IC Determination of Residual Amount of Sulfite in Shrimp and Crab

Four grams of the homogenized sample of meat of shrimp or crab were extracted with 40 mL of the extractant which contains 0.1 mL of 1 mol·L-1 NaOH solution and 0.1 mL of formaldehyde-H2O (37+63) solution per 1 L, after centrifugation, the supernatant was taken and treated by freezing coagulation and on-line dialyzing to remove protein and fat. The extract was diluted 6 times with extrapure water before introduction into the IC instrument for determination of SO32- ion. Metrosep A supp 15 column (150 mm×4 mm) was used as ion-exchange column, and an acetone-H2O (20+80) solution, containing 0.386 g of Na2CO3 and 0.084 g of NaHCO3 per liter, was used as eluant, and conductivity detector was used in the detection. Linear relationship between values of conductivity and mass concentration of sulfite was kept in the range within 50 mg·L-1, with lower limit of determination (10S/N) of 0.1 mg·kg-1. The proposed method has been used in the analysis of the samples of meat of shrimp and crab, giving values of recovery and RSD′s (n=9) in the ranges of 89.5%-117% and 2.8%-13% respectively.