关于PEG衍生物末端OH的羧化？ peg 分子量是多少? tlc chcl3-meoh 9:1 try this method for -cooh group: bromocresol green stain this particular stain is excellent for functional groups whose pka is approximately 5.0 and lower. thus, this stain provides an excellent means of selectively visualizing carboxylic acids. these will appear as bright yellow spots on either a dark or light blue background and typically, it is not necessary to heat the tlc plate following immersion. this tlc visualization method has a fairly long lifetime (usually weeks) thus, it is not often necessary to circle such spots following activation by staining. recipe to 100 ml of absolute ethanol is added 0.04 g of bromocresol green. then a 0.1 m solution of aqueous naoh is added dropwise until a blue color just appears in solution (the solution should be colorless prior to addition). ideally, these stains may be stored in 100 ml wide mouth jars. the lifetime of such a solution typically depends upon solvent evaporation. thus, it would be advantageous to tightly seal such jars in-between uses.查看更多
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