Fabrication of stable packed capillary reversed-phase columns for protein structural analysis

Capillary column (< or = 320-micron ID) liquid chromatography is an essential tool for the separation and concentration of low-picomole amounts of proteins and peptides for mass-spectrometric based structural analysis. We describe a detailed procedure for the fabrication of stable and efficient 50- to 180-micron ID polyimide fused-silica columns. Columns were packed by conventional slurry packing with reversed-phase silica-based supports followed by column bed consolidation with acetonitrile and sonication. PVDF membrane or internal fused-silica particles were employed for column end-frit construction. The ability of these columns to withstand high back pressures (300-400 bar) enabled their use for rapid chromatography (> 3400 cm/hr; i.e., approximately 40 microliters/min for 200-micron ID columns) and the loading of large sample volumes (up to 500 microliters). The accurate low flow rates (0.4-4.0 microliters/min) and precise gradient formation necessary to operate these columns were achieved by a simple modification of conventional HPLC systems [Moritz et al. (1992), J. Chromatogr. 599, 119-130]. Column performance was evaluated for ability to resolve low-fmol amounts of all components of a mixture of PTH-amino acids and to separate peptides for on-line LC/MS analysis of peptide mixtures derived from in situ digestion of 2-DE resolved protein spots.