On the Specific Diclofenac–Iron Cation Interaction for Selective Diclofenac Removal from a Water Solution

Diclofenac is one of the most common, commercially available, non-steroidal anti-inflammatory drugs (NSAIDs) in the world, with thousands of tons produced and consumed per year, which creates issues related to its presence in water bodies and the need for its removal from them. Diclofenac forms complexes with cations of each metal, which has inspired a study to check if the formation/precipitation of such complexes can be used for effective diclofenac removal from water solutions. It was found that iron salts, e.g., FeCl3, can be used to remove diclofenac from a water solution in the form a of precipitated complex, provided that a high excess of iron salt was used. It has been observed that the diclofenac initial concentration of 5 × 10−4 M, as a result of FeCl3 addition, after 48 h, decreased by two orders of magnitude. Salts of other metals were found less effective in reducing diclofenac concentration. The iron cation–diclofenac interaction was found to be specific, since the precipitation of other drugs by iron cations has not been observed. In order to quantitively analyze the diclofenac removal (precipitation) by iron and other metal cations, the HPLC/ESI-MS analyses were performed.