Capillary electrophoretic bioanalysis of therapeutically active peptides with UV and mass spectrometric detection after on-capillary preconcentration

An earlier developed capillary electrophoresis, (CE) system with an on-capi llary adsorptive phase is investigated for its suitability to quantitate lo w concentrations of angioten-sin II and gonadorelin in plasma. An off-line solid-phase extraction is used for sample preparation. The on-line preconce ntration CE system allows multiple capillary volumes of sample solution to be injected, increasing the concentration sensitivity of CE with 3-4 orders of magnitude. Furthermore, possible influence of matrix salts can be ruled out by employing a rinsing step after sample application. Using short-wave length UV detection, reproducibility and linearity in the low nanomolar ran ge were satisfactory. The capillary could be efficiently-regenerated using a programmed between-run rinsing procedure, allowing 20-30 large injections of sample extracts. Coating of the capillary, improved the robustness of t he method. Mass spectrometric detection via a previously reported sheathles s interface increased the selectivity and sensitivity substantially. Recomm endations are provided for the sample preparation process, the most critica l part of the system. Further purification of the sample is required to all ow the loading of larger sample volumes and to optimize the system's robust ness.