Cloud point extraction and determination of Cd(II) in water by spectrophotometry and application of central composite design

A method for the determination of trace Cd+2 in water by cloud point extraction: a preconcentration step in conjunction with detection by spectrophotometry is described. The effects of some important variables were studied using central composite design and the optimum experimental conditions were evaluated by the desirability function combined with response surface methodology (RSM). In this work 10 mL analyte solution containing 20 mu g L-1 cadmium, pH was adjusted to 4.50 x 10(-6)mol L-1 concentration of dithizone and 2.5% (v/v) triton X-114 was kept in thermostated bath at 60 degrees C for 30 min. The conical tubes were then immersed in ice-water mixture for 5 min, allowing ease of removing the supernatant bulk aqueous phase. A small volume of surfactant-rich phase remained at the bottom of the tube. To facilitate sampling of the surfactant-rich phase 3 mL of ethanol was added. The proposed method allowed the determination of cadmium (II) in the range 5-60 mu g L-1 with good precision and accuracy and the detection limit was found to be 2.85 mu g L-1.