Hydrogen sulfide electrode

Electrochemical treeing is appHed in those cases of water treeing in which the water contains solute ions which move under the action of an electric field and are detected within the insulation layer, or at an electrode surface after having passed through the insulation. They are not encountered as often as the first two classes, for example, trees formed in a cable exposed to a hydrogen sulfide environment called sulfide trees. 

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. 

Similar to the pH meter, gas meters employ specific ion electrodes. The electrodes generate a potential proportional to the activity of a specific ion in solution. The calibration is achieved in standard solution and results read in mV or concentration in mg/L or ppm on the meter. The water can be adapted to monitor the concentration of carbon dioxide, hydrogen sulfide, ammonia, chloride, calcium, potassium and sodium to name a few. 

Puacz et al. (1995) developed a catalytic method, based on the iodine-azide reaction, for the determination of hydrogen sulfide in human whole blood. The method involves the generation of hydrogen sulfide in an evolution-absorption apparatus. In addition, the method allows for the determination of sulfide in blood without interference from other sulfur compounds in blood. A detection limit of 4 g/dm3 and a percent recovery of 98-102% were achieved. Although the accuracy and precision of the catalytic method are comparable to those of the ion-selective electrode method, the catalytic method is simpler, faster, and would be advantageous in serial analysis. 

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. 

Potentiometric titration with a sulfide ion-selective electrode as an indicator has been used to measure hydrogen sulfide in the air at ppb levels (Ehman 1976). The method has been shown to have very good accuracy and precision. No interference could be found from nitrogen dioxide, sulfur dioxide, or ozone. 

Some problems were encountered with the pH probes used in the pH measurements because the reference electrode is saturated with AgCl. Hydrogen sulfide can react with the AgCl in solution, thus precipitating AgS at the KC1 junction between the reference electrode and the solution. In this regard it was found that certain probes work better than others. Our observations are as follows. 

Elemental composition H 11.83%, N 41.11%, S 47.05%. It may be analyzed by measuring its decomposition gaseous products, ammonia and hydrogen sulfide, either by gas chromatography using an FID or a TCD or by selective ion electrode or colorimetric techniques. 

Elemental composition Na 58.93%, S 41.07%. An aqueous solution is analyzed to determine sodium content. Also, an aqueous solution may be analyzed for sulfide by methylene blue colorimetric test or by iodometric titration (APHA, AWWA, and WEF. 1999. Standard methods for the Examination of Water and Wastewater, 20 ed. Washington, DC American Pubhc Health Association). The methylene blue test is based on reacting sulfide, ferric chloride and dimethyl-p-phenylenediamine to produce methylene blue. Also, sulfide can be measured by using a sdver-sdver sulfide electrode. Quahtatively, sulfide may be identified from the hberation of H2S on treatment with acid. The H2S turns the color of paper soaked with lead acetate black (See Hydrogen Sulfide). 

The oxidation of sulfite and thiosulfate becomes facile in the presence of iodide and novel disposable microband sensor electrodes have been developed by Williams and coworkers [187] to allow fast amperometric determination. A similar approach was proposed for the determination of sulfite in wine [188]. In this method, a coulometric titration is carried out in which S(IV) is indirectly oxidized to S(VI). Speciation of SO2 and sulfite was achieved down to micromolar levels. Sulfide and hydrogen sulfide can be determined elec-trochemically in the presence of an iodide mediator [189]. This process may be further enhanced at elevated temperatures. 

The corrosion behavior and dissolution mechanism of nickel in acid solutions with hydrogen sulfide (H2S) was studied. It was found that the dissolution of nickel is influenced by both the nickel sulfide layer formed on the electrode surface and the acceleration effect of H2S [56]. 

Figure 15-23 Standard addition graph for ion-selective electrode based on Equation 15-12. [Data from G. LI, B. J. Polk, L. A. Meazell, and D. W. Hatchett, ISC Analysis of Hydrogen Sulfide in Cigarette Smoke," J. Chem. Ed. 2000, 77. 1049.]...

The potentiometric measurement of hydrogen sulfide via a Ag/Ag2 electrode is well known and such electrodes are commercially available. Boulggue (22) has used the electrode to measure changes in potential during a titration with HgC. This method can measure sulfide, polysulfide, thiols, sulfite and thiosulfate. Weaknesses of die method are the following there is no method of sample preservation the pH must be adjusted to pH 13 for the measurement of sulfide, thiol and polysulfide then adjusted to pH 7 for the measurement of thiosulfate and sulfite polysulfide is determined by difference after attack on the polysulfides with added sulfite (if elemental sulfur is present in the sample it will also participate in this reaction) the identity of the organic thiols is unknown and sulfite can not be measured in seawater samples because of competition with halides (21). 

Hydrogen bonding, 16, 110,122 Hydrogen electrode, 234 Hydrogen ion, 22-24 See Proton Hydrogen sulfide, 437 Hydrolysis, 69, 75 Metal-ions, 75-76... 

Recent work reveals that SCC occurs only in hot MEA solutions when the electrochemical potential of the steel surface is more negative than -700 mV vs a silver-silver chloride electrode. The tendency for SCC increases with an increase in solution concentration and in temperature. Saturating the hot MEA solution with hydrogen sulfide makes the potential of the steel more positive (i.e., decreases the tendency for SCC). This latter result raises a question about the practice of some operators who require stress relief only for steels exposed to amine solutions containing hydrogen sulfide. 

The Eh values are too high to be explained by the formation of either PtS or PtS2. The rest potentials of the platinum electrode are dependent upon the concentration of dissolved hydrogen sulfide (z[H2S]]. This can be explained by selective adsorption of H2S species on the platinum followed by the discharge of the proton mediated via chemisorbed H2S. The corresponding reactions are (11] ... 

Oxidized sulfur species occurring in natural waters (sulfate, sulfite, thiosulfate] do not interact with the platinum electrode when in the presence of H2S and the pH-Eh-E52- relations found were similar to the above relations. Thus, the unambiguous relations found between pH, Eh and E22- in aqueous solutions of hydrogen sulfide can be employed to characterize solutions and water samples where hydrogen sulfide is the only reduced sulfur species present. 

Berner R.A., Electrode studies of hydrogen sulfide in marine sediments. Geochim. Cosmochim. Acta 27, 563-575 [1963). 

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