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Licensed Unlicensed Requires Authentication Published by De Gruyter January 23, 2016

Determination of the stability constant of the calcium binding ligand in black liquor (BL) by potentiometric titration

  • Kim Granholm EMAIL logo , Tomasz Sokalski , Andrzej Lewenstam and Ari Ivaska
From the journal Holzforschung


The calcium binding ligand in black liquor (BL) has been investigated by the new CSSP (circumvention of slope and standard potential) method, which converts the potential of an ion-selective electrode to concentration or activity. The advantage of this approach is that the knowledge about the electrode standard potential and the slope of the calibration curve is not needed. Instead, two activities of calcium ion on the titration curve have to be estimated, for instance the starting activity before the titration begins and the activity at the end of the titration in presence of a large excess of the titrant. A solid-contact Ca2+-selective electrode was used to determine the stability constant of the Ca binding ligand in BL. In addition, the concentration of free and bound calcium was determined. The total Ca concentration obtained by the CSSP approach agreed well to that obtained by the ICP-OES technique. Other metal ions did not influence the determination if the BL concentration is around 3%.

Corresponding author: Kim Granholm, Process Chemistry Centre, c/o Laboratory of Analytical Chemistry, Åbo Akademi University, Biskopsgatan 8, FIN-20500 Åbo-Turku, Finland, e-mail:


The authors would like to express their gratitude to Finnish Funding Agency for Technology and Innovation, TEKES for their financial support. We also want to thank Dr. Nikolai DeMartini for the valuable discussions. This work is part of the activities at the Johan Gadolin Process Chemistry Centre, a Centre of Excellence financed by Åbo Akademi University.


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Received: 2015-9-10
Accepted: 2016-1-5
Published Online: 2016-1-23
Published in Print: 2016-8-1

©2016 Walter de Gruyter GmbH, Berlin/Boston

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