Development of a capillary zone electrophoresis assay to examine the disposition of [D-pen(2,5)]enkephalin in rats

A novel capillary zone electrophoresis (CZE) assay method was developed to evaluate the systemic disposition of [D-pen(2,5)]enkephalin (DPDPE) in rats. DPDPE was recovered from serum samples (200 mu l) by solid-phase extraction. Complete resolution of DPDPE and the internal standard ([D-ser(2)]leucine-enkephalin; DSLET) from other serum components was achieved within 15 min on a 50-mu m I.D. capillary column with berate buffer (25 mM, pH 8.3). The peak-height ratio (DPDPE to DSLET) was linear through 100 mu g/ml, with a detection limit of 250 ng/ml in serum, when absorbance of the column eluent was monitored at 210 nm. Serum samples obtained from rats after a 10 mg/kg intravenous bolus dose of DPDPE were analyzed with the present CZE method. The results suggest that CZE is a useful technique for quantitating therapeutic peptides in biological matrices.