Study of the heavy atom-induced room temperature phosphorescence properties of melatonin and its analytical application

Liquid phase room temperature phosphorescence (RTP) properties of melatonin were studied using heavy atom induced-room temperature phosphorescence (HAI-RTP) technique. 1.2 M potassium iodide was used as a heavy atom reagent together with 0.002 M sodium sulphite as deoxygenating agent to produce the RTP signal. The maximum phosphorescence emission and excitation wavelengths of melatonin were 290 and 457 nm, respectively. The effect of potassium iodide concentration on the RTP lifetime of melatonin was also investigated and based on the results, the rate constants for phosphorescence decay (kp) and radiationless deactivation through reaction with heavy atom (kh) were determined. Based on the obtained results, a simple and sensitive room temperature phosphorimetric method was developed for the determination of melatonin. The method allowed the determination of 10.0–200 ng ml−1 melatonin in aqueous solution with the limits of detection and quantification of 3.6 and 12 ng ml−1, respectively. The proposed method was satisfactorily applied to the determination of melatonin in commercial pharmaceutical formulations.