Products and mechanism of verapamil removal in water by air non-thermal plasma treatment

Verapamil, a drug widely used to treat cardiovascular disorders and an important water pollutant, has been subjected for the first time to advanced oxidation by air non-thermal plasma (NTP) in a previously described DBD reactor. Product analysis was performed to assess the extent of mineralization to CO2, quantified by FT-IR analysis, and to detect and identify oxidation intermediates by LC/ESI-MS/MS. Many intermediates form and their time profile was monitored during the treatment. Thorough mass spectrometric analysis and comparison with literature data on the oxidation of the functional groups of verapamil by the reactive species present in the air plasma allowed us to identify most of the intermediates formed by non-thermal plasma activation. The majority of the identified compounds can be attributed to reactions of verapamil with ozone, one of the major oxidizing species in our DBD reactor. A few intermediates, though, appear to form following direct attack by hydroxyl radicals, whereas there is no evidence of any byproduct attributable to reaction with reactive nitrogen species. When treated at low initial concentration verapamil is almost completely mineralized (98%), as determined by total carbon analysis.