Objective: To develop and validate simple, sensitive, precise and free of organic solvents method for the determination of sildenafil (SIL) and vardenafil (VAR) in bulk and pharmaceutical formulation. Methods:The method is based on the reaction of studied drugs with a mixture of potassium iodide and potassium iodate in an aqueous medium at (25±2 °C) to form yellow coloured triiodide ions (I3 -) within 45 min. The reaction is followed spectrophotometrically by measuring the absorbance at 288, 351 nm and 285, 351 nm for sildenafil and vardenafil respectively. Results:The effects of analytical parameters on the reported systems were investigated. Beer's law of SIL was obeyed in the range of (0.4-12) μg ml -1 and (0.6-16) μg ml -1 . Molar absorptivity was found to be (67.659 ×10 3 ) lmol/cm and (37.955×10 3 ) lmol/cm at 288 nm, 351 nm respectively. Beer's law of VAR was obeyed in the range of (0.2-13) μg/ml and (0.5-40) μg/ml. Moreover, molar absorptivity's were found to be (68.719 ×10 3 ) l mol -1 cm -1 and (26.691×10 3 ) l mol -1 cm -1 at 285 nm, 351 nm respectively. Conclusion:The proposed method has been applied to determine the components in dosage forms with an average recovery of 98.15% to 103.45% and the results have been found in good agreement with those results obtained by the reference methods.

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Background simple, sensitive, free of organic solvents, kinetic spectrophotometric method has been developed for the determination of Clindamycin Hydrochloride, both in pure form and Capsules. Method is based on reaction of Clindamycin with potassium iodide and potassium iodate in an aqueous medium at (25 ± 2 °C) to produce yellow-coloured tri iodide ions (I3−). The reaction is followed spectrophotometrically by measuring the absorbance at wavelength 350 nm during 40 min. Results the effects of analytical parameters on reported kinetic methods were investigated. Under the optimized conditions, the initial rate and fixed time (at 10 min) methods were used for constructing the calibration graphs. The graphs were linear in concentration ranges 1–20 μg ml−1 with limit of detection of 0.12 and 0.22 μg ml−1for the initial rate and fixed time methods, respectively. The results were satisfactory and the analytical performance for both methods was validated. Conclusion The proposed methods have been applied to determine the components in capsules with an average recovery of 98.25–102.00% and the results are in good agreement with those found by the reference method.

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