Extraction and spectrophotometric determination of zinc with 1-(2-pyridylazo)-2-naphthol and a non-ionic surfactant

Abstract

Zinc was extracted with 1-(2-pyridylazo)-2-naphthol, PAN, and polyoxyethylene nonyl phenyl ether with on average 7.5 ethylene oxide units, PONPE-7.5. This is 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, CP. Zinc in quantities up to 3.0 μg was placed in a certrifuge tube, along with 0.50 g of PAN solution (PAN, 0.040 g : PONPE-7.5, 20 g : water, 80 g) and 1 ml of pH 10.0 carbonate buffer. The mixture was diluted to 80 g with water. On standing this turbid solution (CP, 0°C) at room temperature, a lower phase (about 0.7 ml) rich in PONPE-7.5 separates out from the solution. The zinc chelate of PAN is extracted into the lower phase. The two phases can be separated by centrifuging for 1 min at 9500 rpm. After most of the supernatant solution has been poured off the whole solution in the tube was made up to 2.00 g with 0.5 g of 20% PONPE-20 solution and water. This final solution (CP, 60°C) is clear at room temperature. At the maximum wavelength (555 nm) of the chelate the absorbance was measured. Concentration factors up to 40 can be obtained. When sodium tartrate, triethanolamine, N-(dithiocarboxy)-sarcosine and sodium metaphosphate are used as a masking agent, the method can be applied to the determination of zinc in water.