4500-S2 SULFIDE*

4500-S2 A. Introduction

1. Occurrence and Significance

Sulfide is often present in groundwater and sediment. It is

produced by decomposition of organic matter and bacterial reduction of sulfate. It is sometimes found in industrial or municipal wastewater. Hydrogen sulfide escaping into the air from

sulfide-containing wastewater causes odor nuisances. The

threshhold odor concentration of H2S in clean water is between

0.025 and 0.25 g/L. Gaseous H2S is very toxic and has claimed

the lives of numerous workers. At levels toxic to humans it

interferes with the olfactory system, giving a false sense of the

safe absence of H2S. It attacks metals directly, and indirectly has

caused serious corrosion of concrete sewers because it is oxidized biologically in the presence of oxygen to H2SO4 on the

pipe wall. Dissolved H2S is toxic to fish and other aquatic

organisms.

Hydrogen sulfide combines with iron and other metals in

natural sediments and sludges to form slightly-soluble precipitates. Acid-volatile sulfide (AVS) is an important class of metal

sulfides in these anoxic environments. The determination of

AVS concentrations has become more prevalent because AVS is

considered to be a key binding phase for controlling bioavailability of toxic metals in anoxic sediments.

AVS typically is determined by a purge-and-trap method in

which hydrochloric acid is used to volatilize AVS at room

temperature. The metals associated with the sulfides can be

determined from the supernatant of the purged sample solution

by using methods such as those in Part 3000. The hydrogen

sulfide produced is trapped in zinc-acetate absorbing solution.

AVS concentrations are measured by iodometric titration of the

ZnS precipitated in the trap (4500-S2.F). Certain minerals,

including iron pyrite, are partially digested by the AVS reagents

at elevated temperatures, which may result in a significant overestimation of AVS. Iron pyrite can be partially digested to the

extent of less than 10% of the total pyrite present. The addition

of stannous chloride (SnCl2) prevents the oxidation of sulfides by

any liberated ferric iron.

2. Categories of Sulfides

Four categories of sulfide in water, wastewater, and sediment

can be operationally defined:

a. Total sulfide includes dissolved H2S and HS and acidvolatile metallic sulfides present in particulate matter. The pKa2

of H2S is so high that the concentration of S2 is negligible at all

pH values. Copper and silver sulfides are so insoluble that they

do not respond in ordinary sulfide determinations; they can be

ignored for practical purposes.

b. Dissolved sulfide is that remaining after suspended solids

have been removed by flocculation and settling. Flocculation and

settling are used to separate dissolved and particulate sulfide

because sulfide may be oxidized during filtration. Centrifugation

also may be used.

c. Acid-volatile sulfide includes amorphous iron monosulfides,

including mackinawite (FeS), greigite (Fe3S4), and pyrrhotite

(FeS), and amorphous monosulfides of other metals. Pyrite,

another iron sulfide mineral, is not included in the acid-volatile

sulfides.

d. Un-ionized hydrogen sulfide can be calculated from the

concentration of dissolved sulfide, the sample pH, and the conditional ionization constant of H2S.

Figure 4500-S2:1 shows analytical flow paths for sulfide

determinations under various conditions and options. None of

the operationally defined sulfide categories includes pyrite or

marcasite (FeS2).

3. Sampling and Storage

Collect water samples with minimum aeration. Either analyze

samples immediately after collection or preserve with zinc acetate solution for later analysis. To preserve a sample for a total

sulfide determination, put zinc acetate and sodium hydroxide

solutions into sample bottle before filling it with sample. Use

0.2 mL 2M zinc acetate solution per 100 mL sample. Increase

volume of zinc acetate solution if the sulfide concentration is

expected to be greater than 64 mg/L. The final pH should be at

least 9. Add more NaOH if necessary. Fill bottle completely and

stopper.

Sample sediments and sludges under nitrogen atmosphere if

possible. Store samples at 4°C or frozen, and analyze within 2

weeks (1 month for frozen samples) of collection. Do not freezedry because acid-volatile sulfide may decompose as a result of

oxidation artifacts.

4. Qualitative Tests

A qualitative test for sulfide often is useful. It is advisable in

the examination of industrial wastes containing interfering substances that may give a false negative result in the methylene

blue method (D).

a. Antimony test: To about 200 mL sample, add 0.5 mL

saturated solution of antimony potassium tartrate and 0.5 mL 6N

HCl in excess of phenolphthalein alkalinity.

Yellow antimony sulfide (Sb2S3) is discernible at a sulfide

concentration of 0.5 mg/L. Comparisons with samples of known

sulfide concentration make the technique roughly quantitative.

The only known interferences are metallic ions, such as lead,

which hold the sulfide so firmly that it does not produce Sb2S3,

* Approved by Standard Methods Committee, 2000. Editorial revisions, 2011.

Joint Task Group: 21st Edition—(4500-S2.A, H, I, J )—Thomas R. Holm (chair),

Robert P. Fisher, Martin S. Frant, Christian Gagnon, Lorne R. Goodwin; 20th

Edition—(4500-S2.I)—Scott Stieg (chair), Bradford R. Fisher, Owen B. Mathre,

Theresa M. Wright.

1
and dithionite, which decomposes in acid solution to produce

sulfide.

b. Silver-silver sulfide electrode test: Dilute sample 1:1 with

alkaline antioxidant reagent (see 4500-S2.G.3a). Measure electrode potential relative to a double-junction reference electrode

and estimate the sulfide concentration from an old calibration

curve or the example calibration curve in the electrode manual.

This gives a reasonable estimate of sulfide concentration if the

electrode is in good condition.

c. Lead acetate paper and silver foil tests: Confirm odors

attributed to H2S with lead acetate paper. On exposure to the

vapor of a slightly acidified sample, the paper becomes blackened by formation of PbS. A strip of silver foil is more sensitive

than lead acetate paper. Clean the silver by dipping in NaCN

solution and rinse. CAUTION: NaCN is toxic; handle with care.

Silver is suitable particularly for long-time exposure in the

vicinity of possible H2S sources because black Ag2S is permanent, whereas PbS slowly oxidizes.

5. Selection of Quantitative Methods

Iodine oxidizes sulfide in acid solution. A titration based on

this reaction is an accurate method for determining sulfide at

concentrations above 1 mg/L if interferences are absent† and if

loss of H2S is avoided. The iodometric method (F) is useful for

standardizing the methylene blue colorimetric methods (D, E,

and I) and is suitable for analyzing samples freshly taken from

wells or springs. The method can be used for wastewater and

partly oxidized water from sulfur springs if interfering substances are removed first. The automated methylene blue method

with distillation (I) is useful for a variety of samples containing

more than 1 mg S2/L.

The methylene blue method (D) is based on the reaction of

sulfide, ferric chloride, and dimethyl-p-phenylenediamine to produce methylene blue. Ammonium phosphate is added after color

development to remove ferric chloride color. The procedure is

applicable at sulfide concentrations between 0.1 and 20.0 mg/L.

