Total SO2 content determination in shrimp paste by modified Monnier-Williams Method

Total SO2 is defined as “the total of all the various forms of sulfur dioxide present in the sample, either in the free state or combined with their constituents”. Its determination in solid samples poses a challenge because SO2 is withheld in adducts and is released slowly during boiling. Recognized results are obtained by means of the generally accepted Optimized Monier-Williams method according to AOAC 990.28 which suggests the use of nitrogen-assisted boiling of the acidified sample to release the Total SO2. The method presented in this study provides equally quantitative results with much less time required per sample and is based on steam distillation followed by pH titration.

In this application note recovery results for a widely used reference standard HMS, and a certified sample of shrimp paste (41±9.7ppm) for total sulfite analysis are presented. A representative concentration of 1 mg SO2 /sample tube is selected to demonstrate the robust performance of modified Monier-Williams method by steam distillation. 

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