High-performance thin-layer chromatography method for estimating the stability of a combination of irbesartan and amlodipine besylate

A simple, sensitive, precise high-performance thin-layer chromatographic (HPTLC) method has been developed for estimating irbesartan and amlodipine besylate in combination. It involves TLC aluminium plates pre-coated with silica gel 60-F254 as the stationary phase and a solvent system of chloroform/toluene/methanol/acetic acid (6/2.5/1.5/0.5, v/v/v/v). The Rf values were 0.57 ± 0.02 for irbesartan and 0.30 ± 0.02 for amlodipine besylate. The separated spots were analysed densitometrically in absorbance mode at 244 nm. The results were linear in the range 50–500 ng per band for irbesartan and 400–900 ng per band for amlodipine besylate, with limits of detection of 14.4 ng per band and 12.7 ng per band, respectively. The limits of quantification were 47.4 ng per band for irbesartan and 42.0 ng per band for amlodipine. After irbesartan and amlodipine stock solutions were subjected to acid and alkaline hydrolysis, chemical oxidation, dry heat degradation and photodegradation, the peaks for degraded product were well resolved from that for pure drug, with significant differences in their Rf values when assayed by the HPTLC method. The method was validated with respect to linearity, accuracy, precision and robustness and was used successfully to estimate irbesartan and amlodipine besylate in a synthetic mixture.