Determination of the phenolic-group capacities of humic substances by non-aqueous titration technique

Akira Kirishima, Takashi Ohnishi, Nobuaki Sato, Osamu Tochiyama

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)446-453
Number of pages8
JournalTalanta
Volume79
Issue number2
DOIs
Publication statusPublished - 2009 Jul 15

Keywords

  • Dimethylsulphoxide (DMSO)
  • Fulvic acid
  • Humic acid
  • Non-aqueous titration
  • Phenolic-group

ASJC Scopus subject areas

  • Analytical Chemistry

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