Retardation factor

In chromatography, the retardation factor (R) is the fraction of an analyte in the mobile phase of a chromatographic system. In planar chromatography in particular, the retardation factor R_f is defined as the ratio of the distance traveled by the center of a spot to the distance traveled by the solvent front. Ideally, the values for R_F are equivalent to the R values used in column chromatography.

Although the term retention factor is sometimes used synonymously with retardation factor in regard to planar chromatography the term is not defined in this context. However, in column chromatography, the retention factor or capacity factor (k) is defined as the ratio of time an analyte is retained in the stationary phase to the time it is retained in the mobile phase, which is inversely proportional to the retardation factor.

General definition

In chromatography the retardation factor, R, is the fraction of the sample in the mobile phase at equilibrium, defined as:

Planar chromatography