Abstract
Capillary zone electrophoretic (CZE) separations were performed after the injection of large sample volumes by use of a discontinuous buffer system for analyte focusing. Up to 700 nL were injected into a 75 μm i.d. capillary, corresponding to a 23 cm long sample zone. Automated analyses were performed in a commercially available instrument, which was modified to work with a larger pressure drop for hydrodynamic injection. The method was adapted to the determination of a low-molecular-weight enzyme inhibitor, DuP 714, in aqueous samples and a structurally related test compound in extracts from plasma samples. The separation system based on a coated capillary was stable and reproducible over several weeks use for aqueous samples, but the analysis of large volumes (> 600 nL) of solid-phase extracts from plasma, containing acetonitrile, indicated that there is a need for more stable coatings or more extensive sample cleanup. Calibration curves are presented for the test substances, showing a linear relationship between the area ratio of the solute vs. an internal standard and the concentration. Samples containing 50–100 nmol L−1 of solute could be successfully analyzed by CZE with UV detection at 215 nm, approaching levels that are relevant for bioanalytical applications.
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