High-efficiency liquid chromatography on conventional columns and instrumentation by using temperature as a variable: I. Experiments with 25 cm × 4.6 mm I.D., 5 μm ODS columns

High plate numbers were obtained in conventional LC by coupling columns and by using temperature to reduce the viscosity of the mobile phase. At 80 °C up to eight columns of 25 cm × 4.6 mm I.D. packed with 5 μm ODS particles could be coupled generating 180,000 effective plates while the pressure drop was only 350 bar. For routine work, a set of four columns is preferred. The analysis times on one column operated at 30 °C and 1 mL/min flow rate and on four columns at 80 °C and 2 mL/min flow rate are the same in isoeluotropic conditions while the resolution is doubled. Multicolumn systems were successfully applied in isocratic and gradient mode for the analysis of pharmaceutical and environmental samples.