Rapid liquid chromatography–tandem mass spectrometry analysis of 4-hydroxynonenal for the assessment of oxidative degradation and safety of vegetable oils

Highlights: • A novel method for the UPLC–MS/MS analysis of 4-HNE is described. • The method allows complete analysis of a vegetable oil in 21 min with LOD ≤ 7 ng g⁻¹. • Excellent recovery from lipid matrices without deuterium-labeled internal standards. • Requires straightforward sample manipulation and routine equipment. • Allows fast, reliable, cost-effective assessment of safety and quality of oils. - Abstract: A novel method for the UHPLC–MS/MS analysis of (E)-4-hydroxynonenal (4-HNE) is described. The method is based on derivatization of 4-HNE with pentafluorophenylhydrazine (1) or 4-trifluoromethylphenylhydrazine (2) in acetonitrile in the presence of trifluoroacetic acid as catalyst at room temperature and allows complete analysis of one sample of vegetable oil in only 21 min, including sample preparation and chromatography. The method involving hydrazine 1, implemented in an ion trap instrument with analysis of the transition m/z 337 → 154 showed LOD = 10.9 nM, average accuracy of 101% and precision ranging 2.5–4.0% RSD intra-day (2.7–4.1% RSD inter-day), with 4-HNE standard solutions. Average recovery from lipid matrices was 96.3% from vaseline oil, 91.3% from sweet almond oil and 105.3% from olive oil. The method was tested on the assessment of safety and oxidative degradation of seven samples of dietary oil (soybean, mixed seeds, corn, peanut, sunflower, olive) and six cosmetic-grade oils (avocado, blackcurrant, apricot kernel, echium, sesame, wheat germ) and effectively detected increased 4-HNE levels in response to chemical (Fenton reaction), photochemical, or thermal stress and aging, aimed at mimicking typical oxidation associated with storage or industrial processing. The method is a convenient, cost-effective and reliable tool to assess quality and safety of vegetable oils