Kirishima Akira, Ohnishi Takashi, Sato Nobuaki, Tochiyama Osamu
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 1-1 Katahira, 2-Chome, Aoba-ku, Sendai 980-8577, Japan.
Talanta. 2009 Jul 15;79(2):446-53. doi: 10.1016/j.talanta.2009.04.008. Epub 2009 Apr 10.
The phenolic-group capacities of five humic substances, such as, the Aldrich humic acid, the humic and fulvic acids extracted from a soil, the humic and fulvic acids extracted from a peat have been precisely determined by the non-aqueous potentiometric titration technique. The titration by KOH in the mixed solvent of DMSO:2-propanol:water=80:19.3:0.7 at [K(+)]=0.02 M enabled to measure the potential change in a wide range of pOH (=-log[OH(-)]), and thus to determine the capacities of phenolic groups which could not be precisely determined in the aqueous titration. The results of the titration revealed that the mean protonation constants of the phenolic groups were nearly the same for all humic substances and close to that of phenol in the same medium, indicating that each phenolic-group in the humic substances is rather isolated and is not electronically affected by other affecting groups in the humic macromolecule.
通过非水电位滴定技术精确测定了五种腐殖质的酚基容量，这五种腐殖质分别是Aldrich腐殖酸、从土壤中提取的腐殖酸和富里酸、从泥炭中提取的腐殖酸和富里酸。在[K⁺]=0.02 M时，于DMSO:2-丙醇:水 = 80:19.3:0.7的混合溶剂中用KOH进行滴定，能够在较宽的pOH（=-log[OH⁻]）范围内测量电位变化，从而确定在水溶液滴定中无法精确测定的酚基容量。滴定结果表明，所有腐殖质中酚基的平均质子化常数几乎相同，且与相同介质中苯酚的质子化常数相近，这表明腐殖质中的每个酚基相当孤立，不受腐殖大分子中其他影响基团的电子影响。
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