Degradation of antihypertensive drug valsartan in water matrices by heat and heat/ultrasound activated persulfate: Kinetics, synergy effect and transformation products

Abstract

The oxidation of Valsartan (VAL), an antihypertensive drug, via heat activated sodium persulfate (SPS) was investigated. Operating parameters such as: VAL concentration (0.5–1.5 mg/L), SPS dosage (50–250 mg/L), solution pH (3–10) and temperature (40–60 °C) were examined. Complete destruction of 500 μg/L VAL was observed in ultrapure water (UPW) after 30 min of reaction at 50 °C, [SPS]= 100 mg/L near-neutral pH, while the observed pseudo-first-order kinetic constant was estimated equal to 0.1453 min−1.The observed kinetic constants were decreased as the water matrix's complexity increased and were found equal to 0.0098 and 0.0020 min −1 for bottled water and secondary effluent, respectively. Interestingly, the addition of 250 mg/L chlorides resulted in a slight enhancement of VAL removal rate from 0.1453 to 0.2341 min−1. The presence of 250 mg/L bicarbonates or 10 mg/L humic acid retarded the reaction almost 15.5 and 6 times, respectively. The combination of heat-activated SPS with low-frequency ultrasound in different water matrices unveiled a synergistic effect. The ratio of synergy S was calculated equal to 53% and 51% in BW and WW, respectively. VAL degradation followed four major pathways a) cyclization; b) hydroxylation in biphenyl or tetrazole moiety; c) cleavage of the amide bond; and d) cleavage of CN bonds in the tertiary amine group.