Introduction
As a readily-automated, fast, solvent-free technique, solid‑phase microextraction (SPME) has become widely adopted for a broad range of samples and applications, including analysis of foods and beverages, profiling of aromas and off-odours, as well as environmental, clinical and industrial investigations.
This application range is supported by 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.
Sample preconcentration is a powerful approach to dealing with this issue. Following sample extraction, analytes desorbed from the SPME fiber are first focused onto a narrow, cryogen-free, sorbent-packed focusing trap. By using this SPME–trap method, analytes are enriched/preconcentrated before being injected into the GC-MS in a narrower band, improving peak shape (especially for the early-eluting compounds), and so improving sensitivity.
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