# The Mechanism of Chromatographic Retention - Mixed Phases > Page 28

(4)

If the
corrected retention volume of the solute eluted by the pure strong solvent is
very small compared with the retention volume of the solute in the pure weak
solvent. *i.e*., (which can frequently occur in practical LC)
then equation (4) simplifies to the simple reciprocal relationship

(5)

It is found, that under the conditions stipulated, this reciprocal relationship fits the data extremely well, particularly at volume fractions below 0.5 of the strongly eluting solute.

In addition,
under the stipulated conditions the inverse relationship will also apply, *i.e*.
,

(6)

Equation (6) has been validated by the results from a number of workers (8,9) and an example of the expected correlation is given by the curves in figure 12, (9).

Courtesy of the Royal Society of Chemistry (ref. 14)

**Figure
12. Graphs Relating the Reciprocal of
the Corrected Retention Volume to the Volume Fraction of the Polar Solvent in
n-Heptane.**