The stability of tetrathioantimonate in the presence of oxygen, light, high temperature and arsenic

The recent development of methods to measure thioantimonate species, and their discovery in natural waters, mean that knowledge regarding their preservation is essential to understand their role in natural systems. We show that thioantimonate species can be preserved for more than three weeks if they are flash-frozen and/or stored in anoxic, dark conditions. When tetrathioantimonate is exposed to oxygen, light, or temperatures greater than room temperature, it transforms partially to trithioantimonate, but mainly to antimonite or antimonate. Thioantimonate formation and stability increase with increasing ionic strength. Compared to the thio species of arsenic, an element in the same group on the periodic table, thioantimonates are kinetically more labile. Excess arsenic decreases the percentage of thioantimonate species formed and favours formation of trithioantimonate over tetrathioantimonate. Excess antimonite decreases thioarsenate formation which is indicative of competition between the two metalloids for available sulfide. Sequestration of sulfur from thioarsenate to antimonite was not observed. In direct competition for sulfide, thioantimonate species form faster than thioarsenates. As an extension to previous reports from alkaline hot springs in Yellowstone National Park, thioantimonate species have now also been observed in mildly acidic conditions (pH 5–6) in New Zealand's Champagne Pool. In natural waters, the proportion of thioantimonates in total antimony is considerably lower than thioarsenates in total arsenic, probably because they are kinetically more labile.

► First data for stability and behaviour of thioantimonate species at low temperature.
► Thioantimonates are unstable in presence of oxygen, light, and increased temperature.
► Flash-freezing preserves thioantimonates in environmental samples for three weeks.
► Thioantimonate species are kinetically more labile than thioarsenate species.
► Kinetics may control thioantimonate concentrations in natural systems.