Evaluation of quadrupole-time-of-flight mass spectrometry in comprehensive two-dimensional gas chromatography

Quadrupole time-of-flight mass spectrometry (Q-TOFMS) has been evaluated with respect to its applicability in comprehensive two-dimensional gas chromatography (GC × GC). At a maximum acquisition frequency, while approximately 50 full accurate mass spectra on disk were acquired per s (50 Hz) in scan mode, the sampling rate in target mode (MS/MS) was strongly dependent on the number of target ions selected. The number of selected precursor ions per time window proportionally decreased the acquisition rate for each ion; one precursor ion ≅31.35 Hz; two ions ≅16.68 Hz; and for 8 precursor ions, a sampling rate of just 4.18 Hz was found. When Q-TOFMS was used in simultaneous mode, where in addition to the acquisition of target ion MS/MS signals, it also collects the full mass spectrum, sampling rates were even lower. It is demonstrated that Q-TOFMS generates sufficient data points over each peak in GC × GC operation in scan mode using TOFMS acquisition only, or is able to collect sufficient data points for relatively wide chromatographic peaks (≥600 ms) in the target mode (MS/MS), however only if one or two precursor ions are selected per time window. Mass accuracy was found to perform within specification (<5 ppm), even for the fastest acquisition operation (50 Hz). Spectral deconvolution is demonstrated to work better in GC × GC than in 1D GC mode. Data visualisation in target GC × GC mode presents difficulties when there are overlapping target windows comprising different numbers of precursor ions.