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Home > Technical Articles > Sulfite
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Home > Technical Articles > Sulfite
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Sulfite by ICSulfite (SO3-2) in solution is easily oxidized by air to sulfate (SO4-2). Since sulfate is very common, this complicates the direct analysis of sulfite. This sulfite test is used to test for free sulfite in solution as well as for sulfur dioxide trapped in impingers or on impregnated filters. We have recently found an improved method for analysis of sulfite in aqueous samples. The method is based on NIOSH 6004, and uses 2% glycerol to stabilize the sulfite ion, minimizing oxidation to sulfate. We have seen good stability of a sulfite standard sitting overnight at room temperature. Sulfite elutes between phosphate and sulfate in our standard EPA 300.0 inorganic anion system. |
Some researchers (1-2) have reported improving the stability of sulfite by using alcohols such as glycerol, saccharides, and formaldehyde. The latter is reported to work even in the presence of ferric ions. This suggests that one should consider adding a preservative in the field to environmental samples to stabilize the sulfite. At a minimum, fill the bottle excluding air bubbles. The chromatograms below show rain water samples spiked with 150 ug/L sulfite and sulfate, with and without glycerol added, and allowed to stand 3 days. With glycerol, sulfite was recovered at almost 80%. 1. Michigami, et al., J. Chromatogr. A
(1994) 663(2), 255-258. |
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