788

METHOD 11 - DETERMINATION OF HYDROGEN SULFIDE CONTENT

OF FUEL GAS STREAMS IN PETROLEUM REFINERIES

1.0 Scope and Application.

1.1 Analytes.

Analyte CAS No. Sensitivity

Hydrogen sulfide 7783-06-4 8 mg/m3 - 740 mg/m3
(H2S) (6 ppm - 520 ppm)

1.2 Applicability. This method is applicable for the

determination of the H2S content of fuel gas streams at

petroleum refineries.

1.3 Data Quality Objectives. Adherence to the

requirements of this method will enhance the quality of the

data obtained from air pollutant sampling methods.

2.0 Summary of Method.

2.1 A sample is extracted from a source and passed

through a series of midget impingers containing a cadmium

sulfate (CdSO4) solution; H2S is absorbed, forming cadmium

sulfide (CdS). The latter compound is then measured

iodometrically.

3.0 Definitions. [Reserved]

4.0 Interferences.

4.1 Any compound that reduces iodine (I2) or oxidizes

the iodide ion will interfere in this procedure, provided it

is collected in the CdSO4 impingers. Sulfur dioxide in

concentrations of up to 2,600 mg/m3 is removed with an

 789

impinger containing a hydrogen peroxide (H2O2) solution.

Thiols precipitate with H2S. In the absence of H2S, only

traces of thiols are collected. When methane- and ethane-

thiols at a total level of 300 mg/m3 are present in addition

to H2S, the results vary from 2 percent low at an H2S

concentration of 400 mg/m3 to 14 percent high at an H2S

concentration of 100 mg/m3. Carbonyl sulfide at a

concentration of 20 percent does not interfere. Certain

carbonyl-containing compounds react with iodine and produce

recurring end points. However, acetaldehyde and acetone at

concentrations of 1 and 3 percent, respectively, do not

interfere.

4.2 Entrained H2O2 produces a negative interference

equivalent to 100 percent of that of an equimolar quantity

of H2S. Avoid the ejection of H2O2 into the CdSO4 impingers.

5.0 Safety.

5.1 Disclaimer. This method may involve hazardous

materials, operations, and equipment. This test method may

not address all of the safety problems associated with its

use. It is the responsibility of the user of this test

method to establish appropriate safety and health practices

and determine the applicability of regulatory limitations

prior to performing this test method.

 790

5.2 Corrosive reagents. The following reagents are

hazardous. Personal protective equipment and safe

procedures are useful in preventing chemical splashes. If

contact occurs, immediately flush with copious amounts of

water for at least 15 minutes. Remove clothing under shower

and decontaminate. Treat residual chemical burns as thermal

burns.

5.2.1 Hydrogen Peroxide. Irritating to eyes, skin,

nose, and lungs. 30% H2O2 is a strong oxidizing agent.

Avoid contact with skin, eyes, and combustible material.

Wear gloves when handling.

5.2.2 Hydrochloric Acid. Highly toxic. Vapors are

highly irritating to eyes, skin, nose, and lungs, causing

severe damage. May cause bronchitis, pneumonia, or edema of

lungs. Exposure to concentrations of 0.13 to 0.2 percent

can be lethal in minutes. Will react with metals, producing

hydrogen.

6.0 Equipment and Supplies.

6.1 Sample Collection. The following items are

needed for sample collection:

6.1.1 Sampling Line. Teflon tubing, 6- to 7-mm (1/4-

in.) ID, to connect the sampling train to the sampling

valve.
 791

6.1.2 Impingers. Five midget impingers, each with

30-ml capacity. The internal diameter of the impinger tip

must be 1 mm ± 0.05 mm. The impinger tip must be positioned

4 to 6 mm from the bottom of the impinger.

6.1.3 Tubing. Glass or Teflon connecting tubing for

the impingers.

6.1.4 Ice Water Bath. To maintain absorbing solution

at a low temperature.

6.1.5 Drying Tube. Tube packed with 6- to 16- mesh

indicating-type silica gel, or equivalent, to dry the gas

sample and protect the meter and pump. If the silica gel

has been used previously, dry at 175 EC (350 EF) for 2

hours. New silica gel may be used as received.

Alternatively, other types of desiccants (equivalent or

better) may be used, subject to approval of the

Administrator.

NOTE: Do not use more than 30 g of silica gel.

