Hydrogen sulfide sampling

Carbonate is measured by evolution of carbon dioxide on treating the sample with sulfuric acid. The gas train should iaclude a silver acetate absorber to remove hydrogen sulfide, a magnesium perchlorate drying unit, and a CO2-absorption bulb. Sulfide is determined by distilling hydrogen sulfide from an acidified slurry of the sample iato an ammoniacal cadmium chloride solution, and titrating the precipitated cadmium sulfide iodimetrically. 

Hydrogen SulBde. Sulfide ion from 10 to 1 Af can be measured potentiometricaHy with an ion-selective electrode. Mercuric ion interferes at concentrations >10 M. The concentration of hydrogen sulfide can be calculated knowing the sample pH and the piC for H2S. 

Ion-selective electrodes can also become sensors (qv) for gases such as carbon dioxide (qv), ammonia (qv), and hydrogen sulfide by isolating the gas in buffered solutions protected from the sample atmosphere by gas-permeable membranes. Typically, pH glass electrodes are used, but electrodes selective to carbonate or sulfide may be more selective. 

Corrosion products and deposits. All sulfate reducers produce metal sulfides as corrosion products. Sulfide usually lines pits or is entrapped in material just above the pit surface. When freshly corroded surfaces are exposed to hydrochloric acid, the rotten-egg odor of hydrogen sulfide is easily detected. Rapid, spontaneous decomposition of metal sulfides occurs after sample removal, as water vapor in the air adsorbs onto metal surfaces and reacts with the metal sulfide. The metal sulfides are slowly converted to hydrogen sulfide gas, eventually removing all traces of sulfide (Fig. 6.11). Therefore, only freshly corroded surfaces contain appreciable sulfide. More sensitive spot tests using sodium azide are often successful at detecting metal sulfides at very low concentrations on surfaces. 

Alkalinity and Lime Content. The whole mud alkalinity test procedure is a titration method which measures the volume of standard acid required to react with the alkaline (basic) materials in an oil mud sample. The alkalinity value is used to calculate the pounds per barrel unreacted excess lime in an oil mud. Excess alkaline materials, such as lime, help to stabilize the emulsion and also neutralize carbon dioxide or hydrogen sulfide acidic gases. 

An Alka-Seltzer tablet gives off carbon dioxide when dissolved in aqueous solution. The gas is used to drive hydrogen sulfide out of drilling fluid samples. The H S then reacts with lead acetate paper in the bottle cap. The degree of discoloration is related to hydrogen sulfide concentrations. 

Samples are hydrolyzed with hydrochloric acid and stannous chloride solution at elevated temperature, and the evolved carbon disulfide is drawn with an air steam through two gas washing tubes in series containing lead acetate and sodium hydroxide solutions and an absorption tube containing an ethanolic solution of cupric acetate and diethanolamine. Lead acetate and sodium hydroxide remove hydrogen sulfide and other impurities. In the absorption tube, the carbon disulfide forms two cupric complexes of Af,Af-bis(2-hydroxyethyl)dithiocarbamic acid with molecular ratios Cu CS2 of 1 1 and 1 2. These complexes are measured simultaneously by spectrophotometry at 453 nm. 

Analytical Methods for Determining Hydrogen Sulfide in Biological Samples... 

In the case of life-threatening hydrogen sulfide poisoning, measurements of blood sulfide or urinary thiosulfate levels may be used to confirm exposure. However, samples need to be taken within two hours of exposure in order to be useful. The tests for measuring sulfide in the blood or thiosulfate in the urine are described in Section 2.7.1. 

Three of five men, who lost consciousness within a few minutes of entering a partially drained underground liquid manure storage tank, died before reaching the hospital autopsy showed that two had massive liquid manure pulmonary aspiration, while the third had fulminant pulmonary edema without manure aspiration (Osbem and Crapo 1981). Markedly elevated heart-blood sulfide-ion levels indicated significant hydrogen sulfide exposure. Air samples analyzed about a week after the accident detected only 76 ppm of hydrogen sulfide, but the study authors noted that the environmental conditions were probably different (e g., warmer weather, less-concentrated manure). 

As discussed in more detail in Section 2.2.1.1, Bates et al. (1997) found a significant increase in mortality from diseases of the respiratory system for residents of the Rotorua area of New Zealand for the period of 1981-1990. Rotorua is in an area of high geothermal activity sampling from a campaign in 1978 indicated a median concentration for hydrogen sulfide of about 20 g/m3 with 35% of the measurements >70 g/m3 and 10% >400 g/m3. Problems with the analysis, however, led these authors to conclude that there were no clear indications of excess mortality. 

The usefulness of urinary thiosulfate as an indicator of nonfatal hydrogen sulfide toxicity has been studied (Kangas and Savolainen 1987). Urinary samples for thiosulfate were obtained from volunteers exposed by inhalation to 8, 18, or 30 ppm of hydrogen sulfide for 30-45 minutes (the occupational exposure limit of 10 ppm for 8 hours was never exceeded). Excretion of urinary thiosulfate increased linearly up to 15 hours postexposure. Beyond 15 hours, the urinary thiosulfate concentration remained low, possibly indicating that most of the absorbed hydrogen sulfide was metabolized or excreted within 15 hours. 

