Environmental Sampling and Analysis for Metals - Chapter 15 pdf

Transfer a suitable volume 50 to 100 ml of well-mixed sample into a 125-ml flask orbeaker.. Transfer a suitable volume of the well-mixed, acid-preserved sample appropriate for theexpecte

for Metals Analysis

15.1 GENERAL DISCUSSION

Samples containing particulate or organic material generally require pretreatment before analysis

15.1.1 S AMPLE P RETREATMENT FOR T OTAL M ETALS

Colorless, transparent samples (primarily drinking water) containing a turbidity of less than 1 NTU(nephelometric turbidity unit), and single-phase samples can be analyzed directly via atomic absorp-tion spectroscopy or inductively coupled plasma spectroscopy for total metals without digestion Forfurther verification or to determine changes in existing matrices, compare digested and undigestedsamples to ensure comparable results Digest all other samples before determination of total metals.Take care not to introduce metals into samples during preliminary treatment During pretreat-ment, avoid contact with rubber, metal base paints, cigarette smoke, paper tissues, and all metal prod-ucts, including those made of stainless steel, galvanized metal, and brass Conventional fume hoodscan contribute significantly to sample contamination, particularly during acid digestion in open con-tainers Plastic pipet tips are often contaminated with copper, iron, zinc, and cadmium Before use,soak pipets in 2N HCl or HNO3for several days and rinse with deionized (DI) water Check reagent-grade acids used for preservation, extraction, and digestion for purity If excessive metal concentra-tions are found, purify the acids by distillation or use ultra-pure acids Carry blanks through all di-gestion and filtration steps and apply necessary corrections to the results

15.1.2 S AMPLE P RETREATMENT FOR D ISSOLVED M ETALS

To analyze for dissolved metals, filter the sample (as in Section 15.1.4), acidify the filtrate, and lyze directly

ana-15.1.3 S AMPLE P RETREATMENT FOR S USPENDED M ETALS

To determine suspended metals, filter the sample, digest the filter and the material on it, and analyze

15.1.4 P RELIMINARY F ILTRATION OF S AMPLES

If dissolved or suspended metals are to be determined, filter the sample at the time of collection Use

a preconditioned, plastic, vacuum (or pressure) device equipped with a filter support made of plastic

or TFE The filter should have the following characteristics: prewashed, ungridded, 0.45-µm brane, and made of polycarbonate or cellulose acetate Before use, filter a blank consisting of reagentwater to ensure freedom from contamination Precondition the filter and filter device by rinsing with50-ml of DI water If the filter blank contains significant metal concentrations, soak membrane filters15

mem-in approximately 0.5N HCl or 1+1 HNO3and rinse with water before use If the filter is to be digestedfor suspended metals, record the sample volume filtered, and analyze a digested filter as a blank.Before filtering, centrifuge highly turbid samples in acid-washed TFE or a high-density plastic tube

to reduce loading on filters Stirred-pressure filter units foul less readily than vacuum filters Filter at

a pressure of 70 to 130 kPa (kiloPascal; 1 atm (atmosphere) = 100 kPa)

After filtration, acidify filtrate to pH 2 with HNO3concentrate and analyze directly If a tate forms on acidification, digest acidified filtrate before analysis Retain filter and digest it for di-rect determination of suspended metals

precipi-15.1.5 S AMPLE P RETREATMENT FOR A CID -E XTRACTABLE M ETALS

To determine acid-extractable metals, extract metals as indicated below and analyze extract.Extractable metals are lightly absorbed on particulate material Because some sample digestion may

be unavoidable, use rigidly controlled conditions to obtain meaningful and reproducible results.Maintain constant sample volume and contact time Express results as extractable metals and spec-ify extraction procedure

At the time of collection, acidify the entire sample with 5 ml of HNO3concentrate per liter ofsample Extract metals as follows:

