Identification of ultraviolet transformation products of diclofenac by means of liquid chromatography and mass spectrometry

• The removal of diclofenac from water samples by UV light was investigated.
• Transformation products were observed by reversed-phase LC/MS.
• Identification of seven transformation products not described in literature so far has been achieved.
• Fragmentation experiments were carried out to support proposed product structures.

The removal of the anti-inflammatory drug diclofenac, which can be determined in concentrations up to 1 μg/mL in the aquatic environment, from water samples by the use of UV light is investigated by liquid chromatography/mass spectrometry (LC/MS). It is very important to find out whether diclofenac is fully mineralized into non-toxic products or if the UV treatment leads to other potentially bioactive products. The irradiation of an aqueous solution of diclofenac with light in the wavelength range of 220 nm–500 nm provides a fast degradation of diclofenac in less than four minutes. Eleven transformation products have been detected by means of reversed-phase LC/MS, seven of which have not been described in literature before. Fragmentation experiments allowed their characterization and lead to proposed structures for most of them. Some of the structures may explain the increased toxicity, which was observed after irradiation of diclofenac solution by other groups.