ABSTRACT
Theophylline was determined in human plasma by capillary electrophoresis (CE). The drug was used as a model substance to study a simple sample pretreatment often used in HPLC: to 200 microliters of plasma were added 400 microliters of acetonitrile to precipitate the plasma proteins and the supernatant was injected into the capillary after centrifugation. Three capillary electrophoretic systems were compared with respect to migration time and electrophoretic migration reproducibility. UV detection at 280 nm was applied. The separation was preferably made in an uncoated fused-silica capillary (57 cm x 75 microns I.D.) with 10 mM phosphate-borate buffer (pH 9.0) as the electrophoretic buffer. A linear calibration graph was obtained in the concentration range studied, 1.8-36 micrograms/ml (10-200 microM). The method permits the determination of theophylline in plasma at therapeutic concentrations of 4.5-20 micrograms/ml (25-110 microM) with acceptable precision.
