To simplify capillary electrophoresis–mass spectrometry (CE–MS) operation, a background electrolyte (BGE) containing a polymer additive is introduced that allows the analysis of peptides and protein mixtures in underivatized fused-silica capillaries without any pretreatment, thereby increasing throughput. The most important characteristic of these polymer additives is that they do not significantly suppress the signals of the proteins and peptides under electrospray ionization, thereby allowing them to be used as an additive to common BGEs that are used for CE–MS analysis of peptide and protein mixtures. In addition, because the fused-silica capillary inner wall is continuously coated with the polymer additive, migration irreproducibility, due to the degradation of the capillary inner wall coating, under CE–MS is minimized. High sensitivity of detection, migration reproducibility, and ease of fabrication allow CE–MS analyses that require long analysis time, such as (CE–MS/MS) n , to be performed with ease. The utility of this background electrolyte has been demonstrated for the analysis of complex protein digests and intact proteins.
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