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 tropical shrimps were spiked with sodium metabisulfite (Na2S2O5) and hydroxymethylsulfonate (HMS) at a level of 25–90 mg SO2/kg. Most of the laboratories determined the sulfite content with (modified) methods of Monier-Williams or De Vries et al. The overall mean recovery of sulfite was rather low (47–60%), which may be attributed to an irreversible reaction of sulfite with the tropical shrimps. The repeatability of the methods within the participating laboratories was good. However, reproducibility among the laboratries was poor. It has been shown that the sulfite content in tropical shrimps spiked with Na2S2O5 decreased during storage at −20°C and at +4°C. Hydroxymethyl- sulfonate was stable during storage.