ION CHROMATOGRAPHY OF ORGANIC-RICH NATURAL-WATERS FROM PEATLANDS .4. DISSOLVED FREE SULFIDE AND ACID-VOLATILE SULFUR

Organic-rich, acidic, anaerobic pore waters from two peat bogs in Switzerland were analyzed for sulfide using ion chromatography (IC) with electrochemical detection. With one Dionex CarboPac PA1-Guard as separator column and another one in front of the 100-mu l injection loop, it was possible to separate sulfide and cyanide with detection limits as low as 1 ng/g sulfide. Pore water samples were obtained using in situ diffusion-equilibrium pore water samplers (peepers). Samples were collected under N-2 to prevent sample oxidation. Instead of preserving the dissolved sulfide with zinc acetate, sulfide was preserved by collecting the samples into 5-ml syringes containing 1 mi of concentrated eluent. In this way, the pH of the sample increased to 12 and no volatile H2S was lost. Measured sulfide concentrations in the pore waters were all below 20 ng/g. Some samples were spiked in the field to contain 5 ng/g sulfide. This amount could be detected using IC, whereas unspiked aliquots of the same samples yielded no sulfide peak. Based on the measurements of total dissolved sulfur, sulfate and sulfide, almost all of the sulfur in the pore waters is organically bound. The IC method presented here is well suited for the measurement of acid-volatile sulfur (AVS), and was applied to AVS measurements of some pore water samples. Trapping the volatilized H2S in eluent gave low detection limits and allowed rapid analyses without further treatment of the solution. The measured concentrations of AVS were not significantly different from the concentrations of free dissolved sulfide, suggesting that metal-sulfide complexes are relatively unimportant sulfur species in these waters.