Improved solid-phase extraction procedure for the isolation and in-sorbent pentafluorobenzyl alkylation of polyfunctional mercaptans. Optimized procedure and analytical applications

A fast method for the determination of aroma-powerful polyfunctional thiols at ng L(-1) level has been developed. Mercaptans are selectively retained in a 50mg solid-phase extraction cartridge and derivatization takes place in the same cartridge at room temperature (25 degrees C) in 20 min by adding small amounts of pentafluorobenzyl bromide (PFBBr) and a strong alkali: 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The corresponding derivatives are further eluted and determined by gas chromatography-negative ion mass spectrometry (GC-NCI-MS). Isolation, derivatization, clean-up, elution and calibration conditions were examined. Carrying the reaction in the cartridge makes it possible to use water and non-polar reagents simultaneously, to avoid large volumes of toxic solvent, and to eliminate the excess of reagent. This was last accomplished by the reaction with mercaptoglycerol and further rinsing with a hydromethanolic solution. The method makes it possible to simultaneously determine 2-methyl-3-furanthiol (MF), 2-furfurylthiol (2-furanmethanethiol) (FFT), 4-mercapto-4-methyl-2-pentanone (MP) (as its methoxime), 3-mercaptohexylacetate (MHA) and 3-mercaptohexanol (MH). Absolute limits of detection were 0.2 (MF), 0.1 (FFT), 0.1 (MP), 0.3 (MHA) and 2 (MH) ng L(-1). Repeatability (1%