1 Mix sample well

2 Transfer 100 ml of the sample to a beaker or flask

3 Add 5 ml of 1+1 HCl

4 Heat for 15 min over a steam bath

5 Filter through a membrane filter, adjust filtrate volume to 100 ml with laboratory-purewater, and analyze

15.2 DIGESTION PROCEDURES FOR METALS

15.2.1 I NTRODUCTION

To reduce interference by organic matter and to convert metal associated with particulate to a form(usually a free metal) that can be determined by AAS or ICP, use one of the digestion techniques pre-sented below Use the least rigorous digestion method required to provide complete and consistentrecovery compatible with the analytical method and the metal being analyzed

HNO3will digest most samples adequately Nitrate is an acceptable matrix for both FAAS andGrAAS Some samples may required the addition of perchloric, hydrochloric, or sulfuric acid forcomplete digestion These acids may interfere in the analysis of some metals and all provide a poormatrix for GrAA analysis Confirm metal recovery for each digestion and analytical procedure used.Table 15.1 lists the acids used in conjunction with HNO3 As a general rule:

• HNO3alone is adequate for clean samples or easily oxidized materials

• HNO3–H2SO4or HNO3–HCl digestion is adequate for readily oxidizable organic matter

• HNO3–HClO4or HNO3–HClO4–HF digestion is necessary for difficult-to-oxidize organicmatter or minerals

Report the digestion technique used Because acid digestion techniques do not normally achievetotal digestion, the microwave digestion procedure may be used as an alternate The microwavemethod is a closed-vessel procedure, and thus typically provides improved precision when comparedwith the hot-plate technique Suggested sample volumes for digesting are presented in Table 15.2.Larger samples require additional acid

15.2.2 N ITRIC A CID D IGESTION

1 Transfer a suitable volume (50 to 100 ml) of well-mixed sample into a 125-ml flask orbeaker

2 Add 5 ml of HNO3concentrate and a few boiling chips or glass beads Bring to a slow boiland evaporate on a hot plate to the lowest volume (10–20 ml) before precipitation occurs

3 Continue heating and adding acid until digestion is complete, as indicated by a ored, clear solution Do not let sample dry during digestion

light-col-4 Wash down flask or beaker walls with DI water and filter, if necessary Transfer filtrate to

a 100-ml volumetric flask Cool and dilute to the mark, and mix thoroughly

Alternatively, take a larger sample volume using the procedure for concentration

15.2.3 N ITRIC A CID –H YDROCHLORIC A CID D IGESTION

1 Transfer a suitable volume of the well-mixed, acid-preserved sample appropriate for theexpected metal concentrations to a flask or beaker

2 Add 3 ml of HNO3concentrate Heat on a hot plate and evaporate to less than 5 ml, ing certain that the sample does not boil and is not allowed to dry

mak-3 Cool and add another 5 ml of acid Cover container with a watch glass and return to a hotplate Increase temperature of the hot plate so that a gentle reflux action occurs

4 Continue heating, adding additional acid as necessary until digestion is complete, cated by a light-colored and clear digestate

indi-5 Evaporate to less than 5 ml and cool Add 10 ml of 1+1 HCl and 15 ml of DI water per100-ml total volume Heat for an additional 15 min to dissolve any precipitate or residue

6 Cool, wash down beaker walls and watch glass with DI water, and filter to remove uble material that could clog the nebulizer Alternatively, centrifuge or let settle overnight

insol-7 Adjust to a predetermined volume based on expected metal concentrations

TABLE 15.1

Acid Recommended For May Be Helpful for Not Recommended for

Suggested Sample Volumes for Digestion

Estimated Metal Concentration (mg/l) Sample Volume (ml)

15.2.4 N ITRIC A CID –S ULFURIC A CID D IGESTION

1 Transfer a suitable volume of the well-mixed, acid-preserved sample into a flask or beaker

2 If sample is not already acidified, acidify to methylorange endpoint with H2SO4trate and add 5 ml of HNO3concentrate and a few boiling chips or glass beads

concen-3 Bring to slow boil on a hot plate and evaporate to 15 to 20 ml

4 Add 5 ml of HNO3concentrate and 10 ml of H2SO4 Evaporate on a hot plate until densewhite fumes of SO3begin to form If the solution does not clear, add 10 ml of HNO3con-centrate and repeat evaporation until fumes of SO3begin to form Heat to remove all HNO3

before continuing treatment All HNO3will be removed when the solution is clear and nobrownish fumes are evident Do not let sample dry during digestion

