Multiple Dimensions of Separations: SPME with GCxGC and GCxGC-TOF-MS

Two-dimensional gas chromatography (GCxGC) and GCxGC-time of flight (TOF)-mass spectrometry (MS) have received increasing attention as powerful techniques for separation and analysis of extremely complex mixtures. Over the past 20 years, solid-phase microextraction (SPME) has become a staple sample preparation technique for a large variety of GC analyses. With a few additional considerations, SPME is combined readily with GCxGC or GCxGC TOF-MS to provide easily automated and solvent-free sample preparation. This combination provides up to six dimensions of separation power in analytical method development that can be used to provide needed selectivity or can cause unwanted selectivity through sample losses or slow kinetics. In this article, the combination of SPME with GCxGC and GCxGC-TOF-MS is discussed using mixtures of solvents as example analytes. Optimization of the injection process is emphasized, as extractions remain generally the same as in traditional SPME-GC. To ensure good peak shapes, the injection liner, carrier gas flow rate, and column temperatures must be optimized carefully. The differences in carrier gas flow optimization between GCxGC with flame ionization detection and GCxGC-TOF-MS also are discussed.