The automated methylene blue method (E) is similar to

Method D. A gas dialysis technique separates the sulfide from

the sample matrix. Gas dialysis eliminates most interferences,

including turbidity and color. The addition of the antioxidant

ascorbic acid improves sulfide recoveries. The method is applicable at sulfide concentrations between 0.002 and 0.100 mg/L.

Potentiometric methods using a silver/sulfide ion-selective

electrode (G) may be suitable. The sulfide concentration can be

estimated from the potential of the electrode relative to a reference electrode, but careful attention to details of procedures and

frequent standardizations are needed to secure good results. The

electrode is useful particularly as an endpoint indicator for

titration of dissolved sulfide with silver nitrate. The ion-selective

electrode method is unaffected by sample color or turbidity and

is applicable for concentrations greater than 0.03 mg/L. † Many substances can reduce iodine; all of these are potential interferences in

procedures using this chemistry.

Figure 4500-S2:1. Analytical flow paths for sulfide determination.

SULFIDE (4500-S2)/Introduction

2
6. Preparation of Sulfide Standards

Take care in preparing reliable stock solutions of sulfide for

calibration and quality control. Prepare sulfide standards from

sodium sulfide nonahydrate (Na2S  9H2O) crystals. These crystals usually have excess water present on the surface, in addition

to a layer of contamination from oxidation products (polysulfides, polythionates, and sulfate) of sulfide reacting with atmospheric oxygen. Further, solutions of sulfide are prone to ready

oxidation by dissolved and atmospheric oxygen. Use reagent

water to prepare sulfide standards and sample dilutions. Degas

the water with either argon or nitrogen. Purchase the smallest

amount of solid standards possible and keep no longer than

1 year. Preferably handle and store solid sulfide standards and

stock solutions in an inert atmosphere glove bag or glove box to

reduce contamination due to oxidation.

Preferably remove single crystals of Na2S  9H2O from reagent bottle with nonmetallic tweezers; quickly rinse in degassed

reagent water to remove surface contamination. Blot crystal dry

with a tissue, then rapidly transfer to a tared, stoppered weighing

bottle containing 5 to 10 mL degassed reagent water. Repeat

procedure until desired amount of sodium sulfide is in weighing

bottle. Avoid excess agitation and mixing of the solution with

atmospheric oxygen. Quantitatively transfer and dilute entire

contents of weighing bottle to an appropriate size volumetric

flask with degassed reagent water to prepare a known concentration sulfide stock solution (3.75 g Na2S  9H2O diluted to a

final volume of 500 mL will give a stock solution of which

1.00 mL 1.00 mg S2). Standardize stock solution using the

iodometric method, 4500-S2.F. Alternatively, purchase precertified stock solutions of sulfide. Verify concentration of stock

solution daily using the iodometric method (F). Store stock

solution with minimum headspace for no more than 1 week.

7. Bibliography

CRUSE, H. & R.D. POMEROY. 1969. Hydrogen sulfide odor threshold.

J. Amer. Water Works Assoc. 61:677.

KARCHMER, J.H., ed. 1970. The Analytical Chemistry of Sulfur and Its

Compounds. Wiley-Interscience, New York, N.Y.

NICKLESS, G., ed. 1970. Inorganic Sulphur Chemistry. Elsevier Publ.,

Amsterdam, The Netherlands.

U.S. ENVIRONMENTAL PROTECTION AGENCY. 1974. Process Design Manual

for Sulfide Control in Sanitary Sewerage Systems. Publ. 625/1-74-

005.

BAGARINAO, T. 1992. Sulfide as an environmental factor and toxicant:

Tolerance and adaptations in aquatic organisms. Aquat. Toxicol.

24:21.

BUTLER, I.B., M.A.A. SCHOONEN & D.T. RICKARD. 1994. Removal of

dissolved oxygen from water: a comparison of four common techniques. Talanta 41:211.

4500-S2 B. Separation of Soluble and Insoluble Sulfides

Unless the sample is entirely free from suspended solids (dissolved

sulfide equals total sulfide), to measure dissolved sulfide first remove

insoluble matter. This can be done by producing an aluminum hydroxide floc that is settled, leaving a clear supernatant for analysis.

1. Apparatus

Glass bottles with stoppers: Use 100 mL if sulfide will be determined by the methylene blue method and 500 to 1000 mL if by the

iodometric method.

2. Reagents

a. Sodium hydroxide solution, NaOH, 6N.

b. Aluminum chloride solution: Because of the hygroscopic

and caking tendencies of this chemical, purchase 100-g bottles of

AlCl3  6H2O. Dissolve contents of a previously unopened 100-g

bottle in 144 mL distilled water.

3. Procedure

a. To a 100-mL glass bottle, add 0.2 mL (nominally 4 drops)

6N NaOH. Fill bottle with sample and immediately add 0.2 mL

(4 drops) AlCl3 solution. Stopper bottle with no air under

stopper. Rotate back and forth about a transverse axis vigorously for 1 min or longer to flocculate contents. Vary volumes

of these added chemicals to get good clarification without

using excessively large amounts and to produce a pH of 6 to

9. If a 500- or 1000-mL bottle is used, add proportionally

larger amounts of reagents.

b. Let settle until reasonably clear supernatant can be drawn

off. With proper flocculation, this may take 5 to 15 min. Do not

wait longer than necessary.

c. Either analyze the supernatant immediately or preserve with

2N zinc acetate (see 4500-S2.C).

4500-S2 C. Sample Pretreatment to Remove Interfering Substances or

to Concentrate the Sulfide

The iodometric method suffers interference from reducing

substances that react with iodine, including thiosulfate, sulfite,

and various organic compounds, both solid and dissolved.

Strong reducing agents also interfere in the methylene blue

method (D) by preventing formation of the blue color. Thiosulfate

at concentrations about 10 mg/L may retard color formation or

SULFIDE (4500-S2)/Sample Pretreatment

3
completely prevent it. Ferrocyanide produces a blue color. Sulfide

itself prevents the reaction if its concentration is very high, in the

range of several hundred milligrams per liter. To avoid the possibility of false negative results, use the antimony method to obtain a

qualitative result in industrial wastes likely to contain sulfide but

showing no color by the methylene blue method. Iodide, which is

likely to be present in oil-field wastewaters, may diminish color

formation if its concentration exceeds 2 mg/L. Many metals (e.g.,

Hg, Cd, Cu) form insoluble sulfides and give low recoveries.

Eliminate interferences due to sulfite, thiosulfate, iodide, and

many other soluble substances, but not ferrocyanide, by first precipitating ZnS, removing the supernatant, and replacing it with

distilled water. Use the same procedure, even when not needed for

removal of interferences, to concentrate sulfide. The automated

methylene blue method (E) is relatively free from interferences

because gas dialysis separates the sulfide from the sample matrix.

1. Apparatus

Glass bottles with stoppers: See 4500-S2.B.1.

