Practical aspects of ultrahigh pressure capillary liquid chromatography

A novel pressure-balanced injection valve was evaluated for use with ultrahigh pressure liquid chromatography (UHPLC) at pressures up to 120 MPa (1,200 bar). Fused-silica capillaries (30-33 cm x 100 microm I.D.) packed with nonporous 1.5 microm isohexylsilane-modified (C6) silica particles were employed to study maximum pressure, injection reproducibility, injection time, and sample amount consumed for an injection. The new valve was more reproducible, convenient, and required much less sample than previously used injection systems. The effect of column diameter on efficiency and sensitivity was studied. The 100 microm I.D. columns demonstrated approximately 40% lower efficiency but 10-fold higher sensitivity than the 29 microm I.D. columns. Columns packed with nonporous C6 particles produced higher efficiencies than columns packed with a 1.5 microm porous octadecylsilane-modified (C18) material.