This study investigates the efficiency of the photocatalytic degradation of metoprolol tartrate (MET), a widely used beta(1)-blocker, in TiO2 suspensions of Wackherr's "Oxyde de titane standard" and Degussa P25. The study encompasses transformation kinetics and efficiency, identification of intermediates and reaction pathways. In the investigated range of initial concentrations (0.01-0.1 mM), the photocatalytic degradation of MET in the first stage of the reaction followed approximately a pseudo-first order kinetics. The TiO2 Wackherr induced a significantly faster MET degradation compared to TiO2 Degussa P25 when relatively high substrate concentrations were used. By examining the effect of ethanol as a scavenger of hydroxyl radicals ((OH)-O-center dot), it was shown that the reaction with (OH)-O-center dot played the main role in the photocatalytic degradation of MET. After 240 min of irradiation the reaction intermediates were almost completely mineralized to CO2 and H2O, while the nitrogen was predominantly present as NH4+. Reaction intermediates were studied in detail and a number of them were identified using LC-MS/MS (ESI+), which allowed the proposal of a tentative pathway for the photocatalytic transformation of MET as a function of the TiO2 specimen. (C) 2011 Elsevier B.V. All rights reserved.