Methyl and ethyl chloroformate derivatizations for compound-specific stable isotope analysis of fatty acids-II

Abstract

Methyl (MCF) and ethyl chloroformate (ECF) derivatizations are potentially useful for rapid and simple esterifi cation (i.e., at room temperature for 5 min) prior to compound-specifi c stable isotope analysis (CSIA) of fatty acids. In this study, we have used acetonitrile as an organic solvent in the esterifi cation process to improve the yields of derivatives, and we evaluated whether the improved esterifi cation is suitable for carbon and hydrogen CSIA. Six saturated (14:0, 16:0, 18:0, 20:0, 22:0, and 24:0) and three unsaturated (18:1 n-9, 18:2 n-6, and 18:3 n-3) fatty acids were used in this study. The yields of derivatives are 67 – 107% for MCF and 84 – 89% for ECF derivatizations, which are approximately twice the yields obtained in MCF and ECF derivatizations that did not use acetonitrile. The accuracy of the CSIA is < ± 0.4‰ (1σ) for carbon and < ± 11‰ (1σ) for hydrogen, with no signifi cant differences in these uncertainties observed for saturated and unsaturated fatty acids. Thus, MCF and ECF derivatizations using acetonitrile are suitable for the CSIA of fatty acids.