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介绍一种测定多元有机酸数均分子量的冰点下降—pNa校正法。供试有机酸用稀碱液溶解,以阳离子交换树脂调节溶液pH值至中和等当点,用低阻pNa电极测定溶液中游离的钠离子浓度和解离度,校正表观分子量,求得真实分子量。方法的精度在1~3%之间。用本法测定了不同来源腐殖酸的数均分子量,它们变动在600—3600间,适合各种腐殖酸的分子量测定。
A freezing point depression-pNa correction method for the determination of the number average molecular weight of polybasic organic acids is introduced. The test organic acids dissolved with dilute lye, the cation exchange resin to adjust the pH value of the solution to neutral point, with low resistance pNa electrode determination of the solution of free sodium ion concentration and dissociation, corrected apparent molecular weight, to obtain real Molecular weight. The accuracy of the method is between 1 and 3%. This method was used to determine the number-average molecular weight of humic acids from different sources. They vary between 600 and 3600 and are suitable for the determination of the molecular weights of various humic acids.