Potentiometric acidity determination in humic substances influenced by different analytical procedures

Carboxylic (CA), phenolic (PhA) and total (TA) acidity contents of five International Humic Substances Society (IHSS) standards and four model compounds were determined via the potentiometric titration method. Titration curves were scrutinized both by the BEST7 algorithm and the modified Henderson-H...

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Bibliographic Details
Published inJournal of the Brazilian Chemical Society Vol. 20; no. 9; pp. 1715 - 1723
Main Authors Fernandes, Andreia N., Giacomelli, Cristiano, Giovanela, Marcelo, Vaz, Denise O., Szpoganicz, Bruno, Sierra, Maria M. D.
Format Journal Article
LanguageEnglish
Published Sociedade Brasileira de Química 2009
Subjects
CHEMISTRY, MULTIDISCIPLINARY
humic substances
potentiometry
phenolic acidity
carboxylic acidity
total acidity
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Summary:Carboxylic (CA), phenolic (PhA) and total (TA) acidity contents of five International Humic Substances Society (IHSS) standards and four model compounds were determined via the potentiometric titration method. Titration curves were scrutinized both by the BEST7 algorithm and the modified Henderson-Hasselbalch model (MHHM). In the case of IHSS samples, the fitting data depended on the analytical procedure undertaken. Whilst high CA and low PhA were usually recorded using the MHHM, the opposite trend was observed employing the BEST7 algorithm. In contrast, in the case of model compounds the acidity values matched well with theoretical data regardless of the procedure. In order to better understand the reasons for such discrepancies changes in the titrations procedure (e.g.: fast or slow) were also considered. General data strongly suggest that acidity determination of humic substances (HS) by potentiometric methods is extremely dependent on both the choice of mathematical model to fit experimental data points as well as the experimental conditions employed.
ISSN:0103-5053
1678-4790
DOI:10.1590/S0103-50532009000900021