Simultaneous total analysis of core and polar membrane lipids in archaea by high-performance liquid chromatography/high-resolution mass spectrometry coupled with heated electrospray ionization.

Abstract

Archaea have characteristic membrane lipids including diether and/or tetraether isoprenoidal core lipids with various polar head groups. Since the polar group is removed soon after the end of archaeal activity, the occurrences of core and polar lipids are regarded as dead and active signals, respectively. The core and polar lipids have generally been analyzed separately using atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), respectively, coupled with mass spectrometry. In this study, simultaneous analyses of core and polar archaeal lipids have been examined using heated electrospray ionization (HESI) by high-performance liquid chromatography/high-resolution mass spectrometry (HPLC/HRMS). Both core and intact polar lipids can be analyzed simultaneously by HESI with good sensitivity (sub ng to 100 ng) and separation using a semi-bore diol column by normal-phase chromatography. The core lipids eluted firstly to separate archeaol, then glycerol dibiphytanyl glycerol tetraethers (GDGTs), followed by the polar lipids with glycosides and glycophosphates. The relative GDGT composition is identical between HESI and APCI methods. The simultaneous analysis has the benefit of minimizing sample amount and elution solvent as well as preparation work. The method can also be applied to a compound class fractionation for compound-specific carbon and hydrogen isotope analysis.