Hirst A D, Stevens J F
Ann Clin Biochem. 1985 Sep;22 ( Pt 5):460-88. doi: 10.1177/000456328502200503.
On theoretical grounds it would appear preferable to use calibrants which are not adjusted to a constant ionic strength, whether concentration or activity is being estimated directly. For indirect methods, when sample and calibrant are diluted in an ionic strength adjusting buffer, there is probably little difference between adjusted and unadjusted calibrants. In this case a simple calculation of concentration is possible. A simple algorithm may be used for activity estimation. The algorithm for direct concentration estimation is more complex. If concentration, rather than activity, is required an indirect method must be used. If activity is required a direct method must be used. The quantitative effects of variations in calibration procedure may be smaller than variations in junction potential.
