Application of two new LC–ESI–MS methods for improved detection of intact polar lipids (IPLs) in environmental samples

Intact polar lipid distributions have become a valuable tool for the study of microbial ecosystems. In order to expand the detection and interpretation of the presence of these lipids, improved analytical methods are needed. Therefore, two high pressure liquid chromatography–electrospray ionization tandem mass spectrometry (HPLC–ESI–MS2) methods, based on hydrophilic interaction chromatography (HILIC) and reversed phase (RP) chromatography were developed, taking advantage of new chromatographic possibilities such as smaller particle size and recently developed column packing material. Both were optimized to cover the broad range of compounds found in environmental samples and to cope with the associated complex sample matrices. The capabilities of the methods were tested on pure standards and an environmental sample. Both methods offer improved peak resolution and detection limit, and reduced chromatographic background at twofold shorter run time compared with the previous method based on a diol column. The HILIC method offers separation according to lipid class similar to a diol column, so can be recommended for lipid fingerprinting. The method based on RP separation offers the unique possibility of analyzing intact polar lipids and core lipids in the same chromatographic run and an alternative mode of lipid separation based mainly on side chain structure. The method is especially suitable for separation of compounds based on side chain length, degree of saturation and/or presence of acyl/ether bonds. The combination of both newly developed chromatographic methods provides a powerful tool for the analysis of lipid distributions in environmental samples at ultra-low concentration.