Chromatography (rf Value)

Question

In a thin layer chromatography experiment a particular component travels 2.4 cm while the solvent front advances 8.0 cm from the baseline; what is the retardation factor of that component?

RankGuru · Accepted Answer

Chromatography separates the components of a mixture based on their differential movement between a stationary phase and a moving mobile phase. In thin layer chromatography the stationary phase is a thin layer of silica gel or alumina on a plate, and the mobile phase is a solvent that rises by capillary action. Each component is characterised by its retardation factor, defined as Rf = (distance travelled by the component from baseline) / (distance travelled by the solvent front from baseline). Here the component moves 2.4 cm and the solvent front moves 8.0 cm, so Rf = 2.4 / 8.0 = 0.30. A component more strongly adsorbed on the stationary phase moves slower and has a smaller Rf. The value 0.33 wrongly uses 8.0/24 or a miscalculated ratio. The value 3.33 inverts the ratio, dividing solvent distance by component distance, which is dimensionally and conceptually wrong because Rf cannot exceed one. The value 0.24 misreads the component distance as fixed digits without dividing properly. The Rf definition is exactly as given in NCERT chromatography. Plausibility check: Rf must lie between 0 and 1, and 0.30 satisfies this, unlike 3.33.

Chromatography (rf Value)

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