The history and development of a rigorous metrological basis for pH measurements |
| |
Authors: | Petra Spitzer Kenneth W Pratt |
| |
Institution: | (1) Physikalisch-Technische Bundesanastalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany;(2) National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 8391, Gaithersburg, MD 20899-8391, USA |
| |
Abstract: | This paper discusses the basis and historical development of the traceability chain for pH. The quantity pH, first introduced
in 1909, is among the most frequently measured analytical quantities. The practical measurement of the pH value of a sample
is inexpensive, easy to perform, and yields a rapid result. However, the problems posed by the traceability of pH are not
easy to solve. Most pH measurements are performed by potentiometry, using a glass electrode as the pH sensor. Such pH electrodes
must be calibrated at regular intervals. Confidence in the reliability of pH measurements requires establishment of a metrological
hierarchy including an uncertainty budget for calibration that links the pH measured in the sample to an internationally agreed
and stated reference. For pH, this reference is the primary measurement of pH. A traceability chain can be established that
links field measurements of pH to primary buffer solutions that are certified using this primary method. This allows the user
in the field to estimate the measurement uncertainty of the measured pH data. As the realization of the primary measurement
is sophisticated and time-consuming, primary standards are generally realized at national metrology institutes. A number of
potentiometric methods are suitable for the determination of the pH of reference buffer solutions by comparison with the primary
standard buffers. The choice between the methods should be made according to the uncertainty required for the application.
For reference buffer solutions that have the same nominal composition as the primary standard, the differential potentiometric
cell, often called the Baucke cell, is recommended. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|