The easiest way to find the chromatographic retention is to measure the time between the injection point and maximum of the detector response for correspondent compound. This parameter usually called "retention time". Retention time, tR is inversely proportional to the eluent flow rate.
The product of retention time and eluent flow rate, so called "retention volume", is more of a global retention parameter. Retention volume, VR represent the volume of the eluent passed through the column while eluting a particular component.
The second part is equal to the volume of the liquid phase in the column (dead volume, Vo), and it will be the same for any component eluted on this column.
Retention volume is independent of the flow parameters for the particular run, but it depend on the geometrical parameters of the column. VR will be different for the same compound eluted on the different columns packed with the same type of adsorbent.
The more universal and fundamental retention parameter is the ratio of the retention volume and dead volume (k).
k = VR/Vo
Historically, a slightly different retention parameter, called "capacity factor" (k') was introduced by the analogy with the liquid partitioning theory and widely accepted in chromatographic practice.
Capacity factor is dimentionless and independent on any geometrical parameters of the
column or HPLC system. It could be considered to be a thermodynamic characteristic of
the adsorbent-compound-eluent system.