Bratskaya S, Golikov A, Lutsenko T, Nesterova O, Dudarchik V
Institute of Chemistry FEBRAS, 159, Prospect 100-letiya Vladivostoka, Vladivostok 690022, Russia.
Chemosphere. 2008 Sep;73(4):557-63. doi: 10.1016/j.chemosphere.2008.06.014. Epub 2008 Jul 26.
Charge characteristics of humic and fulvic acids of a different origin (inshore soils, peat, marine sediments, and soil (lysimetric) waters) were evaluated by means of two alternative methods - colloid titration and potentiometric titration. In order to elucidate possible limitations of the colloid titration as an express method of analysis of low content of humic substances we monitored changes in acid-base properties and charge densities of humic substances with soil depth, fractionation, and origin. We have shown that both factors - strength of acidic groups and molecular weight distribution in humic and fulvic acids - can affect the reliability of colloid titration. Due to deviations from 1:1 stoichiometry in interactions of humic substances with polymeric cationic titrant, the colloid titration can underestimate total acidity (charge density) of humic substances with domination of weak acidic functional groups (pK>6) and high content of the fractions with molecular weight below 1kDa.
采用两种替代方法——胶体滴定法和电位滴定法，对不同来源（近海土壤、泥炭、海洋沉积物和土壤（渗漏计）水）的腐殖酸和富里酸的电荷特性进行了评估。为了阐明胶体滴定法作为腐殖质低含量快速分析方法可能存在的局限性，我们监测了腐殖质的酸碱性质和电荷密度随土壤深度、分级和来源的变化。我们已经表明，腐殖酸和富里酸中的两个因素——酸性基团强度和分子量分布——都会影响胶体滴定的可靠性。由于腐殖质与聚合阳离子滴定剂相互作用时偏离1:1化学计量比，胶体滴定可能会低估以弱酸性官能团（pK>6）为主且分子量低于1kDa的组分含量较高的腐殖质的总酸度（电荷密度）。
