title: High-performance capillary electrophoresis/frontal analysis for the study of protein binding of a basic drug.
abstract: A simple high-performance capillary electrophoresis (HPCE) method based on the principle of frontal analysis was applied to the determination of the concentration of unbound basic drug in protein binding equilibrium. A small volume of sample solution (approximately 80 nL) containing 113-340 microM of verapamil (VER) and 100-550 microM of human serum albumin was introduced into the fused silica capillary (effective length, 22 cm; 50-microns i.d.) by suction. Because the silanol groups on the inner surface of the capillary were bound with linear polyacrylamide through Si-C bonds, electroosmotic flow was not generated even at pH 7.4 with an applied voltage of +10 kV. The unbound drug bearing positive charge migrated electrophoretically from the drug-protein mixed zone toward the detection end, whereas human serum albumin did not co-migrate because of its negative charge. The bound drug migrated after it was released from the protein. As a result of an 80-nL injection of the sample solution, VER was eluted as a zonal peak with a plateau region. The VER concentration calculated from the plateau height agreed well with the unbound VER concentration determined by the conventional ultrafiltration-HPLC method, with good reproducibility (CV, < 6.23%, n = 15). The present HPCE/FA system was applied to the Scatchard analysis of VER and alpha 1-acid glycoprotein binding, and the estimated binding parameters agreed well with literature values.
authors.affiliation: Faculty of Pharmaceutical Sciences, Kyoto University, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Shibukawa
authors.forename: Y
authors.initials: Y
authors.lastname: Yoshimoto
authors.forename: T
authors.initials: T
authors.lastname: Ohara
authors.forename: T
authors.initials: T
authors.lastname: Nakagawa
mesh_terms: D001798:Blood Proteins / Q000378:metabolism*; D002021:Buffers; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004586:Electrophoresis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009961:Orosomucoid / Q000378:metabolism; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D011485:Protein Binding; D012709:Serum Albumin / Q000378:metabolism; D013696:Temperature; D014700:Verapamil / Q000378:metabolism
chemical_list: D001798:Blood Proteins; D002021:Buffers; D009961:Orosomucoid; D004364:Pharmaceutical Preparations; D012709:Serum Albumin; D014700:Verapamil