On-stage liquid-phase lipid microextraction coupled to nanospray mass spectrometry for detailed, nano-scale lipid analysis

RATIONALE Developments in instrumentation aimed at microscopic sampling have led to an emphasis on applications analyzing small volumes and molecular concentrations within biological, chemical, and industrial samples. Simultaneous improvements in the sensitivity and versatility of nanospray mass spectrometers have made it possible to directly couple these sampling and analysis processes. METHODS We developed a versatile liquid-phase lipid microextraction (LPME) technique for nanoliter to microliter volumes that is amenable to direct nanospray mass spectrometry (NMS). Lipophilic analytes within several types of biological samples were extracted and analyzed by partitioning and concentrating the analytes based on their solubility within two immiscible or partially miscible liquid phases. RESULTS The utility of LPME-NMS is demonstrated by extracting and analyzing molecules in four different types of applications: (1) visualization of an extracted neutral lipid-specific fluorescent dye from an aqueous solvent; (2) identification of controlled acid-catalyzed hydrolysis of triacylglycerols within nanospray capillaries; (3) reproducible sampling of a fatty acid emulsion; and (4) profiling of diverse lipids in a complex biological matrix of rabbit serum. CONCLUSIONS The modified instrumentation of a multi-port, on-stage bioworkstation shows considerable versatility by combining nanomanipulation, microextraction and direct NMS for a variety of chemical, biological, industrial, and clinical applications.