UC Davis

Here, we explored two different ways to measure and reduce the in-source fragmentation of cholesteryl esters occurring in liquid chromatography coupled with electrospray ionization (ESI) mass spectrometry. Seven ‘in-source’ parameters (sweep gas flow rate, auxiliary gas flow rate, sheath gas flow rate, RF level, auxiliary gas heater temperature, spray voltage, and capillary temperature) were individually optimized and combined for an overall optimal set of parameter values. The optimized method resulted in a 4-20x greater peak intensity for all cholesteryl esters in human plasma when compared to the parameters currently used in the UC Davis service core laboratory while also increasing peak intensities for other classes of lipids. Additionally, a lower-flow ESI source designed to decrease in-source fragmentation was tested in comparison to the built-in source. The lower-flow source was found to have comparable abundances to the standard flow source in most lipid classes in positive ESI mode and higher abundances in negative ESI mode. The sources differed in the presence or peak intensity of some lipid classes, including for monoacylglycerols that were only detectable when using the low-flow source and triacylglycerols that were absent or largely reduced in peak intensities in the high-flow source.