Aim and Objective: Melatonin is an essential biomarker for sleep-related disorders.
Reliable methods of analysis are needed for melatonin. Therefore, a new chromophore (Rhodamine
B) was proposed for the assay of melatonin; this method succeeded to enlarge the working
concentration range and to decrease the limit of determination comparing with the method that just
used the native fluorescence of melatonin.
Materials and Methods: Rhodamine B was proposed as a new chromophore for the assay of
melatonin in biological, food, and pharmaceutical samples. Fluorescence was used for the
determination of melatonin.
Results: The results obtained using Rhodamine B were compared with those obtained by the native
fluorescence of melatonin. Using the new chromophore, melatonin was determined in the
concentration range between 0.01 and 50 pmol L-1, with the detection limit of 2.4 fmol L-1. The
recovery of melatonin was higher than 98.00% with a relative standard deviation of less than
0.10%, when the method was applied for the assay of melatonin in samples such as breast milk,
whole blood, milk powder, and pharmaceutical formulations.
Conclusion: Utilization of Rhodamine B enlarged the linear concentration range for the assay of
melatonin and decreased the detection limit, making possible the assay of melatonin in a variety of
samples such as pharmaceuticals, food, and biological samples.