Forthesamplepreparation,adjustmentofthesampletoanalka-line pH value is important for several reasons: (1) the release of reversibly bound sulfites is most effective in alkaline media; (2) the sulfite oxidase is solely able to process the sulfite ion (SO2−3 ),
which dominates at high pH values; (3) the maximum activity of the sulfite oxidase is at pH 8.6. Therefore, prior to injection into the HPLC, the sample is treated with alkaline solution in order to releaseboundsulfitesandtoturnallformsofsulfur(IV)-oxospecies into the desired ionic sulfite (SO2−3 ) form.