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.

目的和目的：褪黑激素是睡眠相关疾病的重要生物标志物。褪黑激素需要可靠的分析方法。因此，提出了一种新的生色团（若丹明B）用于褪黑激素的测定。与仅使用褪黑素天然荧光的方法相比，该方法成功地扩大了工作浓度范围并降低了测定范围。

材料和方法：罗丹明B被提议作为一种新型生色团，用于测定生物，食品和药物样品中的褪黑激素。荧光用于测定褪黑激素。

结果：将若丹明B所得的结果与褪黑素的天然荧光得到的结果进行了比较。使用新的生色团测定褪黑激素的浓度范围为0.01至50 pmol L-1，检测极限为2.4 fmol L-1。当该方法用于分析母乳，全血，奶粉和药物制剂等样品中的褪黑激素时，褪黑激素的回收率高于98.00％，相对标准偏差小于0.10％。

结论：若丹明B的使用扩大了褪黑激素测定的线性浓度范围，并降低了检出限，从而使得在各种样品（例如药品，食品和生物样品）中测定褪黑素成为可能。