Non-targeted discovery-based analysis for gas chromatography with mass spectrometry: A comparison of peak table, tile, and pixel-based Fisher ratio analysis

Chris E Freye; Patrick R Bowden; Margo T Greenfield; Bryce C Tappan

doi:10.1016/j.talanta.2019.120668

Non-targeted discovery-based analysis for gas chromatography with mass spectrometry: A comparison of peak table, tile, and pixel-based Fisher ratio analysis

Talanta. 2020 May 1:211:120668. doi: 10.1016/j.talanta.2019.120668. Epub 2019 Dec 28.

Authors

Chris E Freye¹, Patrick R Bowden², Margo T Greenfield², Bryce C Tappan²

Affiliations

¹ Los Alamos National Laboratory, M-7, High Explosives Science and Technology, Los Alamos, NM, 87545, USA. Electronic address: cfreye@lanl.gov.
² Los Alamos National Laboratory, M-7, High Explosives Science and Technology, Los Alamos, NM, 87545, USA.

PMID: 32070612
DOI: 10.1016/j.talanta.2019.120668

Abstract

The ability to discover minute differences between samples or sample classes for gas chromatography coupled to mass spectrometry (GC-MS) can be a challenging endeavor, especially when those differences are not a priori. Fisher ratio (F-ratio) analysis is an apt technique to probe the differences between GC-MS chromatograms. F-ratio analysis is a supervised, non-targeted, discovery-based method that compares two different samples (or sample classes) to reduce the GC-MS dataset into a hit list composed of class distinguishing compounds. Three different F-ratio techniques, peak table, tile, and pixel-based were used to "discover" nine non-native analytes that were spiked into gasoline at four different nominal concentrations of 250, 85, 25, 5 parts-per-million (ppm). For the tile and pixel-based F-ratio calculations, a novel methodology is introduced to improve the sensitivity of the F-ratio calculations while reducing false positives. Furthermore, we use a combinatorial technique using null class comparisons, termed null distribution analysis, to determine a statistical F-ratio cutoff for analysis of the hit lists. The pixel-based algorithm was the most sensitive method and was able to "discover" all nine spiked analytes at a nominal concentration of 250 ppm albeit with one false positive interspersed towards the bottom of the hit list. The pixel-based software was also able to "discover" more of the spiked analytes at the lower concentrations with seven of the spiked analytes "discovered" at 85 ppm, four of the spiked analytes "discovered" at 25 ppm, and one analyte "discovered" at 5 ppm.

Keywords: ANOVA; Fisher ratio; GC-MS; Gas chromatography; Mass spectrometry.