Stability-Indicating HPTLC Method for Simultaneous Quantification of Moxonidine and Amlodipine Besylate in Their Combined Pharmaceutical Dosage Form

A sensitive, selective and precise high performance thin layer chromatographic method has been developed and validated for simultaneous determination of moxonidine and amlodipine besylateboth as a bulk drug and in formulation. The method employed TLC aluminium plates pre-coated with silica gel 60F-254 as stationary phase while the solvent system was methanol: toluene: ethyl acetate: ammonia (10% v/v) (2: 3.5: 5: 1, v/v/v/v). The Rf values of moxonidine and amlodipine besylate were observed to be 0.46 ± 0.05 and 0.28 ± 0.03, respectively. The densitometric analysis was carried out in absorbance mode at 237 nm. The linear regression analysis data for the calibration plots showed a good linear relationship for moxonidine and amlodipine besylate over a concentration range of 100-3500 ng/band and 200?3500 ng/band, respectively. The method was validated for precision, robustness and recovery. The limit of detection and limit of quantification for moxonidine and amlodipine besylate were found to be 45.69 and 138.44 ng/band, 27.60 and 83.63ng/band respectively. Moxonidine and amlodipine besylate stock solutions were subjected to acid and alkali hydrolysis, chemical oxidation, dry heat degradation and photo degradation. The degraded product peaks were well resolved from the pure drug peak with significant difference in their Rf values. Stressed samples were assayed using developed HPTLC method. Sstatistical analysis showed that the method is repeatable, selective, and precise. Degradation products produced as a result of stress studies did not interfere with the detection of moxonidine and amlodipine besylate and the assay can thus be considered stability-indicating.