Microcapillary liquid chromatography in open tubular columns with diameters of 10–50 μm

Abstract The theoretical separation efficiency of open microcapillary liquid chromatography (LC) columns, including peak-broadening effects resulting from interphase resistance to mass transfer, has been considered and an expression is derived for the plate height caused by interphase resistance. The use of such columns with internal diameters down to 10 μm is explored for LC separations. The columns were prepared from soft glass tubing and coated with polar and non-polar stationary phases. Several applications in straight phase as well as reversed-phase systems demonstrate the high separation speed (up to 50 effective plates per second). Relatively wide (30–50 μm) and short (1–5 m) columns allow rapid analyses within minutes. Smaller (10–30 μm) and longer (5–25 m) columns yield extremely high plate numbers (up to 5·10 6 ), permitting very difficult separations in a reasonable time (2–5 h). The required pressure never exceeds the generally accepted value of 400 bar. Preliminary results obtained with fused silica columns are discussed. Split-injection and addition of make-up mobile phase through the (UV) detector have been applied. In order to avoid undesirable dilution of the sample zones by the make-up liquid, the microcapillaries were directly coupled to a mass spectrometer (in the chemical ionization mode). This technique has yielded promising results.