Spectrophotometric determination of cetylpyridinium chloride in pharmaceutical products.

The aim of this work is to study the formation of chelate compound of strontium (Sr(II)) with bromopyrogallol red (BPR) and cetylpyridinium chloride (CPC) and to develop a simple, rapid and sensitive method for spectrophotometric determination of CPC in pharmaceutical products, based on the influence of micellar media on the absorption spectra of the complex of Sr(II) with BPR. The formation of the ternary complex (Sr(II)-BPR-CPC) is accompanied by a marked increase in the absorbance and a bathochromic shift in the maximal absorption of the complex from 555 to 627.5 nm, hence, there is a difference (Deltalambda=lambda(Sr) (BPR) (CPC)-lambda(Sr) (BPR)=72.5 nm) and large hyperchromic shift in lambda(max) (DeltaA=A(Sr) (BPR) (CPC)-A(Sr) (BPR)=0.258), and the ternary complex is stable for at least 2 days. The optimum pH range for the reaction is 4.0-5.0 and Beer's law is obeyed over the concentration range 0.01-0.07 mg/ml. The method has been successfully applied to the direct determination of cetylpyridinium chloride in pharmaceutical product where excellent agreement between reported and obtained results were achieved. The relative standard deviation was better than 1% in all cases.