2. Reagents

a. Zinc acetate solution: Dissolve 220 g Zn(C2H3O2)2  2H2O

in 870 mL water; this makes 1 L solution.

b. Sodium hydroxide solution, NaOH, 6N.

3. Procedure

a. Put 0.20 mL (4 drops) zinc acetate solution and 0.10 mL (2

drops) 6N NaOH into a 100-mL glass bottle, fill with sample,

and add 0.10 mL (2 drops) 6N NaOH solution. Stopper with no

air bubbles under stopper and mix by rotating back and forth

vigorously about a transverse axis. For the iodometric procedure,

use a 500-mL bottle or other convenient size, with proportionally

larger volumes of reagents. Vary volume of reagents added

according to sample so the resulting precipitate is not excessively bulky and settles readily. Add enough NaOH to raise the

pH above 9. Let precipitate settle for 30 min. The treated sample

is relatively stable and can be held for several hours. However,

if much iron is present, oxidation may be fairly rapid.

b. If the iodometric method is to be used, collect precipitate on a

glass fiber filter and continue at once with titration according to the

procedure of Method F. If the methylene blue method (D) is used,

let precipitate settle for 30 min and decant as much supernatant as

possible without loss of precipitate. Refill bottle with distilled water,

shake to resuspend precipitate, and quickly withdraw a sample. If

interfering substances are present in high concentration, settle, decant, and refill a second time. If sulfide concentration is known to be

low, add only enough water to bring volume to one-half or one-fifth

of original volume. Use this technique for analyzing samples of

very low sulfide concentrations. After determining the sulfide concentration colorimetrically, multiply the result by the ratio of final to

initial volume. No concentration or pretreatment steps to remove

interferences are necessary for Method E.

4500-S2 D. Methylene Blue Method

1. Apparatus

a. Matched test tubes, approximately 125 mm long and 15 mm

OD.

b. Droppers, delivering 20 drops/mL methylene blue solution.

To obtain uniform drops hold dropper in a vertical position and

let drops form slowly.

c. If photometric rather than visual color determination will be

used, either:

1) Spectrophotometer, for use at a wavelength of 664 nm with

cells providing light paths of 1 cm and 1 mm, or other path

lengths, or

2) Filter photometer, with a filter providing maximum transmittance near 660 nm.

2. Reagents

a. Amine-sulfuric acid stock solution: Dissolve 27 g

N,N-dimethyl-p-phenylenediamine oxalate* in an iced mixture

of 50 mL conc H2SO4 and 20 mL distilled water. Cool and dilute

to 100 mL with distilled water. Use fresh oxalate because an old

supply may be oxidized and discolored to a degree that results in

interfering colors in the test. Store in a dark glass bottle. When

this stock solution is diluted and used in the procedure with a

sulfide-free sample, it first will be pink but then should become

colorless within 3 min.

b. Amine-sulfuric acid reagent: Dilute 25 mL amine-sulfuric

acid stock solution with 975 mL 1  1 H2SO4. Store in a dark

glass bottle.

c. Ferric chloride solution: Dissolve 100 g FeCl3  6H2O in

40 mL water.

d. Sulfuric acid solution, H2SO4, 1  1.

e. Diammonium hydrogen phosphate solution: Dissolve 400 g

(NH4)2HPO4 in 800 mL distilled water.

f. Methylene blue solution I: Use USP grade dye or one

certified by the Biological Stain Commission. The dye content

should be reported on the label and should be 84% or more.

Dissolve 1.0 g in distilled water and make up to 1 L. This

solution will be approximately the correct strength, but because

of variation between different lots of dye, standardize against

sulfide solutions of known strength and adjust its concentration

so 0.05 mL (1 drop) 1.0 mg sulfide/L.

Standardization—Prepare five known-concentration sulfide

standards ranging from 1 to 8 mg/L as described in 4500-

S2.A.6, or proceed as follows: Put several grams of clean,

washed crystals of Na2S  9H2O into a small beaker. Add some-

* Eastman catalog No. 5672 has been found satisfactory for this purpose. what less than enough water to cover crystals. Stir occasionally

SULFIDE (4500-S2)/Methylene Blue Method

4
for a few minutes, then pour solution into another vessel. This

solution reacts slowly with oxygen but the change is insignificant

if analysis is performed within a few hours. Prepare solution

daily. To 1 L distilled water, add 1 drop of Na2S solution and

mix. Immediately determine sulfide concentration by the methylene blue procedure and by the iodometric procedure. Repeat, using more than 1 drop Na2S solution or smaller volumes of water, until at least five tests have been made, with a

range of sulfide concentrations between 1 and 8 mg/L. Calculate average percent error of the methylene blue result as

compared to the iodometric result. If the average error is

negative (i.e., methylene blue results are lower than iodometric results), dilute methylene blue solution by the same percentage, so a greater volume will be used in matching colors.

If methylene blue results are high, increase solution strength

by adding more dye.

g. Methylene blue solution II: Dilute 10.00 mL of adjusted

methylene blue solution I to 100 mL with reagent water.

3. Procedure

a. Color development: Transfer 7.5 mL sample to each of two

matched test tubes, using a special wide-tip pipet or filling to

marks on test tubes. If sample has been preserved with zinc

acetate, shake vigorously before taking subsample. Add to

Tube A 0.5 mL amine-sulfuric acid reagent and 0.15 mL

(3 drops) FeCl3 solution. Mix immediately by inverting

slowly, only once. (Excessive mixing causes low results by

loss of H2S as a gas before it has had time to react). To Tube B add

0.5 mL 1  1 H2SO4 and 0.15 mL (3 drops) FeCl3 solution and

mix. The presence of S2 will be indicated by the appearance of

blue color in Tube A. Color development usually is complete in

about 1 min, but a longer time often is required for fading out of

the initial pink color. Wait 3 to 5 min and add 1.6 mL

(NH4)2HPO4 solution to each tube. Wait 3 to 15 min and make

color comparisons. If zinc acetate was used, wait at least 10 min

before making a visual color comparison.

b. Color determination:

1) Visual color estimation—Add methylene blue solution I or

II, depending on sulfide concentration and desired accuracy,

dropwise, to the second tube, until color matches that developed

in first tube. If the concentration exceeds 20 mg/L, repeat test

with a portion of sample diluted tenfold.

With methylene blue solution I, adjusted so 0.05 mL (1 drop)

1.0 mg S2/L when 7.5 mL of sample are used:

mg S2/L no. drops solution I  0.1 (no. drops solution II)

2) Photometric color measurement—A cell with a light path of

1 cm is suitable for measuring sulfide concentrations from 0.1 to

2.0 mg/L. Use shorter or longer light paths for higher or lower

concentrations. This method is suitable for sample concentrations up to 20 mg/L. Zero instrument with a portion of treated

sample from Tube B. Prepare calibration curves on basis of

colorimetric tests made on Na2S solutions simultaneously analyzed by the iodometric method, plotting concentration vs. absorbance. A linear relationship between concentration and absorbance can be assumed from 0 to 1.0 mg/L.

