Determination of amitriptyline in plasma samples by high-performance liquid chromatography

A simple and selective high-performance liquid chromatographic method for the determination of amitriptyline in human plasma has been developed. For plasma samples, the protein was removed with 1 M NaOH and 0.7 M ZnSO4. aqueous solutions. The chromatographic separation was performed on an analytical mbondapak C18 column (250 3.9 mm, i.d) with an isocratic mobile phase consisting of phosphate buffer-acetonitrile-triethylamine (65:35:0.1 v/v/v) adjusted to pH 5.1. Clomipramine was used as an internal standard. Using ultraviolet detection at 239 nm, the detection limit for amitriptyline in plasma was 5 ng/ml. No interferences were found with tricyclic antidepressant drugs, which allows this method to be used in clinical studies. The calibration curve was linear over the concentration range 5-200 ng/ml. The recovery was complete for plasma. The inter-day and intra-day assay coefficients of variation were found to be less than 10%.