The change in the colorimetric pH with changes in salt concentration is determined with reference to the quinhydrone electrode. The salts used caused a more alkaline reading with the quinhydrone electrode and a more acid reading with the colorimetric method. The effect is much more pronounced in the lower concentrations. The "colorimetric pH" does not change appreciably in concentrations from about 1 molar to saturation.
Proceedings of the Iowa Academy of Science
©1933 Iowa Academy of Science, Inc.
Dudycha, John A. and Peterson, Ben H.
"The Salt Effect of Certain Indicators in Slightly Buffered Solutions,"
Proceedings of the Iowa Academy of Science, 40(1), 97-97.
Available at: https://scholarworks.uni.edu/pias/vol40/iss1/43