Sulforaphane Determination by GC-MS Analysis: Mitigation of Thermal Degradation and Quality Evaluation of Two Broccoli-Based Supplements.

Sulforaphane (SF), the renowned hydrolysis product of glucoraphanin from broccoli, is known to undergo thermal degradation to 3-butenyl isothiocyanate (3-BITC) during gas chromatography-mass spectrometry (GC-MS) analysis. In this study, the effects on SF degradation associated with exposure to oven temperature during column transit, passage through the split/splitless injector, and through the transfer line to the mass spectrometer were investigated. Massive degradation was observed during column transit when the oven temperature exceeded 150 °C. Degradation during the passage through the injector increased with temperature, from 150 °C to 250 °C, and with decreasing split ratio, from 100:1 to 20:1. Conventional splitless conditions with the injector temperature set at 250 °C resulted in a degradation > 60%. Operating the GC-MS system with oven temperature below 150 °C prior to SF elution, an injector at 225 °C and a split ratio of 20:1, SF degradation was reduced to less than 1%. Under these optimized analytical conditions, the concentration of free SF in two broccoli-based dietary supplements was estimated based on external calibration and using 2,6-dimethylphenyl isothiocyanate as an internal standard. The GC-MS method proved to be a valuable tool for the quality evaluation of SF-labeled supplements integrated with the official EU ISO 9167:2019 HPLC-PDA glucosinolates analysis.