A novel method has been developed for the rapid desalting of proteins and peptides for electrospray ionization mass spectrometry (ESI-MS). Protein and peptide solutions having high salt concentrations were infused into a microdialysis tube which was directly interfaced with a micro-ESI source. The microdialysis tube was surrounded by a counter-current flow of a buffer solution consisting of 10 mM ammonium acetate. Desalting was completed in one to four minutes for samples containing up to 250 mM NaCl, which would otherwise have required several hours using alternative off-line desalting schemes. The on-line desalting method also increased the signal-to-noise ratio by a factor of more than 40 compared with that obtained without desalting. Detection of subpicomole samples of apomyoglobin having a high salt concentration was also achieved. Initial results for apomyoglobin, albumin and angiotensin I indicate broad applicability of the method.
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Wu et al. (1996) studied this question.