A Novel Spectrophotometric and RP-HPLC methods for Determination of Nortriptyline hydrochloride and Pregabalin in Tablets

A Simple, rapid, specific, accurate, economical and precise UV spectrophotometric and RP-HPLC methods (in accordance with ICH guidelines) were developed and validated for determination of Nortriptyline hydrochloride and Pregabalin in tablet dosage form. The first method was based on Q - absorbance ratio, and absorbances of both drugs were determined at 239 nm (lambda max of Nortriptyline Hydrochloride) and 235 nm (Iso-absorptive Point) when dissolved in methanol. It is found that Pregabalin does not have chromophoric group. To be UV -sensitive, it was compulsory to introduce chromophoric group in Pregabalin structure and make it UV -sensitive. This was achieved by converting the primary amine group of Pregabalin through reaction with benzoyl chloride to form benzoylated derivative of Pregabalin. Benzoylated Pregabalin was determined at 225 nm using UV -visible spectrophotometer. The second method was based on RP-HPLC. The chromatographic separation was performed on an Inertsil ODS C18 column (250 x 4.6mmx 5 mu m) with a mobile phase of 0.56 %w/v Sodium hexane sulphonic acid dissolved in water acetonitrile (50:50 %v/v, pH 4.5 adjusted with Glacial Acetic Acid) at flow rate of 1.0 mL/min with DAD detection wavelength at 210 nm. Retention times of Nortriptyline Hydrochloride and Pregabalin were 7.3894 min and 4.0506 min, respectively. Beer-Lambert's law obeyed the concentration range of 2-12 mu g/mL for Nortriptyline Hydrochloride and 10-60 mu g/mL for Pregabalin. The results indicated that both spectrophotometric and RP-HPLC methods were linear, accurate, precise and robust with RSD values less than 0.2% and % recovery was within the standard limits (99 - 102%) .