Fractionation of carbon isotopes during acetylation of alcohols

抄録

Compound-specific isotope analysis (CSIA) of organic compounds with a gas chromatograph - isotope ratio mass spectrometer (GC-IRMS) has been employed as one of the most powerful techniques in molecular isotope studies. This analysis is applicable not only for volatile and non-polar compounds (e.g., hydrocarbons), but also for non-volatile and polar compounds (e.g., alcohols and fatty acids) when such low volatility and high-polarity are reduced by derivatization. However, derivatization frequently causes isotopic fractionation, which considerably reduces the accuracy on the isotope ratios determined. In the present study, we investigated change in the carbon isotope ratio (δ¹³C value) of 1-hexadecanol that acetylated with a variable molar balance between substrate and derivative reagent, to illustrate the fractionation of carbon isotopes during acetylation of alcohols. The results illustrate that the δ¹³C values of acetyl group of the 1-hexadecanol derivative asymptotically change from −38.8‰ to −60.8‰, with the molar balance decreasing from 1:10 to 1:30000 in the acetylation. Moreover, the isotopic fractionation factor (α) calculated is 0.9711 if the Rayleigh fractionation model is applied. Thus, we demonstrated that there is a large fractionation of carbon isotopes in the acetylation of alcohols, and that the degree of fractionation is correlated with the molar balance between substrate and derivative reagent of the acetylation.