Abstract: The factors, viz, image diameter and intensity, which affect the refractive-index gradient in a Z-pattern flow-cell are incorporated into a ray-tracing model where the flow cell is regarded as a dynamic lens. For methanol - water and THF - water test systems, the detector response predicted by this model correlated well with experimental measurement of the general shape, magnitude and direction of the refractive index artefact observed in LC and flow injection analysis.

Abstract: Direct in-line injection is successfully demonstrated for capillary electrophoresis using a commercially available injection valve designed for liquid chromatographic applications. The internal, fluid-contacting materials in this valve injector are composed of ceramics and PEEK (polyetheretherketone). In studies up to 20 kV, this materials design provides a sufficient dielectric interface to insulate the high-voltage buffer from the metal valve body. Partial-loop injections from 6 to > 60 nL are shown to be highly reproducible and generally consistent with direct electrokinetic injections under the same experimental conditions. The small extracolumn variance contributed hy the valve injection system is symmetrical, and the measured theoretical plates for 75-mum- and 100-mum-i.d., separation capillaries are 1.6 x 10(5) and 2.5 x 10(5), respectively, As a result, the separation performance is quite good, demonstrating the viability of in-line valve injection for capillary electrophoresis. This development in capillary electrophoretic instrumentation has important implications for the advancement of electrophoretic applications as well as for the design of completely integrated analysis systems.