On-line field-amplified sample stacking in capillary electrophoresis for analysis of amitriptyline and its metabolite nortriptyline in plasma

A field-amplified sample stacking and capillary electrophoresis method is described for the determination of amitriptyline (Ami) and its metabolite nortriptyline (Nor) in human plasma. An untreated fused-silica capillary was used (31.2 cm, effective length 21 cm, 50 mum i.d.) for the analysis. The background buffer was Tris (1.4 M, pH 4.50) containing beta-cyclodextrin (beta-CD, 1.0 mM) and 50% (v/v) ethylene glycol. The separation voltage was 25 kV with a detection wavelength of 200 nm. In the method validation, the calibration curves were linear over a range of 10.0-500.0 ng/mL (rgreater than or equal to0.9975). The R.S.D. and R.E. were all less than 5% for the intra- and inter-day assay. The relative recoveries were greater than 99%. The limits of detection (S/N = 5, electric-driven injection 99.9 s) of Ami and Nor were 2.0 ng/mL (6.3 and 6.7 nM, respectively). After ingesting an Ami tablet, the blood sample from one healthy male volunteer (26-year-old, 70kg) was pretreated and analyzed. The levels of Ami and its metabolite Nor were determined, and closely matched the calculated data from pharmacokinetics of dosing Ami. (C) 2004 Elsevier B.V. All rights reserved.