The measurement and meaning of void volumes in reversed-phase liquid chromatography

The seemingly simple process of measuring the mobile phase volume, V0, in reversed-phase liquid chromatography has eluded unambiguous agreement for over 25 years. Examples exist in the literature where the reported volume is physically impossible, either equal to or larger than the empty column volume, or being so small that it would represent a total porosity of half the theoretical limit for well-packed columns. Here we review the many proposals for methods of measurement, and compare and critique them. At this time, there is still no consensus for the best method of measurement, and workers are urged to critically examine values they measure, to insure they are at least physically possible.