The peak capacity gain (Gn) of a GC×GC system is the ratio of the system peak capacity to that of an optimized one-dimensional GC analysis lasting the same time and providing the same detection limit. A near-theoretical maximum in Gn has been experimentally demonstrated in GC×GC-TOF based on a 60m×0.25mm primary column. It was found that Gn was close to 9 compared to the theoretical maximum of about 11 for this system. A six-sigma peak capacity of 4500 was obtained during an 80min heating ramp from 50°C to 320°C. Using peak deconvolution, 2242 individual peaks were determined in a Las Vegas runoff water sample. This is the first definitive experimental demonstration known to us of an order-of-magnitude Gn. The key factors enabling this gain were: relatively sharp (about 20ms at half height) reinjection pulses into the secondary column, relatively long (60m) primary column, the same diameters in primary and secondary columns, relatively low retention factor at the end of the secondary analysis (k≅5 instead of 15, optimal for ideal conditions), optimum flow rate in both columns, and helium (rather than hydrogen) used as the carrier gas. The latter, while making the analysis 65% longer than if using H2, was a better match to the reinjection bandwidth and cycle time.

We report a method for the peak list alignment of gas chromatography high resolution time-of-flight mass spectrometry data. The alignment is performed in a z-score transformed retention time domain to standardize a peak distribution across samples. A mixture score is developed to assess the similarity between two peaks by simultaneously evaluating the mass spectral similarity and the closeness of retention time. An analysis of experimental data acquired under three different flow rates indicates that the proposed method is able to correctly align the heterogeneous data. The effectiveness of method is further validated by analyzing experimental data of multiple mixtures of metabolite extract from mouse liver with 28 spiked-in acids. All of the detected spiked-in acids were correctly aligned. A statistical test correctly detected the concentration differences of the spiked-in compounds between sample groups using the alignment table. The area under curve (AUC) value in the receiver operating characteristic (ROC) curve is larger than 0.85 in all three of the compared sample groups, indicating a high accuracy of peak alignment and supporting the potential application of the proposed method for metabolomics projects such as biomarker discovery.

Optimal heating rate is the one resulting in the shortest analysis time for achieving a required separation performance of a column. The previously recommended default heating rate (RT,Def) was optimal for temperature‐programmed gas chromatography analyses in constant pressure mode. It has been shown herein that the same recommendation can be extended to constant flow mode with fixed heating rate (RT). The numerical value of RT,Def has been herein rescaled from previous 100.28em∘C/tnormalM (10°C per void time) where tM was measured at 50°C, to 120.28em∘C/tnormalM with tM measured at 150°C—a round number in the middle of the gas chromatography temperature range, chosen as a reference temperature for numerical values of all temperature‐dependent gas chromatography parameters. It has been experimentally found based on theory developed herein that RT,Def=120.28em∘C/tnormalM is optimal for columns with φ=0.001 (φ=dnormalf/d is dimensionless film thickness, d and df  are the column internal diameter and film thickness, respectively) in constant pressure mode and constant flow mode with fixed RT. Theory shows that, for arbitrary φ, RT,Def=12(1000φ)0.090.28em∘C/tnormalM. The theory also shows that the fixed RT is optimal for constant pressure mode. In constant flow mode, however, the optimal RT should gradually increase with increasing temperature (T). The optimal theoretical curves RT(T), different for different flow rates, were found. However, only the optimization of the fixed RT was experimentally evaluated due to limited capability of existing gas chromatography instrumentation and resources. It has been shown that the separation‐time tradeoff in constant pressure mode is slightly better than that in constant flow mode. The experimental data are compiled in the Supporting information.