Analysis of Lipids: Metal Oxide Laser Ionization Mass Spectrometry

Abstract

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been used for lipid analysis; however, one of the drawbacks of this technique is matrix interference peaks at low masses. Metal oxide surfaces are described here for direct, matrix-free analysis of small (MW < 1000 Da) lipid compounds, without interferences in the resulting spectra from traditional matrix background peaks. Spectra from lipid standards produced protonated and sodiated molecular ions. More complex mixtures including vegetable oil shortening and lipid extracts from bacterial and algal sources provided similar results. Mechanistic insight into the mode of ionization from surface spectroscopy, negative ion mass spectrometry, and stable isotope studies is also presented. The metal oxide system is compared to other reported matrix-free systems.

Lipid profiling using catalytic pyrolysis/metal oxide laser ionization-mass spectrometry

“…Previous work showed that metal oxides facilitate laser ionization to produce strong molecular ions of FAMEs [14]. Thus, NiO, MgO, SB15, and a bare MALDI plate were evaluated for matrix-free THM of tripalmitin.…”

“…We recently reported the use of metal oxide laser ionization mass spectrometry (MOLI MS) as a matrix-free system for laser ionization of lipid materials [13,14]. Using this method, analyte ionization occurs by protonation, or sodiation due to interactions with Lewis acid/base sites on the metal oxide.…”

Nanostructured Indium Tin Oxide Slides for Small-Molecule Profiling and Imaging Mass Spectrometry of Metabolites by Surface-Assisted Laser Desorption Ionization MS

“…The method produced goodquality spectra down to 0.5 pmol of deposited analyte with a signal-to-noise ratio of 13, comparable to the sensitivity of reported nanostructured gold 46 and metal oxide LDI methods, 47 although a direct comparison has not been made ( Figure 4).…”

Direct Mass Spectrometry-Based Approaches in Metabolomics

“…Many other matrix-free methods have been developed for laser desorption/ionization of small molecules, with potential applications in metabolomics. A variety of surface properties have been studied for matrix-free ionization of small molecules, for example: diamond nanowires [17] sol-gel derived silver-nanoparticles-impregnated thin biofilm [18], nanoporous gallium nitride-silver nanoparticles [19], metal oxide surfaces [20], nanofilament silicon [21], etc. Comprehensive reviews of innovative technologies using energy-absorbing materials for matrix-free LDI-MS have been recently published [22][23][24].…”