Silica gel adsorbs gases such as propane from the fuel gas

stream, and use of excessive amounts of silica gel could

result in errors in the determination of sample volume.

6.1.6 Sampling Valve. Needle valve, or equivalent,

to adjust gas flow rate. Stainless steel or other

corrosion-resistant material.
 792

6.1.7 Volume Meter. Dry gas meter (DGM),

sufficiently accurate to measure the sample volume within 2

percent, calibrated at the selected flow rate (about

1.0 liter/min) and conditions actually encountered during

sampling. The meter shall be equipped with a temperature

sensor (dial thermometer or equivalent) capable of measuring

temperature to within 3 EC (5.4 EF). The gas meter should

have a petcock, or equivalent, on the outlet connector which

can be closed during the leak-check. Gas volume for one

revolution of the meter must not be more than 10 liters.

6.1.8 Rate Meter. Rotameter, or equivalent, to

measure flow rates in the range from 0.5 to 2 liters/min (1

to 4 ft3/hr).

6.1.9 Graduated Cylinder. 25-ml size.

6.1.10 Barometer. Mercury, aneroid, or other

barometer capable of measuring atmospheric pressure to

within 2.5 mm Hg (0.1 in. Hg). In many cases, the

barometric reading may be obtained from a nearby National

Weather Service station, in which case, the station value

(which is the absolute barometric pressure) shall be

requested and an adjustment for elevation differences

between the weather station and the sampling point shall be

applied at a rate of minus 2.5 mm Hg (0.1 in Hg) per 30 m

(100 ft) elevation increase or vice-versa for elevation

decrease.
 793

6.1.11 U-tube Manometer. 0- to 30-cm water column,

for leak-check procedure.

6.1.12 Rubber Squeeze Bulb. To pressurize train for

leak-check.

6.1.13 Tee, Pinchclamp, and Connecting Tubing. For

leak-check.

6.1.14 Pump. Diaphragm pump, or equivalent. Insert

a small surge tank between the pump and rate meter to

minimize the pulsation effect of the diaphragm pump on the

rate meter. The pump is used for the air purge at the end

of the sample run; the pump is not ordinarily used during

sampling, because fuel gas streams are usually sufficiently

pressurized to force sample gas through the train at the

required flow rate. The pump need not be leak-free unless

it is used for sampling.

6.1.15 Needle Valve or Critical Orifice. To set air

purge flow to 1 liter/min.

6.1.16 Tube Packed with Active Carbon. To filter air

during purge.

6.1.17 Volumetric Flask. One 1000-ml.

6.1.18 Volumetric Pipette. One 15-ml.

6.1.19 Pressure-Reduction Regulator. Depending on

the sampling stream pressure, a pressure-reduction regulator

may be needed to reduce the pressure of the gas stream

entering the Teflon sample line to a safe level.

 794

6.1.20 Cold Trap. If condensed water or amine is

present in the sample stream, a corrosion-resistant cold

trap shall be used immediately after the sample tap. The

trap shall not be operated below 0 EC (32 EF) to avoid

condensation of C3 or C4 hydrocarbons.

6.2 Sample Recovery. The following items are needed

for sample recovery:

6.2.1 Sample Container. Iodine flask, glass-

stoppered, 500-ml size.

6.2.2 Volumetric Pipette. One 50-ml.

6.2.3 Graduated Cylinders. One each 25-and 250-ml.

6.2.4 Erlenmeyer Flasks. 125-ml.

6.2.5 Wash Bottle.

6.2.6 Volumetric Flasks. Three 1000-ml.

6.3 Sample Analysis. The following items are needed

for sample analysis:

6.3.1 Flask. Glass-stoppered iodine flask, 500-ml.

6.3.2 Burette. 50-ml.

6.3.3 Erlenmeyer Flask. 125-ml.

6.3.4 Volumetric Pipettes. One 25-ml; two each 50-

and 100-ml.

6.3.5 Volumetric Flasks. One 1000-ml; two 500-ml.

6.3.6 Graduated Cylinders. One each 10-and 100-ml.

7.0 Reagents and Standards.

 795

NOTE: Unless otherwise indicated, it is intended that

all reagents conform to the specifications established by

the Committee on Analytical Reagents of the American

Chemical Society, where such specifications are available.

Otherwise, use the best available grade.

