Quantitative Analysis of Metabolites at the Single-Cell Level by Hydrogen Flame Desorption Ionization Mass Spectrometry.

To date, direct quantitation of cellular metabolites at the picoliter level or in a single cell is still a challenge due to tiny sampling materials, the accuracy of the sampling volume, and the ubiquitous matrix effect. Herein, picoliter magnitude quantitative analysis was performed using a pressure-assisted microsampling probe coupled to the hydrogen flame desorption ionization mass spectrometer (HFDI-MS). The sampling was accurately controlled with a picoliter pump, and the analytes were rapidly vaporized and quantitatively transferred to the gas phase by adequate heat. The vapor-phase analytes reacted with protonated water cluster ions by the proton-transfer reaction (PTR). The accurate sampling, flash thermal desorption, and proton-transfer ionization processes were conducted spatiotemporally, which could greatly reduce matrix effects to facilitate the quantitation of analytes without the internal standard. Furthermore, this workflow enabled the quantitation of cellular metabolites at the picoliter/single-cell level.