Development of a 1.0 mm inside diameter temperature-assisted focusing precolumn for use with 2.1 mm inside diameter columns.

On-column solute focusing is a simple and powerful method to decrease the influence of precolumn band spreading and increase the allowable volume injected increasing sensitivity. It relies on creating conditions so that the retention factor, k', is transiently increased during the injection process. Both solvent composition and temperature control can be used to effect solute focusing. In the case of temperature, the release of the transiently delayed solute band requires increasing the temperature rapidly and with a minimum of radial thermal gradients. Thus, the focus of attention in temperature-based efforts to carry out on-column focusing has been on capillary columns. As a result, the benefits of this simple and reliable approach, temperature-assisted solute focusing or TASF, are not available to those using larger diameter columns, in particular the highly successful 2.1mm inside diameter columns. Based on considerations of thermal entrance length at the volume flow rates used with 2.1mm inside diameter columns, TASF would not be effective with such columns. However, we determined that the thermal entrance length for a 1.0mm inside diameter precolumn is sufficiently short, about 2mm, that it could work as a precolumn before a 2.1mm inside diameter analytical column. Finite element calculations demonstrate that a 1.0×20mm precolumn packed with 5μm reversed phase particles is effective at a flow rate of 250μL/min, suitable for the 2.1mm inside diameter column. Eight 1-cm