Spectrophotometric Determination of Tetracycline by Coupling with Diazotised 4-Aminoantipyrine in Presence of Cetylpyridinium Chloride

A spectrophotometric method for the determination of microgram amounts of tetracycline -HCl(TCH) has been proposed. The method is based on coupling of tetracycline-HCl with diazotized 4-aminoantipyrine in presence of cetylpyridinium chloride in alkaline medium. The molar absorptivity of the formed dye reached to 1.92×10 l.mol. cm at 537 nm and Beers law is obeyed within the range of 10-300 μg of tetracycline-HCl /10 ml (i.e.1.0 – 30 ppm). The colour reaction was highly stable, a relative error ranged from 2.5 to + 0.21 % and a relative standard deviation of ± 0.37 to ± 0.73 %, depending on concentration level of tetracycline-HCl. The proposed method has been applied successfully to the determination of tetracycline-HCl in pharmaceutical preparations.