Extraction and the application:

We know from Eq. that

D = K*[HR]ⁿ_o/[H⁺]ⁿ_a

If the reagent concentration is constant, after that

D = K* K*´ 1 [H⁺]ⁿ_a

And, assuming V_a and V_o to be equal,

E = 100 D / D + 1

or

D =      E/100 - E

D = K*´ 1/[H+ ]n      = E/ 100 - E

When E = 50

pH1/2 = 1/n log K*´

This indicates that pH at E = 50% is constant. The difference in pH1/2 values of two metal ions in a specific system is a measure of separability of these two metal ions. A detailed discussion on the effect of pH on extraction and the application of difference in pH ½  in the metal ion separations will be taken up in sub- Secs. 3.3.1 and 3.4.2, respectively.