Quantification of diclofenac in natural waters by the photo-induced fluorescence (PIF) method

A photo-induced fluorescence (PIF) method was developed for the quantification of diclofenac sodium, sodium 2-[2-(2,6-dichloroanilino)phenyl]acetate (NaDCF), in natural waters. Since diclofenac is not naturally fluorescent, its photoconversion under UV irradiation was carried out to produce highly fluorescent photoproduct(s) in various media (water, methanol, isopropanol, acetonitrile, ethyl acetate, dimethyl sulfoxide (DMSO), and a water-isopropanol mixture). The photoproduct responsible for the intense fluorescence of NaDCF in aqueous media was identified as chloro-carbazole by gas chromatography-mass spectrometry (GC-MS). Several PIF parameters were optimized. Using the PIF method, a highly fluorescent diclofenac photoproduct was obtained at λex/λem = 235/360 nm, with optimum fluorescence achieved after 10 min irradiation in a water-isopropanol mixture (90:10 v/v). The limit of detection (LOD) and quantification (LOQ) for diclofenac sodium in this medium were 0.11 ng ml–1 and 0.37 ng ml–1, respectively, with low relative standard deviation (RSD) values. The PIF calibration curves demonstrated good linearity, extending over one to three orders of magnitude, with correlation coefficients (R2) near unity, indicating good reproducibility. Analytical applications of this method to natural water samples yielded satisfactory results, with average recovery rates ranging from 84.77 to 101.72 %.