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
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!
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多酚一般情况下的水溶性都是比较差的,
即使是配置多酚类标准品,有些都需要醇类先溶解后,再用水稀释。
谢谢!那我先稀释5-10倍再试。就是有点担心浓度稀释太大UV 读数太低。另:担心跑HPLC时也会析出颗粒(刚开始的流动相是0.05%甲酸水)。
或者你查一下各个溶剂的极性和非极性 换一种溶剂呢? 我的一些实验步骤和你相像 做了一年多 从没出现过这样的情况 很好的问题
你是什么样品,是不是有脂溶性东西。
为什么 非要用乙酸乙酯萃取呢?样品很浑浊么?直接过滤不行么,然后调节ph到酸性。
如果是已经提取出来的多酚,水溶性应该是不错的啊,出现白色沉淀,感觉是脂溶性的东西被乙酸乙酯提取出来,浓度变大。
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,