Ozonation of Metoprolol: Elucidation of Oxidation Pathways and Major Oxidation Products

Abstract

Oxidation products (OPs) formed during ozonation of metoprolol were identified via liquid chromatography and hybride Qq LIT-MS. Experiments carried out at pH 3 and 8 showed the formation of different OPs, depending on pH. The analysis of samples with and without tertiary butanol (t-BuOH) revealed the influence of OH radical reactions. The OH radical exposure was measured by adding a probe compound (para-chlorobenzoic acid, pCBA). Elucidation of chemical structures confirmed the formation of aldehyde moieties as well as the occurrence of hydroxylation reactions. Several reaction pathways for the formation of the oxidation products are proposed. Analysis of ozonated raw wastewater and the effluent of a municipal wastewater treatment plant spiked with 10 microM metoprolol exhibited a similar OP formation pattern as detected in the reaction system at pH 8 without a radical scavenger. This indicates a significant impact of OH radical exposure on the formation of OPs in real wastewater matrices.