Sulfide is often present in groundwater and sediment and is sometimes found in industrial or municipal wastewater. Sulfide is produced by the decomposition of organic matter and reduction of sulfate by bacteria.
One form of sulfide is gaseous hydrogen sulfide (H2S) which is very toxic to humans. The dissolved H2S is also toxic to fish and other aquatic organisms. Hydrogen sulfide can escape into the air from sulfide-containing wastewater causing nuisance orders. The odor threshold odor concentration of H2S in clean water is between 0.025 and 0.25 μg/L. Hydrogen sulfide also attacks metals directly and indirectly causes the corrosion of concrete sewers.
Hydrogen sulfide combines with iron and other metals, in natural sediments and sludges, to form slightly soluble acid-volatile sulfide (AVS). The determination of AVS concentrations has become more prevalent because it plays a key part in controlling the bioavailability of toxic metals in anoxic sediments.
Hanna Instruments offers a wide variety of instrumentation for measuring sulfide. Products include portable and benchtop pH/ISE meters that can use a solid-state sulfide Ion-Selective Electrode (ISE) for direct measurement.
Below are the most common products used for measuring sulfide.
Benchtop pH/ISE meters
Benchtop pH/ISE meters include two channel options in which a pH probe can be connected to one channel and the sulfide ISE to the other. The benchtop meters have the ion charge and formula weight pre-programmed for use with the sulfide ISE. The benchtop meters also have incremental methods pre-programmed including the known addition, known subtraction, analyte addition and analyte subtraction methods.
Portable pH/ISE Meters
Portable pH/ISE allow the flexibility to perform an ISE measurement in spaces where there is limited bench space, then can be stored in a carrying case when not in use. The meter can accept other ISEs and has the ion charge and weight pre-programmed for the specific parameter.
Sulfide ion determinations are made in ground waters, soils, and paper liquors. The silver/silver-sulfide pellet is practically insoluble in the test solutions being measured, and produces a potential change due to changes in the sample’s ion activity. When the ionic strength of the sample is fixed by the addition of ISA, the voltage is proportional to the concentration of sulfide ions in solution and the electrode follows the Nernst equation.
The sulfide ISE is available as either a single half-cell or combination design that is complete with a reference cell. The ISE is a convenient way to measure sulfide.
Solutions for sulfide measurement include the ISA for calibration and measurement. Other solutions include the Sulfide Anti-Oxidant Buffer (SAOB). The SAOB is a two component solution and is used with preparing of sulfide standards from sodium sulfide nonahydrate.
Accessories include polishing strips for the solid-state ISE and magnetic stirrers to ensure adequate mixing.