QUANTITATIVE-EVALUATION OF CARBON ISOTOPIC FRACTIONATION DURING REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

The fractionation of C-13 during low-performance preparative LC and hi gh-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 materia l, 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 fractiona tion. These results emphasize the importance of quantitative peak coll ection for high-precision IR-MS studies, particularly the first part o f the peak where the isotope ratio changes rapidly.