5 research outputs found
Mass Spectrometric Sampling of a Liquid Surface by Nanoliter Droplet Generation from Bursting Bubbles and Focused Acoustic Pulses: Application to Studies of Interfacial Chemistry
The complex chemistry occurring at the interface between liquid and vapor phases contributes significantly to the dynamics and evolution of numerous chemical systems of interest, ranging from damage to the human lung surfactant layer to the aging of atmospheric aerosols. This work presents two methodologies to eject droplets from a liquid water surface and analyze them via mass spectrometry. In bursting bubble ionization (BBI), droplet ejection is achieved via the formation of a jet following bubble rupture at the surface of a liquid to yield 250 μm diameter droplets (10 nL volume). In interfacial sampling by an acoustic transducer (ISAT), droplets are produced by focusing pulsed piezoelectric transducer-generated acoustic waves at the surface of a liquid, resulting in the ejection of droplets of 100 μm in diameter (500 pL volume). In both experimental methodologies, ejected droplets are aspirated into the inlet of the mass spectrometer, resulting in the facile formation of gas-phase ions. We demonstrate the ability of this technique to readily generate spectra of surface-active analytes, and we compare the spectra to those obtained by electrospray ionization. Charge measurements indicate that the ejected droplets are near-neutral (<0.1% of the Rayleigh limit), suggesting that gas-phase ion generation occurs in the heated transfer capillary of the instrument in a mechanism similar to thermospray or sonic spray ionization. Finally, we present the oxidation of oleic acid by ozone as an initial demonstration of the ability of ISAT-MS to monitor heterogeneous chemistry occurring at a planar water/air interface
High-Throughput Measurement of Lipid Turnover Rates Using Partial Metabolic Heavy Water Labeling
Novel analytical
platforms for high-throughput determination of
lipid turnover in vivo have been developed based on partial metabolic <sup>2</sup>H<sub>2</sub>O labeling. The performance on lipid kinetics
measurement of our methods was validated in three different liquid
chromatography–mass spectrometry (LC-MS) setups: MS-only, untargeted
MS/MS, and targeted MS/MS. The MS-only scheme consisted of multiple
LC-MS runs for quantification of lipid mass isotopomers and an extra
LC-MS/MS run for lipid identification. The untargeted MS/MS format
utilized multiple data-dependent LC-MS/MS runs for both quantification
of lipid mass isotopomers and lipid identification. An in-house software
was also developed to streamline the data processing from peak area
quantification of mass isotopomers to exponential curve fitting for
extracting the turnover rate constant. With HeLa cells cultured in
5% <sup>2</sup>H<sub>2</sub>O media for 48 h, we could deduce the
species-level turnover rates of 108 and 94 lipids in the MS-only and
untargeted MS/MS schemes, respectively, which covers 13 different
subclasses and spans 3 orders of magnitude. Furthermore, the targeted
MS/MS setup, which performs scheduled LC-MS/MS experiments for some
targeted lipids, enabled differential measurement between the turnover
rates of the head and tail groups of lipid. The reproducibility of
our lipid kinetics measurement was also demonstrated with lipids that
commonly detected in both positive and negative ion modes or in two
different adduct forms
Kinetic and mechanistic diversity of intestinal immune homeostasis characterized by rapid removal of gut bacteria
ABSTRACTSymbiotic microbiota critically contribute to host immune homeostasis in effector cell-specific manner. For exclusion of microbial component, germ-free animals have been the gold standard method. However, total removal of the entire gut microbiota of an animal from birth significantly skews physiological development. On the other hand, removal of gut microbiota from conventional mice using oral antibiotics has its own limitations, especially lack of consistency and the requirement for long-term treatment period. Here, we introduce an improved regimen to quickly remove gut microbiota and to maintain sterility, that is well received by animals without refusal. Rapid and consistent exclusion of resident bacteria in the gut lumen revealed kinetic differences among colonic lymphocyte subsets, which cannot be observed with typical germ-free animal models. Furthermore, the proposed method distinguished the mechanism of microbiota contribution as a direct stimulus to capable effector cells and a homeostatic cue to maintain such cell types