CO-DETERMINATION OF SODIUM METABISULFITE AND STARCH IN CORN SYRUP BY FLOW-INJECTION COULOMETRY

During the processing of corn syrup for commercial use, starch, in the form of alpha-amylose, must be completely broken down to its D-glucop yranose units. Sodium metabisulfite is added to the corn syrup as a pr eservative. Flow Injection Coulometry was used to perform an automated assay of these analytes, both individually and jointly. The sodium me tabisulfite concentration, over a range of 3.5 x 10(-4)-2.9 x 10(-2)M, is determined by coulometric flow injection titration with generated iodine, using spectrophotometric endpoint detection at 530 nm. Analysi s over this range produced a relative standard deviation of <1.5% and was found to correlate very well with manual titrations. The determina tion was performed in the presence of varying amounts of starch, and w as found to be independent of the starch concentration. Starch was det ermined, when no sodium metabisulfite was present, from the absorbance level after the reaction of the sample with a specific amount of iodi ne. In the presence of sodium metabisulfite, the rate of the accumulat ion of the starch/iodine interaction product after the metabisulfite t itration endpoint, at a constant reagent generation rate, was used. A relative standard deviation of < 1.4% was obtained for all starch anal yses, with a very good correlation (correlation coefficients greater-t han-or-equal-to 0.997) with the known relative concentration. The use of the FIC technique to perform analyses by specific amount and excess reagent generation is demonstrated, along with dual analyte determina tion.