What Does Void Volume Mean?
Void volume is the volume of the pores or space between particles in:
- Ion exchanger
- Filter media
- Other granular material
This is often expressed as a percentage of the total volume occupied by the material.
Void volume refers specifically to the volume of the liquid phase contained inside a column. The same term is sometimes also used informally to refer to the volume of a cavity in the column/tubing or fittings.
Void volume is also known as dead volume.
Corrosionpedia Explains Void Volume
Void volume is the volume of mobile phase (Vm or V0) in a column. In an ideal case, it is equal to the mobile phase hold-up volume. For example, if the stationary phase occupies 40% of the total column volume, the void volume would be 60% of the total column volume. Consider a column that is 25 cm long with an inner diameter of 1 cm. The total column volume is 19.6 mL. If the mobile phase occupies 60% of the column volume, the void volume is 11.8 mL.
In column chromatography, the volume of the mobile phase is the total bed volume of the column minus the volume occupied by the support particles.
In gel chromatography or exclusion volume, it is the volume of the mobile phase passing through the gel required to elute a molecule that never entered the stationary phase.
Various methods to estimate the total void volume include:
- Minor disturbance method
- Tracer pulse method
- Hold-up volume based on unretained compounds
- Accessible volume based on Martin's rule and its descendants
In post-tensioned ducts, where voids are discovered or suspected, a simple pressure test using compressed air can be used to determine the approximate void volume. It is the presence of corrosion, which may occur in the void, which is a cause for concern.
Void volume is an important carbon black structure property. A profile of void volume as a function of applied pressure provides a means to assess carbon black structure at varying levels of density and aggregate reduction.