Reliable evaluation of the potential for human exposure to hydrogen sulfide depends in part on the reliability of supporting analytical data from environmental samples and biological specimens. In reviewing data on hydrogen sulfide levels monitored or estimated in the environment, it should also be noted that the amount of chemical identified analytically is not necessarily equivalent to the amount that is bioavailable. 

Accurate measurements of hydrogen sulfide water levels are usually complicated by the presence of other sulfide compounds. A method of determining sulfide concentration in waste water by first transforming it to hydrogen sulfide and then measuring the atomic absorption of the product yielded results ranging from 3.1 to 5.1 ppm of sulfide sulfur (Parvinen and Lajunen 1994). Total sulfide levels in samples from the Mississippi River were about 0.92 ppm, while levels in pond and well water in St. Paul, Minnesota were 1.6 and 1.9 ppm, respectively (Slooff et al. 1991). 

Concentrations of hydrogen sulfide in soil gas from samples taken at some NPL sites ranged from 75 to 47,000 ppm (HazDat 1997). Data on soil gas concentrations at all NPL sites were not available. 

For occupational measurements of airborne concentrations, NIOSH (1977a) recommended the use of a midget impinger for sampling breathing zone air and the methylene blue/spectrophotometric method for the analysis of hydrogen sulfide. The detection limit was 0.20 g/m3 (0.14 ppb). 

GC/FID has been used for quantifying sulfur volatiles such as hydrogen sulfide in human saliva (Solis and Volpe 1973). This method included microcoulometric titrations and a procedure for incubation of saliva and sampling of headspace sulfur volatile components. The amount of total sulfur volatiles detected in control samples of saliva incubated at 37°C for 24 hours ranged from 4.55 to 13.13 ppm. 

Fresh and frozen human tissue samples obtained from brain, liver, and kidney have been analyzed for hydrogen sulfide levels by sulfide-derived methylene blue determination using ion-interaction reversed-phase HPLC (Mitchell et al. 1993). This method can quantify nmol/g levels of sulfide. Gas dialysis/ion chromatography with ECD has been utilized for measurement of sulfide in brain tissue with 95-100% recovery (Goodwin et al. 1989). 

The methods most commonly used to detect hydrogen sulfide in environmental samples include GC/FPD, gas chromatography with electrochemical detection (GC/ECD), iodometric methods, the methylene blue colorimetric or spectrophotometric method, the spot method using paper or tiles impregnated with lead acetate or mercuric chloride, ion chromatography with conductivity, and potentiometric titration with a sulfide ion-selective electrode. Details of commonly used analytical methods for several types of environmental samples are presented in Table 6-2. 

NIOSH (method 6013) describes the measurement of hydrogen sulfide in the air by ion chromatography (NIOSH 1994b). This method has a working range of 0.9-20 mg/m3 for a 20-L air sample and an estimated limit of detection of 11 g per sample. However, sulfur dioxide may interfere with the measurement of hydrogen sulfide. 

The Iodometric method has also been utilized in analyzing hydrogen sulfide in the air (EPA 1978). The method is based on the oxidation of hydrogen sulfide by absorption of the gas sample in an impinger containing a standardized solution of iodine and potassium iodide. This solution will also oxidize sulfur dioxide. The Iodometric method is suitable for occupational settings. The accuracy of the method is approximately 0.50 ppm hydrogen sulfide for a 30-L air sample (EPA 1978). 

Paper tapes impregnated with lead acetate have been widely used for air sample measurements of hydrogen sulfide in the field (EPA 1978 WHO 1981). The presence of other substances capable of oxidizing lead sulfide can lead to errors. This method has been improved by impregnating the paper with... 

GC/FPD has been used to measure hydrogen sulfide, free disulfide, and dissolved metal sulfide complexes in water (Radford-Knoery and Cutter 1993). Hydrogen sulfide was measured in the headspace of the sample (100 mL) with a detection limit of 0.6 pmol/L. A detection limit of 0.2 pmol/L was obtained for total dissolved sulfide. This method allows for the determination of the concentration of free sulfide that is in equilibrium with hydrogen sulfide. Complexed sulfide can be estimated from the difference between total dissolved sulfide and free sulfide. 

A molecular absorption spectrophotometry method, using a sharp-line irradiation source, has been developed for the determination of sulfide (as hydrogen sulfide) in water and sludge samples. The method was tested with measurements of real waste-water samples. The limit of detection was 0.25 g (1-10 mL sample volume). 

Kring EV, Damrell DJ, Henry TJ, et al. 1984. Laboratory validation and field verification of a new passive colorimetric air monitoring badge for sampling hydrogen sulfide in air. Am Ind Hyg Assoc J 45 1-9. 

Parvinen P, Lajunen LHJ. 1994. Determination of sulfide as hydrogen sulfide in water and sludge samples by gas phase molecular AS. Atomic Spectres 15 83-86. 

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