Nanoliter-Volume Selective Sampling of Peptides Based on Isoelectric Points for MALDI-MS

摘要

A simple way to selectively isolate peptides based on their isoelectric points(pi)for MALDI mass spectral analysis is described.An applied voltage was used to electromi-grate peptides into a capillary.The capillary was modified with a zwitterionic surfactant,1,2-dilauroyl-sre-phosphati-dylcholine(DLPC),to suppress the electroosmotic flow(EOF)during injection.Hence,eitiier the cationic or the anionic peptides were introduced,depending on the voltage polarity.By controlling the pH,selective loading of peptides was performed to isolate trace components from a mixture.The injected sample plugs were subse-quendy spotted in nanoliter volumes for MALDI-MS analysis.No significant sample losses resulting from selective sampling were detected.Low attomole-level detection of peptides(adrenocorticotropic hormone fragment 18-39,pi 4.25)was achieved from a mixture containing other peptides(angiotensin I,pi 6.92,and bradykinin,pi 12.00)at 100 000-fold higher concentrations.