Univariate and multivariate kinetic and structural analysis of photoinduced tetracycline degradation

Abstract

Tetracycline antibiotics found in waters worldwide pose a tremendous ecological and human health hazard due to bacterial resistances. Various processes are currently investigated to eliminate such anthropogenic micropollutants, among them advanced oxidation processes, where hydroxyl radicals cause disintegration of many organic substances. For mechanistic understanding and optimization for potential in-field use, kinetic descriptions and chemical reaction knowledge are important. Structural identification, quantitation and kinetic description of the substances are investigated via a univariate method, i.e. high-performance liquid-chromatography coupled with mass spectrometry and curve-fitting, and a multivariate method, i.e. absorption spectroscopy and curve resolution-alternating least squares fitting. The latter represented a fast, non-laborious analytical method. The univariate approach revealed four known and two new transformation products. First-order kinetics with follow-up reactions were observed. The univariate method yielded rate constants of about 0.33 min−1 for the degradation of both tetracyclines and distinct rate constants for transformation products, while rate constants of about 0.22 and 0.27 min−1 and an overall rate constant for non-identified transformation products were obtained from multivariate analysis due to the insufficient discriminatory power. Structural characterization, fast and easy kinetic parameter determination of photoinduced degradation may contribute to optimize advanced oxidation processes for the removal of antibiotics from waste water.