Multi-step enrichment (MSE®) enhances the performance of headspace–SPME–trap (HS– SPME–trap). The aroma profile of olive oil was analysed using GC–MS to identify volatile and semi-volatile organic compounds (VOCs/SVOCs). SPME extraction was performed using an automated multi-mode sample extraction and enrichment platform (Centri®) containing a sorbent-based focusing trap to retain and preconcentrate analytes. Multiple sequential extractions were loaded onto the same trap from the same vial to produce an enriched sample profile. The technique was used to distinguish between olive oil samples using ChromCompare+, software that transforms complex data into meaningful results.
Introduction
SPME is a solvent-free sample preparation technique in which samples are extracted by immersive or headspace sampling. SPME is used for a wide range of sample classes and applications, including foods and beverages, environmental, clinical, industrial and defence. This is made possible by the availability of a variety of SPME fiber phases (including PDMS, polyacrylate and multi-phase DVB/CAR/PDMS), which allow analyte selectivity to be optimised. However, workflows for conventional (‘direct’) SPME sometimes suffer from its limited sensitivity. This stems from the small volume of sorptive phase on the fiber (typically ~0.5 μL of PDMS), as well as from the relatively slow heating rate of commonly used GC injection ports, resulting in broad peaks.
The primary focus of this work was to assess the incremental gain in peak area, and therefore sensitivity, for a range of representative analytes in olive oils when using the automated Centri sample extraction and enrichment platform. Linear retention index values were calculated to confirm peak identification with MS results from the NIST17 database. A commonly used multi-phase fiber for edible oils (divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/ PDMS)) was selected for extraction and, as such, both absorptive and adsorptive processes took place with the potential for lower volatility compound displacement using longer sampling times. A balance between extraction time and sensitivity (across the broad volatility range of compounds in the aroma profile) needed to be achieved. A single sample extraction was compared to cumulative three-fold and six-fold extractions from the same vial using various incubation times. Furthermore, the advantage of using shorter extraction times for MSE compared to an equivalent single extraction time is shown; e.g. 3 x 10 minutes (total extraction time 30 mins) is compared to a single 30-minute extraction time. The successful application of MSE to the distinction of extra virgin olive oil, virgin olive oil and lampante olive oil has been extensively shown by research conducted by Purcaro et al.1,2 and is presented here
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