The exponential of the ratio of the @C01032@, \(\mu\), to \(R\,T\) where \(R\) is the @G02579@ and \(T\) the @T06321@, \(\lambda=\text{e}^{\,\mu/RT}\).
Green Book, 2nd ed., p. 40 [Terms] [Book]
See also:
PAC, 1984, 56, 567. (Physicochemical quantities and units in clinical chemistry with special emphasis on activities and activity coefficients (Recommendations 1983)) on page 569 [Terms] [Paper]
PAC, 1996, 68, 957. (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 959 [Terms] [Paper]