5 Cool and dilute to about 50 ml with DI water Heat to almost boiling to dissolve slowlysoluble salts Filter if necessary

6 Complete procedure by transferring filtrate into a volumetric flask and dilute to the mark.Mix thoroughly

15.2.5 N ITRIC A CID –P ERCHLORIC A CID D IGESTION

1 Mix sample and transfer a suitable volume into a flask or beaker

2 If sample is not already acidified, acidify to methylorange endpoint with HNO3trate, add an additional 5 ml of HNO3concentrate and a few boiling chips or glass beads,and evaporate on a hot plate to 15 to 20 ml

concen-3 Add 10 ml each of HNO3concentrate and HClO4, cooling flask or beaker between tions Evaporate gently on a hot plate until dense white fumes of HClO4begin to appear

addi-4 If solution is not clear, cover container with a watch glass and keep solution at boiling perature (but no higher), boiling until it clears

tem-If Pb is to be determined in the presence of high amounts of sulfate (e.g., determination of Pb inpower-plant fly ash in samples), dissolve PbSO4precipitate as follows:

1 Add 50 ml of ammonium acetate solution to flask or beaker in which digestion was ried out, and heat to incipient boiling Rotate container occasionally to wet all interior sur-faces and dissolve any deposited residue

car-2 Using a preconditioning plastic filtering device with either vacuum or pressure and ing a filter support of plastic or TFE, filter the sample through a prewashed ungridded 0.45-

contain-mm membrane filter as described in Section 15.1.4

3 Transfer filtrate to a 100-ml volumetric flask, cool, dilute to the mark, mix thoroughly, andset aside for determination of Pb

Caution: Heated mixtures of perchloric acid (HClO4) and organic matter may violently explode.Avoid this hazard by taking the following precautions:

• Do not add HClO4to a hot solution containing organic matter (Always pretreat samplescontaining organic matter with HNO3before adding HClO4!)

• Avoid repeated fuming with HClO4in ordinary hoods (For routine operations, use a waterpump attached to a glass fume eradicator Stainless-steel fume hoods with adequate waterwash-down facilities are available commercially and are acceptable when using HClO4.)

• Never let samples being digested with HClO4evaporate to dryness

15.2.6 N ITRIC A CID –P ERCHLORIC A CID –H YDROFLUORIC A CID D IGESTION

Caution: See precautions for using HClO4in Section 15.2.5 Handle with extreme care and provideadequate ventilation, especially for the heated solution Avoid all contact with exposed skin Seekmedical attention for hydrofluoric acid burns

1 Mix sample and transfer a suitable volume into a 250-ml TFE beaker

2 Add a few boiling chips and bring to a slow boil Evaporate to 15 to 20 ml

3 Add 12 ml of HNO3concentrate and evaporate to near dryness Repeat HNO3addition andevaporation

4 Cool solution and add 20 ml of HClO4and 1 ml of HF, and boil until solution is clear andwhite fumes of HClO4have appeared

5 Cool, add about 50 ml of DI water, filter, and proceed as directed in Section 15.4.2, step 4

evaporat-2 Evaporate to dryness over a steam bath

3 Transfer dish to a muffle furnace and heat sample to a white ash If volatile elements are

to be determined, keep temperature at 400 to 450°C

4 If only Na is to be determined, create the ash sample at a temperature up to 600°C

5 Dissolve ash in a minimum quantity of HNO3concentrate and warm water Filter dilutedsample and adjust to a known volume, preferably so that the final HNO3concentration isabout 1%

6 Use a portion of this solution for metal determination

15.2.8 M ICROWAVE -A SSISTED D IGESTION

Caution: This method is designed for microwave digestion of waters only It is not intended for thedigestion of solids, in which high concentrations of organic compounds may result in high pressureand possibly unsafe conditions

15.2.8.1 Requirements for Microwave Unit

Use a microwave unit with programmable power (minimum 545 W) to within ±10 W of requiredpower, with a corrosion-resistant, well-ventilated cavity, and with all electronics protected againstcorrosion for safe operation Use a unit with a rotating turntable with a minimum speed of 3 rpm toensure homogeneous distribution of microwave radiation Only laboratory-grade microwave equip-ment and closed digestion containers with pressure relief that are specifically designed for hot acidshould be used

