腐殖酸的数均分子量测定

腐殖酸是广泛存在于土壤、污泥、泥炭、煤和水域中的天然大分子电解质,它对土壤肥力、植物生长、环境中元素的迁移和富集有重要作用,近廿年来日益为人们所重视,但其化学结构和分子量的确切范围目前尚不甚清楚。迄今为止,尚没有一种测定各种腐殖酸分子量的良好方法^[11]。

THE DETERMINATION OF NUMBER-AVERAGE MOLECULAR WEIGHT OF HUMIC ACIDS

A cryoscopic method has been used for the determination of number-average molecular weight of humic substances. Samples were dissolved in dilute alkali solution and then the pH of the sample solution was adjusted to that of the equivalent point of neutralization with the aid of canon exchange resin. Apparent molecular weight was corrected by determining the concentration of Na⁺ in the sample solution by means of the sodium ion electrode. The accuracy of this method is about 1-3%. For water soluble humic substance, it gave identical value as that obtained by Hansen and Schnitzers method. The Mn of humic substances from different origins examined by this method ranged from 600 to 3600.