Real-time analysis of metabolites in vivo by online extraction electrospray ionization mass spectrometry coupled to microdialysis

In vivo and real-time analysis could reflect a more real biological state, which was of great significance to the study of complex life processes. In this work, we constructed an online extraction electrospray ionization (OE-ESI) ion source as the interface of microdialysis and mass spectrometry, which realized real-time analysis of metabolites in vivo without sample pretreatment process. The ion source was consisted of three coaxial capillaries, and the parameters of the ion source were optimized. The OE-ESI ion source could simultaneously extract, desalt and ionize the analyte, successfully perform MS analysis of analyte in high salt system, and overcome the ion suppression caused by salt ion. Compared with commercial ESI MS, the OE-ESI ion source had excellent salt tolerance and stability. MD-OE-ESI MS realized the real-time MS detection of metabolites in the living body, avoiding the complex desalting process. In the rat liver ischemia-reperfusion model, a total of 24 metabolites, including glucose, glutamate, glutamine, etc., were monitored in real time mode, and their concentrations had varying degrees of change during the experimental process compared with the control group. This platform, we believed, would be helpful for real-time monitoring of biological metabolites in vivo, and had great application prospects to study physiological processes.