Development of a Liquid Chromatography-Tandem Mass Spectrometry Method for the Determination of Sulfite in Food

Sulfites are widely used food preservatives that can cause severe reactions in sensitive individuals. As a result, the U.S. FDA requires that sulfites be listed on the label of any food product containing >10 mg/kg (ppm) sulfite (measured as sulfur dioxide). Currently, the optimized Monier-Williams (MW) method (AOAC Official Method 990.28) is the most common approach for determining sulfite concentrations in food samples. However, this method is time-consuming and lacks specificity in certain matrices. An improved rapid, sensitive, and selective method has been developed using electrospray ionization (ESI) high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the determination of sulfite in various food matrices. A total of 12 different types of foods were evaluated. These included dried fruits and vegetables, frozen seafood, sweeteners, and juices. The matrix is extracted with a buffered formaldehyde solution, converting free and reversibly bound sulfite to the stable formaldehyde adduct, hydroxymethylsulfonate (HMS). Extracts are prepared for injection using a C18 SPE cartridge to remove any lipophilic compounds. HMS is then separated from other matrix components using hydrophilic interaction chromatography (HILIC) and detected using multiple reaction monitoring (MRM). The method was validated at 5 concentrations in 12 food matrices. Accuracy data showed spiked recoveries ranging from 84 to 115% in representative foods. Six commercially available sulfited products were analyzed using the LC-MS/MS method, as well as the MW method, to determine if differences exist.