7.1 Sample Collection. The following reagents are

required for sample collection:

7.1.1 CdSO4 Absorbing Solution. Dissolve 41 g of

3CdSO4·8H2O and 15 ml of 0.1 M sulfuric acid in a 1-liter

volumetric flask that contains approximately 3/4 liter of

water. Dilute to volume with deionized, distilled water.

Mix thoroughly. The pH should be 3 ± 0.1. Add 10 drops of

Dow-Corning Antifoam B. Shake well before use. This

solution is stable for at least one month. If Antifoam B is

not used, a more labor-intensive sample recovery procedure

is required (see Section 11.2).

7.1.2 Hydrogen Peroxide, 3 Percent. Dilute 30

percent H2O2 to 3 percent as needed. Prepare fresh daily.

7.1.3 Water. Deionized distilled to conform to ASTM

D 1193-77 or 91, Type 3 (incorporated by reference - see

§60.17). The KMnO4 test for oxidizable organic matter may

be omitted when high concentrations of organic matter are

not expected to be present.

 796

7.2 Sample Recovery. The following reagents are

needed for sample recovery:

7.2.1 Water. Same as Section 7.1.3.

7.2.2 Hydrochloric Acid (HCl) Solution, 3 M. Add 240

ml of concentrated HCl (specific gravity 1.19) to 500 ml of

water in a 1-liter volumetric flask. Dilute to 1 liter with

water. Mix thoroughly.

7.2.3 Iodine (I2) Solution, 0.1 N. Dissolve 24 g of

potassium iodide (KI) in 30 ml of water. Add 12.7 g of

resublimed iodine (I2) to the KI solution. Shake the

mixture until the I2 is completely dissolved. If possible,

let the solution stand overnight in the dark. Slowly dilute

the solution to 1 liter with water, with swirling. Filter

the solution if it is cloudy. Store solution in a brown-

glass reagent bottle.

7.2.4 Standard I2 Solution, 0.01 N. Pipette 100.0 ml

of the 0.1 N iodine solution into a l-liter volumetric

flask, and dilute to volume with water. Standardize daily

as in Section 10.2.1. This solution must be protected from

light. Reagent bottles and flasks must be kept tightly

stoppered.

7.3 Sample Analysis. The following reagents and

standards are needed for sample analysis:

7.3.1 Water. Same as in Section 7.1.3.

 797

7.3.2 Standard Sodium Thiosulfate Solution, 0.1 N.

Dissolve 24.8 g of sodium thiosulfate pentahydrate

(Na2S2O3·5H2O) or 15.8 g of anhydrous sodium thiosulfate

(Na2S2O3) in 1 liter of water, and add 0.01 g of anhydrous

sodium carbonate (Na2CO3) and 0.4 ml of chloroform (CHCl3) to

stabilize. Mix thoroughly by shaking or by aerating with

nitrogen for approximately 15 minutes, and store in a glass-

stoppered, reagent bottle. Standardize as in Section

10.2.2.

7.3.3 Standard Sodium Thiosulfate Solution, 0.01 N.

Pipette 50.0 ml of the standard 0.1 N Na2S2O3 solution into a

volumetric flask, and dilute to 500 ml with water.

NOTE: A 0.01 N phenylarsine oxide (C6H5AsO) solution

may be prepared instead of 0.01 N Na2S2O3 (see Section

7.3.4).

7.3.4 Standard Phenylarsine Oxide Solution, 0.01 N.

Dissolve 1.80 g of (C6H5AsO) in 150 ml of 0.3 N sodium

hydroxide. After settling, decant 140 ml of this solution

into 800 ml of water. Bring the solution to pH 6-7 with

6 N HCl, and dilute to 1 liter with water. Standardize as

in Section 10.2.3.

7.3.5 Starch Indicator Solution. Suspend 10 g of

soluble starch in 100 ml of water, and add 15 g of potassium

hydroxide (KOH) pellets. Stir until dissolved, dilute with

 798

900 ml of water, and let stand for 1 hour. Neutralize the

alkali with concentrated HCl, using an indicator paper

similar to Alkacid test ribbon, then add 2 ml of glacial

acetic acid as a preservative.

NOTE: Test starch indicator solution for

decomposition by titrating with 0.01 N I2 solution, 4 ml of

starch solution in 200 ml of water that contains 1 g of KI.

If more than 4 drops of the 0.01 N I2 solution are required

to obtain the blue color, a fresh solution must be prepared.

