| In packed capillary liquid chromatography, the best possible efficiency in the least amount of time is obtained when using very small (<3 mum) diameter packing materials. However, columns packed with small particles have low permeability and require high column inlet pressure. Most conventional high performance liquid chromatography (HPLC) pumping systems have upper pressure limits of ∼6,000 psi. Consequently, commercial columns packed with small particles are very short (∼30 mm long), and thus provide less than 10,000 theoretical plates, ultimately resulting in shorter analysis time without gain of separation efficiency.;An ultra-high pressure capillary liquid chromatograph (UHPLC) was used to overcome the pressure limitations. The UHPLC was constructed from a commercial pneumatic amplifier pump. The pump required no modifications and was capable of generating 52,000 psi. A custom-made high pressure valve manifold was used for static-split sample introduction and the UV absorbance was monitored via on-column detection.;The high pressures employed in UBPLC place extraordinary demands on the preparation of suitable capillary columns. This necessitated the construction of a high pressure column packing apparatus. A pumping system constructed from a pneumatic amplifier pump could generate packing pressures up to 20,000 psi. Using a supercritical fluid enhanced slurry method, columns in excess of 1 m could be packed with 1.5 mum and 3 mum particles.;The UHPLC was used to perform packed capillary LC at pressures as high as 40,000 psi. Due to the high pressure capacity of the system, particles as small as 1.5 mum could be used to accomplish highly efficient chromatographic separations with long capillary columns. At optimum linear velocity, efficiencies as high as 600,000 plates m-1 (k = 0.5) were obtained. The columns used in this work exhibited a very flat van Deemter curve profile, resulting in excellent efficiencies, even at linear velocities much higher than the optimum. Therefore, high speed separations with short capillary columns could be accomplished while maintaining excellent column efficiencies. Selected benzodiazepines and triazine herbicides were separated in less than 60 s. The UBPLC was also coupled to a time-of-flight mass spectrometer (TOFMS) for the separation and detection of selected benzodiazepines. |
