By diazotization coupling reaction is one of the most frequently employed technique in pharmaceutical analysis. It involves measuring the amount of ultraviolet or visible radiation absorbed by a substance in solution as a method for estimation drug of Phenylephrine hydrochloride by reliant on azo-coupling reaction between (PHE)HCl and Clonazepam as a reagent. To reach to the aim of obtaining the colored product with a maximum absorbance 466nm. The linearity range for Phenylephrine hydrochloride was (0.5_9μg\ml) while the detections limit 0.006 and quantification limit 0.02μg\ml The Molar Absorptivity 2.5457 ×104L/mol.cm with Sandal’s sensitivity 0.01μg\cm2. Eventually these methods were successfully completed to determination of PHE.HCl in pure and commercial form.

Depending on the oxidative coupling reaction as a rapid and selective spectrophotometric method, reduced clonazepam and nitrazepam drugs were evaluated by using potassium bromate as oxidation agent for these drugs and phenylephrine hydrochloride as a new chromogenic reagent to give red coloured products for clonazepam and nitrazepam at a maximum absorption of 491 and 488 nm, respectively. The linear ranges was 2-60 µg mL -1 and 5-90 µg mL -1 while the molar absorptivity are 3.157 × 10 3 L mol -1 cm -1 and 3.825 × 10 3 L mol -1 cm -1 and their detection limits are 0.141 µg mL -1 and 0.104 µg mL -1 , respectively for clonazepam and nitrazepam. The proposed methods did not require any temperature control and also not affected by foreign excipients and henceforth successfully applied to determine clonazepam and nitrazepam in pharmaceutical preparations.