Read sulfide concentration from calibration curve.

4. Precision and Bias

In a study by two chemists working in the same laboratory, the

standard deviation estimated from 34 sets of duplicate sulfide

measurements was 0.04 mg/L for concentrations between 0.2

and 1.5 mg/L. The average recoveries of known additions were

92% for 40 samples containing 0.5 to 1.5 mg/L and 89% for

samples containing less than 0.1 mg/L.

5. Quality Control

The quality control practices considered to be an integral part

of each method are summarized in Table 4020:I.

6. Bibliography

POMEROY, R.D. 1936. The determination of sulfides in sewage. Sewage

Works J. 8:572.

NUSBAUM, I. 1965. Determining sulfides in water and waste water. Water

Sewage Works 112:113.

4500-S2 E. Gas Dialysis, Automated Methylene Blue Method

1. Apparatus

Automated analytical equipment: An example of the continuous-flow analytical instrument consists of the interchangeable

components shown in Figure 4500-S2:2.

The sampler is equipped with a mixer to stir samples before

analysis and the gas dialysis membrane, which is maintained at

room temperature, separates H2S from the sample matrix.

2. Reagents

a. N,N-dimethyl-p-phenylenediamine stock solution: Dissolve

1 g N,N-dimethyl-p-phenylenediamine dihydrochloride in 500 mL

6N HCl. Prepare fresh monthly. Store in an amber bottle.

b. N,N-dimethyl-p-phenylenediamine working solution: Dilute

190 mL N,N-dimethyl-p-phenylenediamine stock solution to 1 L.

Store in an amber bottle. Prepare weekly.

c. Ferric chloride stock solution: Dissolve 13.5 g

FeCl3  6H2O in 500 mL 5N HCl. Store in an amber bottle.

Prepare fresh monthly.

d. Working ferric chloride solution: Dilute 190 mL ferric

chloride stock solution to 1 L. Store in an amber bottle. Prepare

fresh weekly.

e. Hydrochloric acid, HCl, 6N:

f. Sodium hydroxide stock solution, NaOH, 1N.

g. Sodium hydroxide, NaOH, 0.01N: Dilute 10 mL NaOH

stock solution to 1 L.

SULFIDE (4500-S2)/Gas Dialysis, Automated Methylene Blue Method

5
h. Sulfide stock solution, 1.00 mg S2/1.00 mL: See 4500-

S2.A.6.

i. Sulfide intermediate standard solution: Dilute 10 mL sulfide

stock solution to 1 L with water. Prepare fresh daily. Standardize by

iodometric titration method, 4500-S2.F. 1 mL  0.01 mg S2.

j. Sulfide tertiary standard solution: Dilute 50 mL sulfide

intermediate solution to 500 mL with 0.01N NaOH. Prepare

fresh daily. Use standardization value from ¶ i above to determine exact concentration. 1.00 mL  0.001 mg S2.

k. Working sulfide standard solutions: Prepare a suitable series

of standards by diluting appropriate volumes of sulfide tertiary

standing solutions with 0.01N NaOH. Prepare fresh daily.

l. Zinc acetate preservative solution: Dissolve 220 g

Zn(C2H3O2)2  2H2O in 870 mL water (this makes 1 L solution).

3. Procedure

For unpreserved, freshly collected samples and sulfide working standards, add, in order, 4 drops 2N zinc acetate, 0.5 mL 6N

NaOH, and 400 mg ascorbic acid/100 mL. For preserved samples, add 0.5 mL 6N NaOH and 400 mg ascorbic acid/100 mL.

Shake well.

Let precipitate settle for at least 30 min. Pour a portion of

well-mixed sample or working standard into a sample cup. Set

up manifold as shown in Figure 4500-S2:2 and follow the

general procedure described by the manufacturer. Determine

absorbance at 660 nm.

4. Calculation

Prepare standard curves by plotting peak heights of standards

processed through the manifold against S2 concentration in the

standards. Compute S2 sample concentration by comparing

sample response with standard curve.

5. Precision and Bias

In a single laboratory, samples with S2 concentrations of

0.012, 0.015, 0.034, and 0.085 mg/L had standard deviations of

0.001, 0.001, 0.001, and 0.001 mg/L, respectively, with coefficients of variation of 8.3%, 6.3%, 2.9%, and 1.2%, respectively.

In two environmental samples with added S2, recoveries were

104.2 and 97.6%.

Figure 4500-S2:2. Sulfide manifold.

SULFIDE (4500-S2)/Gas Dialysis, Automated Methylene Blue Method

6
6. Quality Control

The quality control practices considered to be an integral part

of each method are summarized in Table 4020:I.

7. Bibliography

FRANCOM, D., L.R. GOODWIN & F.P. DIEKEN. 1989. Determination of low

level sulfides in environmental waters by automated gas dialysis/

methylene blue colorimetry. Anal. Lett. 22:2587.

4500-S2 F. Iodometric Method

1. Reagents

a. Hydrochloric acid, HCl, 6N.

b. Standard iodine solution, 0.0250N: Dissolve 20 to 25 g KI

in a little water and add 3.2 g iodine. After iodine has dissolved,

dilute to 1000 mL and standardize against 0.0250N Na2S2O3,

using starch solution as indicator.

c. Standard sodium thiosulfate solution, 0.0250N: See Section

4500-O.C.2e.

d. Starch solution: See Section 4500-O.C.2d.

2. Procedure

a. Measure from a buret into a 500-mL flask an amount of

iodine solution estimated to be an excess over the amount of

sulfide present. Add distilled water, if necessary, to bring volume

to about 20 mL. Add 2 mL 6N HCl. Pipet 200 mL sample into

flask, discharging sample under solution surface. If iodine color

disappears, add more iodine until color remains. Back-titrate

with Na2S2O3 solution, adding a few drops of starch solution as

endpoint is approached, and continuing until blue color disappears.

b. If sulfide was precipitated with zinc and ZnS filtered out,

return filter with precipitate to original bottle and add about

100 mL water. Add iodine solution and HCl and titrate as in ¶ a

above.

3. Calculation

One milliliter 0.0250N iodine solution reacts with 0.4 mg S2:

mg S2/L [(A B)  (C D)]  16 000

mL sample

where:

A mL iodine solution,

B normality of iodine solution,

C mL Na2S2O3 solution, and

D normality of Na2S2O3 solution.

4. Precision

The precision of the endpoint varies with the sample. In clean

waters it should be determinable within 1 drop, which is equivalent to 0.1 mg/L in a 200-mL sample.

5. Quality Control

The quality control practices considered to be an integral part

of each method are summarized in Table 4020:I.

