Revision History for U.S. Geological Survey Techniques and Methods; Book 9, Handbooks for Water-Resources Investigations;
Section A, National Field Manual for the Collection of Water-Quality Data, Chapter 6.4, Measurement of pH

U.S. Geological Survey

Measurement of pH

Posted online - first release: 1998, as Techniques of Water-Resources Investigations (TWRI), book 9, chapter A6.4, version 1.0

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Revised: 2003, online as TWRI, book 9, chapter A6.4, version 1.2

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Revised: 2006, online as TWRI, book 9, chapter A6.4, version 1.3

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Revised: 2008, online as TWRI, book 9, chapter A6.4, version 2.0

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Revised and reposted February 22, 2021 online as Techniques and Methods (T&M), book 9, chapter A6.4

U.S. Geological Survey, 2021, Measurment of pH: U.S. Geological Survey Techniques and Methods, book 9, chap. A6.4, 21 p., https://doi.org/10.3133/tm9A6.4. [Supersedes USGS Techniques of Water-Resources Investigations, book 9, chap. A6.4, version 2.0.]

The personal authors were changed to the agency, U.S. Geological Survey.
The report series was changed as indicated above.
The layout was changed to match the current style and format of a USGS series report, and the text was set in two columns. A front cover, back cover, title page, and back-of-title page were added and show the following: the change of series (to a T&M), the change in authorship, and a statement that this 2021 release of chapter A6.4 in the T&M series supersedes TWRI, book 9, chapter A6.4, version 2.0.

Substantive changes made in book 9, chapter A6.4, in 2021 are summarized below.
Deleted:
Sections on calibration of the pH meter specific to measurements in low- and high-ionic-strength waters.
Procedure change:
The preferred location for meter calibration is the laboratory.
The procedure for checking of measurements made when the water temperature is more than 10 degrees Celsius different from the calibration temperature was added.
The electrode performance metric around the pH-7 isopotential point was precisely defined.
Expanded and updated:
Sections on calibration of the pH meter and measurement of pH made by using multiparameter instruments.