Comparability and reproducibility of biomarker ratio values measured by GC-QQQ-MS

The Norwegian Geochemical Standard North Sea Oil-1 was analyzed by gas chromatography triple quadrupole mass spectrometry (GC-QQQ-MS) on two instruments using independently developed analytical methods. Biomarker ratios determined by GC-QQQ-MS were compared to each other and to previously reported values determined by gas chromatography single quadrupole mass spectrometry (GC-Q-MS) or flame ionization detection (GC-FID). Hopane, sterane, and tricyclic ratio values determined by GC-QQQ-MS in multiple reaction monitoring (MRM) mode are comparable to each other, but their comparability to reported values measured by GC-Q-MS in selected ion monitoring (SIM) mode depends in part on whether the compounds in the ratio have similar or dissimilar mass spectral responses. For example, sterane and hopane stereoisomer thermal maturity ratios measured by GC-QQQ-MS in MRM mode agree with previously reported GC-Q-MS SIM values, but an offset is observed for ratios of rearranged hopanes or steranes to their non-rearranged counterparts. Triaromatic steroid, monoaromatic steroid, phenanthrene, and methylphenanthrene ratios measured by GC-QQQ-MS are comparable to each other and to reported GC-Q-MS SIM values. The carbon preference index is comparable across GC-QQQ-MS measurements and reported GC-FID values, while comparability is more variable for other ratios based on pristane, phytane, and/or n-alkanes. Comparability of variably acquired biomarker data could be enhanced in the future by developing instrument- and ratio-specific correction factors or by modifying GC-QQQ-MS parameters and MRM transitions to more closely reproduce previously reported values.