The oxidation process of sulfur (IV) species (SO2, HSO3- e SO32-) by oxygen, catalysed by trace metal ion and complexes, can play an important role in atmospheric, analytical and bioinorganic chemistry. An overview of the most important reactions in these fields is presented. A fascinating redox cycling of the metal ions and complexes during such autoxidation process was revealed by the combination of kinetics and coordination chemistry studies.

In this way it is very important to know the sulfate concentration in vinasse samples before to make the biodigestor design. A previous developed and indirect method (Anal. Chim. Acta. 1996, 329, 197), was used to determine sulfate in samples of vinasse, after previous treatments, done in order to eliminate organic matter with hydrogen peroxide 30% and concentrated nitric acid mixture (3:1), under heating. Interferent cationic ions were isolated by using ion exchange columns. The results obtained for some samples from Araraquara and Penápolis are here presented. The phosphate concentration was also determined.