Direct accurate analysis of cysteinylated and glutathionylated precursors of 4-mercapto-4-methyl-2-pentanone and 3-mercaptohexan-1-ol in must by ultrahigh performance liquid chromatography coupled to mass spectrometry

•Method validation to determine CYSMP, GLUMP, CYSMH and GLUMH by UHPLCMS.•Direct analysis of filtered must with the consecutive injection of the spiked must.•Reproducibility was satisfactory (RSD between 3 and 13%, except for GLUMP 16%).•LOD in real-must was <1 μg L−1 for CYSMP and GLUMP and 2 and 7 μg L−1 for CYSMH and GLUMH.

A direct method for the quantitative determination in grapes of four known precursors of the varietal aromas of the thiol character of wine has been optimized and validated. A small volume of centrifuged and filtered must is directly injected in the ultrahigh liquid performance chromatography coupled to mass spectrometry system (UHPLC-MS–MS). Must sugars and other early eluting polar compounds are diverted to the waste, not entering the ion source. Cysteinyl (CYS) and glutathionyl (GLU) precursors from 3-mercaptohexanol (3MH) and 4-mercapto-4-methylpentanone (4M4MP) are separated in 5 min rendering narrow peaks (W1/2 < 9 s). No system performance degradation has been noticed in series of more than 200 injections. A standard addition procedure using the consecutive injection of a spiked sample made it possible to satisfactorily correct for matrix effects, with recoveries very close to 100% in all cases. Intermediate reproducibility was satisfactory (RSD between 1 and 10%), except for the glutathione-4-mercapto-4-methyl-2-pentanone (GLUMP) precursor, for which this value is around 20%. The limits of detection in real-must were below 1 μg L−1 for the precursors of the 4M4MP and for cysteine-3-mercaptohexan-1-ol (CYSMH) and glutathione-3-mercaptohexan-1-ol (GLUMH), 2 and 7 μg L−1, respectively, what is enough for the determination of these precursors in musts of any variety.

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