Unbound extractant:

The problem of finding out the unbound extractant in the organic phase is resolved in an indirect way by the use of radiotracers preferably carrier - free. When we say radiotracers preferably carrier - free, the metal ion concentration used is several orders of magnitude lower and the extraction of the metal ion does not make a significant change in the concentration of the extractant. Thus, the equilibrium concentration of the extractant concentration is taken to be the same as the initial concentration.

Sometimes, these plots are drawn by taking the total concentration of the extractant without the use of radiotracers. This is based on two assumptions. The first one is that under the specified conditions, negligible transfer of the extractant from the organic phase to the aqueous phase takes place. The second is that the extractant concentration is so high compared to the metal ion concentration that the concentration of the extractant is taken equivalent to the total concentration. The two types of examples cited below refer to both type of situations - one using a radiotracer and the other without it.

Figure:  Variation of the distribution coefficient for Cd tracer in HCl as a function of Alamine 336 concentration in benzene. Curve 1,  0.25 M HCl; Curve 2,  2.0 M HCl; Curve 3,  6.0 M HCl