Metoprolol was the compound from which the most TPs originated (4). -Hydroxymetoprolol and -ketometoprolol were reported once in STP effluent [31]. -Hydroxymetoprolol was positively confirmed by the mass spectrum and RT of the reference standard. Although no such standard was available for-ketometoprolol, its presence is likely as a ketone-group is a potential oxidation product of a secondary alcohol [32]. The time-trend also shows that the decreasing abundance of -hydroxymetoprolol is followed by an increasing abundance of-ketometoprolol (Fig. 3), suggesting that -hydroxymetoprolol isa potential precursor of -ketometoprolol. In addition, a TP witha similar temporal trend as -ketometoprolol and which has notbeen described before was detected (Met 210). We propose this to be the product of an amide hydrolysis and N-dealkylation.
Furthermore, metoprolol acid as a major biotransformation product of metoprolol [33] was unambiguously identified. This was also the most abundant among the four identified metoprolol TPs. It sdecrease toward the end of incubation period points to a limited persistence.