A novel method for tizanidine hydrochloride determination in aqueous solution based on fluorescence quenching of functionalised CdS quantum dots as luminescent probes

A novel, sensitive and convenient method for the determination of tizanidine hydrochloride (TZD) based on the fluorescence quenching of thioglycolic acid-capped CdS quantum dots (TGA-CdS QDs) is proposed. Luminescent CdS semiconductor quantum dots modified by thioglycolic acid were synthesized from cadmium nitrate and sodium sulfide in alkaline aqueous solution. The modified CdS QDs are water-soluble, stable and highly luminescent. When TZD was added into the CdS QDs colloidal solution, the surface of CdS QDs generates the electrostatic interaction in aqueous medium, which induces the quenching of fluorescence emission at 518 nm upon excitation at 340 nm. Under the optimal conditions, the Stern-Volmer calibration plot of F-ο/F against concentration of TZD was linear in the range of 3.0-18.0 μg/mL with a correlation coefficient of 0.9953. The detection limit was 1.35 μg/mL. The relative standard deviation for five determinations of 9 μg/mL TZD was 2.29%. The proposed method was successfully applied to commercial tablets with satisfactory results. The results were found to be in good agreement with those obtained by the reference method. The possible fluorescence quenching mechanism for the reaction is also discussed.