An improved method to determine the absolute abundance of glycerol dibiphytanyl glycerol tetraether lipids

Isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) are specific membrane lipids derived from archaea, one of the three domains of life. These lipids can be used as biomarkers in paleo-ecological studies. GDGTs can be analyzed by high performance liquid chromatography (HPLC)/mass spectrometry (MS). To quantify GDGTs, external standard curves were run monthly on the HPLC/MS. However, external standard curves represented a snapshot and do not adjust for changes during storage, dissolution and manipulation of samples or drifts in HPLC/MS conditions. To measure absolute GDGT abundances more accurately, we tested the use of a newly synthesized C46 GDGT as an internal standard. The accuracy in the determination of GDGT concentration improved significantly when using the internal standard (5% standard deviation) compared to that obtained with the monthly external standard curve (43% standard deviation). Thus, the new internal standard technique will greatly improve the accuracy of GDGT abundance measurements, increase the potential of GDGTs in paleo-ecological studies.