Coupling reaction.

Sensitive spectrophotometric method is described for the determination of tetracycline HCl in bulk and in pharmaceutical formulations. The method is based on the coupling of tetracycline HCl with diazotized 8-hydroxy quinoline reagent in basic medium at room temperature to form a reddish to brown mono azo dye soluble in water with maximum absorption at 395 nm. The reaction was followed up spectrophotometrically by measuring the increase in absorbance at 395 nm. The analytical performance of the method, in terms of accuracy and precision, was statistically validated; the results were satisfactory. The calibration graph is linear in the concentration range 1-20 μg ml-1 ,with 0.005 μg ml-1 detection limit and 0.324 μg ml-1 , 0.980 μg ml-1  Limit of detection(LOD) and Limit of quantification(LOQ) respectively. The method has been successfully applied to the determination of the studied drugs in commercial pharmaceutical formulations.