8.0 Sample Collection, Preservation, Storage, and

Transport.

8.1 Sampling Train Preparation. Assemble the

sampling train as shown in Figure 11-1, connecting the five

midget impingers in series. Place 15 ml of 3 percent H2O2

solution in the first impinger. Leave the second impinger

empty. Place 15 ml of the CdSO4 solution in the third,

fourth, and fifth impingers. Place the impinger assembly in

an ice water bath container, and place water and crushed ice

around the impingers. Add more ice during the run, if

needed.

8.2 Leak-Check Procedure.

8.2.1 Connect the rubber bulb and manometer to the

first impinger, as shown in Figure 11-1. Close the petcock

on the DGM outlet. Pressurize the train to 25 cm water with

 799

the bulb, and close off the tubing connected to the rubber

bulb. The train must hold 25 cm water pressure with not

more than a 1 cm drop in pressure in a 1-minute interval.

Stopcock grease is acceptable for sealing ground glass

joints.

8.2.2 If the pump is used for sampling, it is

recommended, but not required, that the pump be leak-checked

separately, either prior to or after the sampling run. To

leak-check the pump, proceed as follows: Disconnect the

drying tube from the impinger assembly. Place a vacuum

gauge at the inlet to either the drying tube or the pump,

pull a vacuum of 250 mm Hg (10 in. Hg), plug or pinch off

the outlet of the flow meter, and then turn off the pump.

The vacuum should remain stable for at least 30 seconds. If

performed prior to the sampling run, the pump leak-check

should precede the leak-check of the sampling train

described immediately above; if performed after the sampling

run, the pump leak-check should follow the sampling train

leak-check.

8.3 Purge the connecting line between the sampling

valve and the first impinger by disconnecting the line from

the first impinger, opening the sampling valve, and allowing

process gas to flow through the line for one to two minutes.

Then, close the sampling valve, and reconnect the line to

 800

the impinger train. Open the petcock on the dry gas meter

outlet. Record the initial DGM reading.

8.4 Open the sampling valve, and then adjust the

valve to obtain a rate of approximately 1 liter/min (0.035

cfm). Maintain a constant (± 10 percent) flow rate during

the test. Record the DGM temperature.

8.5 Sample for at least 10 minutes. At the end of

the sampling time, close the sampling valve, and record the

final volume and temperature readings. Conduct a leak-check

as described in Section 8.2 above.

8.6 Disconnect the impinger train from the sampling

line. Connect the charcoal tube and the pump as shown in

Figure 11-1. Purge the train [at a rate of 1 liter/min

(0.035 ft3/min)] with clean ambient air for 15 minutes to

ensure that all H2S is removed from the H2O2. For sample

recovery, cap the open ends, and remove the impinger train

to a clean area that is away from sources of heat. The area

should be well lighted, but not exposed to direct sunlight.

8.7 Sample Recovery.

8.7.1 Discard the contents of the H2O2 impinger.

Carefully rinse with water the contents of the third,

fourth, and fifth impingers into a 500-ml iodine flask.

NOTE: The impingers normally have only a thin film of

CdS remaining after a water rinse. If Antifoam B was not

 801

used or if significant quantities of yellow CdS remain in

the impingers, the alternative recovery procedure in Section

11.2 must be used.

8.7.2 Proceed to Section 11 for the analysis.

9.0 Quality Control.

Quality Control
Section Measure Effect
8.2, Sampling equipment Ensure accurate
10.1 leak-check and measurement of sample
calibration volume
11.2 Replicate titrations Ensure precision of
of blanks titration determinations

10.0 Calibration and Standardization.

NOTE: Maintain a log of all calibrations.

10.1 Calibration. Calibrate the sample collection

equipment as follows.

10.1.1 Dry Gas Meter.

10.1.1.1 Initial Calibration. The DGM shall be

calibrated before its initial use in the field. Proceed as

follows: First, assemble the following components in

series: Drying tube, needle valve, pump, rotameter, and DGM.