4500-S2 G. Ion-Selective Electrode Method

1. General Discussion

a. Principle: The potential of a silver/sulfide ion-selective

electrode (ISE) is related to the sulfide ion activity. An alkaline

antioxidant reagent (AAR) is added to samples and standards to

inhibit oxidation of sulfide by oxygen and to provide a constant

ionic strength and pH. Use of the AAR allows calibration in

terms of total dissolved sulfide concentration. All samples and

standards must be at the same temperature. Sulfide concentrations between 0.032 mg/L (1  106

M) and 100 mg/L can be

measured without preconcentration. For lower concentrations,

preconcentration is necessary.

b. Interferences: Humic substances may interfere with Ag/SISE measurements. For highly colored water (high concentration

of humic substances), use the method of standard additions to

check results. Sulfide is oxidized by dissolved oxygen. Sulfide

oxidation may cause potential readings to drift in the direction of

decreasing concentration, i.e., to more positive values. Flush

surface of samples and standards with nitrogen to minimize

contact with atmospheric oxygen for low-level measurements.

Temperature changes may cause potentials to drift either upward

or downward. Therefore, let standards and samples come to the

same temperature. If samples cannot be analyzed immediately,

preserve dissolved sulfide by precipitating with zinc acetate

(4500-S2.C).

c. Quality control (QC): The QC practices considered to be an

integral part of each method are summarized in Table 4020:I.

2. Apparatus

a. Silver/sulfide electrode.*

b. Double-junction reference electrode.

* Orion 941600, or equivalent.

SULFIDE (4500-S2)/Ion-Selective Electrode Method

7
c. Electrode polishing strips.†

d. pH meter with millivolt scale, capable of 0.1-mV resolution.

Meters that can be calibrated in concentration and that perform

standard-additions calculations are available.

e. Electrochemical cell: Make suitable cell from a 150-mL

beaker and a sheet of rigid plastic (PVC or acrylic) with holes

drilled to allow insertion of the electrodes and a tube for flushing

the headspace with nitrogen. Alternatively, purchase a polarographic cell with gas transfer tube.‡

f. Gas dispersion tube: Use to deaerate water for preparing

reagents and standards.

g. Magnetic stirrer and stirring bar: Use a piece of styrofoam

or cardboard to insulate the cell from the magnetic stirrer.

3. Reagents

a. Alkaline antioxidant reagent (AAR): To approximately

600 mL deaerated reagent water (DRW) in a 1-L volumetric

flask, add 80 g NaOH, 35 g ascorbic acid, and 67 g Na2H2EDTA.

Swirl to dissolve and dilute to 1 L. The color of freshly prepared

AAR will range from colorless to yellow. Store in a tightly

capped brown glass bottle. Discard when solution becomes

brown.

b. Lead perchlorate, 0.1M: Dissolve 4.60 g Pb(ClO4)2  3H2O

in 100 mL reagent water. Standardize by titrating with

Na2H2EDTA. Alternatively, use commercially available 0.1M

Pb(ClO4)2 solutions.

c. Sulfide stock solution, 130 mg/L: See 4500-S2.A.6, and

dilute 13.0 mL of 1.00 mg S2/mL stock to 100.0 mL with AAR.

Alternatively, add 500 mL AAR and 1 g Na2S  9H2O to a 1-L

volumetric flask; dissolve. Dilute to 1 L with DRW. Use deaerated artificial seawater (DASW), Table 8010:III, or 0.7M NaCl if

sulfide concentrations are to be determined in seawater. Standardize stock solution by titrating with 0.1M Pb(ClO4)2. Pipet

50 mL sulfide stock solution into the electrochemical cell. (Use

10 mL with a small-volume polarographic cell.) Insert Ag/S

electrode and reference electrode and read initial potential.

Titrate with 0.1M Pb(ClO4)2. Let electrode potential stabilize

and record potential after each addition. Locate equivalence

point as in Section 4500-Cl.D.4a. Alternatively, linearize the

titration curve.1 Calculate the function F1 for points before the

equivalence point.

F1 (Vo  V)10 E

m

where:

Vo volume of stock solution, mL,

V titrant volume, mL,

E potential, mV, and

m slope of calibration curve, mV/log unit.

Plot F1 as a function of titrant volume. Extrapolate to find

the intersection with the x-axis; that is, the equivalence point.

Calculate sulfide concentration in the stock solution from:

C Veq[Pb]

Vo

where:

C sulfide concentration, mg/L,

Veq equivalence volume, mL,

[Pb] concentration of Pb in titrant, mg/L, and

Vo volume of stock solution, mL.

Store stock solution in a tightly capped bottle for 1 week or

less. The stock solution also can be standardized iodometrically

(see 4500-S2.E). CAUTION: Store in a fume hood.

d. Sulfide standards: Prepare sulfide standards daily by serial

dilution of stock. Add AAR and Zn(C2H3O2)2 solutions to

100-mL volumetric flasks. Add sulfide solutions and dilute to

volume with DRW (or DASW). Refer to Table 4500-S2:I for

volumes. Prepare at least one standard with a concentration less

than the lowest sample concentration.

4. Procedure

Check electrode performance and calibrate daily. Check electrode potential in a sulfide standard every 2 h. The procedure

depends on the sulfide concentration and the time between sample

collection and sulfide determination. If the total sulfide concentration is greater than 0.03 mg/L (1  106

M) and the time delay is

only a few minutes, sulfide can be determined directly. Otherwise,

precipitate ZnS and filter as described in 4500-S2.C.

a. Check electrode performance: Pipet 50 mL AAR, 50 mL

DWR, and 1 mL sulfide stock solution into the measurement

cell. Place Ag/S and reference electrodes in the solution and read

potential. Add 10 mL stock solution and read potential. The

change in potential should be 28  2 mV. If it is not, follow

the troubleshooting procedure in the electrode manual.

b. Calibration: Place electrodes in the most dilute standard but

use calibration standards that bracket the sulfide concentrations

in the samples. Record potential when the rate of change is less

than 0.3 mV/min. (This may take up to 30 min for very low

sulfide concentrations, i.e., less than 0.03 mg/L.) Rinse electrodes, blot dry with a tissue, and read potential of the next

highest standard. For a meter that can be calibrated directly in

concentration, follow manufacturer’s directions. For other meters,

plot potential as a function of the logarithm (base 10) of the

sulfide concentration. For potentials in the linear range, calculate

the slope and intercept of the linear portion of the calibration plot.

c. Sulfide determination by comparison with calibration curve,

no ZnS precipitation: Add 40 mL AAR, 0.15 mL (3 drops) zinc

acetate, and 50 mL sample to a 100-mL volumetric flask. Dilute

to 100 mL with AAR. Pour into the electrochemical cell and † Orion 948201, or equivalent.

‡ EG&G Princeton Applied Research K0066, K0060, G0028, or equivalent.

