Improved method for identifying and quantifying olive oil phenolic compounds and their metabolites in human plasma by microelution solid-phase extraction plate and liquid chromatography–tandem mass spectrometry

Two methods based on solid-phase extraction (SPE) using traditional cartridges and microelution SPE plates (μSPE) as the sample pre-treatment, and an improved liquid chromatography coupled to tandem mass spectrometry (UPLC–MS/MS) were developed and compared to determine the phenolic compounds in virgin oil olive from plasma samples. The phenolic compounds studied were hydroxytyrosol, tyrosol, homovanillic acid, p-coumaric acid, 3,4-DHPEA-EDA, p-HPEA-EDA, luteolin, apigenin, pinoresinol and acetoxypinoresinol. Good recoveries were obtained in both methods, and the LOQs and LODs were similar, in the range of low μM. The advantage of μSPE, in comparison with SPE cartridges, was the lack of the evaporation step to pre-concentrate the analytes. The μSPE-UPLC–ESI-MS/MS method developed was then applied to determine the phenolic compounds and their metabolites, in glucuronide, sulphate and methylated forms, in human plasma after the ingestion of virgin olive oil.