The determination of the sulphite content of some foods and beverages by capillary electrophoresis

A method for the determination of the sulphite content in foods and beverages by capillary electrophoresis (CE) is described. The sulphite is converted to sulphur dioxide and finally to sulphate using a Monier-Williams distillation. The sulphate is then determined by CE using a 75 mu m fused silica capillary column with a buffer consisting of 5 mM sodium chromate and 0.5 mM OFM Anion-BT reagent, pH 8.0, with indirect UV detection at 254 nm. Nitrate was used as the internal standard. The levels of sulphite in the products are in good agreement with those determined by titrimetry, except for one sample of fresh prawns, fresh garlic and some processed foods containing garlic and onion, where the levels determined by CE are lower. The instrument repeatability of the CE procedure is satisfactory and the level of detection is 5 mg/kg.