Retention factor (k')
The retention factor (also known as capacity factor) is a measure of how retained an analyte is. It is calculated using the retention time (tR) and the hold-up time (tM). The hold-up time is the time needed for the sample to reach the detector after the injection. Therefore, it measures the time that non-retained compounds need to reach the detector. The expression can also be written as a function of the relative retention time (t’R). This is the time that the analyte needs to reach the column after the non-retained compounds.
If the distribution constant is independent of sample component concentration, then the retention factor (k') is also equal to the ratio of the amounts of a sample component in the stationary and mobile phases respectively, at equilibrium:
