The Establishment of Tandem Mass Spectrometric Fingerprints of Phytosterols and Tocopherols and the Development of Targeted Profiling Strategies in Vegetable Oils

Phytosterols and tocopherols are essential for plant biochemistry, and they possess beneficial health effects for humans. Evaluating the tandem mass spectrometric (MS/MS) behavior of phytosterols and tocopherols is needed for the development of a qualitative and quantitative method for these biologically active plant metabolites. Herein, the MS/MS dissociation behavior of phytosterols and tocopherols is elucidated to establish generalized MS/MS fingerprints. MS/MS and multistage (MS³) analysis revealed common fragmentation behavior among the four tested phytosterols, namely β-sitosterol, stigmasterol, campesterol, and brassicasterol. Similar analysis was conducted for the tocopherols (i.e., alpha (α), beta (β), gamma (γ), and delta (δ)). As such, a universal MS/MS fragmentation pathway for each group was successfully established for the first time. Based on the generalized MS/MS fragmentation behavior of phytosterols, diagnostic product ions were chosen for the development of profiling methods for over 20 naturally occurring phytosterols. A precursor ion scan-triggered-enhanced product ion scan (PIS-EPI) method was established. Due to enhanced chromatographic peaks, multiple ion monitoring-triggered-enhanced product ion scan (MIM-EPI) was employed for confirmation. The screening approach was applied successfully to identify blinded samples obtained from standard mixtures as well as sesame and olive oils. The oil samples contain other phytosterols, and their successful identification indicates that, the generalized MS/MS fragmentation behavior is applicable to various structures of phytosterols. A similar approach was attempted for tocopherols and was only hindered by the low concentration of these bioactive metabolites present in the oil samples.