PH-sensitive hydrogel for coacervative cloud point extraction and spectrophotometric determination of Cu (II): optimization by central composite design

Abstract

In this work a new coacervative extraction method using pH-sensitive hydrogel has been developed for preconcentration and spectrophotometric determination of Cu (II) based on the complex formation with Zincon (2-carboxy-2″-hydroxy-5″-sulfoformazylbenzene) in water samples. In the extraction step, appropriate amounts of poly (styrene-alt-maleic anhydride), as a pH-sensitive hydrogel, was added into the aqueous solution, so a rather cloudy solution was formed. Organic and inorganic compounds having the potential to interact with polymer particles could be extracted into the organic phase. The surface area between the polymer particles and the aqueous sample becomes very large, so the equilibrium state is achieved quickly. After centrifuging, hydrogel-rich phase was sedimented in the bottom of sample tube. The sedimented phase was diluted with methanol and the absorbance of the solution was measured at 615 nm (λmax of the complex in hydrogel media). Central composite design (CCD) was performed at five levels to optimize the main experimental parameters including, concentration of hydrogel, HCl, Zincon and salting-out effect. Under the optimum conditions the linear analytical range was 5–500 ng mL−1 with a correlation coefficient of 0.991. The limit of detection was 3.4 ng mL−1. The proposed method is an efficient, rapid, simple and inexpensive microextraction technique and was successfully applied for the determination of copper in various water samples.