Use of a mixing chamber for sample preparation and multiple collection in sequential injection analysis: determination of sulfate in wines

A sequential injection system for determination of sulfate in wines was developed. It was based on the formation of BaSO4, measured turbidimetrically at 420 nm. As sample dilution and acidification were required, both sample and acid were sent to a mixing chamber placed in a lateral port of the selection valve; after thorough mixing, up to six aliquots could be drawn and analyzed. A linear calibration curve was established using 10% v/v ethanol standards with concentrations between 300 and 1500 mg L-1 of K2SO4. The results obtained by the present methodology were statistically comparable with those furnished by the reference procedure, with relative deviations < 3.5%. The sample frequency was about 5 samples per h with relative standard deviations (RSD) < 10%.