Research On Key Fluorescent Substances In Caffeine

Caffeine belongs to xanthine alkaloid compounds and is widely used in industries such as food,medicine,and cosmetics.However,due to its complex production process,fluorescence has always been a problem in industrial caffeine,and research on key fluorescent substances is of great significance.Comparing the caffeine spectra of qualified and unqualified products,it is determined that the substance with a retention time of 15.16 minutes is the key fluorescent substance that causes the fluorescence index of the product to be unqualified.The high-purity key fluorescent substance sample was purified by extraction and liquid preparation chromatograp Hy.Its structure was characterized by high performance liquid chromatograp Hy（HPLC）,high resolution mass spectrometry（TOF/Q-MS）,nuclear magnetic resonance spectroscopy(¹HNMR,¹³CNMR)and Fourier transform infrared spectroscopy（FT-IR）.The final molecular structure of the impurity was determined as8-hydroxy-1,3-dimethyl-7,8-dihydro-1H-imidazo[5,1-f]purine-2,4,6（3H）-trione.Based on the obtained samples of key fluorescent substances,a standard quantitative analysis method for this substance was established in high-performance liquid chromatograp Hy with a fluorescence detector,and accurate quantitative analysis of key fluorescent substances in various processes of caffeine industrial production samples was completed.The basic p Hysical properties of key fluorescent substances were measured,including liquid-liquid p Hase equilibrium data and solubility data in water.It was found that the key fluorescent substances were circulating and accumulating in the system due to their low solubility,which was the reason for the abnormally high concentration of fluorescent substances in a concentrated product.Analysis of the content of caffeine samples found that the content of key fluorescent substances in chlorine extract and crude coffee was relatively low.The source of key fluorescent substances was verified through potassium permanganate oxidation experiment,and the possible formation mechanism was inferred from the obtained molecular structure.Caffeine recrystallization is a very effective method for removing fluorescent substances.A concentrated product can be recrystallized once in aqueous solution to remove more than 90%of the key fluorescent substances,and can be recrystallized three times to remove more than 99%and meet the requirements of qualified products;A concentrated product can be recrystallized once in the methylated mother liquor or saturated crude coffee solution,which can remove over 80%of the key fluorescent substances;In industry,it is more suitable to add 16 methylated mother liquor per concentrated product,or to add 12-14 saturated coarse coffee liquor per concentrated product,so that the concentration of key fluorescent substances in the solution is lower than the saturation solubility,breaking their circulation and accumulation in the production system,and discharging the system.This solution can reuse methylated mother liquor,reduce fresh water consumption,and achieve energy conservation and emission reduction.The 3-aminopropyl trimethoxysilane（APS）was selected as the diatomite modifier,which can react with the hydroxyl groups on the surface of diatomite to form coupling,and the modified diatomite can adsorb key fluorescent substances to a certain extent.The optimal modification conditions for diatomaceous earth were determined:the modified p H was 11,the amount of modifier added/diatomaceous earth was 1.25,and the modification temperature was 70℃.When the amount of modified diatomaceous earth added to a concentrated solution is 2.0g/L,its maximum adsorption rate can reach64.96%.Using modified diatomaceous earth as a decolorizing agent in refining experiments can reduce the ratio of potassium permanganate to activated carbon,and can break the cyclic accumulation of key fluorescent substances in the production system.The adsorbed modified diatomaceous earth does not require regeneration,and the production process is simple and pollution-free.It has guiding significance for improving the caffeine refining process and determining the next research direction.