Hydrogen sulfide sensor

Figure 20.9 AGS, principles of operation. Cells for hydrogen sulfide, for carbon monoxide and for oxygen. For hydrogen sulfide sensor, the reference electrode helps to extend the working range of the sensor and improves the linearity of response. The electrochemical reactions consume the species present in the cell. This can be the anode itself (cell for oxygen), the electrolyte or even a reagent which should be present (oxygen is necessary for the cell detecting carbon monoxide).

Each molecule of H2S that is oxidized at the sensing electrode produces a current flow of eight electrons. The amount of current produced is a function of the number of H2S molecules that enter the sensor. For every 1.0 ppm of H2S in the atmosphere being monitored, a typical hydrogen sulfide sensor shows a raw electrical output of 0.7 pA (miao amps). This relationship is linear over a very wide range such that 10 ppm produces 7.0 pA, 100 ppm produces 70.0 pA and so on. 

Confined space gas detectors include sensors used to measure the most commonly encountered hazards oxygen deficiency (and enrichment), percent LEL combustible gas, carbon monoxide and hydrogen sulfide. Sensors utilized in these portable gas detectors are extremely good at detecting what they are designed to measure. However, they still have limitations. 

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. 

Cardoso AA, Liu H, Dasgupta PK. 1997. Fluorometric fiber optic drop sensor for atmospheric hydrogen sulfide. Talanta 44 1099-1106. 

Electrochemical sensors for the determination of hydrogen sulfide production in biological samples... 

Electrochemical Sensors for the Determination of Hydrogen Sulfide Production in Biological Samples... 

Total sulfide can be measured photometrically by the methylene blue method (Cline, 1969 Standard Methods for the Examination of Water and Wastewater, 1998). Reliable sensors exist for the measurement of hydrogen sulfide in air. 

Only the VDI Richtlinie gives criteria from which it is possible to compare sensorical measurement methods with each other. Results taken from the VDI-ringtest are the base for this comparison. However some olfactometers in this ringtest did not conform to the VDI Richtlinie. Maybe because of this the range between the highest allowable threshold value for hydrogen sulfide and the lowest is great (namely from 0.4 to 8 um/m3 (factor 20)). 

Elemental composition H 5.92%, S 94.08. Hydrogen sulfide may be distinguished by its characteristic odor. The gas turns a paper soaked in lead acetate solution black. Many infrared sensors are commercially available for in-situ measurements of H2S. It may be monitored semiquantitatively by Draeger tubes. It also may be analyzed by GC following trapping over molecular sieves and thermal desorption. Either a flame photometric detector or a sulfur chemiluminescence detector may be used for GC analysis. It may be separated on a capillary column such as Carboxen 1006 PLOT or SPB-1 SULFUR (Supelco Catalog 1999 Supelco Inc., BeUefonte, PA). 

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. 

Fig. 7 Vertical distribution versus density (agy kg m 3) of temperature (T), salinity (S), transmission (Xmiss), dissolved oxygen measured with YSI oxygen sensor (02SB), dissolved oxygen measured by Winkler titration (02), hydrogen sulfide (H2S), phosphate (PO4), silicate (Si), nitrite (N02), ammonia (NH4), dissolved manganese (Mn diss), bivalent iron (Fe(II)), and trivalent iron (Fe(III)) at a station near the Bosporus (Cast 16, RV Knorr 172-05 cruise, April 04,2003). Concentrations of chemical parameters are in xM...

Coated piezoelectric quartz crystals as sensors for water, hydrocarbons, polar molecules, and hydrogen sulfide [8]... 

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