Multiple Precursor Ion Scanning of Gangliosides and Sulfatides with a Reversed-Phase Microfluidic Chip and Quadrupole Time-of-Flight Mass Spectrometry

Precise profiling of polar lipids including gangliosides and sulfatides is a necessary step in understanding the diverse physiological role of these lipids. We have established an efficient method for the profiling of polar lipids using reversed-phase nano high-performance liquid chromatography microfluidic chip quadrupole time-of-flight mass spectrometry (nano-HPLC-chip Q-TOF/MS). A microfluidic chip design provides improved chromatographic performance, efficient separation, and stable nanospray while the advanced high-resolution mass spectrometer allowed for the identification of complex isobaric polar lipids such as NeuAc- and NeuGc-containing gangliosides. Lipid classes were identified based on the characteristic fragmentation product ions generated during data-dependent tandem mass spectrometry (MS/MS) experiments. Each class was monitored by a postprocessing precursor ion scan. Relatively simple quantitation and identification of intact ions was possible due to the reproducible retention times provided by the nano-HPLC chip. The method described in this paper was used to profile polar lipids from mouse brain, which was found to contain 17 gangliosides and 13 sulfatides. Types and linkages of the monosaccharides and their acetyl modifications were identified by low-energy collision-induced dissociation (CID) (40 V), and the type of sphingosine base was identified by higher energy CID (80 V). Accurate mass measurements and chromatography unveiled the degree of unsaturation and hydroxylation in the ceramide lipid tails.