Structural characterization of polypeptides and proteins by combination of capillary electrophoresis and (252)Cf plasma desorption mass spectrometry.

An efficient and sensitive method for the isolation and transfer of peptides and proteins from capillary zone electrophoresis separation for subsequent analysis by 252Cf plasma desorption mass spectrometry was developed. Sample isolation on to nitrocellulose-coated targets for mass spectrometric analysis is performed by using a stainless-steel microtube pre-filled with aqueous buffer solution, to which the capillary end is connected, and the peptide is collected by applying a suitable transfer voltage according to the separation voltage. Low-and sub-picomolar sample amounts were isolated with high transfer efficiency and reproducibility, without the necessity for independent determination of electroosmotic flow-rates. Plasma desorption mass spectra of several peptides and proteins showed predominantly intact molecular ions; however, for several peptides partial oxidative modification was found which can be accounted for by the electrophoretic separation and/or transfer conditions. First applications to peptides and proteins show the feasibility of this off-line combination for primary structure characterization, such as by in situ chemical modification and enzymatic proteolysis reactions on the sample target prior to mass spectrometric analysis.