Development of a Spectrophotometric Method to Assay Tetracycline Hydrochloride by Coupling with Diazotized p-Aminobenzoic Acid,: Application to Pharmaceutical Forms

This work comprises developing a sensitive and precise spectrophotometric procedure to analyze tetracycline hydrochloride in the bulk and in the drug forms. In this method, p-aminobenzoic acid reagent was diazotized with an equimolar NaNO 2 (sodium nitrite) solution in the existence of HCl (hydrochloric acid) to produce corresponding diazonium salt subsequently coupling with tetracycline hydrochloride in a basic solution of NH 4 OH to produce a yellow azo dye which was water soluble and has a maximum absorption at 422 nm versus a reagent blank. Under optimal conditions, the linearity of Beer's law was estimated to cover the concentration range of 0.25-17.5 µ g/ml with an exceptional determination coefficient (R 2 = 0.9993) and molar absorptivity of 1.66×10 4 l/mol.cm. The calculated values of detection limit (LOD) and quantitation limit (LOQ) were equal to 0.012 and 0.040 µ g/ml, respectively. The values of error percentage and precision (RSD%) ranges were calculated and found in the range of -0.08% to 3.3% and 0.16% to 1.59%, respectively. The stoichiometry of the product was set up to be 1:1 tetracycline hydrochloride: diazotized p-aminobenzoic acid. The mentioned procedure has been utilized successfully to the evaluation of tetracycline hydrochloride in capsules and ointment.