Cyclodextrin enhanced spectrofluorimetric determination of melatonin in pharmaceuticals and urine

Melatonin forms a 1:1 inclusion complex with methyl-beta-cyclodextrin with an association constant of 139 +/- 30 M-1 at 20 degrees C. The effect of several cyclodextrins and derivatives on the fluorescence spectra of melatonin was studied with a great increase of fluorescence signal when methyl-beta-cyclodextrin was employed. Optimal conditions of the method were: [methyl-beta-cyclodextrin] = 0.01 M and temperature 20 degrees C; the pH does not affect the luminescence emission. The linear dynamic range (LDR) was 50-3000 ng ml(-1) and a limit of detection of 10 ng ml(-1) of melatonin was obtained with a relative standard deviation (RSD) of 0.77 % (at 0.3 mu g ml(-1) level). This simple method was satisfactorily applied to the determination of melatonin ia pharmaceutical preparations and urine.