Determination Of Melatonin In Food Supplements And Grains

Melatonin(MT)is an endogenous hormone secreted mainly by the pineal gland.It plays a significant role in physiological cycles and anti-aging.The synthesis ability tends to a downtrend with aging,especially for the middle-aged ones.People often take exogenous MT as compensation.If without proper control for dosage,the usually higher content in food supplements would weaken its own secretion,meanwhile,inhibit that of thyroid hormone and adrenaline.Therefore a simple and rapid method to detect the MT content in food supplements is necessary.Food is superior to medicine,for it is a healthy and safe way to acquire MT.In the present work,some routine grains have been selected and contrasted in the terms of the content of MT.The results are expected to offer some advice for target population.Due to low content in grains,traditional methods are difficult to meet measurement demand.It will be significant to propose a new method to determine MT in grains.A method for determination of MT and pyridoxine(PN)in food supplements has been proposed by capillary electrophoresis with UV detection.The proposed method has the merits of easy operation,high separation efficiency,low cost and high speed.After optimization,the method was evaluated.The recoveries(n=3),precisions(RSD%,n=3),detection limits are 87.6%～104.9% and 92.1%～102.7%,0.98%～1.65% and 0.95%～1.01%,1.5 mg/L and 1.0 mg/L for MT and PN,respectively,suggesting a good potential to be used for routine quick analysis.In addition,an on-line coupling system of solid-phase extraction(SPE)with high performance liquid chromatography(HPLC)has been developed by using a home-made interface.This is a new method for the determination of MT in grains(red rice,rice).The sample solution was concentrated,and then a distinct volumetric part of SPE elution was transferred to LC system with the delay time set at the best value.That is so-called zone-cutting technique,through which the sensitivity was improved.The method was evaluated after optimization of the experimental conditions.The recoveries(n=3),precisions(RSD%,n=3)are 89.2%～102.8% and 94.9%～103.8%,2.1%～4.1% and 2.8%～ 3.6% for red rice and rice respectively.The detection limit is 1.3 μg/L(S/N=3).The above experimental results demonstrate that the proposed method is accurate,reproducible,sensitive and applicable for the analysis of MT in grains.