A new, rapid and reliable method for the determination of sulphur reduced (S-II) species in natural water discharges.

The determination of reduced S species in natural waters is particularly difficult due to their high instability and chemical and physical interferences in the current analytical methods. In this paper a new, rapid and reliable analytical procedure is presented, named the Cd-IC method, for their determination as Sigma S2- via oxidation to SO42- after chemical trapping with an ammonia-cadmium solution that allows precipitation of all the reduced S species as US. The S2--SO4 is analysed by ion-chromatography. The main advantages of this method are: low cost, high stability of US precipitate, absence of interferences, low detection limit (0.01 mg/L as SO4 for 10 mL of water) and low analytical error (about 5%). The proposed method has been applied to more than 100 water samples from different natural systems (water discharges and cold wells from volcanic and geothermal areas, crater lakes) in central-southern Italy.