A study has been made of the extraction of sodium into bis (2,4,4 -trimelhylpentyl) phosphinic acid. The following basic constants were measured at 25°C using two-phase titration techniques: the solubility in water, S, the ionization constant, pKa the dimerization constant, K2, and the distribution coefficient, Kd. The results were found to be in agreement with values reported in the literature for other phosphorus based extractants. A comparison was made with the data reported for sodium extraction iD phosphorous, phosphonic and phosphinic acid based ex-tractants. The data indicated that similar behaviour can be expected for all these compounds.