Selectivity comparisons of comprehensive two-dimensional gas chromatography systems through the use of a standardized synthetic mixture

Comprehensive two-dimensional gas chromatography (GC × GC) systems can be broadly classified according to three important components: the modulator (cryogenic or flow-based), the column set (normal or reversed orthogonality), and the detector (MS or non-MS). In this work a methodology for the comparison of GC × GC systems has been developed. This method is based on the use of a synthetic mixture of chemicals called the Century Mix, which provides a fingerprint of the relative retention coordinates of the mixture components on each system. These retention coordinates are then normalized through the use of temperature-programmed retention indexing (TPRI), and the comparison of these TPRI values from one system to another can establish the degree to which they are similar. A metric called the retention index correlation (RIC) is introduced to measure the goodness-of-fit between systems. In the first phase of the project, the variation of operating parameters (such as flow rate, temperature programming rate, and modulation period) were investigated to determine their impact on the reproducibility of the TPRI values on a single instrument. In the second phase of the project, Century Mix fingerprints were generated on 11 different GC × GC systems, and pairwise comparisons between thermal and flow-based systems with the same stationary phase combination yielded RIC plot r2 values above 0.999. Advanced data processing techniques (such as principal component analysis, and dendrogram and heatmap plots) were also used to characterize and classify the bidimensional retention maps as a collective group. The method successfully demonstrates the ability to distinguish between significant differences in systems, and will ultimately be helpful in establishing effective comparisons in larger-scale studies.