The interparticle volume of a packed column per unit column volume: \[\varepsilon = \frac{V_{0}}{V_{\text{c}}}\] It is also called the interstitial fraction of the column.
Source: PAC, 1993,
65, 819. (
Nomenclature for chromatography (IUPAC Recommendations 1993)) on page 832 [
Terms] [
Paper]