Nonionic Surfactants in Photometric Determination of Trace Metals

Abstract

The usual explanation offered for solubilization leads to solubilized species being regarded as distributed between a micellar phase and an bulk aqueous phase, with the micellar phase playing the same role as the organic solvent in ordinary liquid-liquid extraction. Water-insoluble metal chelates are made soluble in micellar solutions of nonionic surfactants. When the two phases can be separated physically, it should be possible to concentrate the metal chelates into a small volume of the micellar phase in a similar manner to ordinary liquid-liquid extraction. This can be carried out depending on the fact that a micellar solution of a nonionic surfactant separates into two phases above a certain temperature, defined as the cloud point. Polyoxyethylene nonyl phenyl ether, with on average 7.5 ethylene oxide units (PONPE-7.5), was used. The cloud point of a dilute micellar solution of PONPE-7.5 is 1°, and hence the solution is turbid at room temperature. The two phases are readily separated by centrifuging. The zinc chelate of l-(2-pyridylazo)-2-naphthol was quantitatively extracted from 80 g of the solution into a small volume (1.3 ml) of the lower phase rich in PONPE-7.5. Nonionic surfactants will be useful as a new solvent for liquid-liquid extraction of metal ions.