SPECTROPHOTOMETRIC DETERMINATION OF OXYTETRACYCLINE BY FLOW-INJECTION

A flow injection spectrophotometric method is proposed for the determination of oxytetracycline. The method is based on the reaction of this drug with iron(III) in the presence of sulphuric acid to form a coloured complex. Less than 10-mu-g ml-1 of the drug (defined as the amount of the drug that gave a signal of twice the background noise) can be determined by measuring the absorbance at 435 nm of the complex formed. Parameters affecting the absorbance such as the acid concentration, sample volume and the reaction coil length were all studied in order to optimize them. The method was applied to the determination of oxytetracycline in real samples and some pharmaceutical preparations. The relative standard deviation was 1.7% for 80-mu-g ml-1 (for ten replicate injections). The sample throughput is 17 samples h-1. The effect of some foreign species was also investigated.