Determination of dissolved total sulfur in aqueous extracts and seepage water of forest soils

Four methods for determining the concentration of dissolved total sulfur (DTS) in aqueous extracts and seepage water of forest soils characterized by elevated amounts of dissolved organic matter are compared using various standards and aqueous extracts: (i) oxidation with NaBrO followed by HI reduction and methylene blue reaction, (ii) direct determination by ICP-OES, analysis by (iii) ICP-OES or (iv) ion chromatography (IC) after H₂O₂/UV oxidation. The NaBrO oxidation method showed the best recovery for analysis of DTS in standard samples. In most cases, results of the ICP-OES procedures were not significantly different from those of the NaBrO oxidation method, but more precise. The H₂O₂/UV-IC procedure severely underestimated DTS in some standards. For aqueous soil extracts, the NaBrO method and direct determination by ICP-OES showed equal results, irrespective of sample type and S concentration. Due to its excellent analytical and economical features, we recommend the ICP-OES method for routine determination of dissolved total sulfur in seepage water and aqueous soil extracts containing more than 1 mg S/L.