Characterisation of captopril photolysis and photocatalysis by-products in water by direct infusion, electrospray ionisation, high-resolution mass spectrometry and the assessment of their toxicities

ABSTRACT

Pharmaceuticals of different therapeutic classes are found in the environment. Captopril is used worldwide as an antihypertensive drug, and it has been found in the influent, effluent and secondary sludge of wastewater treatment plants. Advanced oxidation processes, such as direct photolysis (UV-C) and heterogeneous photocatalysis (TiO₂/UV-C), are alternatives to enhance mineralisation of pharmaceuticals and their removal during water treatment. In this article, it was evaluated the degradation of captopril in aqueous solution induced by UV-C and TiO₂/UV-C systems. The process focused on the identification and monitoring of the by-products formed under these conditions by applying direct-infusion electrospray ionisation high-resolution mass spectrometry in the negative ion mode (ESI(-)-HRMS) and high-performance liquid chromatography coupled to high-resolution mass spectrometry (HPLC/HRMS). To evaluate the by-products toxicity, acute ecotoxicity tests were performed with the crustacean Artemia salina, and the cytotoxicity was evaluated with (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay using HepG2 cells. It was observed by ESI(-)-HRMS that after 120 min of light exposure, there was almost complete removal of captopril, with 93.5% removal efficiency during photolysis and 99.9% during photocatalysis. At these conditions, the rate of mineralisation, by total organic carbon (TOC), was only 2.92% for photolysis and 9.09% for photocatalysis, evidencing the formation of degradation by-products. Nine by-products of captopril photodegradation were identified, and their respective chemical structure elucidations were proposed. The treated samples were nontoxic to A. salina and HepG2 cells, indicating that both oxidative treatments (photocatalytic or photolytic processes) can be conveniently employed to remove captopril from aqueous media.

KEYWORDS:

• Photocatalysis
• captopril
• high-resolution mass spectrometry
• photolysis by-product elucidation
• toxicity assay

Acknowledgements

The authors would also like to thank Dr Versiane Albis Leão for the TOC analyses.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors wish to thank the Minas Gerais State Research Foundation (FAPEMIG) [process APQ 00918-13] and the Brazilian National Council for Scientific and Technological Development (CNPq) [process 473893-2013-1] for their financial support and the granting of research fellowships.