The determination of acid-reactive sulfide

Acid-reactive sulfide minerals make up a large fraction of total sulfur in freshwater sediments, waste sludges, and waterlogged soils. Quantitative determinations of acid-reactive sulfide (ARS) by hydrogen sulfide evolution methods have been hampered by sample handling losses, standardization problems, and poor overall recoveries. A systematic study has been made of the optimal conditions for the determination of ARS. The modified method employs a zinc sulfide suspension as a standard in contrast with the current standard of sodium sulfide solution. This change resulted in a great improvement in precision; the addition of sodium hydroxide to the hydrogen sulfide absorption solution improved recoveries to better than 95% in the range of interest, 0.4-4 mg sulfide. ARS in freshly collected lake sediment samples was determined with an average of less than ±14% relative standard deviation. Storage of sediment samples for periods exceeding 6 months was found to increase variability only slightly. The method should prove applicable to various sulfide-containing samples and, with prescribed handling precautions, samples may be stored for extended periods.