Typesetting of the retardation factor (Rf)

Question

What should be the typesetting for the symbol of the retardation factor as used in thin-layer chromatography?

These are the possibilities:

• R_f - only f in italics
• R_f - both R and f in italics
• R_f - only R in italics

On Wikipedia, they have used all sorts of typesetting. There is also R_F with a capital F.

Answer 1

According to Nomenclature for Chromatography (IUPAC Recommendations 1993) [1, pp. 843, 845] (also listed in IUPAC Gold Book), retardation factor is denoted as follows:

1. Column chromatography: $R$ (capital $R$ in italics).

   3.7.13 Retardation Factor $(R)$

   The fraction of the sample component in the mobile phase at equilibrium; it is related to the retention factor and other fundamental chromatography terms:

   $$R = 1/(k + 1)$$

2. Planar chromatography: $R_\mathrm{F}$ (capital $R$ in italics and upright capital $\mathrm{F}$ in subscript).

   3.8.04 Retardation Factor ($R_\mathrm{F}$)

   Ratio of the distance travelled by the center of the spot to the distance simultaneously travelled by the mobile phase. Using the symbols of Fig. 2:

   $$R_\mathrm{F} = b/a$$

   By definition the $R_\mathrm{F}$ values are always less than unity. They are usually given to two decimal places. In order to simplify this presentation the $hR_\mathrm{F}$ Values may be used: they correspond to the $R_\mathrm{F}$ values multiplied by 100.

   Ideally, the $R_\mathrm{F}$ values are identical to the $R$ values (see 3.7.13).

   

Reference

1. Ettre, L. S. Nomenclature for Chromatography (IUPAC Recommendations 1993). Pure Appl. Chem. 1993, 65 (4). DOI: 10.1351/pac199365040819.