A Comparison of Selected Methods for Determining Sulfite in Prawns

As the standard technique for sulfite analysis, the Monier-Williams distillation, is time consuming and relatively insensitive, many alternative methods have been developed. Three of these methods were tested for their suitability for the routine determination of residual sulfite in prawns: i) a rapid steam distillation; ii) high performance liquid chromatography (HPLC), and iii) an enzyme-based procedure. Testing of the three selected methods involved analyses of standard sulfite solutions, prawns of known sulfite levels and prawns of unknown sulfite levels and comparison of results with those determined by the Monier-Williams procedure. Statistical analysis showed that the sulfite levels determined on standard solutions by rapid distillation were in close agreement with those obtained by the Monier-Williams distillation. However, a correction factor had to be introduced when analyzing prawns by the rapid distillation method to obtain comparable results with those produced by the Monier-Williams distillation. The same statistical analysis performed on levels determined by HPLC and the Monier-Williams distillation gave close agreement for both standard solutions and prawns. The enzyme test, after promising results for the standard solutions, proved to be unsatisfactory for analysis of sulfite in prawns.