Capillary electrophoretic determination of sulfite using the zone-passing technique of in-capillary derivatization

A new capillary electrophoretic (CE) method was developed for the simple and selective determination of sulfite. The proposed method is based on the in-capillary derivatization of sulfite with iodine using the zone-passing technique and direct UV detection of iodide formed. The optimal conditions for the separation and derivatization reaction were established by varying concentration of iodine, electrolyte pH and applied voltage. The optimised separations were carried out in 20 mmol l−1 Tris–HCl electrolyte (pH 8.5) using direct UV detection at 214 nm. Experimental results showed that the injection of the iodine zone from anodic end of the capillary gives significantly better precision. Common UV absorbing anions such as Br−, I−, S2O32−, NO3−, NO2−, SCN− did not give any interferences. Valid calibration (r2=0.998) is demonstrated in the range 1·10−5–8·10−4 mol l−1 of sulfite. The detection limit (S/N=3) was 2·10−6 mol l−1. The proposed system was applied to the determination of free sulfite in wines. The recovery tests established for wine samples were within the range 92–103%. The CE results were compared with those obtained by iodometric titration technique.