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Errors in pH measurement with colorimetric indicators in low alkalinity waters |
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| Authors: | Terry A Haines John J Akielaszek Stephen A Norton Ronald B Davis |
| Institution: | 1. United States Fish and Wildlife Service, Columbia National Fisheries Research Laboratory, Department of Zoology, University of Maine at Orono, 04469, Orono, ME, U.S.A. 2. Department of Geological Sciences, University of Maine at Orono, 04469, Orono, ME, U.S.A. 3. Department of Botany and Plant Pathology, University of Maine at Orono, 04469, Orono, ME, U.S.A. |
| Abstract: | A series of laboratory and field studies were conducted to evaluate the reliability of colorimetric pH indicators in dilute, acidic surface waters in New England. Laboratory studies consisted of comparing colorimetric and electrometric pH results in synthetic solutions with a range of ionic strength and buffering capacity. Field studies involved simultaneous colorimetric and electrometric pH determinations in 52 New England lakes with differing water chemistry. Colorimetric indicators deviated from electrometric pH results at low alkalinities and near the end of their operating range. They agreed with electrometric values, within 0.2 unit, at alkalinities of 20 µeq 1-1 and greater, or near the center of their operating range. Changing ionic strength without changing buffering capacity did not affect results. When indicators were selected that bracketed sample pH, colorimetric determinations of pH in New England lakes agreed well with electrometric determinations. |
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