COLORIMETYRIC ASSAY OF TOBRAMYCIN SULPHATE IN BULK AND IN DOSAGE FORMS

Three rapid, accurate and sensitive visible spectrophotometric methods for the assay of tobramycin sulphate have been development. Method A (λmax; 470 nm) is based on the reaction of tobramycin with 3-methyl-2-benzothiazolinone hydrazone hydrochloride in the presence of ceric ammonium sulphate. Method B (λmax; 505 nm) involves the reaction with p-dimethylaminobenzaldehyde in presence of sulphuric acid and ferric chloride. Method C (λmax; 579 nm), is based on the formation of a coloured ion-pair complex between tobramycin and rose bengal. All variables have been optimized and the reaction mechanisms presented. Regression analysis of the Beer’s plots showed good correlation in concentration ranges 1.0-12, 1.5-30, and 3.5-71 μg/mL for method A, B, and C, respectively. No interferences were observed from excipients and analyzing pharmaceutical dosage forms containing tobramycin tested the validity of the methods. The relative standard deviations were within 1.42%. For more accurate results, Ringbom optimum concentration ranges are 1.5-11, 3.0-27, and 7.0-68 μg mL, respectively. The apparent molar absorptivity, Sandell sensitivity, detection and quantification limits are also calculated.