Sulfite Quantification in Foods and Beverages Using Single Quadrupole LC-MS

Importance of the Topic

Sulfites are widely used as antioxidants and bleaching agents in foods and beverages, including dried fruits and wines. Regulatory agencies require accurate labeling and quantification of sulfites due to potential allergic reactions. Developing reliable, efficient methods for sulfite analysis is critical for consumer safety and regulatory compliance.

Objectives and Study Overview

This study aimed to establish a quantitative method for determining sulfite levels in dried fruits and wines using a single quadrupole UHPLC-MS system. Key goals included eliminating dichloromethane from sample preparation, improving safety, and ensuring compliance with the US FDA labeling threshold of 10 mg/kg of sulfites.

Methodology and Instrumentation

Sample preparation involved grinding frozen dried fruit or diluting wine with 0.2% formaldehyde solution to convert sulfite to hydroxymethylsulfonate (HMS). Ultrasonic extraction and centrifugation yielded clear extracts.
SPE cleanup used C18 cartridges conditioned with methanol and formaldehyde solution under positive pressure (Biotage PRESSURE+). Lipids were removed without dichloromethane. After discarding the first eluate, the next fraction was heated at 80 °C for 30 minutes to complete derivatization.
For analysis, 100 µL of cooled eluate was mixed with internal standard solution and acetonitrile, filtered, and injected into the LC-MS.

Used Instrumentation

• UHPLC system: Nexera X3
• Column: InertSustain AX-C18, 100 mm × 2.1 mm, 3.0 µm
• Mobile phases: 2 mM ammonium formate with 0.1% formic acid (A) and acetonitrile with 0.1% formic acid (B)
• Gradient: 30% to 100% B over 10 minutes, then re-equilibration
• Flow rate: 0.2 mL/min; column temperature 30 °C; injection 2 µL
• Mass spectrometer: LCMS-2050 single quadrupole with ESI/APCI dual ionization in negative mode
• Detection: Selected ion monitoring of m/z 111 (HMS) and m/z 113 (internal standard)

Main Results and Discussion

Calibration curves for HMS showed excellent linearity (R2 > 0.999) across 0.02 to 2 ppm. Dried fruit samples revealed non-detectable sulfites in raisins, 14.8 ppm in pineapple, and 10.4 ppm in mango expressed as SO2 equivalents. Wine samples exhibited low levels in white wine (0.2 ppm) and non-detectable in red wine. Recovery tests at the 10 mg/kg level yielded rates between 95% and 104%, meeting regulatory requirements.
MS chromatograms confirmed clear separation and reliable quantification of HMS and internal standard peaks without interference.

Benefits and Practical Applications

This method offers a safer sample preparation by avoiding regulated solvents and streamlining cleanup with positive pressure SPE. The single quadrupole LC-MS approach delivers cost-effective, accurate sulfite measurements suitable for routine quality control in food and beverage industries.

Future Trends and Opportunities

Potential developments include applying the protocol to broader food matrices, integrating automated sample preparation workflows, and expanding the method for multi-residue analysis of other additives. Advances in detector sensitivity and high-throughput platforms will enhance monitoring capabilities.

Conclusion

The presented single quadrupole LC-MS method achieves accurate sulfite quantification in dried fruits and wines at regulatory levels. High recovery rates, robust calibration, and safe, dichloromethane-free preparation make it well suited for routine compliance testing.

References

1 Carlos KS and de Jager LS. Determination of sulfite in food by liquid chromatography tandem mass spectrometry: Collaborative study. Journal of AOAC International 100(6):1785–1794, 2017.
2 U S Food and Drug Administration. Method C-004.03 Determination of Sulfites in Food using LC-MS/MS, 2021.