Post-Column Derivatization-Ion-pair RP-HPLC Determination of Sulfite in Samples of Different Matrixes

Ion-pair RP-HPLC was applied to the determination of sulfite in samples of different matrixes.Sulfite in different sample was extracted with mixed solution of dil.HCl and sorbitol and with mixed solution of NaOAc and sorbitol in succession,and separated by centrifugation.Free sulfite anion in the supernatant was fixed by reacting with formaldehyde to form hydroxymethyl sulfonate (HMS),which was separated on the Venusil MP-C18 column with mixed solution of ammonium triethyloctane phosphonate solution (pH 5.0) and methanol (mixed in the ratio of 9 to 1 by volume) as mobile phase.In the post derivatization system,HMS was reacted first with KOH to regenerate SO2-3 and then derivatized with 5,5-dimercapto-2,2-dinitrobenzoic acid to give 5-mercapto-2-nitrobenzoic acid,which was detected at 450 nm spectrophotometrically.Detection limit (3S/N) of the method was found to be 0.15 mg·L-1.Test for recovery was made by standard addition method,values of recovery were found in the range of 85.9%-105.2%.