Aerodynamic mass spectrometry interfacing of microdevices without electrospray tips

Abstract

A new concept for electrospray coupling of microfluidic devices with mass spectrometry was developed. The sampling orifice of the time-of-flight mass spectrometer was modified with an external adapter assisting in formation and transport of the electrosprayed plume from the multichannel polycarbonate microdevice. The compact disk sized microdevice was designed with radial channels extending to the circumference of the disk. The electrospray exit ports were formed by the channel openings on the surface of the disk rim. No additional tips at the channel exits were used. Electrospray was initiated directly from the channel openings by applying high voltage between sample wells and the entrance of the external adapter. The formation of the spatially unstable droplet at the electrospray openings was eliminated by air suction provided by a pump connected to the external adapter. Compared with the air intake through the original mass spectrometer sampling orifice, more than an order of magnitude higher flow rate was achieved for efficient transport of the electrospray plume into the mass spectrometer. Additional experiments with electric potentials applied between the entrance sections of the external adapter and the mass spectrometer indicated that the air flow was the dominant transport mechanism. Basic properties of the system were tested using mathematical modeling and characterized using ESI/TOF-MS measurements of peptide and protein samples.