[deutdeut]

In determining the value of distribution coefficient, the concentration of a solute in one solvent is divided by the same soluite concentration in other solvent in the mixture, say iodine concentration in ether and water. But are there any rules saying that which value should be put as the denominator and numerator?

[DevaDevil]

The distribution coefficient (m) or partition coefficient for a component (A) is defined as the ratio of concentration of a A in extract phase to that in raffinate phase.

Find it here

[chiralic]

In aqueous/organic systems the organic phase concentration is, by convention, the numerator and the aqueous phase concentration the denominator.