Photolytic and photocatalytic degradation of doxazosin in aqueous solution

Abstract

Doxazosin (DOX), a selective alpha blocker, is widely used in medical therapy as an effective antihypertensive agent. It is a frequently prescribed drug and for this reason, environmental and ecotoxicological research is of great importance in terms of exposure and risk for both aquatic species and humans. In this study we focused on photolytic and TiO₂ photocatalytic degradation processes of doxazosin under different simulated conditions, with the emphasis on identification of degradation products. Photolytic (without TiO₂) experiments were performed in the presence and absence of oxygen, while photocatalytic degradation of doxazosin aqueous solution has been carried out under constant oxygen flow. DOX degradation was more efficient in the TiO₂/UVA photocatalytic experiment than during photolytic processes (UVA and UVC, UVC-N₂). LC-HRMS analyses with electrospray ionization allowed observing the formation of several major degradation products depending on the reaction conditions (presence or absence of oxygen, photocatalysis). The transformation products were identified based on exact mass measurements, isotopic distribution, and fragmentation pattern. Among them, dominated C₁₇H₂₁N₅O₃ and C₁₇H₂₃N₅O₄ (cleavage of the dioxane cycle), and C₂₃H₂₅N₅O₇ (hydroxylation). The detailed degradation pathway has been proposed. Toxicity testing with V. fischeri luminescent bacteria revealed higher toxicity of samples in photolytic rather than photocatalytic experiments which might be attributed to the formation of different products.

Keywords: Doxazosin; LC-MS; Photocatalysis; Photolysis; Toxicity.