Simple and Rapid Method for the Quantitation of Trace-Level 3-Alkyl-2-methoxypyrazines in Fragrant Vegetable Oils by Gas Chromatography–Tandem Mass Spectrometry

3-Alkyl-2-methoxypyrazines (MPs) are characteristic aroma compounds found in fragrant vegetable oils, a type of specially processed oils with enhanced flavor. MP contents in these oils are usually at trace level, which makes their quantification a big challenge. In this work, we describe an optimized approach with a double-step acid/alkali extraction for the analysis of such compounds, namely, 3-isopropyl-2-methoxypyrazine, 3-isobutyl-2-methoxypyrazine, and 3-sec-butyl-2-methoxypyrazine, in those fragrant oils using gas chromatography-tandem mass spectrometry (GC-MS/MS). The sample preparation conditions including selections and percentages of acids, alkalis, and extraction solvents, as well as the stability of MPs, were optimized and examined. Method validation was conducted with a good linearity (r2 > 0.999), and average recoveries between 93.9 and 109.3% were achieved. The limit of detection ranged from 0.2 to 0.4 μg/kg, and the relative standard deviations varied from 0.4 to 12.2% for samples spiked with the MPs at different concentrations. Overall, the method satisfactorily meets the requirements for the measurement of trace-level MPs in the fragrant vegetable oils via odor activity value calculation, and the results indicate that the improved acid/alkali extraction method is suitable for the routine analysis of MPs in those vegetable oils.