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

The effect of using high isothermal temperatures and temperature programmin g above ambient in liquid chromatography has been investigated by the use o f relatively long packed reversed phase capillary columns and non-aqueous m obile phases. Efficiency measurements have been performed in the temperatur e interval 50-175 degrees C, indicating that the best efficiency was achiev ed at 100 degrees C, with a corresponding optimum linear velocity of approx imately 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 r educed plate height at elevated temperatures. The contribution from extra-c olumn volumes increased the plate height at temperatures above 100 degrees C where the solute had low retention. This effect was closely examined by i ntroducing larger pre-column dead volumes, demonstrating the need to minimi ze dead volumes. Temperature programming has successfully been used for par tial characterization and for purity testing of different polymer additives . The within and between day precision of retention times for the temperatu re-programmed separations gave a relative standard deviation of 0.3-2.9%.