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Direct sensing of total alkalinity profile in a stratified lake

M. Ghahraman Afshar1,

1Department of Inorganic and Analytical Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211 Geneva, Switzerland

M.-L. Tercier-Waeber1,

1Department of Inorganic and Analytical Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211 Geneva, Switzerland

B. Wehrli2,3,

2Department of Surface Waters Research and Management, Eawag−Swiss Federal Institute of Aquatic Science and Technology, Seestrasse 79, CH-6047 Kastanienbaum, Switzerland
3Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätsstrasse 16, CH-8092 Zürich, Switzerland

E. Bakker1

1Department of Inorganic and Analytical Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211 Geneva, Switzerland

Affiliations  |  Corresponding Author  |  Cite as  |  Funding information

Ghahraman Afshar, M.-L., Tercier-Waeber, M., Wehrli, B., Bakker, E. (2017) Direct sensing of total alkalinity profile in a stratified lake. Geochem. Persp. Let. 3, 85-93.

Swiss National Science Foundation EU FP7

Geochemical Perspectives Letters v3, n1  |  doi: 10.7185/geochemlet.1709
Received 6 June 2016  |  Accepted 17 October 2016  |  Published 10 November 2016
Copyright © 2017 European Association of Geochemistry




Figure 1 (a) Schematic illustration of the alkalinity probe. (b) Electrochemical cell composed of a proton pump and a pH probe placed directly opposite. The two reference electrodes (RE1 and RE2) and counter electrode (CE) are inserted in the bulk sample solution. The carbonate species are titrated with the hydrogen ions released from the proton pump. The resulting change of pH is subsequently assessed potentiometrically at the pH probe.
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Figure 2 (a) The titration curve for various depths in the range of 1 to 12.5 m using the thin layer instrument. Solid line is theoretical. (b) Correlation between the thin layer chemical modulation method and volumetric acid-base titration reference method (ISO 9963-1:1994). Solid line shows ideality with unity slope and zero intercept.
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Figure 3 (a) Total alkalinity depth profile and (b) pH depth profile obtaining during field monitoring on the Lake Greifen (31 August 2015).
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Supplementary Figures and Tables


Figure S-1 Schematic illustration of the electrochemical cell. The proton pump was placed directly opposite the pH sensor while the thin layer sample gap was between the pH sensor and the proton pump. The counter electrode and reference electrode for the proton pump (not shown) were placed in the sample solution. The reference electrode for the pH sensor was also in the sample solution in the beaker.
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Figure S-2 (a) Potentiometric time trace for the pH sensor in the pH range of 3 to 12. (b) Corresponding pH calibration curve. The observed electrode slope was 57.3 mV.
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Figure S-3 (a) Potentiometric time trace at the pH probe for the titration of the Lake Greifen sample obtained at 12 m depth. (b) The obtained EMF value after applying each pulse as a function of the pulse number. (c) The calculated pH value at the pH sensor for each pulse.
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Figure S-4 (a) Absolute error for the alkalinity detection in mM. (b) Percentage relative error for the alkalinity determination. The average relative error of 0.95 % (less than 1 %) was obtained for the alkalinity detection by the methodology.
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Figure S-5 Long-term stability for both pH sensor and proton pump.
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Figure S-6 (a) Reproducibility of the potential pulse by applying potential pulse of 300 mV vs. OCP for 30 s within one day. (b) Integrated charge of the potential pulse for every 4 hours.
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Figure S-7 (a) Influence of temperature on the released charge by applying potential pulse of 600 mV vs. OCP over 60 s. (b) The obtained charge value for various temperature within the range of 20 to 30 oC.
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Figure S-8 (a) The influence of the background concentration on the released charge by applying potential pulse of 600 mV vs. OCP for 60 s. (b) Integrated charge for various sodium chloride concentrations within the range of 10-5 to 10-1 M as a background electrolyte.
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Figure S-9 (a) Classical acid-base titration for Lake Greifen sampled at 1 m depth. (b) Thin layer chemical titration for Lake Greifen sampled at 1 m depth. The alkalinity level at this depth is obtained as 2.59 mM. The red line is a theoretical fit.
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Figure S-10 (a) Classical acid-base titration for Lake Greifen sampled at 2.5 m depth. (b) Thin layer chemical titration for Lake Greifen sampled at 2.5 m depth. The alkalinity level at this depth is obtained as 2.64 mM. The red line is a theoretical fit.
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Figure S-11 (a) Classical acid-base titration for Lake Greifen sampled at 4 m depth. (b) Thin layer chemical titration for Lake Greifen sampled at 4 m depth. The alkalinity level at this depth is obtained as 2.69 mM. The red line is a theoretical fit.
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Figure S-12 (a) Classical acid-base titration for Lake Greifen sampled at 5.5 m depth. (b) Thin layer chemical titration for Lake Greifen sampled at 5.5 m depth. The alkalinity level at this depth is obtained as 3.04 mM. The red line is a theoretical fit.
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Figure S-13 (a) Classical acid-base titration for Lake Greifen sampled at 7 m depth. (b) Thin layer chemical titration for Lake Greifen sampled at 7 m depth. The alkalinity level at this depth is obtained as 3.30 mM. The red line is a theoretical fit.
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Figure S-14 (a) Classical acid-base titration for Lake Greifen sampled at 8.5 m depth. (b) Thin layer chemical titration for Lake Greifen sampled at 8.5 m depth. The alkalinity level at this depth is obtained as 3.60 mM. The red line is a theoretical fit.
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Figure S-15 (a) Classical acid-base titration for Lake Greifen sampled at 12 m depth. (b) Thin layer chemical titration for Lake Greifen sampled at 12 m depth. The alkalinity level at this depth is obtained as 4.11 mM. The red line is a theoretical fit.
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