https://doi.org/10.1351/goldbook.M03779

The interstitial velocity, u of the carrier gas multiplied by the pressure-gradient correction-factor, j: \[\bar{u} = u\ j\] \[\bar{u} = \frac{F\ j}{\varepsilon_{\text{I}}}\] where F is the nominal linear flow, ɛI is the interstitial fraction.*Source: *

Orange Book, 2^{nd} ed., p. 103 (https://media.iupac.org/publications/analytical_compendium/)

Orange Book, 2