Application of quinone-based fluorophore and native fluorescence for the spectrofluorimetric determination of agomelatine in dosage form: Identification of acidic and alkaline- induced degradation products by LC–MS/TOF

Three spectrofluorimetric methods were developed for agomelatine (AGM) determination in commercial tablets. Method A is based on measuring the native fluorescence of AGM aqueous solution at 230/360 nm. Methods B and C are based on the formation of a charge transfer complex between AGM and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) with measurement of the formed fluorophore at 365/475 nm and 250/304 nm, respectively. The relative fluorescence intensity (RFI) of AGM–DDQ complex was greatly enhanced in the presence of methyl-β-cyclodextrin (CD). The methods were linear over the concentration ranges of 0.015–0.5, 0.5–8.0, 0.09–6.0 and 0.05–0.2 μg/ml for AGM-native fluorescence, AGM–DDQ, AGM–DDQ–CD and AGM–TCNQ complexes, respectively with excellent correlation coefficients (r = 0.9999). The methods were validated as per the International Conference on Harmonization (ICH) guidelines and all validation requirements were satisfied. The developed methods were extended to the analysis of AGM in commercial tablets. Furthermore, the stability of AGM was studied under different stress conditions (alkaline, acidic, oxidative and photolytic). The potential alkaline and acidic degradation products were identified by LC–MS/TOF.