Enabling cuboid-based fisher ratio analysis using total-transfer comprehensive three-dimensional gas chromatography with time-of-flight mass spectrometry

Abstract

Comprehensive three-dimensional (3D) gas chromatography with time-of-flight mass spectrometry (GC³-TOFMS) is a promising instrumental platform for the separation of volatiles and semi-volatiles due to its increased peak capacity and selectivity relative to comprehensive two-dimensional gas chromatography with TOFMS (GC×GC-TOFMS). Given the recent advances in GC³-TOFMS instrumentation, new data analysis methods are now required to analyze its complex data structure efficiently and effectively. This report highlights the development of a cuboid-based Fisher ratio (F-ratio) analysis for supervised, non-targeted studies. This approach builds upon the previously reported tile-based F-ratio software for GC×GC-TOFMS data. Cuboid-based F-ratio analysis is enabled by constructing 3D cuboids within the GC³-TOFMS chromatogram and calculating F-ratios for every cuboid on a per-mass channel basis. This methodology is evaluated using a GC³-TOFMS data set of jet fuel spiked with both non-native and native components. The neat and spiked jet fuels were collected on a total-transfer (100 % duty cycle) GC³-TOFMS instrument, employing thermal modulation between the first (¹D) and second dimension (²D) columns and dynamic pressure gradient modulation between the ²D and third dimension (³D) columns. In total, cuboid-based F-ratio analysis discovered 32 spiked analytes in the top 50 hits at concentration ratios as low as 1.1. In contrast, tile-based F-ratio analysis of the corresponding GC×GC-TOFMS data only discovered 28 of the spiked analytes total, with only 25 of them in the top 50 hits. Along with discovering more analytes, cuboid-based F-ratio analysis of GC³-TOFMS data resulted in fewer false positives. The increased discoverability is due to the added peak capacity and selectivity provided by the ³D column with GC³-TOFMS resulting in improved chromatographic resolution.

Keywords: Chemometrics; Comprehensive three-dimensional gas chromatography; Fisher ratio analysis; Non-targeted analysis; Time-of-flight mass spectrometry.