Then, leak-check the metering system as follows: Place a

vacuum gauge (at least 760 mm Hg) at the inlet to the drying

tube, and pull a vacuum of 250 mm Hg (10 in. Hg); plug or

pinch off the outlet of the flow meter, and then turn off

the pump. The vacuum shall remain stable for at least 30

 802

seconds. Carefully release the vacuum gauge before

releasing the flow meter end. Next, calibrate the DGM (at

the sampling flow rate specified by the method) as follows:

Connect an appropriately sized wet-test meter (e.g., 1 liter

per revolution) to the inlet of the drying tube. Make three

independent calibration runs, using at least five

revolutions of the DGM per run. Calculate the calibration

factor, Y (wet-test meter calibration volume divided by the

DGM volume, both volumes adjusted to the same reference

temperature and pressure), for each run, and average the

results. If any Y value deviates by more than 2 percent

from the average, the DGM is unacceptable for use.

Otherwise, use the average as the calibration factor for

subsequent test runs.

10.1.1.2 Post-Test Calibration Check. After each

field test series, conduct a calibration check as in Section

10.1.1.1, above, except for the following two variations:

(a) three or more revolutions of the DGM may be used and

(b) only two independent runs need be made. If the

calibration factor does not deviate by more than 5 percent

from the initial calibration factor (determined in Section

10.1.1.1), then the DGM volumes obtained during the test

series are acceptable. If the calibration factor deviates

by more than 5 percent, recalibrate the DGM as in Section

10.1.1.1, and for the calculations, use the calibration

 803

factor (initial or recalibration) that yields the lower gas

volume for each test run.

10.1.2 Temperature Sensors. Calibrate against

mercury-in-glass thermometers.

10.1.3 Rate Meter. The rate meter need not be

calibrated, but should be cleaned and maintained according

to the manufacturer's instructions.

10.1.4 Barometer. Calibrate against a mercury

barometer.

10.2 Standardization.

10.2.1 Iodine Solution Standardization. Standardize

the 0.01 N I2 solution daily as follows: Pipette 25 ml of

the I2 solution into a 125-ml Erlenmeyer flask. Add 2 ml of

3 M HCl. Titrate rapidly with standard 0.01 N Na2S2O3

solution or with 0.01 N C6H5AsO until the solution is light

yellow, using gentle mixing. Add four drops of starch

indicator solution, and continue titrating slowly until the

blue color just disappears. Record the volume of Na2S2O3

solution used, VSI, or the volume of C6H5AsO solution used,

VAI, in ml. Repeat until replicate values agree within 0.05

ml. Average the replicate titration values which agree

within 0.05 ml, and calculate the exact normality of the I2

solution using Equation 11-3. Repeat the standardization

daily.
 804

10.2.2 Sodium Thiosulfate Solution Standardization.

Standardize the 0.1 N Na2S2O3 solution as follows: Oven-dry

potassium dichromate (K2Cr2O7) at 180 to 200 EC (360 to

390 EF). To the nearest milligram, weigh 2 g of the

dichromate (W). Transfer the dichromate to a 500-ml

volumetric flask, dissolve in water, and dilute to exactly

500 ml. In a 500-ml iodine flask, dissolve approximately 3

g of KI in 45 ml of water, then add 10 ml of 3 M HCl

solution. Pipette 50 ml of the dichromate solution into

this mixture. Gently swirl the contents of the flask once,

and allow it to stand in the dark for 5 minutes. Dilute the

solution with 100 to 200 ml of water, washing down the sides

of the flask with part of the water. Titrate with 0.1 N

Na2S2O3 until the solution is light yellow. Add 4 ml of

starch indicator and continue titrating slowly to a green

end point. Record the volume of Na2S2O3 solution used, VS,

in ml. Repeat until replicate values agree within 0.05 ml.

Calculate the normality using Equation 11-1. Repeat the

standardization each week or after each test series,

whichever time is shorter.

10.2.3 Phenylarsine Oxide Solution Standardization.

Standardize the 0.01 N C6H5AsO (if applicable) as follows:

Oven-dry K2Cr2O7 at 180 to 200 EC (360 to 390 EF). To the

nearest milligram, weigh 2 g of the dichromate (W). Transfer

the dichromate to a 500-ml volumetric flask, dissolve in

 805

water, and dilute to exactly 500 ml. In a 500-ml iodine

flask, dissolve approximately 0.3 g of KI in 45 ml of water,

then add 10 ml of 3 M HCl. Pipette 5 ml of the dichromate

solution into the iodine flask. Gently swirl the contents

of the flask once, and allow it to stand in the dark for 5

minutes. Dilute the solution with 100 to 200 ml of water,

washing down the sides of the flask with part of the water.

