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[求助]
碱法提取结合态多酚，吹干后100%甲醇复溶，测量总酚时出现沉淀 已有2人参与
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本人在提取结合态多酚过程：80%甲醇提取游离态多酚后的固体残留，再用4M NaOH 处理2小时。调pH 到2， 用乙酸乙酯萃取5次，氮气吹干乙酸乙酯，然后用100%甲醇复溶。复溶后的液体澄清（复溶时小心吸取清液）。 在用福林酚法测总酚时发现加了福林酚后出现浑浊（100uL提取液+200uL福林酚试剂），再加碳酸钠后白色沉淀（800uL) （图）。开始排除原因时发现：100%甲醇复溶后的提取液加水即出现浑浊，静止后白色颗粒。溶液调整至80%甲醇，过0.45um 尼龙膜得到澄清液，再加水或者福林酚试剂和7.6%碳酸钠依旧有浑浊。 自己还不是很清楚什么原因，但猜测是水不溶性的物质？乙酸乙酯吹干后是不是应该用水复溶？如果是为什么？求各位大神指点！  IMG_0218.JPG |
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dcr408216613: 回帖置顶 2017-08-21 13:21:40
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各位，搜寻到一篇文章： “The Influence of Initial Carbonate Concentration on the Folin-Ciocalteu Micro-Method for the Determination of Phenolics with Low Concentration in the Presence of Methanol: A Comparative Study of Real-Time Monitored Reactions” https://file.scirp.org/pdf/AJAC20110700012_31845055.pdf “Moreover, an important F-C method drawback/limitation is that under some conditions precipitates can form. Consequently, it is necessary to resort to additional techniques, such as filtration or centrifugation, which are time-consuming and can sometimes reduce the blue col- our yield [3]. In order to prevent the precipitate formation, Singleton and Rossi [3] suggest accomplishing the assay at room temperature and not exceeding the 3% concentration of the sodium carbonate in the final mixture, although the initial carbonate solution to be used may be relatively concentrated (20%). Moreover, to obtain reproducible re- sults, Singleton et al. [14] suggest not exceeding the 1% alcoholic concentration in the final reaction mixture. In this regard, a sample dilution is carried out to avoid problem of precipitate formation but, sometimes, no dilution of alcoholic extracts can be carried out because of their low phenolic content.” 我觉得可以解释白色沉淀的发生。但是还是不能解释我的甲醇提取液加水即浑浊。以及出现这种情况应该怎么办的问题。 |
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