A fast and sensitive HPLC method for sulfite analysis in food based on a plant sulfite oxidase biosensor

A reliable and sensitive analysis of sulfites in food is essential in food monitoring. However, the established methods exhibit deficiencies in the very low concentration ranges (below 10 mg/L SO 2 ), especially with more complex food matrices. With a focus on these challenges, an HPLC method with immobilized enzyme reactor (HPLC–IMER) for the analysis of sulfites in food was optimized and compared to a standard method. A modulated sample preparation procedure and the use of a novel sulfite oxidase from Arabidopsis thaliana were explored to make the method applicable for most food samples. The plant sulfite oxidase turned out to be superior to the commercially available animal sulfite oxidase in terms of detection limit (0.01 mg/L SO 2 ), linear range (0.04–20 mg/L SO 2 ) and stability. In a small scale comparison within our laboratory, as well as in a standardized proficiency testing, the HPLC–IMER was compared to an established distillative method. The enzyme-based method is not only more sensitive and specific, it also yields higher sulfite recoveries in almost all samples while exhibiting better statistic method parameters.