Aspects and applications of non-aqueous high temperature packed capillary liquid chromatography

The effect of using high isothermal temperatures and temperature programming above ambient in liquid chromatography has been investigated by the use of relatively long packed reversed phase capillary columns and non-aqueous mobile phases. Efficiency measurements have been performed in the temperature interval 50– 175 °C, indicating that the best efficiency was achieved at 100 °C, with a corresponding optimum linear velocity of approximately 0.07 cm s–1. The efficiency measurements revealed that the linear velocity had to be slightly increased in order to operate at the optimum reduced plate height at elevated temperatures. The contribution from extra-column volumes increased the plate height at temperatures above 100 °C where the solute had low retention. This effect was closely examined by introducing larger pre-column dead volumes, demonstrating the need to minimize dead volumes. Temperature programming has successfully been used for partial characterization and for purity testing of different polymer additives. The within and between day precision of retention times for the temperature-programmed separations gave a relative standard deviation of 0.3–2.9%.