TABLE 4500-S2:I. DILUTION OF SULFIDE STOCK SOLUTION FOR

PREPARATION OF STANDARDS (100 ML TOTAL VOLUME)

Dilution

Alkaline

Antioxidant

Reagent

mL

Sulfide

Solution

Sulfide

Solution

mL

1M Zinc

Acetate

mL

1:10 45 Stock 10 0.15

1:100 50 Stock 1 0.15

1:1 000 45 1:100 10 0.14

1:10 000 50 1:100 1 0.15

SULFIDE (4500-S2)/Ion-Selective Electrode Method

8
insert the electrodes. Record potential when the rate of change is

less than 0.3 mV/min. Read sulfide concentration from the

calibration curve. Alternatively, for potentials in the linear range,

calculate the sulfide concentration from:

STot 10

Eb

m

where:

E electrode potential and

b and m are the intercept and slope of the calibration curve.

For a meter that can be calibrated directly in concentration,

follow the manufacturer’s directions.

d. Sulfide determination by comparison with calibration curve,

with ZnS precipitation: Place filter with ZnS precipitate in a

150-mL beaker containing a stir bar. Wash sample bottle with

50 mL AAR and 20 mL DRW and pour the washings into the

beaker. Stir to dissolve precipitate. Remove filter with forceps

while rinsing it into the beaker with a minimum amount of

DRW. Quantitatively transfer to a 100-mL volumetric flask and

dilute to mark with DRW. Pour into the electrochemical cell and

place the electrodes in the solution. Measure potential as in ¶ c

above. Calculate sulfide concentration (¶ c above).

e. Sulfide determination by standard addition with or without

ZnS precipitation: Measure the Ag/S-ISE electrode potential as

in ¶ c or d above. Add sulfide stock solution and measure

potential again. Calculate sulfide concentration as follows:

Co fCs

(1  f)10

EsEo

m  1

where:

Co and Cs sulfide concentrations in sample and known addition,

Eo and Es potentials measured for sample and known addition,

m slope of calibration curve (approximately 28 mV/log

S2, and

f ratio of known-addition volume to sample volume.

f. Sulfide determination by titration: Use the same procedure

as for standardizing the sulfide stock solution (4500-S2.G.3c).

The minumum sulfide concentration for determination by titration is 0.3 mg/L (105

M).

5. Precision

For sulfide determination by comparison with the calibration

curve, the relative standard deviation varies with the sulfide concentration. RSD values of 23% for 0.0091 mg/L and 5% for

0.182 mg/L have been reported.2 (0.0091 g/L was below the range

for which the potential varied linearly with the logarithm of the

sulfide concentration, i.e., the Nernstian range.) For sulfide determination by standard addition, the precision is greatest if the amount

of sulfide added is as large as possible while staying within the

linear range.3

6. References

1. GRAN, G. 1952. Determination of the equivalence point in potentiometric titrations. Part II. Analyst 77:661.

2. BAUMANN, E. 1974. Determination of parts per billion sulfide in water

with the sulfide-selective electrode. Anal. Chem. 46:1345.

3. RATZLAFF, K.L. 1979. Optimizing precision in standard addition

measurement. Anal. Chem. 51:232.

7. Bibliography

ORION RESEARCH, INC. 1980. Instruction Manual for Silver-Sulfide Electrode.

VIVIT, D.V., J.W. BALL & E.A. JENNE. 1984. Specific-ion electrode

determinations of sulfide preconcentrated from San Francisco Bay

waters. Environ. Geol. Water Sci. 6:79.

4500-S2 H. Calculation of Un-ionized Hydrogen Sulfide

Hydrogen sulfide (H2S) and bisulfide ion (HS), which together constitute dissolved sulfide, are in equilibrium with hydrogen ions:

H2S o H  HS

The fraction of sulfide present as un-ionized H2S can be

estimated with an error of less than 40% from Figure 4500-

S2:3. If more accuracy is needed, use the methods given below.

For both fresh water and seawater, it is convenient to define

“conditional” dissociation constants, which are valid for the

temperature and ionic strength of the water of interest. In the

following mass-action equation for fresh water, KFW is a mixed

equilibrium constant that relates the hydrogen ion activity (calculated from the pH) and the concentrations of H2S and HS:

KFW [H] HS	

H2S	

The square brackets indicate concentrations and the braces

indicate activity. The value of pKFW for H2S is approximately

7.0  0.3 for the ionic strengths and temperatures likely to be

encountered in water-quality monitoring. For seawater, it is

convenient to use a stoichiometric equilibrium constant (KSW),

which relates the concentrations of H, HS, and H2S:

KSW H	 HS	

H2S	

The mass-action equations can be rearranged to give:

SULFIDE (4500-S2)/Calculation of Un-ionized Hydrogen Sulfide

9
pH  pK  log HS	

H2S	

In this equation, pK can be either pKFW or pKSW. The

fraction of un-ionized H2S can either be read from Figure

4500-S2:3 or calculated with the following equation:

H2S  H2S	

ST

 1

10pH  pK  1

where:

ST total dissolved sulfide concentration.

1. Calculation for Fresh Water (I  0.01M)

Calculate ionic strength I as in Table 2330:I. Read value of

pKFW from Table 4500-S2:II.

Sample calculation: Total sulfide concentration, 1.5 mg S2/L;

pH, 6.87; temperature, 10°C; ionic strength, 0.04. From Table

4500-S2:II, pKFW 7.11.

pH  pKFW  0.24

10pHpKFW  10  0.24  0.575

H2S  1

1  0.575  0.63

0.63 1.5  0.95

The concentration of un-ionized H2S is 0.95 mg S2/L.

2. Calculation for Seawater, Estuarine Water, and Brackish

Water

This procedure is the same as that for fresh water. A potential

source of error is the determination of the hydrogen ion concenFigure 4500-S2:3. Proportion of H2S and HS in dissolved sulfide.

SULFIDE (4500-S2)/Calculation of Un-ionized Hydrogen Sulfide

10
tration. If the pH electrode is calibrated using NIST buffers as in

Section 4500-H, then a correction factor2 must be determined.

Add acid (HNO3, HCl, or HClO4, not H2SO4) to artificial seawater diluted to the salinity of interest and at the temperature of

interest to give an acid concentration of 0.001N. (Prepare artificial seawater as in Table 8010:III, substituting NaCl for Na2SO4

on an equimolar basis and omitting NaF, SrCl2  6H2O, H3BO3,

KBr, Na2SiO3  9H2O, Na4EDTA, and NaHCO3.) Measure the

pH. The difference between the negative logarithm of the known

acid concentration and the measured pH is the correction factor.

For example, if the acid concentration is 0.001N and the measured pH is 3.15, the correction factor is 0.15. Subtract 0.15 from

measured pH values to get pc

H, the negative logarithm of the

hydrogen ion concentration. (The pH in fresh water corresponds

to the negative logarithm of the hydrogen ion activity.) Alternatively, calibrate the pH electrode with Tris* buffer in artificial

seawater diluted to the salinity of interest and at the temperature

of interest.3 Read pKSW from Table 4500-S2:III. Calculate the

fraction of un-ionized H2S as for fresh water.

