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Determining Trace Levels Of Tetracycline In Solid And Liquid Samples Utilizing Complexation With A Transition Metal Cation

Ronald Bartzatt

Determination of tetracycline is achieved by incorporation into an octahedral complex with the transition metal cation iron(III), producing a red-brown mixture. An absorption spectrum, of the iron(III)-tetracycline complex shows an absorption maximum at 435 nm, which was monitored for determination by spectro-photometer. The complex formed was stable for more than 48 hours at room temperature. A spot test assay was found to be sensitive to less than 30 mg of the antibiotic. An interpolative assay which is performed in micro-reaction tubes was able to detect amounts to less than 30 μg of tetracycline. A microvolume assay for microliter samples of tetracycline (volumes less than 30 μicroliters) demonstrated sensitivity to as little as 6 μg tetracycline. Determination by standard curve allows rapid analysis of multiple samples and is shown linear over a sixteen fold range of concentration from 2.813 × 10-5 molar to 4.501 × 10-4 molar erythromycin, ampicillin, and streptomycin, which are common antibiotics, do not interfere with the assay results and can be present. Inorganic salts such as phosphates, azides, chlorides, carbonates, and bromides do not interfere with the assay result for tetracycline. Medicinal compounds such as aspirin, sulfanilamide, and quinine did not cause interference. The colorimetric response is easily discerned. Key Words: Tetracycline; Iron(III); Colorimetric; Assay, Spot test.