Abstract
For the first time two simple and selective spectrophotometric methods have been developed for the determination of Retigabine in pure and pharmaceutical formulations. Of two methods, method M1 was based on the oxidative coupling of Retigabine with 3-Methyl-2-Benzothiazolinone hydrazone hydrochloride reagent in the presence of 0.1 % FeCl3 formed red coloured complex showed maximum absorbance at 501.6 nm at reagent blank. Under the reaction conditions, MBTH on oxidation with Fe (III) loses two electrons and one proton forming an electrophilic intermediate which has been postulated to be the active coupling species and to form colored species and in method M2 based on reaction of Retigabine on treatment with 1, 10-phenanthroline to give blood red coloured chromogen which shows the absorbance maximum at 508 nm under the optimized experimental conditions. The developed method obeyed Beer’s law over the concentration ranges of 2-10 µg/mL and 1-5 µg/mL for method M1 and method M2 respectively. In both cases the R2 is more than 0.9997. These methods were validated in pursuance of ICH Q2 (R1) guidelines. The % recovery was found to be in the range of 99.05 to 99.98 % for M1 and 99.06 to 99.86 % for method M2. With regard to precision, the intraday and interday precision for methods M1 and M2 were found to be 0.144 µg/mL, 0.219 µg/mL and 0.206 µg/mL, 0.203 µg/mL, respectively. The results relating to LOD and LOQ for methods M1 and M2 were found to be 0.207µg/mL, 0.049 µg/mL and 0.629 µg/mL, 0.150 µg/mL respectively. The molar absorptivity, Sandell’s sensitivity, for both methods were also reported. No interference due to the commonly used excipients as well as the method is specific for detecting Retigabine. So the developed methods can be applied successfully for the determination of Retigabine in bulk and pharmaceutical formulations.
