Determination of volatile thiols in roasted coffee by derivatization and liquid chromatography-high resolution mass spectrometric analysis

A fast derivatization/extraction method followed by LC-ESI-HRMS was optimized for the determination of volatile thiols in roasted coffee powder, using ebselen as the derivatization agent. The analytical conditions were optimized on real coffee matrix, which was spiked with representative volatile thiols. The method sensitivity, precision, accuracy and selectivity were evaluated by using representative standard thiols. Estimated LOQs were between 0.02 and 14.8 ng/kg for the thiols evaluated. Recoveries and intra-day and inter-day RSD values obtained in coffee matrix were in general around 40% and between 11 and 30%, respectively. The optimized and validated method was applied to real coffee samples. According to the established identification criteria, target thiols were identified and quantified in coffee powder samples. Among them, 4-mercapto-1-butanol and 2-methyl-3-tetrahydrofuranthiol were identified and quantified for the first time in roasted coffee. Moreover, an approach based on the formation of a diagnostic product ion was applied to detect non-target thiols, allowing the detection of nineteen thiol derivatives, fourteen of them were tentatively identified on the basis of their molecular formula. Some of them, such as methanethiol and 3-mercapto-3-methylbutyl acetate were known to be present in coffee volatile fraction, while the rest were not previously described in this product.