Determination of total sulfur dioxide residues in dried vegetables by precolumn derivatization HPLC method

Sulfur dioxide (SO 2 ) and its derivatives are commonly used as preservatives in dried vegetables, yet excessive residues pose significant food safety concerns. This study applied the precolumn 2,2′-dithiobis(5-nitropyridine) (DTNP) derivatization HPLC method to dried vegetables with high starch and polysaccharide content. The shift of the detection wavelength to 320 nm substantially alleviated the severe matrix interference observed at 213 nm. The validated method demonstrated excellent linearity (R 2 > 0.9999) over 3.20–51.2 mg/L, with limits of detection (LOD) and quantification (LOQ) of 0.0039 and 0.013 g/kg in dried vegetable samples, matrix effects within ±10%, and recoveries of 79.17%–115.04%. Application to 19 commercial samples revealed that all white fungus samples complied with the maximum residue limit (MRL) of 0.2 g/kg specified in GB 2760–2024, while one lily bulb sample from Gansu Province contained total SO 2 residues of 4.05 g/kg, exceeding the MRL by approximately 20-fold. Dietary exposure assessment indicated a high-exposure case Hazard Quotient of 0.984 for adults. The proposed method provided a sensitive, matrix-specific analytical tool for routine SO 2 surveillance in dried vegetables.