mean activity of an electrolyte in solution

in mass spectrometry
https://doi.org/10.1351/goldbook.M03774
Defined by the equation: \[a_{\pm }=\mathrm{e}^{(\mu _{\text{B}}- \mu _{\text{B}}^{\text{⦵}})\ \nu \ R\ T}\] where \(\mu _{\text{B}}\) is the @C01032@ of the solute B in a solution containing B and other species. The nature of B must be clearly stated: it is taken as a group of ions of two kinds carrying an equal number of positive and negative charges, e.g. Na+ + NO3 or Ba2+ + 2Cl or 2Al3+ + 3SO42− . \(v\) is the total number of ions making up the group i.e. 2, 3 and 5 respectively in the above examples. \(\mu _{\text{B}}^{\text{⦵}}\) is the @C01032@ of B in its @S05925@, usually the hypothetical ideal solution of concentration \(1\ \mathrm{mol}\ \mathrm{kg}^{- 1}\) and at the same temperature and pressure as the solution under consideration.
See also:
activity
Source:
PAC, 1974, 37, 499. (Electrochemical nomenclature) on page 510 [Terms] [Paper]