A quantitative high-performance liquid chromatography (HPLC) laboratory experiment which entails the isocratic separation and simultaneous determination of the two active components of a commercial antipsychotic tablet has been developed. The prescription formulation used in this experiment contains amitriptyline hydrochloride (a tricyclic antidepressant) and perphenazine (a tranquilizer). Our experiment makes use of a straightforward HPLC separation on a cyanopropyl-packed column with an acetonitrile:methanol:aqueous monopotassium phosphate mobile phase pumped at a flow rate of 2.0 mL/min. Analytes are detected by UV absorbance at 215 nm. These conditions yield highly symmetrical and well-resolved peaks in less than 5 min after the injection of a mixture.
In the experiment, students are given amitriptyline hydrochloride-perphenazine tablets without the manufacturer's labeled composition claim and a stock solution mixture with known concentrations of amitriptyline hydrochloride and perphenazine. They prepare four standards and a pharmaceutical sample of unknown concentration, assay each solution in quadruplicate, and plot average peak areas of the concentrations of the known solutions in the construction of a standard curve. From the mathematical relationships that result, the average masses of amitriptyline hydrochloride and perphenazine in the prescription tablet are determined. Finally, the standard deviations of the mean masses are calculated. The entire laboratory procedure and statistical data analysis can be completed in a single 3-hour period.
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