A non-ionic surfactant as a new solvent for liquid-liquid extraction of zinc(II) with 1-(2-pyridylazo)-2-naphthol

A new method for extracting zinc(II) with 1-(2-pyridylazo)-2-naphthol (PAN) has been developed, based on the fact that a micellar solution of a non-ionic surfactant separates into two phases above a certain temperature, defined as the cloud point. Polyoxyethylene nonyl phenyl ether, (PONPE-7.5; average number of ethylene oxide units 7.5) was used as the surfactant. The cloud point of a 0.40% PONPE-7.5 solution is 1 degrees , and hence the solution is turbid at room temperature. The two phases can be separated by centrifuging for 8 min at room temperature. The zinc chelate of PAN is quantitatively extracted from 50g of the solution into a small volume (about 1 ml) of the lower (surfactant-rich) phase over the pH range 8.0-11.5. After most of the supernatant solution has been removed, the amount of final solution is adjusted to 2.00 g with 0.5 g of 10% of PONPE-20 solution and water. This mixture is transparent at room temperature. The absorbance is measured as 535 nm. Concentration factors of up to 25 can be obtained by choosing appropriate amounts of final ( 2.0 g) and initial solution ( 50 g). This new technique has been applied to the determination of zinc(II) in tap water.