Vessels should be constructed of perfluoroalkoxy (PFA) Teflon capable of withstanding sures of at least 760±70 kPa (±110 psi) and capable of controlled pressure relief at the manufacturer’smaximum pressure rating Acid wash all digestion vessels and rinse with reagent water When using

pres-a new PFA Teflon vessel or when chpres-anging between high- pres-and low-concentrpres-ation spres-amples, clepres-an by

leaching with hot 1+1 HCl for a minimum of 2 h and then with hot 1+1 HNO3for a minimum of 2 h,rinse with reagent water, and dry in a clean environment.

15.2.8.2 Procedure

The following procedure is based on heating acidified samples in two stages where the first stage is

to reach 160±4°C in 10 min, and the second stage is to permit a slow rise to 165–170°C during thesecond 10 min A verified program that meets this temperature-time profile is 545 W for 10 min fol-lowed by 344 W for 10 min using five single-wall PFA Teflon digestion vessels The usable number

of vessels is determined by vessel design and power output

1 Weigh entire digestion vessel assembly to 0.1 g before use and record (A).

2 Accurately transfer 45 ml of well-shaken sample into the digestion vessel

3 Pipet 5 ml of HNO3concentrate into each vessel Make sure that pressure-cap relief disksare inserted according to manufacturer’s directions Tighten caps to manufacturer’s spec-ification

4 Weigh each capped vessel to the nearest 0.1 g (B).

5 Evenly distribute the appropriate number of vessels in the carousel

6 Treat sample blanks, known additions, and duplicates in the same manner as samples

7 When fewer samples than the appropriate number are digested, fill the remaining vesselswith 45 ml of reagent water and 5 ml of HNO3concentrate to obtain the full complement

of vessels for the particular program in use

8 Place carousel in microwave and set it carefully on the turntable Program microwave unit

to heat samples to 160±4°C in 10 min; for the second stage, permit a slow rise to 165 to

170°C for 10 min Start microwave generator, making sure that the turntable is turning andthat the exhaust fan is on

9 Upon completion of the microwave program, let vessels cool for at least 5 min in the unitbefore removal Samples may then be cooled further outside the unit by removing thecarousel and letting them cool on a bench or in a water bath When cooled to room tem-

perature, weigh (to 0.1 g) each vessel and record weight (C).

10 If the net weight of sample plus acid decreased by more than 10%, discard sample

11 Complete sample preparation by carefully uncapping and venting each vessel in a fumehood Transfer to acid-cleaned, noncontaminating plastic bottles If the digested samplecontains particulate, centrifuge at 2000 to 3000 rpm for 10 min and then filter or let settleovernight

15.2.8.3 Calculation

Dilution correction: Multiply results by 50/45, or 1.11, to account for the dilution caused by

the addition of 5 ml of acid to a 45-ml sample

Discarding of sample: To determine if the net weight of the sample plus acid decreased by

more than 10% during the digestion process, use the following calculation:

[(B−A) −(C−A)]/(B− A) × 100 > 10% (15.1)

15.2.8.4 Quality Control (QC)

Including a QC sample in each loaded carousel is recommended Prepare samples in batches, cluding preparation blanks, sample duplicates, and predigested known additions Determine size ofbatch and frequency of QC samples according to the analytical method and laboratory practice Thepower of the microwave unit and batch size may prevent including one or more QC samples in eachcarousel Do not group QC samples together but distribute them throughout the various carousels torender the best monitoring of digestion

in-15.3 ACID DIGESTION FOR TOTAL AND DISSOLVED METALS

15.3.1 I NTRODUCTION

This procedure is used to prepare surfacewater and groundwater samples for analysis by flameatomic absorption spectroscopy (FAAS) or by inductively coupled plasma spectroscopy (ICP),for the following metals: Al, Sb, As*, Ba, Be, Cd, Ca, Cr, Co, CI, Fe, Pb, Mg, Mn, Ni, K, Se*,

Ag, Na, Ta, V, and Zn (* = ICP only) Note that this digestion procedure may not be vigorousenough to destroy some metal complexes Total metal samples must be acidified at the time ofcollection with HNO3 For dissolved metals, all samples must be filtered through a 0.45-µm fil-ter and the filtrate acidified with HNO3(see Section 15.1) (For discussion of sample preserva-tion, see Section 14.4.)

to 15 to 20 ml Do not boil! Antimony (Sb) is easily lost by volatilization from HCl media.

