The volume occupied by the mobile phase between the particles in the packed section of a column. It is also called the interstitial volume or the void volume of the column. In liquid chromatography, the interparticle volume is equal to the mobile-phase hold-up volume () in the ideal case, neglecting any extra-column volume. In gas chromatography, the symbol may be used for the interparticle volume of the column. In the ideal case, neglecting any extra-column volume, is equal to the corrected gas hold-up volume ().