Titrate with 0.01 N C6H5AsO until the solution is light

yellow. Add 4 ml of starch indicator, and continue

titrating slowly to a green end point. Record the volume of

C6H5AsO used, VA, in ml. Repeat until replicate analyses

agree within 0.05 ml. Calculate the normality using

Equation 11-2. Repeat the standardization each week or

after each test series, whichever time is shorter.

11.0 Analytical Procedure.

Conduct the titration analyses in a clean area away

from direct sunlight.

11.1 Pipette exactly 50 ml of 0.01 N I2 solution into

a 125-ml Erlenmeyer flask. Add 10 ml of 3 M HCl to the

solution. Quantitatively rinse the acidified I2 into the

iodine flask. Stopper the flask immediately, and shake

briefly.

11.2 Use these alternative procedures if Antifoam B

was not used or if significant quantities of yellow CdS

 806

remain in the impingers. Extract the remaining CdS from the

third, fourth, and fifth impingers using the acidified I2

solution. Immediately after pouring the acidified I2 into

an impinger, stopper it and shake for a few moments, then

transfer the liquid to the iodine flask. Do not transfer

any rinse portion from one impinger to another; transfer it

directly to the iodine flask. Once the acidified I2

solution has been poured into any glassware containing CdS,

the container must be tightly stoppered at all times except

when adding more solution, and this must be done as quickly

and carefully as possible. After adding any acidified I2

solution to the iodine flask, allow a few minutes for

absorption of the H2S before adding any further rinses.

Repeat the I2 extraction until all CdS is removed from the

impingers. Extract that part of the connecting glassware

that contains visible CdS. Quantitatively rinse all the I2

from the impingers, connectors, and the beaker into the

iodine flask using water. Stopper the flask and shake

briefly.

11.3 Allow the iodine flask to stand about 30 minutes

in the dark for absorption of the H2S into the I2, then

complete the titration analysis as outlined in Sections 11.5

and 11.6.
 807

NOTE: Iodine evaporates from acidified I2 solutions.

Samples to which acidified I2 has been added may not be

stored, but must be analyzed in the time schedule stated

above.

11.4 Prepare a blank by adding 45 ml of CdSO4

absorbing solution to an iodine flask. Pipette exactly 50

ml of 0.01 N I2 solution into a 125-ml Erlenmeyer flask.

Add 10 ml of 3 M HCl. Stopper the flask, shake briefly, let

stand 30 minutes in the dark, and titrate with the samples.

NOTE: The blank must be handled by exactly the same

procedure as that used for the samples.

11.5 Using 0.01 N Na2S2O3 solution (or 0.01 N C6H5AsO,

if applicable), rapidly titrate each sample in an iodine

flask using gentle mixing, until solution is light yellow.

Add 4 ml of starch indicator solution, and continue

titrating slowly until the blue color just disappears.

Record the volume of Na2S2O3 solution used, VTT, or the volume

of C6H5AsO solution used, VAT, in ml.

11.6 Titrate the blanks in the same manner as the

samples. Run blanks each day until replicate values agree

within 0.05 ml. Average the replicate titration values

which agree within 0.05 ml.

12.0 Data Analysis and Calculations.

 808

Carry out calculations, retaining at least one extra

significant figure beyond that of the acquired data. Round

off figures only after the final calculation.

12.1 Nomenclature

CH2S = Concentration of H2S at standard

conditions,mg/dscm.

NA = Normality of standard C6H5AsO solution, g-

eq/liter.

NI = Normality of standard I2 solution, g-eq/liter.

NS = Normality of standard (•0.1 N) Na2S2O3 solution,

g-eq/liter.

NT = Normality of standard (•0.01 N) Na2S2O3

solution, assumed to be 0.1 NS, g-eq/liter.

Pbar = Barometric pressure at the sampling site, mm

Hg.

Pstd = Standard absolute pressure, 760 mm Hg.

Tm = Average DGM temperature, EK.

Tstd = Standard absolute temperature, 293 EK.

VA = Volume of C6H5AsO solution used for

standardization, ml.

VAI = Volume of standard C6H5AsO solution used for

titration analysis, ml.

VI = Volume of standard I2 solution used for

standardization, ml.
 809

VIT = Volume of standard I2 solution used for

titration analysis, normally 50 ml.

Vm = Volume of gas sample at meter conditions,

liters.

Vm(std)= Volume of gas sample at standard conditions,

liters.

