Using solid-phase extraction to facilitate a focused tile-based Fisher ratio analysis of comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry data: comparative analysis of aerospace fuel composition.

Tile-based Fisher ratio (F-ratio) analysis of comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOFMS) data is a powerful, supervised discovery methodology for pinpointing sample class-distinguishing analytes between two or more sample classes. Herein, we extend this analytical methodology to focus upon specific chemical groups in kerosene-based aerospace fuel using solid-phase extraction (SPE). Treating samples with SPE removes specific compounds depending on the SPE stationary phase (i.e., silica), creating an altered "pass" sample, identical to the original "neat" sample except for the extracted compounds. Application of F-ratio analysis to the neat samples against the pass samples provides global discovery with a numerically sorted hit list of all analytes affected by the SPE procedure. Sections of GC × GC-TOFMS data from the top analyte hits are reconstructed to form a "stitch" chromatogram to visualize the sample class-distinguishing compounds, revealing excellent agreement with the extract chromatogram. Additionally, utilizing the four-grid tiling scheme developed for tile-based F-ratio analysis, we demonstrate a tile-based pairwise analysis method, referred to as 1v1 analysis, to discover analytes that differ in concentration between two fuel chromatograms. Application of 1v1 analysis is highly efficient since replicates do not necessarily need to be run on the GC × GC-TOFMS instrument, which is beneficial for sample-limited applications. The 1v1 analyses discovered most of the same features as F-ratio analysis, ranging from 69 to 81% of the features discovered by F-ratio analysis while requiring one-sixth the data. Lastly, the overall methodology is applied to three candidate rocket fuels to better understand the compound class-distinguishing differences. The separate hit lists produced for high-concentration bulk hydrocarbon differences and low-concentration level polar compound differences provided valuable insight into these candidate rocket fuels.