3 Remove from hot plate and allow to cool

4 Wash down the beaker walls and watch glass with DI water If necessary (i.e., whensuspended material appears), filter or centrifuge the sample to remove suspended ma-

terials Caution: The filter and filtration apparatus should be washed with 1+1 HNO3fore filtration

be-5 Adjust the final volume to 100 ml with DI water

Note: As and Se determination from this digestate are suitable for the ICP technique only.

15.3.3 Q UALITY C ONTROL (QC)

Together with the samples, at a frequency of 5% or one per analytical batch, the following should bedigested as part of the quality control process:

1 100 ml of analyte-free water, called the preparation blank (prep blank)

2 100 ml of calibration verification standard (CVS), called laboratory control sample (LCS)

3 Spiked sample (spiked sample may be duplicated instead of a sample duplicate)

4 One sample duplicate

15.4 ACID DIGESTION OF AQUEOUS SAMPLES AND EXTRACTS

FOR TOTAL METALS BY FLAME ATOMIC ABSORPTION

SPECTROMETRY (FAAS) AND INDUCTIVELY COUPLED

PLASMA (ICP) ANALYZER

15.4.1 I NTRODUCTION

This digestion procedure is used to determine total metals in the preparation of aqueous samples,EPTOX and mobility-procedure (TCLP) extracts, and wastes that contain suspended solids for FAASand ICP analysis Samples may be analyzed for the following parameters: Al, As, Ba, Be, Cd, Ca, Cr,

Co, Co, Fe, Pb, Mg, Mn, Mo, Ni, K, Se, Na, Tl, V, and Zn This procedure is not suitable for samplesthat will be analyzed by GrAAS because HCl can cause interference during furnace atomization.Collection and preservation of samples are discussed in Section 14.4

15.4.2 P ROCEDURE

1 Transfer 100-ml representative aliquot of well-mixed sample into a beaker (The cleanedbeaker should be rinsed with 1+1 HNO3to avoid contamination.)

2 Add 3 ml of concentrated HNO3

3 Cover the beaker with a ribbed watch glass and place on a hot plate Heat slowly, until it

evaporates to about 5 ml Do not boil sample! Make certain that no portion of the bottom

of the beaker is allowed to dry.

4 Cool and add 3 ml of concentrated HNO3

5 Recover the beaker with the watch glass and return to the hot plate

6 Increase the temperature of the hot plate so that a gentle reflux action occurs

7 Continue heating, adding additional acid if necessary, until the sample is clear and light incolor

8 Evaporate until the volume is about 3 ml Do not dry sample! If a sample is allowed to dry

or burn, discard and redigest

9 Cool, add about 10 ml of 1+1 HCl and warm up for 15 min to dissolve all of the tate and residue

precipi-10 Wash down the beaker wall and watch glass with DI water, and filter or centrifuge, if essary, to remove silicates and other insoluble material that could clog the nebulizer Thisstep may cause contamination, unless the filter and filtering apparatus are thoroughlycleaned and rinsed with diluted HNO3

nec-11 Adjust the final volume to 100 ml with DI water

15.4.3 Q UALITY C ONTROL (QC)

As a QC requirement, the substances listed in Section 15.3.3 should be digested together with the alytical samples at a frequency of 5% or one per analytical batch (as described in Section 15.3.3)

an-15.5 ACID DIGESTION OF AQUEOUS SAMPLES AND EXTRACTS

FOR TOTAL METALS BY GRAPHITE FURNACE

SPECTROSCOPY (GrAAS)

15.5.1 I NTRODUCTION

This digestion procedure is used for the preparation of aqueous samples, EPTOX and cedure (TCLP) extracts, and wastes that contain suspended solids for analysis by GrAAS for the

mobility-pro-following metals: Be, Cd, Cr, Co, Pb, Mo, Tl, and V (Digestion and GrAAS analysis for As, Se, and

