Comparison of gas and liquid chromatography (GC, LC) coupled with isotope ratio mass spectrometry (IRMS): A case study on rice amino acids

Compound-Specific Isotope Analysis (CSIA) of amino acids (AAs) is increasingly applied in food authentication and environmental studies, where precise and accurate δ¹³C measurements are essential. This study systematically compares the performance of Gas Chromatography-Combustion-Isotope Ratio Mass Spectrometry (GC-C-IRMS) and Liquid Chromatography coupled to Isotope Ratio Mass Spectrometry (LC-co-IRMS) for δ¹³C analysis of essential and non-essential AAs. The GC-C-IRMS showed high analytical precision, with standard deviations typically below 0.5 ‰ for standard AAs and 0.8 ‰ for rice samples, in close agreement with EA-IRMS reference values. The LC-co-IRMS, while generally reliable, exhibited higher variability, with deviations up to 1.6 ‰ for standard AAs and 1.9 ‰ for samples. The GC-C-IRMS also provided better chromatographic resolution, shorter run times, and broader amino acid coverage but involved complex workflows, including derivatization and the use of hazardous reagents. In contrast, LC-co-IRMS offered a simpler, safer protocol with fewer correction steps, though with longer analysis times, reduced throughput, and higher water consumption. Despite these trade-offs, both methods yielded comparable δ¹³C values overall, with some differences for specific AAs. This study finds GC-C-IRMS as suitable for high-precision, high-throughput applications, while LC-co-IRMS is more appropriate for simplified, sustainable workflows, with method selection depending on research purposes and operational priorities.