note 2). If the allow the sample mixtures to heat for the programmed time.
sample is to be analyzed by ICP, DCP, or FAAS, add 3 mL of 10.1.7 Attheendofthedigestionperiod,removethevessels
HNO (spgr1.42)and2mLofHCl(spgr1.19).Ifthesample from the microwave and allow the sample solutions to cool to
is to be analyzed by GFAAS, add 5 mL of HNO (sp gr 1.42) room temperature. Shake the vessels to mix the sample
(see Note 3). Install a safety pressure relief valve and cap on solutions and vent to atmosphere any gas pressure that may be
thevesselandsealtothemanufacturer’srecommendedtorque. present in the vessels.
Weigh the vessel, record the weight, and place in the micro-
NOTE 5—Warning: Shake the vessel with caution to prevent any rapid
wave instrument turntable. Attach a vent tube, if required, by
out-gassing of vapor or liquid causing acid burns of the exposed skin of
the manufacturer’s operating instructions. the operator.
10.1.8 Detachtheventtubingandremovethevesselassem-
NOTE 2—Follow the manufacturer’s suggested vessel cleaning instruc-
blyfromtheturntable.Weighthecooledvesselsystem.Ifthere
tions to avoid possible sample contamination.
NOTE 3—Final acid concentration of this procedure is 9%. This may
is a weight loss greater than 0.5 g, open the vessel and add an
shorten graphite tube lifetime, which may cause deterioration of analyte
amount of reagent water equal to the weight loss. Liquid loss
recovery.Theanalystmaychoosetodilutethedigestedsolutiontoalower
of less than 10% has not been found to result in any analyte
acid percentage to increase graphite tube life.
loss(seeNote6).Recapthevesselandthenshakethevesselto
10.1.4 Repeat 10.1.3 until the turntable contains 12 vessels.
mix the sample solution.
Areagentblankshouldbedigestedandanalyzedalongwiththe
NOTE6—Samplescontaininglargeamountsoforganicsmayexperience
samples. If less than 12 samples are to be digested, fill the
excessive loss of liquid (greater than 10%); therefore, a study may be
remaining vessels with 50 mL of water and add an equal
required to determine if any analyte loss occurred.
amount of acid as added to the sample. It is critical to the
10.1.9 Openthevesselsandfilterthesamples,ifrequired,to
procedure that the total volume of solutions equals 660 mL
remove silicates and other insoluble materials. Do not rinse or
duringdigestion,andthateachvesselcontainsanequalvolume
dilute the digested sample. Final sample volume is 55 mL(see
of acid. This is necessary to ensure uniform heating of all
Note 3).
vessel solutions.
NOTE 7—In place of filtering, the sample after mixing may be
NOTE 4—It is not necessary to weigh the blank vessels containing 50
centrifuged or allowed to settle by gravity overnight to remove insoluble
mL of reagent water.
material.
10.1.5 Turn the microwave instrument exhaust on to the
10.1.10 AnalyzethesamplebyICP,DCP,FAASorGFAAS,
maximumfanspeed.Activatetheturntablesothatitisrotating
or a combination of methods, as required.
or alternating 360°.
10.2 Power Temperature Control—procedure for 1 to 6
10.1.6 For instruments delivering a measured power of 575
vessel digestions:
to 635 W, program the instrument time for 50 min and the
10.2.1 Perform an instrument power check as outlined in
power to 100%. For instruments with a measured power of
Annex A2.
635 to 700W, program the instrument time for 30 min and the
10.2.2 Refer to individualASTM test methods for sampling
power for 100%. These heating parameters will allow the
and analysis to determine any sample preservation require-
samples to reach a maximum temperature of 164 6 4°C (refer
ments.
to Fig. 1). Instruments delivering greater than 700 W must be
10.2.3 Transfer 50.0 mL of a representative aliquot of the
operated at reduced powers such that the sample heating rates
well-mixed sample into a clean vessel (see Note 2). If the
sample is to be analyzed by ICP, DCP, or FAAS, add 3 mL of
HNO (spgr1.42)and2mLofHCl(spgr1.19).Ifthesample
is to be analyzed by GFAAS, add 5 mL of HNO (sp gr 1.42)
(see Note 3). Install a safety pressure relief valve and cap on
the vessel and then seal to the manufacturer’s recommended
torque. Weigh the vessel, record the weight, and place in the
microwaveinstrumentturntable.Attachaventtube,ifrequired
by the manufacturer’s operating instructions.
10.2.4 Repeat 10.2.3 until the turntable contains 6 evenly-
spaced vessels. A reagent blank should be digested and
analyzedalongwiththesamples.Iffewerthan6samplesareto
bedigested,fillremainingvesselswith50mLofreagentwater
and add an equal amount of acid to the samples. It is critical to
theprocedurethatthetotalvolumeofsolutionsequals330mL
duringdigestion,andthateachvesselcontainsanequalvolume
of acid. This is necessary to ensure uniform hea
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