Destruction of valsartan using electrochemical and electrochemical/ persulfate process. Kinetics, identification of degradation pathway and application in aqueous matrices

In this paper, the electrochemical oxidation (EO) of antihypertensive drug valsartan (VAL) on a boron-doped diamond anode was investigated. The impact of current density (1.25-25 mA/cm(2)), initial solution pH (3-10), valsartan concentration (0.25-1.5 mg/L), supporting electrolyte (0.1 M sulfate or chloride ion), and the water matrix (bottled water (BW), wastewater (WW), pure water (UPW) and UPW spiked with various water constituents) was systematically investigated. The apparent, pseudo-first order kinetic constant was found to increase with increasing current density and decreasing pH, VAL concentration and matrix complexity. Notably, the use of chloride as the supporting electrolyte was less efficient than the rather "inert" sulfate. The addition of persulfate (50-250 mg/L) in the EO process significantly enhanced performance, i.e. a 4-fold rate increase was recorded for the degradation of 0.5 mg/L VAL at 12.5 mA/cm(2) in UPW added with 250 mg/L persulfate. VAL degradation is accompanied by the formation of various transformation products (TPs), seven of which were identified by UPLC-ESI-MS analysis. Major pathways include cyclization, hydroxylation, cleavage of the amide bond, and decarboxylation-dealkylation of the tertiary amine group reactions; the identified TPs were common regardless of the addition of persulfate, however, their distribution depended on the rate of VAL degradation.