A procedure for obtaining highly stable coated capillaries for use in capillary electrophoresis (CE) is described. Reaction of surface-chlorinated fused silica capillaries with the Grignard reagent, vinyl magnesium bromide, followed by reaction of the vinyl group with acrylamide, results in an immobilized layer of polyacrylamide attached through hydrolytically stable Si-C bonds. This method is an extension of the capillary coating procedure described previously by Hjerten, differing in the means by which the polyacrylamide layer is bonded to the capillary walls. Capillaries treated in the manner described here can be used over a pH range of 2-10.5, without noticeable decomposition of the coating. In comparison to uncoated capillaries, separations of proteins using such coated capillaries are improved due to a reduction in protein adsorption to the capillary walls, although interaction is still present to some degree as evidenced by an inability to obtain plate counts as high as those predicted by theory. Electroosmotic flow is virtually eliminated in the coated capillaries, resulting in improved reproducibilities of protein migration times in comparison to uncoated capillaries. Additionally, peak skew is evaluated for model proteins and improvements are noted for the coated capillaries. Results are presented for separations of model protein mixtures, comparing the performance of the vinyl-bound polyacrylamide coated capillaries and uncoated capillaries at both high and low pH extremes.

The current status of high-performance capillary electrophoresis as an analytical separation method for proteins, peptides and amino acids is assessed. Recent advances in suppressing the effects of electroosmotic flow and irreversible adsorption of proteins at the capillary wall are reviewed, together with procedures for optimal separations of peptides and amino acids. The detection aspects emphasize the role of laser-induced fluorescence and capillary electrophoresis/mass spectrometry in high-sensitivity measurements.

Procedures for the reduced-scale analysis of proteins by peptide mapping have been developed, allowing peptide maps to be obtained from picomole to femtomole quantities of protein. The use of trypsin immobilized on agarose gel and placed in a small reactor column has made it possible to reproducibility digest as little as 50 ng of protein. This represents a decrease in sample size of approximately 3 orders of magnitude from conventional tryptic digestion schemes. Separations of tryptic digests were accomplished by using either microcolumn high-performance liquid chromatography (HPLC) or capillary zone electrophoresis (CZE). Separations of 100 ng (4 pmol) of tryptic digest samples of beta-casein were achieved with microcolumn HPLC, while separations of approximately 2 ng (80 fmol) of beta-casein tryptic digest (from a total sample size of 50 ng) were possible with CZE. Peptide maps from phosphorylated and dephosphorylated forms of beta-casein were readily distinguishable using both separation methods, demonstrating an ability to detect a single amino acid modification in a protein. Relative standard deviations of peak retention or migration times were less than 3% for microcolumn HPLC and less than 1% for CZE.

A variety of different peptide-mapping schemes are presented, with emphasis on the development of procedures which can be done with limited quantities (i.e. 5 pmol) of protein. Results are obtained from model proteins which contain disulfide bonds, which must be broken prior to fragmentation of the protein. A reaction involving the simultaneous use of tributylphosphine and 2-methylaziridine to reduce and alkylate the disulfide bonds is employed, due to favorable attributes of these reagents for the scaled-down procedure. The traditional performic acid oxidation reaction to cleave cystine groups is also successfully used with low-picomole quantities of protein. Three different protein digestion reagents are used: trypsin, chymotrypsin, and cyanogen bromide. Each reagent produces a unique mixture of peptides. Capillary electrophoresis is used to separate the peptides, offering high separation efficiencies, short analysis times, and compatibility with small sample sizes. In addition to the conventional use of UV detection for underivatized peptides, laser-induced fluorescence detection is employed in conjunction with an arginine-selective derivatization reaction. This latter procedure for derivatization and detection offers an alternative peptide-mapping mode, in which only the arginine-containing peptides are detected, and is useful in simplifying the peptide maps of large proteins.

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Abstract. A method for concentrating dilute samples prior to separation by capillary zone electrophoresis (CZE) is described. The principles of isotachophoresis are used to achievc higher local concentrations of the sample solution within a preconcentration capillary that is attached directly to the CZE separation capillary. Through a judicious choice of leading, terminating, and background electrolytes, the isotachophoretic preconcentration step can be performed on-line with the CZE separation using common CZE instrumentation. The use of isotachophoretic preconcentration allows larger volumes of dilute sample solutions to be analyzed effectively in the zone electrophoretic mode, thereby reducing the stringent CZE requirements of small sample volumes and concentrated sample solutions.

Abstract. A procedure for preparing polyacrylamide gel-filled capillaries, for use in capillary gel electrophoresis, is described. The method involves the principle of isotachophoretic polymerization, in which the polymerization initiator is introduced by electromigration to promote gradual polymerization of the acrylamide in a sequential manner along the length of the capillary. This procedure has been found to be superior to other methods for polymerizing gels inside of small-bore (i.e., 50-pm i.d.) capillaries, because of the reduced formation of bubbles in the gels during polymerization. The method described is simple, reproducible, and several capillaries can be prepared simultaneously. A preliminary result showing the use of 50-pm i.d. gel-filled capillaries for SDS-polyacrylamide gel electrophoresis of proteins is shown.

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