Elucidation of phototransformation reactions of the X‐ray contrast medium iopromide under simulated solar radiation using UPLC‐ESI‐QqTOF‐MS

The highly polar, nonionic X‐ray contrast agent iopromide (C₁₈H₂₄N₃O₈I₃; 791 Da) is resistant to microbial degradation during the activated sludge process in wastewater treatment plants and hence is released into the aquatic environment. Against this background, the present study was conducted to evaluate the phototransformation, potentially constituting the most relevant removal mechanism in rivers and streams. The photolysis of the iodinated aromatic compound was investigated in a Suntest solar simulator using aqueous solutions. Following a 120‐min irradiation period, an almost complete primary degradation of iopromide gave rise to a series of photoproducts that were chromatographed on a reversed‐phase UPLC and subsequently characterized by a combination of accurate mass measurements on a ESI‐QqToF‐MS instrument and H/D‐exchange experiments. This analytical approach facilitated confident identification of eight prominent products with the following elemental compositions and molecular weights: C₁₈H₂₅N₃O₉I₂ (681 Da); C₁₈H₂₅N₃O₈I₂ (665 Da); C₁₇H₂₃N₃O₈I₂ (651 Da); C₁₈H₂₄N₃O₉I (553 Da); C₁₇H₂₄N₃O₈I (525 Da); C₁₅H₂₀N₃O₆I (465 Da); C₁₄H₁₈N₃O₆I (451 Da); and C₁₈H₂₅N₃O₉ (427 Da). Their formation was the result of four principal photoreactions: (1) gradual, and eventually complete, deiodination of the aromatic ring; (2) substitution of the halogen by a hydroxyl group; (3) N‐dealkylation of the amide in the hydroxylated side chain; and (4) oxidation of a methylene group in the hydroxylated side chain to the corresponding ketone. In conclusion, the findings of the artificial sunlight irradiation experiments indicated that in real environmental settings iopromide might suffer partial or even complete deiodination. Copyright © 2009 John Wiley & Sons, Ltd.