Tracking the signals of living archaea: A multiple reaction monitoring (MRM) method for detection of trace amounts of intact polar lipids from the natural environment

Isoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs) are biomarkers of archaea, but improvement is needed for more precise analysis of intact polar lipid (IPL)-iGDGTs. Here, we present a multiple reaction monitoring (MRM) method for IPL-iGDGTs using reversed phase liquid chromatography (RP-LC) and triple quadrupole mass spectrometry equipped with electrospray ionization (RP-LC-ESI-MRM). The MRM mode showed much greater sensitivity and lower detection limits than the commonly used selected ion monitoring (SIM) mode. Furthermore, the MRM mode had better stability and repeatability than the SIM mode. Thus, the RP-LC-ESI-MRM method can allow efficient fingerprinting of archaeal IPL-iGDGTs, particularly when they are in trace abundance in natural environments.