Evaluation of iGDGT carbon isotope fractionation in high performance liquid chromatography

Careful assessment of fractionation associated with High Performance Liquid Chromatography (HPLC) is essential for ensuring accurate carbon isotope ratio (??13C) measurements. Here we report these effects for orthogonal dimensions of HPLC separation of iGDGTs. We observe 13C fractionation during normal phase separations using an amino-bonded stationary phase, finding that the heavy isotope preferentially elutes relative to its lighter counterpart, while negligible fractionation occurs during reverse phase HPLC. We argue that the fractionation during normal phase is caused by diminished Van der Waals attraction between 13C-enriched iGDGTs and the stationary phase and appears to depend on the structure of the analyte. Ultimately, these results emphasize the necessity of complete peak collection to preserve the isotopic character of iGDGTs.

Automated summary

Careful assessment of fractionation associated with HPLC is essential for accurate ??13C measurements. This study examines the effects of fractionation in orthogonal dimensions of HPLC separation of iGDGTs. 13C fractionation is observed during normal phase separations, but not during reverse phase HPLC. The fractionation in normal phase is attributed to diminished Van der Waals attraction between 13C-enriched iGDGTs and the stationary phase.