Highly Efficient Desalting by Silica Isoporous Membrane-Based Microfluidic Chip for Electrospray Ionization Mass Spectrometry

Nonvolatile buffers and inorganic salts used for isolation and stabilization of biological samples are essential to be cleaned up prior to mass spectrometry (MS) analysis because of their deleterious effects such as ion suppression and instrumental pollution. In this work, a centimeter-scale continuous silica isoporous membrane (SIM) was prepared and integrated into a facile microfluidic chip for the desalting of protein samples based on dialysis principle. Thanks to the uniform pore size (similar to 2.3 nm in diameter), ultrasmall thickness (90 nm) and high pore density (4.0 x 10(12) pores cm(-2), corresponding to a porosity of 16.7%) of SIM, the device achieved similar to 99% desalting efficiency for the sample with 154 mM NaCI (isotonic saline) at a flow rate of 1 mu L min(-1), while protein loss was only 5%. High-quality electrospray ionization (ESI)-MS spectra of cytochrome c dissolved in isotonic saline was obtained after the desalting treatment. In addition, the SIM-based microfluidic device was successfully online-coupled with microchip ESI-MS for real-time desalting and characterization of proteins.