Stable Carbon Isotope Ratios (δ 13 C Values [‰]) of Individual Sterols in the Oils of C 3 , C 4 , and CAM Plants.

The compound-specific determination of δ 13 C values [‰] by gas chromatography interfaced with isotope ratio mass spectrometry (GC-IRMS) is a powerful analytical method to indicate minute but relevant variations in the 13 C/ 12 C ratio of sample compounds. In this study, the δ 13 C values [‰] of individual sterols were measured in eleven different oils of C 3 , C 4 , and CAM plants ( n = 33) by GC-IRMS. For this purpose, a suitable acetylation method was developed for sterols. Nine of the eleven phytosterols identified by GC with mass spectrometry (GC/MS) could be measured by GC-IRMS. The δ 13 C values [‰] of individual sterols and squalene of C 3 plant oils were between 3‰ and >16‰ more negative (lighter in carbon) than in C 4 and CAM oils. We also showed that the blending of C 4 oils into C 3 oils (exemplarily conducted with one olive and one corn oil) would be precisely determined by means of the δ 13 C value [‰] of β-sitosterol.