Investigation on possible relationships between the content of sulfate and selected metals in Chianti wines

The content of sulfate in water was measured through a back-titration involving addition excess barium chloride, centrifugation and barium quantification in the supernatant via atomic absorption spectroscopy. The results were within 2.0% those found via gravimetric methods (GM). Model hydro-alcoholic solutions (ethanol 13%, v/v) with known amounts of Na2SO4 were analyzed, showing very good recovering factors (relative error <2.0%). The sulfate determination in wines was carried out on mineralized samples. Nine randomly selected wine samples were used to set up the method. Very good agreements were found with values obtained via GM and turbidimetric method (TM). Relative estimated standard deviations for this method average 2.0% of the concentrations, and relative discrepancies from values from GM and TM average 1.0%. The effective execution times were reduced by a factor of four with respect to GM. Eleven more red Chianti bottled wines were analyzed for the content of sulfate, copper and other metals. The sulfate content ranged from 399(12) to 902(17) mg (K2SO4)/L. Sulfate and copper positively correlated when sulfate content was higher than ca. 200 mg (K2SO4)/L and samples were from a certain winery, suggesting that vine or wine treatments with copper sulfate were significant. The linear regression factor was R2 = 0.959 and significance factor P = 0.0001.