Accuracy and precision of gas chromatography/combustion isotope ratio mass spectrometry for stable carbon isotope ratio measurements

Abstract

AbstractWe evaluated the precision, accuracy and linearity of three commercial gas chromatography/combustion isotope ratio mass spectrometry (GC/C‐IRMS) instruments in regard to stable carbon isotope ratio measurements of fatty acids with 13C enrichment levels ranging from natural abundance to 924‰, in comparison to measurements by conventional gas isotope ratio mass spectrometry (GIRMS). Memory effect was also evaluated with a fatty acid mixture containing methyl myristate and methyl stearate at natural abundance levels of 13C but methyl palmitate at 13C enrichment levels of 460 or 924‰. At natural abundance, the δ13C values of fatty acids measured by the GC/C‐IRMS instruments were reproducible to within 0.34‰ (range: 0.11‰ to 0.32‰) and accurate to −0.38±0.40‰ (mean difference ± standard deviation; range: −0.03±0.25‰ to −0.84±0.39‰). At enrichment levels of 13C (23 to 924‰), the δ13C values were reproducible to within 1.48‰ (range 0.20‰ to 1.00‰) and accurate to −1.11±3.16‰ (range: −1.02±3.23‰ to +4.56±13.42‰). Stable carbon isotope ratio measurements by all three GC/C‐IRMS instruments were found to be linear from −30 to 924‰ (r2 > 0.9999; p ⩽ 0.004) in comparison to those measured by GIRMS. Significant memory effect was found in only one system. Based on our data, the GC/C‐IRMS instruments can provide linear, precise and accurate stable carbon isotope ratio measurements and require only pico‐and nanogram quantities of samples.