VSI = Volume of •0.1 N Na2S2O3 solution used for

standardization, ml.

VT = Volume of standard (•0.01 N) Na2S2O3 solution

used in standardizing iodine solution (see

Section 10.2.1), ml.

VTT = Volume of standard (-0.01 N) Na2S2O3 solution

used for titration analysis, ml.

W = Weight of K2Cr2O7 used to standardize Na2s2O3 or

C6H5AsO solutions, as applicable (see Sections

10.2.2 and 10.2.3), g.

Y = DGM calibration factor.

12.2 Normality of the Standard (•0.1 N) Sodium

Thiosulfate Solution.

2.039 W
NS ' Eq. 11-1
VS

where:

2.039 = Conversion factor

= (6 g-eq I2/mole K2Cr2O7)(1,000 ml/liter)/

(294.2 g K2Cr2O7/mole)(10 aliquot factor)

 810

12.3 Normality of Standard Phenylarsine Oxide

Solution (if applicable).

0.2039 W
NA ' Eq. 11-2
VA

where:

0.2039 = Conversion factor.

= (6 g-eq I2/mole K2Cr2O7)(1,000 ml/liter)/

(294.2 g K2Cr2O7/mole)(100 aliquot factor)

12.4 Normality of Standard Iodine Solution.

NT VT
NI ' Eq. 11-3
VI

NOTE: If C6H5AsO is used instead of Na2S2O3, replace NT

and VT in Equation 11-3 with NA and VAS, respectively (see

Sections 10.2.1 and 10.2.3).

12.5 Dry Gas Volume. Correct the sample volume

measured by the DGM to standard conditions (20 EC and 760 mm

Hg).

Tstd Pbar
Vm(std) ' Vm Y Eq. 11-4
Tm P std

12.6 Concentration of H2S. Calculate the

concentration of H2S in the gas stream at standard

conditions using Equation 11-5:

 811

(V IT N I & V TT N T)sample & (V IT N I & V TT N T)blank

CH S ' 17.04 × 103 Eq. 11-5
2 Vm(std)

where:

17.04 × 103 = Conversion factor

= (34.07 g/mole H2S)(1,000 liters/m3)(1,000mg/g)/

(1,000 ml/liter)(2H2S eq/mole)

NOTE: If C6H5AsO is used instead of NaS2O3, replace NT

and VTT in Equation 11-5 with NA and VAT, respectively (see

Sections 11.5 and 10.2.3).

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13.0 Method Performance.

13.1 Precision. Collaborative testing has shown the

intra-laboratory precision to be 2.2 percent and the inter-

laboratory precision to be 5 percent.

13.2 Bias. The method bias was shown to be -4.8

percent when only H2S was present. In the presence of the

interferences cited in Section 4.0, the bias was positive at

low H2S concentration and negative at higher concentrations.

At 230 mg H2S/m3, the level of the compliance standard, the

bias was +2.7 percent. Thiols had no effect on the

precision.

14.0 Pollution Prevention. [Reserved]

15.0 Waste Management. [Reserved]

16.0 References.

1. Determination of Hydrogen Sulfide, Ammoniacal

Cadmium Chloride Method. API Method 772-54. In: Manual on

Disposal of Refinery Wastes, Vol. V: Sampling and Analysis

of Waste Gases and Particulate Matter. American Petroleum

Institute, Washington, D.C. 1954.

2. Tentative Method of Determination of Hydrogen

Sulfide and Mercaptan Sulfur in Natural Gas. Natural Gas

Processors Association, Tulsa, OK. NGPA Publication No.

2265-65. 1965.
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3. Knoll, J.D., and M.R. Midgett. Determination of

Hydrogen Sulfide in Refinery Fuel Gases. Environmental

Monitoring Series, Office of Research and Development,

USEPA. Research Triangle Park, NC 27711. EPA 600/4-77-007.

4. Scheil, G.W., and M.C. Sharp. Standardization of

Method 11 at a Petroleum Refinery. Midwest Research

Institute Draft Report for USEPA. Office of Research and

Development. Research Triangle Park, NC 27711. EPA

Contract No. 68-02-1098. August 1976. EPA 600/4-77-088a

(Volume 1) and EPA 600/4-77-088b (Volume 2).

17.0 Tables, Diagrams, Flowcharts, and Validation Data.

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Figure 11-1. Hydrogen Sulfide Sampling Train.

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