VIEW ARTICLE    DOI: 10.1094/ASBCJ-53-0082

Stabilization of Sulfite for Automated Analysis Using Ion Exclusion Chromatography Combined with Pulsed Amperometric Detection. Herbert P. Wagner (1), Labatt Breweries of Canada, Brewing Research Department, London, Ontario, Canada N6A 4M3. (1) Present address: 84 Hawkesbury Avenue, London, Ontario, Canada N5V 2K1. J. Am. Soc. Brew. Chem. 53(2):82-84, 1995. Accepted December 5, 1994.

Ion chromatography (IC) has been suggested as a viable alternative to the classical methods for the analysis of sulfite. These IC methods have shown some promise in manual applications. Although the difficulties of electrode fouling, associated with normal amperometry, can be eliminated by incorporating pulsed amperometry, the rapid oxidation of sulfite to sulfate by dissolved oxygen and/or metal catalyzed oxidation has, to date, prevented the development of a fully automated method. The addition of formaldehyde to a solution containing sulfite will prevent oxidation of sulfite by forming a sulfite adduct that is stable in slightly acidic media. This complex rapidly hydrolyzes in alkaline solution. Because the total sulfite levels are assayed for most foods, all bound sulfite must be liberated before analysis. It is at this stage that difficulties are encountered because the liberated sulfite is susceptible to rapid oxidation. It is possible to obtain acceptable precision in an IC method in which the sulfite is liberated only immediately before assay. The instability of the liberated sulfite, however, has impeded automation of this analysis. By stabilizing the free and bound sulfite in a slightly acidic solution and automatically adjusting the pH of the sample as it enters the sample loop immediately before injection onto the analytical column, automation has been made possible. Excellent precision has been obtained. Coefficients of variation of 7.0 and 3.2% have been observed for two samples, analyzed continuously, over 5.5 and 4.5 hr, respectively. A fully automated, environmentally friendly, ion chromatographic method (subject to patent applications) has been developed for the analysis of sulfite. Keywords: Automated analysis, Environmentally friendly, IC, Sulfite