Ag are different The digestion procedure for As and Se is described in Section 15.8, and for Ag inSection 15.9.) Aqueous samples must be acidified to a pH of less than 2 with HNO3, while nonaque-ous samples should be refrigerated as soon as possible

15.5.2 P ROCEDURE

1 Transfer 100-ml aliquot from well-mixed sample into a beaker (The cleaned beakershould be rinsed with 1+1 HNO3to avoid contamination.) Cover the beaker with a ribbedwatch glass

2 Heat on a hot plate (do not boil!) until the sample evaporates to a volume of 5 ml (do not dry!).

3 Cool and add another 3 ml of concentrated HNO3

4 Continue heating, and add additional acid if necessary, until the sample is clear, and light

in color

5 Evaporate to about 3 ml of volume Do not dry!

6 Add 10 ml of DI water and heat for about 10 to 15 min

7 Wash down the walls of the beaker and the watch glass with DI water and filter if necessary

8 Complete to 100 ml of volume with DI water

15.5.3 Q UALITY C ONTROL (QC)

See Section 15.3.3

15.6 SAMPLE PREPARATION FOR ARSENIC AND SELENIUM

DETERMINATION BY GRAPHITE FURNACE

SPECTROSCOPY (G r AAS)

15.6.1 I NTRODUCTION

This method is used in the determination of As and Se in groundwater, wastes, extracts, and soils.Aqueous samples must be acidified to a pH of less than 2 with HNO3at the time of collection.Nonaqueous samples must be refrigerated and analyzed as soon as possible Furnace parametersshould be employed by following the method described in Chapter 9 The calibration curve should

be calculated every hour when continuous analysis is employed

15.6.2 P ROCEDURE FOR A QUEOUS S AMPLES

1 Transfer 100 ml of well-mixed sample into a beaker (The cleaned beaker should be rinsedwith 1+1 HNO3to avoid contamination.)

2 Add 2 ml of 30% H2O2and sufficiently concentrated HNO3to result in an acid tion of 1% (v/v)

concentra-3 Heat for 1 h at 95°C or until the volume is slightly less than 50 ml

4 Cool and bring back the volume to 50 ml with DI water

5 Pipet 5 ml of this digested solution into a 10-ml volumetric flask

6 Add 1 ml of 1% nickel nitrate (Ni(NO3)2) solution, and dilute to 10 ml of volume with DIwater The sample is now ready to inject into the furnace

15.6.3 P ROCEDURE FOR S OLID S AMPLES

Solid samples digestion for arsenic and selenium analysis is the same as described in Section 15.10

15.6.4 Q UALITY C ONTROL (QC)

See Section 15.3.3

15.7 SAMPLE PREPARATION FOR SILVER DETERMINATION

The digested samples are analyzed by the flame atomic absorption method and approved for mination of silver in wastes, extracts, soils, and ground waters

deter-1 Transfer a representative aliquot of well-mixed sample to a beaker, add 3 ml concentratedHNO3, and cover the beaker with a watch glass

2 Place the beaker on a hot plate and cautiously evaporate to near dryness, taking care that

the sample does not boil Do not bake!

3 Cool the beaker and add another 3-ml portion of concentrated HNO3and cover again withthe watch glass and return to the hot plate Increase the temperature, so that a gentle reflux

action occurs Note: If the sample contains thiosulfates, this step may result in splatter of

the sample as the sample approaches dryness (as with some photographic types of wastesamples)

4 Continue heating and adding additional acids until the digestate is light in color and doesnot change in appearance with further refluxing

5 Evaporate to dryness and cool

6 Add a small quantity of HNO3, so that the final dilution contains 0.5% (v/v) acid, andwarm to dissolve any precipitate

7 Wash down the wall of the beaker and the watch glass with DI water, filter if necessary,and dilute to volume (Volume depends on the expected concentration of the metal.)

15.8 SAMPLE PREPARATION FOR ANTIMONY DETERMINATION

For antimony (Sb) determination, the recommended sample preparation method is soft digestion, as

discussed in Section 15.1 The addition of HCl to the digestate prevents furnace analysis!

