Multiplexed dual first-dimension comprehensive two-dimensional gas chromatography–mass spectrometry with contra-directional thermal modulation

A multiplexed dual-primary column comprehensive two-dimensional gas chromatography–mass spectrometry approach (2GC × GC–MS) is introduced. The approach splits injected samples into two first-dimension columns with different stationary phases, and recombines the two streams into one second-dimension column that terminates at a single detector. The approach produces two two-dimensional chromatograms for each injection, and is made possible by using a dual-stage modulator operated in contra-directional modulation mode. The dual two-dimensional chromatograms produced by this single detector system provide complementary information due to selectivity differences between the three separation columns used in the column ensemble. An aged Australian tea tree (<i>Melaleuca alternifolia</i>) essential oil was analyzed to demonstrate the 2GC × GC–MS approach. The number of compounds separated by each of the GC × GC separations in the 2GC × GC experiment is comparable to conventional GC × GC experiments with matching column configurations. Robust peak assignment was possible for this sample based on the combination of MS library matches and multiple linear retention index searching. Forty-nine components (22 unique) were identified using a <i>non-polar</i> × <i>mid-polar</i> column combination and 34 components (7 unique) were positively identified using a <i>polar</i> × <i>mid-polar</i> column combination. Twenty-seven peak assignments were corroborated by positive identification in both of the multiplexed separations.