Sample calculation: Total sulfide concentration, 1.5 mg S2/L;

temperature 10°C; pH, 7.15; salinity 25‰. From Table 4500-

S2: III, pKSW 6.87.

pH  pK

SW  0.28

10pHpKSW  100.28  1.91

H2S  1

1  1.91  0.34

0.34 1.5  0.51

The concentration of un-ionized H2S is 0.51 mg S2/L.

3. References

1. MILLERO, F. J. 1986. The thermodynamics and kinetics of the hydrogen sulfide system in natural waters. Mar. Chem. 18:121.

2. SIGEL, H., A. D. ZUBERBUHLER & O. YAMAUCHI. 1991. Comments

on potentiometric pH titrations and the relationship between pHmeter reading and hydrogen ion concentration. Anal. Chim. Acta.

255:63.

3. MILLERO, F. J. 1986. The pH of estuarine waters. Limnol. Oceanogr.

31:839.

4. Bibliography

D’YACHKOVA, I.B. & I.L. KHODAKOVSKIY. 1968. Thermodynamic equilibria in the systems S-H2O, Se-H2O and Te-H2O in the 25–300°C

temperature range and their geochemical interpretations. Geochem.

Internat. 1108.

ARCHER, D.G. & P. WANG. 1990. The dielectric constant of water and

Debye-Huckel limiting law slopes. J. Phys. Chem. Ref. Data

12:817.

STUMM, W. & J.J. MORGAN. 1991. Aquatic Chemistry, 3rd ed. John

* Trishydroxymethylaminomethane. Wiley & Sons, New York, N.Y.

TABLE 4500-S2:III. CONDITIONAL FIRST DISSOCIATION CONSTANT OF HYDROGEN SULFIDE, SEAWATER*

Temperature

°C

pK’SW at Given Salinity

5‰ 10‰ 15‰ 20‰ 25‰ 30‰ 35‰

0 7.17 7.12 7.09 7.07 7.06 7.06 7.06

5 7.08 7.02 6.99 6.97 6.96 6.96 6.96

10 6.99 6.93 6.90 6.88 6.87 6.86 6.86

15 6.91 6.85 6.82 6.80 6.78 6.78 6.77

20 6.83 6.77 6.74 6.72 6.70 6.69 6.69

25 6.76 6.70 6.66 6.64 6.63 6.62 6.61

30 6.70 6.63 6.60 6.57 6.56 6.55 6.54

* Values calculated according to Millero1

.

TABLE 4500-S2:II. CONDITIONAL FIRST DISSOCIATION CONSTANT OF HYDROGEN SULFIDE, FRESH WATER*

Temperature

°C

pKFW at Given Ionic Strength

0.00

mol/L

0.005

mol/L

0.01

mol/L

0.02

mol/L

0.03

mol/L

0.05

mol/L

0.10

mol/L

0 7.36 7.33 7.32 7.30 7.29 7.27 7.24

5 7.28 7.25 7.23 7.22 7.21 7.19 7.16

10 7.20 7.16 7.15 7.13 7.12 7.10 7.07

15 7.12 7.09 7.08 7.06 7.05 7.03 7.00

20 7.05 7.02 7.00 6.99 6.97 6.96 6.92

25 6.98 6.95 6.94 6.92 6.91 6.89 6.86

30 6.92 6.89 6.87 6.86 6.84 6.83 6.79

* Values calculated according to Millero1

.

SULFIDE (4500-S2)/Calculation of Un-ionized Hydrogen Sulfide

11
4500-S2 I. Distillation, Methylene Blue Flow Injection Analysis Method

1. General Discussion

a. Principle: Water and wastewater samples are distilled into

a sodium hydroxide trapping solution and the distillate is analyzed. Hydrogen sulfide (H2S) reacts in acid media and in the

presence of ferric chloride with two molecules of N, N-dimethylp-phenylenediamine to form methylene blue. The resulting color

is read at 660 nm.

b. Sample preservation: Because H2S oxidizes rapidly, analyze samples and standards without delay. To preserve samples,

add 4 drops 2M zinc acetate to 100 mL sample and adjust pH to


9 with 6M NaOH, then cool to 4°C. Samples are distilled into

a trapping solution resulting in 0.25M NaOH matrix.

Also see 4500-S2.A, B, and E, and Section 4130, Flow

Injection Analysis (FIA).

c. Interferences: This method measures total sulfide, which is

defined as the acid-soluble sulfide fraction of a sample. Total

sulfide includes both acid-soluble sulfides, such as H2S, and

acid-soluble metal sulfides present in suspended matter. This

method does not measure acid-insoluble sulfides, such as CuS.

Most nonvolatile interferences are eliminated by distillation.

Strong reducing agents inhibit color formation at concentrations

of several hundred milligrams per liter. Iodide interferes at

concentrations greater than 2 mg I/L.

Also see 4500-S2.A and B.

d. Quality control (QC): The QC practices considered to be an

integral part of each method are summarized in Table 4020:I.

2. Apparatus

a. Distillation apparatus consisting of a glass or polypropylene micro-distillation device* capable of distilling 6 mL or more

of sample into a 0.25M NaOH final concentration trapping

solution.

b. Flow injection analysis equipment consisting of:

1) FIA injection valve with sample loop or equivalent.

2) Multichannel proportioning pump.

3) FIA manifold (Figure 4500-S2:4) with cation exchange

column and flow cell. Relative flow rates only are shown in

Figure 4500-S2:4. Tubing volumes are given as an example

only; they may be scaled down proportionally. Use manifold

tubing of an inert material, such as TFE.

4) Absorbance detector, 660 nm, 10-nm bandpass.

5) Injection valve control and data acquisition system.

3. Reagents

Use reagent water (
10 megohm) to prepare carrier for all

solutions. To prevent bubble formation, degas carrier and buffer

with helium. Pass He at 140 kPa (20 psi) through a helium

degassing tube. Bubble He through 1 L solution for 1 min.

a. Sodium hydroxide diluent, NaOH, 0.25M: In a 2-L volumetric flask, dissolve 20 g NaOH in approximately 1800 mL

water. Dilute to mark and mix with a magnetic stirrer until

dissolved. Store in a plastic container.

b. Hydrochloric acid, HCl, 3M: To a tared 1-L container, add

752 g water and then slowly add 295 g conc HCl. Invert to mix.

c. Hydrochloric acid, HCl, 0.20M: To a tared 1-L container,

add 983.5 g water. Then add 19.7 g conc HCl. Invert to mix.

d. N,N-dimethyl-p-phenylenediamine: In a 1-L volumetric

flask dissolve 1.0 g N,N-dimethyl-p-phenylenediamine dihydrochloride, (CH3)2NC6H4NH2  2HCl, in about 800 mL 3M HCl

(¶ b above). Dilute to mark and invert to mix. If solution appears

dark, it is likely that the N,N-dimethyl-p-phenylenediamine dihydrochloride is decomposed; discard, and use fresh reagent.

e. Ferric chloride: In a 500-mL volumetric flask dissolve

6.65 g ferric chloride hexahydrate, FeCl3  6H2O, in about

450 mL 0.20M HCl (¶ c above). Dilute to mark with water and

invert to mix.

f. Stock sulfide standard, 100 mg S2/L: In a 1-L volumetric

flask dissolve 0.750 g sodium sulfide nonahydrate, Na2S  9H2O,

in approximately 900 mL NaOH diluent (¶ a above). Dilute to

mark and invert to mix. Standardize as in 4500-S2.F; also see

4500-S2.A.6.

g. Standard solutions: Prepare sulfide standards in desired

concentration range, using stock standard (¶ f above), and diluting with NaOH diluent (¶ a above).

h. Sulfuric acid distillation releasing solution, H2SO4, 9M: To

a tared 500-mL container, add 150.0 g water, then add slowly

while swirling, in increments of 40 g, 276 g conc H2SO4.

