relative retardation, R rel in planar chromatography, in trace analysis, in column chromatography

https://dx.doi.org/10.1351/goldbook.R05276
A term which is equivalent to relative retention used in column chromatography: the ratio of the R F value of a component to the R F value of a standard (reference) substance. Since the mobile phase front is common for the two components, the R F value can be expressed directly as the ratio of the distances travelled by the spot of the compound of interest (b i) and the reference substance (b st) respectively:
R rel = R F i R F st = b i b st
In former nomenclatures the symbol R s was used to express relative retardation in planar chromatography. Because of its identity with the symbol for peak resolution the symbol R rel is suggested for relative retardation in planar chromatography.
Source:
PAC, 1993, 65, 819 (Nomenclature for chromatography (IUPAC Recommendations 1993)) on page 845