Cumulative solid phase microextraction sampling for gas chromatography-olfactometry of Shiraz wine

Solid phase microextraction (SPME) coupled to gas chromatography-olfactometry (GC-O) is now commonly used for determination of aroma-active compounds, but the method sensitivity and selectivity is restricted by the small volume and limited type of fibre coating phases. In an attempt to enhance the method performance, a cryogenic trapping (CT) approach was investigated in this study by coupling multiple SPME sampling events for wine headspace using GC-O analysis. By performing multiple SPME sampling employing different chemical polymer coatings, desorbed solute from the integrated sampling is accumulated by the CT at the front section of a Wax separation capillary column prior to chromatographic analysis. Results show that the CT was capable of retaining apolar alkane volatiles of decane and greater, and tested polar alcohols, including methanol. Chromatographic signals eluting later than the ethanol peak were found to progressively increase in response, and correlated well, with the cumulative number of SPME samplings. The approach was developed for GC-O screening of potent odorants in Shiraz wine collected from fibre coatings of polyacrylate (PA) and the triple-phase coated polydimethylsiloxane/divinylbenzene/carboxen (PDC). The aromagram for solute derived from a combined introduction of both PA plus PDC fibres (i.e. sequential fibre introduction into the injector; termed as PADC) compared well to the sum of those sampled by using a single fibre coating alone, which comprised of odorants derived from both fibre coatings. Accumulation in the CT of volatile solutes derived from up to 6 repeat PADC sampling events revealed a similar pattern of their aromagrams, though with stronger olfactory stimulus response. This study demonstrated a simple and effective way for enhancing SPME sensitivity and potentially less discrimination during the analysis of wine volatiles. However, the single dimensional GC separation method requires development of an improved separation strategy to better separate individual compounds.

► Multiple SPME sampling increases the total analyte mass delivered to the GC column.
► Use of different fibre coatings with multiple sampling better integrates the total volatile headspace of the wine sample.
► Sensory assessment using GC-O provides improved evaluation for minor components due to increased solute mass.
► GC–MS and GC-FID/-O analyses are correlated by using retention index methods.