In the present research work, RP-HPLC method coupled with diode array detection for separation and quantitation of impurity-l (2-(5-methoxy-1H-indol-3-yl)ethanamine), impurity-ll (3-(2-aminoethyl)-1 H-indol-5-ol) along with melatonin was developed. Mobile phase containing 10 mMolL~-1 sodium dihydrogenphosphate: acetonitrile (75:25 V/V) was found to give good resolution, effectively separating melatonin and its impurities. Calibration curve for melatonin was found to be linear in the concentration range 2.5 μg ml~-1 to 7.5 μg ml~-1. Calibration curve for impurity-l was found to be linear in concentration range 2.5 μg ml~-1 to 7.5 μg ml~-1 and the calibration curve for impurity-ll was found to be linear in concentration range of 1.8 μg ml~-1 to 5.4 μg ml~-1. The percentage recovery estimated of melatonin, impurity-l and impurity-ll was found to be within 98.20 to 99.91, 97.42 to 104.04, 98.35 to 100.06, respectively with R.S.D. The reported method is simple, precise, accurate and rapid for quantitation of melatonin impurities along with melatonin.
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