AN INTERCOMPARISON STUDY OF THE DETERMINATION OF SULFITE IN TROPICAL SHRIMPS BY THE WEST-EUROPEAN-FISH-TECHNOLOGISTS-ASSOCIATION (WEFTA)

Eight WEFTA laboratories participated in two series of intercomparison exercises on sulfite determination in tropical shrimps. Samples of tr opical shrimps were spiked with sodium metabisulfite (Na2S2O5) and hyd roxymethylsulfonate (HMS) at a level of 25-90 mg SO2/kg. Most of the l aboratories determined the sulfite content with (modified) methods of Monier-Williams or De Vries et al. The overall mean recovery of sulfit e was rather low (47-60%), which may be attributed to an irreversible reaction of sulfite with the tropical shrimps. The repeatability of th e methods within the participating laboratories was good, However, rep roducibility among the laboratries was poor, It has been shown that th e sulfite content in tropical shrimps spiked with Na2S2O5 decreased du ring storage at -20 degrees C and at +4 degrees C. Hydroxymethyl-sulfo nate was stable during storage.