High-resolution capillary electrophoretic separation of proteins and peptides was achieved by coating the inner wall of 75 microm ID fused-silica capillaries with 40-140 nm polystyrene particles which have been derivatized with alpha-omega-diamines such as ethylenediamine or 1,10-diaminodecane. A stable and irreversibly adsorbed coating was obtained upon deprotonation of the capillary surface with aqueous sodium hydroxide and subsequent flushing with a suspension of the positively charged particles. At pH 3.1, the detrimental adsorption of proteins to the capillary inner wall was suppressed efficiently because of electrostatic repulsion of the positively charged proteins from the positively charged coating which enabled protein separations with maximum efficiencies of 400000 plates per meter. A substantial improvement of separation efficiency in particle-coated capillaries was observed after in-column derivatization of amino functionalities with 2,3-epoxy-l-propanol, resulting in a more hydrophilic coating. Five basic and four acidic proteins could be separated in less than 7 min with efficiencies up to 1900000 theoretical plates per meter. Finally, coated capillaries were applied to the high-resolution analysis of protein glycoforms and bioactive peptides.

Peptides and proteins were separated by capillary electrophoresis (CE) in fused-silica capillaries coated with an irreversibly adsorbed monolayer of derivatized polystyrene nanoparticles. Whereas phosphate buffer, pH 3.10, enabled the highly efficient separation of basic proteins with plate counts up to 1,400,000 m-1, volatile buffer components such as formic acid or acetic acid titrated with ammonia to the desired pH had to be used for the direct coupling of CE with electrospray ionization mass spectrometry (ESI-MS). Compared to 40 mM phosphoric acid-sodium hydroxide, pH 3.10, a background electrolyte containing 125 mM formic acid-ammonia, pH 4.00, was shown to yield equivalent separation efficiency. Investigation of the influence of buffered electrolytes on the ESI-MS signal of lysozyme at pH 2.70-4.00 showed that the charge state distribution shifted to lower charge states at higher pH with a concomitant five-fold decrease in signal intensity of the most abundant signal. The presence of trifluoroacetic acid in the background electrolyte greatly increased the level of baseline noise and completely inhibited the observation of any mass signals related to proteins. Full scan spectra could be acquired from 50-500 fmol amounts of proteins during coupled CE-ESI-MS utilizing 100-125 mM formic acid-ammonia, pH 3.10. However, compared to UV detection, considerable band broadening is observed with ESI-MS detection which is mainly attributed to column overloading, band spreading in the interface, and scanning data acquisition. Finally, the major whey proteins beta-lactoglobulin A, beta-lactoglobulin B, and alpha-lactalbumin were identified in a whey drink by comparison of molecular masses determined by CE-ESI-MS to molecular masses calculated from the amino acid sequence.

Key WordsColumn liquid chromatography Electrospray ionization mass spectrometry Micropellicular poly-styrene/divinylbenzene Peptides and proteins SummaryShort columns packed with highly crosslinked 2.3 ~tm poly-styrene/divinylbenzene (PS/DVB) particles were used for rapid and efficient separation of proteins and peptides by reversed-phase high-performance liquid chromatography at elevated temperatures. Enhancement of the diffusivities of the sample components at elevated temperatures together with the short diffusion pathlength with the micropellicular polymeric stationary phases were responsible for high efficiency, high speed of analysis, and short column regeneration times. Underivatized PS/DVB beads as well as PS/DVB microspheres which have been modified with polyvinylalcohol or octadecyl chains on the surface were synthesized, employed, and compared to HY-TACH-C18, a commercially available micropellicular octadecyl-silica stationary phase, for the separation of proteins, octapeptides and tryptic protein digests. Highest performance was obtained with the silica-and PS/DVB-based octadecyl stationary phases, which exhibited similar column efficiencies but different selectivities for proteins and peptides. The minimum detectability at 214 nm and the maximum loading capacity for ribonuclease A using analytical 30 x 4.6 mm I.D. columns were 10 ng (0.6 pmol) and I pg, respectively. Finally, reversed-phase HPLC with a 60 • 2 mm I.D. narrow-bore column packed with micropellicular octadecyl PS/DVB was coupled successfully to electrospray mass spectrometry at a flow-rate of 0.15 mL min -1 and on-line full-scan mass spectra for molecular mass determination and identification of proteins in the lower picomol range were obtained.