Improving the extraction of headspace volatile compounds: development of a headspace multi-temperature solid-phase micro-extraction-single shot-gas chromatography/mass spectrometry (mT-HSSPME-ss-GC/MS) method and application to characterization of ground coffee aroma

Abstract

A multi-temperature headspace solid-phase micro-extraction-single shot-gas chromatography/mass spectrometry (mT-HSSPME-ss-GC/MS) method has been developed for headspace analysis. Three SPME fibers (50/30 μm DVB/CAR/PDMS) were used simultaneously for the extraction of volatile components from the headspace of a sample in three sample chambers at three different temperatures. A cryo-focusing technique was adopted to avoid peak broadening and to maximize resolution during the sequential thermal desorption of the SPME fibers prior to a ‘single-shot’ chromatographic run. The method was developed and validated on a model ethanolic flavor mixture, containing 81 components. Comparison of mT-HSSPME-ss-GC/MS (10 min incubation time, then 30 min extraction time at 22, 50, and 70 °C extraction temperatures) with conventional SPME-GC/MS at a fixed temperature of 22, 50, or 70 °C showed that the former gave a headspace GC profile of the flavor mixture that was much closer to that of the syringe (direct) injection profile. None of the conventional headspace SPME extraction profiles were a good match to the syringe injection profile. The same technique applied to the headspace of coffee grounds gave a plentiful headspace volatile component profile compared to that of a single SPME analysis at a fixed single extraction temperature (22, 50, and 70 °C). The average percent recovery (defined for each component as 100 × mT-SPME (22 °C + 50 °C + 70 °C) TIC peak intensity divided by the arithmetic sum of individual temperature SPME (22 °C, 50 °C, 70 °C) TIC peak intensities) was 89.8% and 132 components were detected by mT-SPME-ss-GC/MS in the headspace of coffee grounds.