Potentiometric determination of trace acidic impurities in lactide
A method for the determination of trace acidic impurities in lactide using potentiometric titration in a non-aqueous medium is described. Lactic acid and its oligomers residue in lactide used for polymerization has a strong influence on the size and molar mass distribution of the resulting polylactide. In the case of the polymers of high quality, lactide with a content of free acids at the level of individual millimoles per kilogram is used. The described method demonstrates a new way for detecting the end point with the potentiometric electrode used for measuring in a non-aqueous environment. The effectiveness of the method has been verified for the methanolic solvent (known from the literature) and acetonitrile (not used previously). Concentration of the titrant and size of the sample were optimized. The determined content of acidic impurities in high-quality lactide determined by direct titration and the standard addition method was consistent with manufacturer’s specifications.
Keywordslactide vlactic acid acid impurities potentiometric titration
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