Detection of biomolecules from solutions with high concentration of salts using probe electrospray and nano-electrospray ionization mass spectrometry

Probe electrospray ionization (PEST) is a recently developed ionization technique which uses a solid needle or wire as sampling probe and ESI emitter instead of capillary. PESI is free from the clogging problem and it has high tolerance to salts and urea. We present herein a comparative study of the probe electrospray ionization (PESI) and nano-electrospray ionization (nano-ESI) for the measurement of biomolecules in the sample solutions with high concentrations of salts and urea. Our results show that PESI could provide equivalent ionization performance with nano-ESI, and in certain cases it could be superior to nano-ESI for the samples with high concentration (> 100 mM) of salts and urea. Therefore, PESI can be useful for the direct analysis of cell/tissue extracts and protein digestion without or reduced procedures in sample purification.