Sequential combination of solid-phase sorbents to enhance the selectivity of organosulfur compounds for flavour analysis.

Flavour analysis remains challenging due to the range of selectivity demands, from the extraction of multiclass volatile compounds to the purification of low-concentration odourants (e.g. organosulfur compounds) amidst the high food matrix noise. In this study, the varying selectivities of solid-phase extraction (SPE) were leveraged upon for both multiclass and organosulfur compound analysis, using coffee as a model matrix. Polymeric SPE (Bond Elut ENV) was screened for significant (p < 0.05) parameters affecting the recovery of 37 multiclass compounds, and the most influential parameters were optimised using a Box-Behnken design (elution solvent of 67:33 dichloromethane:ethyl acetate, loading pH of 4.8, and wash solvent of water). Following this, low-concentration organosulfur compounds which were challenging to detect in the complex coffee matrix were purified by adding a sequential SPE step for selectivity. A silver-based ligand-exchange SPE step (MetaSEP IC-Ag) was optimised for organosulfur compound recovery (wash solvents of dichloromethane and 43% acetonitrile in dichloromethane, elution solvent of 90 mmol/L 1,4-dithiothreitol in dichloromethane). This was found to be complementary to polymeric SPE's matrix clean-up effect (which improved average organosulfur compound recovery by 5.45 times). Finally, both multiclass and sequential organosulfur extraction techniques demonstrated good performance in terms of reproducibility (1.0-9.0%) and linearity (R2 > 0.995), allowing for the detection of 3-mercapto-3-methylbutyl formate (3.741 ± 0.387 ng/mL) in coffee samples. In conclusion, this study highlights the potential for SPE to address a variety of complex flavour analysis demands with the appropriate selection and combination of solid-phases.