15.9 SAMPLE PREPARATION FOR MERCURY DETERMINATION

(COLD-VAPOR TECHNIQUE)

15.9.1 P REPARATION OF A QUEOUS S AMPLES

1 Transfer 100 ml (or an aliquot diluted to 100 ml) to a 300-ml BOD bottle

2 Add 5 ml of 0.5 nitrogen sulfuric acid (H2SO4) and 2.5 ml of concentrated HNO3, mixingafter each addition

3 Add 15 ml of 5% potassium permanganate (KMnO4) solution to each bottle Shake andadd additional portions of KMnO4until the purple color is persistent for at least 15 min.(Be sure that the same amount of permanganate is added to the accompanied standards andblanks!)

4 Add 8 ml of 5% potassium persulfate (K2S2O8)

5 Heat for 2 h in a water bath maintained at 95°C

6 Cool and add 6 ml of sodium chloride–hydroxylamine sulfate or hydroxylaminehydrochloride (12 g per 100 ml of DI water) to reduce excess KMnO4.

7 After a delay of at least 30 sec, add 5 ml of stannous sulfate or stannous chloride sion (10 g per 100 ml of 0.5N H2SO4by stirring continuously), and immediately attach tothe aeration apparatus and analyze

suspen-8 Blanks, calibration standards, QC check standards, and spiked samples must be treated thesame way

15.9.2 P REPARATION OF S OLID AND S EMISOLID S AMPLES

1 Weigh three 0.2-g portions of untreated sample and place in the bottom of a 300-ml BODbottle

2 Add 5 ml of DI water and 5 ml of aqua regia (3:1 HCl and HNO3)

3 Heat for 2 min in a water bath at 95°C

4 Cool and add 50 ml of DI water and 15 ml of 5% KMnO4solution

5 Mix thoroughly and place on the water bath at 95°C for 30 min

6 Cool and add 6 ml of 12% of hydroxylamine hydrochloride or sodium lamine sulfate solution to reduce excess KMnO4 Caution: Add this material under a fume

chloride-hydroxy-hood because chlorine (Cl2) could evolve!

7 Add 55 ml of DI water and 5 ml of 10% stannous chloride or stannous sulfate solution,immediately attach to the aeration apparatus, and analyze

8 Calibration standards and QC checks are treated in the same way

9 For calculations to report on the dry base, the percent moisture content of the sampleshould be determined as described in Appendix I

15.10 ACID DIGESTION OF SEDIMENTS, SLUDGES, AND SOILS

FOR TOTAL METALS ANALYSIS

15.10.1 I NTRODUCTION

This method is an acid digestion procedure used to prepare sediments, sludges, and soil samples foranalysis by FAAS, GrAAS, or ICP Samples prepared with this method may be analyzed by ICP forall listed metals and by FAAS or GrAAS as indicated below:

FAAS: Al, Ba, Be, Cd, Ca, Cr, Co, Cu, Fe, Pb, Mg, Mn, Mo, Ni, K, Na, Tl, V, Zn

GrAAS: As, Be, Cd, Cr, Co, Fe, Mo, Se, Tl, V

A representative (wet weight) sample of 1 to 2 g is digested in HNO3and H2O2 The digestate isthen refluxed with either HNO3or HCl Diluted HCl is used as the final reflux acid for the ICP analy-sis of As and Se, and the FAAS or ICP analysis of Al, Ba, Be, Ca, Cd, Cr, Co, Cu, Fe, Mo, Pb, Ni, K,

Na, Tl, N, and Zn Dilute HNO3is employed as the final dilution acid for GrAAS analysis of As, Be,

Cd, Cr, Co, Pb, Mo, Se, Tl, and V A separate sample should be dried for a total solids determination.All samples must be collected as discussed in Chapter 14

15.10.2 P ROCEDURE

1 Mix sample thoroughly to achieve homogeneity

2 Weigh 1 to 2 g of sample into a beaker (The cleaned beaker should be rinsed with 1+1HNO3before use to avoid contamination.)

3 Add 10 ml of 1+1 HNO3and mix with the solid sample