DETERMINATION OF FREE, BOUND AND TOTAL SULFITES IN FOODS BY INDIRECT PHOTOMETRY-HPLC

Sulphur dioxide and sodium, potassium, calcium salts of hydrogen-sulph ite, disulphite and sulphite ions are extensively used as food additiv es for their technological efficacy and versatility. They are active a s antimicrobial agents, enzyme inhibitors, antioxidants, structure mod ifiers, in the control of enzymatic and nonenzymatic browning reaction s with stabilising and conditioning functions. In this study a modifie d Monier-Williams method has been utilised as a preparative procedure to obtain both the free and bound sulphite fractions. The two fraction s have been analysed by HPLC with indirect photometric detection using a 250 x 4.6 mm LC-SAX column eluted with a solution of potassium hydr ogen phthalate. Levels of 5-10 ppm of SO2 in foods, corresponding to 3 0-60 ng injected are reliably detected by this method. The results con firm that the chromatographic method, unlike the Monier-Williams metho d, is able to avoid the potential interference of volatile substances derived from matrices or utilised chemicals. (C) 1998 Elsevier Science Ltd. All rights reserved.