Imaging regiospecific lipid turnover in mouse brain with desorption electrospray ionization mass spectrometry.

Compartmentalization of metabolism into specific regions of the cell, tissue, and organ is critical to life for all organisms. Mass spectrometric imaging techniques have been valuable in identifying and quantifying concentrations of metabolites in specific locations of cells and tissues, but a true understanding of metabolism requires measurement of metabolite flux on a spatially resolved basis. Here, we utilize desorption ESI-MS (DESI-MS) to measure lipid turnover in the brains of mice. We show that anatomically distinct regions of the brain have distinct lipid turnover rates. These turnover measurements, in conjunction with relative concentration, will enable calculation of regiospecific synthesis rates for individual lipid species in vivo. Monitoring spatially dependent changes in metabolism has the potential to significantly facilitate research in many areas, such as brain development, cancer, and neurodegeneration.

The Effects of Added Hydrogen on Noble Gas Discharges Used as Ambient Desorption/Ionization Sources for Mass Spectrometry.

We demonstrate the effectiveness of using hydrogen-doped argon as the support gas for the dielectric barrier discharge (DBD) ambient desorption/ionization (ADI) source in mass spectrometry. Also, we explore the chemistry responsible for the signal enhancement observed when using both hydrogen-doped argon and hydrogen-doped helium. The hydrogen-doped argon was tested for five analytes representing different classes of molecules. Addition of hydrogen to the argon plasma gas enhanced signals for gas-phase analytes and for analytes coated onto glass slides in positive and negative ion mode. The enhancements ranged from factors of 4 to 5 for gas-phase analytes and factors of 2 to 40 for coated slides. There was no significant increase in the background. The limit of detection for caffeine was lowered by a factor of 79 using H2/Ar and 2 using H2/He. Results are shown that help explain the fundamental differences between the pure-gas discharges and those that are hydrogen-doped for both argon and helium. Experiments with different discharge geometries and grounding schemes indicate that observed signal enhancements are strongly dependent on discharge configuration. Graphical Abstract ᅟ.