Application of inductively coupled plasma mass spectrometry to phospholipid analysis

Phospholipids are the main constituents of membranes in all types of prokaryotic and eukariotic cells. Due to their complexity and heterogeneity in biological samples, qualitative and quantitative analyses of membrane phospholipids in cellular extracts represent major analytical challenges, mainly due to suitable and sensitive detection methods. The inductively coupled plasma mass spectrometer (ICP-MS) is a suitable detector for selective determination of phospholipids as they all contain phosphorus. Phospholipids are extractable with organic solvents, therefore liquid chromatography with an organic mobile phase was used for separation of different lipid species. Solvent load to the plasma was reduced by splitting the mobile phase prior to reaching the nebulizer, by chilling the spray chamber to -5 degreesC and by optimisation of carrier gas flow for maximum condensation of organic vapours. Despite desolvation, oxygen was added to prevent carbon deposition on interface cones. To reduce polyatomic interferences at m/z ratio 31 (e.g. (CH3O+)-C-31) and to improve detection limits, helium was used as a collision gas. The achieved absolute detection limits were between 0.21 and 1.2 ng of phosphorus and were superior to those obtained by an evaporative light scattering detector, which provides an alternative detection system for lipid analysis. The usefulness of the developed method was demonstrated by analysis of lipid extracts from the yeast Saccharomyces cerevisiae.