Integrated droplet analysis system with electrospray ionization-mass spectrometry using a hydrophilic tongue-based droplet extraction interface.

This paper describes a simple, robust, and integrated microchip-based system for droplet analysis with electrospray ionization-mass spectrometry (ESI-MS) detection. The microchip integrated multiple modules including a droplet generator, a droplet extraction interface, and a monolithic ESI emitter. The novel droplet extraction interface based on hydrophilic tongue structure was developed. The interface could transfer droplets from segmented phase to aqueous phase with high reliability and high controllability by coupling with a back pressure regulator. The flow injection mode was adopted to introduce the transferred droplets to the ESI emitter for minimizing the cross-contamination between droplets and achieving droplet matrix modification. The system performance was evaluated using angiotensin as a model sample, and high sensitivity (<1 μM) and a good reproducibility of 5.2% RSD (n = 7) were obtained. The present device was further applied in the online monitoring of droplet-based microreaction for alkylation of peptide.