This study was focused to develop an analytical method to analyze beta-lactam antibiotics in aqueous solutions. The method is based on the chemical reaction between beta-lactam antibiotics with phosphomolybdic acid, a heteropolyacid able to be reduced by the thiols obtained after the acid hydrolysis of the beta-lactam antibiotics. The blue product obtained, which is proportional to the antibiotic amount, is adsorbed on polyurethane foam, and the intensity of color is directly evaluated on the solid material by means of diffuse reflectance spectroscopy.For the evaluated beta-lactam antibiotics, the analytical parameters achieved were: LOD = 0.03 µg/ml, LOQ = 0.1 µg/ml, RSD = 4.0 %. The study of possible interferences showed that using solid phase extraction is possible to eliminate even strong interferences as ascorbic acid, cysteine and reducing salts like stannous chloride. The method has avoided, as many as possible, the use of expensive and contaminating solvents and chemical reagents. The method presents the possibility to be applied using only a desktop scanner and a personal computer for measuring the intensity of color of the adsorbed material on the polyurethane foam.
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