2.2. HPLC instrumental condition
Instrument used in the study was Shimadzu-LC equipped with Auto Sampler, DAD or UV detector and Empower software. A chromatographic separation of the three drugs was achieved with a Inertsil C18 (4.6 250 mm, 5 mm) analytical column using buffer potassium dihydrogen phosphate adjusted pH 4 with orthophosphoric acid: methanol:acetonitrile (70:10:20%v/v) in isocratic mode at a flow rate of 1 mL/min, column at ambient temperature and detection of all the drugs were monitored at 215 nm using a DAD detector. All the solvents were filtered through 0.45-mm nylon filter, and degassed in an ultrasonic bath previous to use. Measurements were carried out by using injection volume 20 mL and detection at 215 nm. For analysis of forced degradation analysis of samples, the PDA detector was used in scan mode with a scan range of 200e400 nm. The peak uniformity was expressed in terms of peak purity and was obtained spectral analysis report using previously mentioned software. Analytical method was optimized by using pure analytical standards (Table