In line valve injection for capillary electrophoresis

Direct in-line injection is successfully demonstrated for capillary electro phoresis 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 diel ectric interface to insulate the high-voltage buffer from the metal valve b ody. Partial-loop injections from 6 to > 60 nL are shown to be highly repro ducible and generally consistent with direct electrokinetic injections unde r the same experimental conditions. The small extracolumn variance contribu ted hy the valve injection system is symmetrical, and the measured theoreti cal plates for 75-mum- and 100-mum-i.d., separation capillaries are 1.6 x 1 0(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 in strumentation has important implications for the advancement of electrophor etic applications as well as for the design of completely integrated analys is systems.