Determination of sulfate in soils by reduction with tin and phosphoric acid

Abstract
A rapid and precise method for determination of SO4 2‐‐S in soils is described. It involves the extraction of SO4 2‐ from soils and its reduction to H2S by a reagent containing Sn and H3PO4 and subsequent determination as methylene blue. The results agreed closely with those obtained by reduction with the a reagent containing HI, H3PO2, and HCOOH and by ion chromatrography. Tests indicated that, in addition to SO4 2‐, the Sn‐H3PO4 reagent reduces certain organic S and reduced inorganic S compounds, but these S compounds are not present in extracts of agricultural soils. By using a bank of 10 distillation units, a single operator can perform 60 analyses in a normal working day.