Quantitative evaluation of carbon isotopic fractionation during reversed-phase high-performance liquid chromatography

The fractionation of C-13 during low-performance preparative LC and high-performance LC is reported quantitatively for methyl palmitate and using high-precision isotope ratio mass spectrometry (IR-MS). For both preparative and high-performance analytical columns, C-13 enrichment is about 7 parts per thousand greater than the parent starting material, drops sharply in the first section of the peak and then settles to a value about 1 parts per thousand below that of the starting material. Recycling over a single HPLC column did not induce greater fractionation. These results emphasize the importance of quantitative peak collection for high-precision IR-MS studies, particularly the first part of the peak where the isotope ratio changes rapidly.