Development of a Spectrophotometric Method to determination Minoxidil by Diazotization-Coupling reaction with Sulfanilic acid

A straightforward, quick, and accurate spectrophotometric method using diazotized sulfanilic acid as reagent to quantify minoxidil in both its pharmaceutical and pure forms.In this method, p-aminobenzen sulfonic acid (sulfanilic acid) was diazotized with low molar sodium nitrite (NaNO2) solution in the presense of hydrochloric acid (HCl) to produce corresponding diazonium salt subsequently coupling with minoxidil drug , a yellow color of azo dye which was water soluble and has a maximum absorption (λmax) at 400 nm compared a reagent blank. An under best conditions, the linearity of Beer's law was estimated in the concentration range of (5-40) μg/ml with an exceptional determination Linearity coefficint (R2= 0.9993) and molar absorptivity of 4.624*103 l/mol.cm. The detection limit (LOD), quantitation limit (LOQ) and precision ranges (RSD%) were calculated equal to 0.012 , 0.040 μg/mLand 0.16% to 1.59%, respectively. The stoichiometry was showed to be 1:1 (minoxidil: diazotized Sulfanilic acid). The procedure has been utilized successfully to determination of minoxidil in tablets.