Large injection volumes in capillary liquid chromatography: Study of the effect of focusing on chromatographic performance

This paper describes a multivariate approach to study the effect on chromatographic conditions and to optimize such conditions in capillary liquid chromatography when high injection volumes are required. Several separations have been evaluated by using isocratic and gradient solvent elution, as well as isocratic elution combined with temperature programming. In this study, easily ionisable organic compounds with low logP have been used as representative analytes. Injection volume and nature of the injection solution have been evaluated in order to increase the sensitivity (peak area) and column performance (N values). The equations obtained by multiple linear regressions and response surfaces allow achieving the optimum on-column focusing conditions for chlorophenoxy acids, carbamates and heterocyclic amines.