Abstract
The evolution of chromatography has led to the reduction in the size of the packing materials used to fabricate HPLC columns. The increase in the backpressure required has led to this technique being referred to as ultrahigh‐pressure liquid chromatography (UHPLC) when the column backpressure exceeds 10 000 psi (∼︁ 700 bar). Until recently, columns packed with sub‐2‐μm materials have generally fitted into two classes; either short (less than 5 cm) columns designed for use on traditional HPLC systems at pressures less than 5000 psi (350 bar), or capillary columns (inner diameters less than 100 μm). By using packing materials with diameters < 2 μm to fabricate UHPLC columns, there is an increase in efficiency and a decrease in the analysis time that are directly proportional to the size of the packing material. In order to realize and exploit the increase in efficiency, however, the columns must maintain lengths typically associated with analytical columns (15–25 cm). We have packed 1 mm diameter, 150 mm in length columns with 1.5 μm packing material, and evaluated their performance in UHPLC. The pressure required to achieve optimum linear velocities in plots of plate height versus linear velocity was in the vicinity of 1104 bar (16 000 psi). The 1.5 μm particle‐packed column was compared with the more traditional 150 mm long analytical columns packed with 3 μm materials. This column showed an efficiency that was approximately twice that observed with the 3 μm packed column and a concomitant reduction in the analysis time, theoretically predicted.