Effect of the diluent:

The effect of the diluent on the variation of the distribution ratio of the metal ion can be summarized as under:

i) At low metal loadings, the distribution ratio is generally higher in aromatic and aliphatic hydrocarbons than in ethers and ketones.

ii) Especially low values are obtained in polar alcohols and chloroform.

iii) It still depends frequently on the aqueous phase conditions whether the unsubstituted aromatic or aliphatic hydrocarbons will show higher distribution ratio.

The most extensively used reagents of this class are tributyl phosphate, tributylphophine oxide, trioctyl phosphine oxide (TOPO). In the Nineteen eighties, the American Cynamid introduced a new extractant Cyanex 923 in the market. It is a mixture of four trialkylphosphine oxides and has shown a great potential for metal ion separations.