Determination of total ionic polysulfides by differential pulse polarography

Ionic polysulfides occur in various natural environments and waste waters f rom industrial processes; however, their direct determination in samples co ntaining additional sulfur species has remained a challenge. Our goal was t o develop a polarographic technique that could be used to directly determin e total ionic polysulfides in the presence of other sulfur species such as polythionates and sulfide. Ionic polysulfides in an aqueous carbonate buffe r (pH 9.5) were measured using differential pulse polarography (DPP) in com bination with a dropping mercury electrode. An adsorption phenomenon associ ated with polysulfide or a product of its cathodic reaction with the Hg ele ctrode created a characteristic current minimum at -1000 mV with a magnitud e proportional to the concentration of S(0) existing in the form of polysul fidic sulfur. Sulfide and thiosulfate did not interfere and polythionates c aused only a decrease in the magnitude of the minimum. The specificity of t he technique and the lack of significant interferences make it an attractiv e alternative for the measurements of samples with polysulfidic sulfur conc entrations between 10(-5) and 10(-3) M. (C) 2001 Elsevier Science B.V. All rights reserved.