Selective Determination of Amitriptyline and Nortriptyline in Human Plasma by HPLC with Ultraviolet and Particle Beam Mass Spectrometry

A selective, sensitive, and reliable method was devised to determine concentrations of amitriptyline and its major metabolite, nortriptyline, in human plasma using high-performance liquid chromatography (HPLC) combined with UV and particle beam mass spectrometry (PBMS). Amitriptyline and nortriptyline were effectively extracted in a three-step solvent extraction procedure. Imipramine was used as the internal standard (IS). Amitriptyline, nortriptyline, and the IS were clearly separated by HPLC on a silica column with the mobile phase of acetonitrile-0.1 M ammonium acetate (94:6, v/v). The calibration curves were linear in the concentration range of 10-1000 ng/g for both compounds with UV and PBMS detections. The lower limits of detection were 5 ng/g for amitriptyline and 10 ng/g for nortriptyline with UV detection and 2 ng/g for amitriptyline and 5 ng/g for nortriptyline with PBMS detection. The absolute recoveries were 58% for amitriptyline and 47% for nortriptyline at a concentration of 50 ng/g. This method proved most useful in accurately identifying amitriptyline and nortriptyline in tissues from an autopsied individual.