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 Humic substances' proton-binding equilibria: Assessment of errors and limitations of potentiometric data
Please use this identifier to cite or link to this item http://hdl.handle.net/10773/6811

title: Humic substances' proton-binding equilibria: Assessment of errors and limitations of potentiometric data
authors: SANTOS, Eduarda B H
ESTEVES, Valdemar I
RODRIGUES, J P C
Duarte, Armando C
keywords: Fulvic acids
Hysteresis
Potentiometric data
issue date: 1999
publisher: Elsevier
abstract: The variability of experimental procedures referred to in the literature for the potentiometric acid±base titrations of humic substances was analysed and the corresponding implications on the titration data were studied. Hysteresis phenomena were observed in the titrations of all the studied samples: two samples of fulvic acids isolated from two different points of river Vouga (Portugal), one XAD-4 fraction isolated from one of those points and the Swannee river reference fulvic acid. Due to those phenomena, carboxyl contents and charge±pH curves calculated from direct and back-titrations can be considerably different. Other sources of variability, such as changes of the moisture content of samples, different calibration procedures or different equations for the calculation of activity coef®cients, are also shown to lead to large variations in the calculated carboxyl contents and charge±pH curves.
URI: http://hdl.handle.net/10773/6811
ISSN: 0003-2670
publisher version/DOI: http://dx.doi.org/10.1016/S0003-2670(99)00227-5
source: Analytica Chimica Acta
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