Photolytic and photocatalytic degradation of antineoplastic drug irinotecan. Kinetic study, identification of transformation products and toxicity evaluation

This study focused on the photolytic and photocatalytic degradation of the antineoplastic drug irinotecan (IRI) in aqueous solutions. Photocatalysis was carried out using commercial TiO2 (Degussa P25) and several operational parameters were studied. Identification and structure elucidation of TPs were carried out with the complementary use of SPE-LC-MS/MS and SPE-LC-TOF-MS. In order to separately study photodegradation and photocatalysis, different initial pH values were selected (7 and 4, respectively), where each process was dominant. Significant photolytic degradation of IRI was observed at neutral and basic pH. Kinetics of photodegradation followed the pseudo-first order model, with the maximum kobs observed at pH 7. Quantum yields of IRI for photolytic degradation were calculated using three different methods, ranging from 0.00022 to 0.00499 mol Einstein(-1). Photocatalysis was the main phenomenon at pH 4 with the optimum concentration of TiO2 at 300 mgL(-1), while different kobs ranged from 0.007 to 0.040 min(-1). 19 TPs were detected during photolysis and 7 were structurally elucidated. 32 TPs were detected for the first time during photocatalysis and for 12 of them chemical structures were proposed. The addition of hydroxyl groups, the formation of open structures and the production of dimers were the main transformations observed during photocatalysis, while conversion of 4-ethylquinoline into quinoline during photolysis. DOC and toxicity values reduced much slower than IRI, possibly due to the subsequent production of TPs that are not easily degraded and remain in the solution as DOC.