Analysis And Removal Of Fluoresecent Substance In Caffeine

Caffeine is a white powdery alkaloid and industrial synthesis is its main source.Fluorescence is one of the major factors affecting the quality of synthetic caffeine product.At present,there are few studies on fluorescent substances in caffeine,so it is of great importance to carry out research on detection and removal of fluorescent substances.High pressure liquid chromatography and fluorescence detector were used to separate and detect the fluorescence substances in caffeine samples.After optimization,the excitation wavelength and emission wavelength were determined to be 220 nm and400 nm,respectively.The relative quantitative method of fluorescent substance content relative to caffeine was established,and the kinds and relative contents of fluorescent substance in different caffeine samples were analyzed under this condition.It was found that there were 6 main kinds of fluorescent substances in crude caffeine,and 4kinds of fluorescent substances in qualified caffeine after refining.By comparing the spectra of qualified and unqualified products,it was determined that the substance with retention time of 9.820min（Substance 3 for short）was the main substance leading to unqualified fluorescence index of products.The caffeine purification methods such as potassium permanganate oxidation,sodium disulfite reduction,activated carbon adsorption,recrystallization and extraction were used to treat the recovered concentrated caffeine,and the effects on the contents of various fluorescent substances were investigated.Each refining method has good removal effect on fluorescent substance 2 and 4.For fluorescent substance 6,activated carbon adsorption can be effectively removed.Extraction can leave a large amount of fluorescent substance 3 in the mother liquor,so as to achieve the effect of removal of fluorescent substance 3 in caffeine recovered.Recrystallization can effectively remove all fluorescent substances,and the removal efficiency of substance 3 can reach 89.5%,indicating that substance 3 has a relatively high solubility in water.Different kinds of anion exchange resin were selected to adsorb a concentrated caffeine,and 717 strong basic anion exchange resin with high selectivity and strong adsorption capacity for fluorescent substance 3 was selected as the adsorbent by comparing the experimental results.Through static adsorption experiment,the optimal technological conditions for 717 resin to adsorb fluorescent substance 3 in caffeine are as follows: under the condition of p H 8 and temperature 40℃,adding 0.6 g resin into50 m L 1% caffeine concentration concentrated solution,717 resin can achieve more than 99% adsorption rate of fluorescent substance 3,and also has good adsorption effect on other fluorescent substances except fluorescent substance 2.717 resin can be used as an effective adsorbent to remove fluorescent substances in caffeine refining process.