CAUTION: Solution will become very hot. Allow to cool before

using.

4. Procedure

a. Distillation: This procedure is designed for the determination of sulfides in aqueous solutions, solid waste materials, or

effluents. To preserve and remove sulfide from interfering substances, distill samples immediately after collection.

Follow manufacturer’s instructions for use of distillation apparatus. Add sufficient 9M H2SO4 (4500-S2.I.3h) to sample to

dissolve ZnS (s), digest total sulfides, and release the sulfide as

hydrogen sulfide gas. Immediately place sample on-line with the

receiving vessel or collector tube and distill hydrogen sulfide and

water in the sample into a 0.25M trapping solution.

* Lachat Instruments MICRO DIST, or equivalent. Figure 4500-S2:4. FIA sulfide manifold.

SULFIDE (4500-S2)/Distillation, Methylene Blue FIA Method

12
b. Flow injection analysis: Set up a manifold equivalent to that

in Figure 4500-S2:4 and follow method supplied by the manufacturer or laboratory standard operating procedure. Follow

quality control protocols outlined in 4020.

5. Calculations

Prepare standard curves by plotting absorbance of standards

processed through the manifold versus sulfide concentration.

6. Precision and Bias (MDL)

a. Method detection level (MDL): A 200-L sample loop was

used in the method described above. Using a published method1

,

analysts ran 21 replicates of 0.02-mg S2/L standard. These gave

a mean of 0.024 mg S2/L, a standard deviation of 0.0021 mg

S2/L, and MDL of 0.006 mg S2/L.

b. Precision: Ten injections of a distilled 0.8 mg S2/L standard gave a mean of 0.82 mg S2/L, a standard deviation of

0.0054 mg S2/L, and percent relative standard deviation of

0.66.

7. Reference

1. U.S. ENVIRONMENTAL PROTECTION AGENCY. 1984. Definition and procedure for the determination of method detection limits. Appendix B

to 40 CFR 136 Rev. 1.11 Amended June 30, 1986. 49 CFR 43430.

4500-S2 J. Acid-Volatile Sulfide

1. Apparatus

See Figure 4500-S2:5.

a. Reaction vessel, 250-mL, 3-neck flask, standard taper.

b. Gas traps, 125-mL gas scrubbers.

c. Dropping funnel, standard taper to fit reaction vessel.

d. Purge-gas tube, standard taper to fit reaction vessel.

e. Tubing, TFE or polypropylene, 0.635 cm (0.25-in.) OD, to

connect reaction vessel to gas traps.

f. Syringe, plastic, 5 mL, lower end cut off to inject sediment

into reaction vessel.

g. Compressed gas, cylinder of high-purity nitrogen, regulator,

needle valve, rotameter or flow meter (optional).

2. Reagents

a. Hydrochloric acid solution, 9N: Add 186 mL conc HCl to

about 50 mL distilled or deionized water. Dilute to 250 mL.

b. Stannous chloride solution, 0.53M : Dissolve 50 g SnCl2 in

250 mL 9N HCl solution.

c. Sodium hydroxide solution, NaOH, 2N.

d. Zinc acetate solution, 1M, 22%: Dissolve 220 g

Zn(CH3COO)2  2H2O in 1 L distilled or deionized water.

e. Alkaline zinc solution: Add 150 mL 22% zinc acetate

solution to 850 mL 2N NaOH solution.

f. Reagents for the iodometric titration method: See Section

4500-S2.F.

3. Procedure

Add 15 mL stannous chloride/hydrochloric acid solution to

digestion vessel and 100 mL alkaline zinc solution to each trap.

Adjust nitrogen flow rate to approximately 40 to 60 mL/min and

flush system for 10 min. Add approximately 6 g fresh wet

sediment to digestion vessel using a 5-mL syringe with its distal

ends removed. Close outlets with clamps and gently stir the

suspension. Allow H2S generation to take place at room temperature (25  3°C) for 3 h while stirring and with the nitrogen

flowing. Combine the solutions from the two traps and titrate as

described in Section 4500-S2.F.

4. Precision and Bias

For marine sediment samples (n6), an average of 97% of the

added ferrous monosulfide was recovered by the diffusion

method. Reproducibility of this measurement performed on four

samples with concentrations of around 40 to 150 mol/g dry

weight (1.3 to 4.8 mg S/g) was better than 5%.

5. Quality Control

The quality control practices considered to be an integral part

of each method are summarized in Table 4020:I.

6. Bibliography

CHANTON, J.P. & C.S. MARTENS. 1985. The effects of heat and stannous

chloride on the active distillation of acid volatile sulfide from

pyrite-rich marine sediment samples. Biogeochemistry 1:375.

MORSE, J.W. & J.C. CORNWELL. 1987. Analysis and distribution of iron

sulfide minerals in recent anoxic marine sediments. Mar. Chem.

Figure 4500-S 22:55. 2:5. Apparatus for acid-volatile sulfide analysis.

SULFIDE (4500-S2)/Acid-Volatile Sulfide

13
HSIEH, Y.P. & C.H. YANG. 1989. Diffusion methods for the determination of reduced inorganic sulfur species in sediments. Limnol.

Oceanogr. 34:1126.

ALLEN, H.E., G.-M. FU & B.-L. DENG. 1993. Analysis of acid-volatile

sulfide (AVS) and simultaneously extracted metals (SEM) for the

estimation of potential toxicity in aquatic sediments. Environ. Toxicol. Chem. 12:1441.

LASORSA, B. & A. CASAS. 1996. A comparison of sample handling and

analytical methods for determination of acid volatile sulfides in

sediment. Mar. Chem. 52:211.

LEONARD, E.N., A.M. COTTER & G.T. ANKLEY. 1996. Modified diffusion

method for analysis of acid volatile sulfides and simultaneously

extracted metals in freshwater sediment. Environ. Toxicol. Chem.

15:1479.

SULFIDE (4500-S2)/Acid-Volatile Sulfide

14