Sampling hydrogen sulphide

Materials Sulphur dioxide prepared in Experiment 60, splinter, copper wire, dyed silk, carnation, potassium chlorate, chlorine water, litmus paper, barium chloride solution, hydrogen sulphide, samples for analysis. 

The method is particularly suitable for measuring very low concentrations of hydrogen sulphide, e.g., in the Baltic Sea. The blank values are negligible, and Beer s law is applicable up to around 60 pmol/L, but determinations of up to 300/miol/L are possible without dilution of the sample. By using the ordinary bottles used for oxygen samples to collect hydrogen sulphide samples, rapid work is possible with minimum risk of losses of sulphide and contact with oxygen. 

Hydrogen sulphide. Samples to be analysed according to this procedure are very seldom anoxic. If sulphide ions are present, a pre-treatment with bromine (see Section 10.2.5.4) is recommended. 

The gas is washed with water to remove any hydrogen chloride. Since iron(II) sulphide is a non-stoichiometric compound and always contains some free iron, the hydrogen sulphide always contains some hydrogen, liberated by the action of the iron on the acid. A sample of hydrogen sulphide of better purity can be obtained if antimony(III) sulphide, (stibnite) SbjSj, is warmed with concentrated hydrochloric acid ... 

In electrochemical cells sample oxidation produces an electric current proportional to the concentration of test substance. Sometimes interferences by other contaminants can be problematic and in general the method is poorer than IR. Portable and static instruments based on this method are available for specific chemicals, e.g. carbon monoxide, chlorine, hydrogen sulphide. 

Wells are purged until stable readings are obtained for field chemical parameters including pH, temperature, dissolved oxygen, redox and electrical conductivity. Samples are then collected for a wide variety of chemical parameters. Time sensitive parameters are analyzed within specific holding times. For example, alkalinity and hydrogen sulphide are measured at the time of sampling, iodide... 

Kupec et al. [180] determined total sulphur in sludge by a method involving magnesium reduction in which the sample is heated with magnesium powder to convert all sulphur compounds into magnesium sulphide. The magnesium sulphide is treated with sulphuric acid and the evolved hydrogen sulphide determined by iodometric titration. 

Any precipitated sulphides being removed by filtration, the filtrate is boiled to expel hydrogen sulphide, then oxidised with a few drops of concentrated nitric acid and boiled with ammonium chloride and ammonia. The liquid is then filtered and the precipitate carefully washed with hot water and dissolved in dilute nitric acid, the nitric acid solution being treated with excess of sodium hydroxide, boiled for a few minutes and filtered when cold. Any ferric and chromium hydroxides remain on the filter, the filtrate containing the alumina as sodium aluminate. If the filtrate is heated to boiling with ammonium chloride, an abundant precipitation of gelatinous white flocks will occur in the case of a sample dyed on an aluminium mordant. 

Goodwin et al. [82] determined trace sulphides in turbid waters by a gas dialysis-ion chromatographic method. The sulphide is converted to hydrogen sulphide which is then isolated from the sample matrix by diffusion through a gas dialysis membrane and trapped in a dilute sodium hydroxide solution. A 200pL portion of this solution is injected into an ion chromatograph for determination with an electrochemical detector. Detection limits were >1.9ng/mL... 

Vitenberg et al. [623] have described a gas chromatographic method for the determination of traces (down to l-10pg kg ) of sulphur compounds, such as hydrogen sulphide, mercaptans, sulphides and disulphides, in industrial waste waters (kraft paper mill effluents) by a combination of headspace analysis and microcoulometiy. This method increases the analytical sensitivity 102-103 times without any preliminary concentration of the sample. 

An alternative approach, adopted by Albery et al. [59-61], is to determine the mechanism giving rise to the sensor response and to use this information together with the measured data at short times to calculate the final response. This was used for an electrochemical sensor system incorporating cytochrome oxidase where the steady-state responses of the measurement system were insufficiently fast for useful measurement of respiratory inhibitors such as cyanide, hydrogen sulphide, etc. By using mechanistic information, it was possible to successfully calculate the concentration in a test sample by real-time analysis of the sensor signals at short times after exposure to the test sample. The analysis could cope with the gradual loss of enzyme activity commonly found in these biosensor devices. 

The second sample contains ozone and nitrogen peroxide and the difference between the nitrite contents of the two bottles is equivalent to the ozone present. The presence in the air of ammonia, sulphur dioxide, and hydrogen sulphide does not interfere with the estimation of ozone and nitrogen peroxide by this method as all three gases are completely absorbed during passage through the chromic anhydride tube. 

Cations of the first group form insoluble chlorides. Lead chloride, however, is slightly soluble in water and therefore lead is never completely precipitated when adding dilute hydrochloric acid to a sample the rest of the lead ions are quantitatively precipitated with hydrogen sulphide in acidic medium together with the cations of the second group. 

Ammonium sulphide (m). Saturate 500 ml ammonia solution (2m) with hydrogen sulphide, until a small sample (1 ml) of the solution does not cause any precipitation in magnesium sulphate (m) solution. Then add 500 ml ammonia solution (2m). Store the solution in a well-stoppered bottle. The solution must be colourless. Yellow or orange colour indicates that considerable amounts of polysulphide are present in the solution. 

To a portion of the sample add 3ml of dilute sulphuric acid and heat the solution. Hydrogen sulphide fumes which turn lead acetate paper black are given by sulphides. 

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