Highly sensitive Spectrophotometric method for the determination of Gabapentin in capsules using Sodium Hypochloride

A simple, selective and highly sensitive spectrophotometric method is described for the determination of gabapentin (GBP) in pure form and in capsules. The method is based on the reaction of GBP with hypochloride in the presence of Kolthoff buffer of pH 7.0 to form the chloro derivative of GBP; followed by the destruction of the excess hypochloride by nitrite ion. The color was developed by the oxidation of iodide with the chloro derivative of GBP to iodine in the presence of starch and forming the blue colored product which was measured at 590 nm. The optimum conditions that affect the reaction were ascertained and under these conditions, linear relationship was obtained in the concentration range of 0.2-5.0 µg/mL GBP. The calculated molar absorptivity and Sandell sensitivity values are 3.07 ×104 L/(mol.cm) and 0.0056 µg/cm2, respectively. The limits of detection and quantification are 0.04 and 0.12 µg/mL, respectively. The proposed method has been applied successfully to the analysis of GBP in pure form and in capsules and no interference was observed from excipients present in the capsules. The reliability of the proposed method was further established by parallel determination by the reference method and also by recovery studies. The reaction mechanism is proposed and discussed