central composite design for the optimization of hydrogel based ph-dependent extraction and spectrophotometric determination of mercury

in the present work a ph-dependent cloud point extraction procedure using ph-sensitive hydrogel polymer was applied for preconcentration and spectrophotometric determination of the hg(ii) as its thio micher's ketone complex. central composite design (ccd) and response surface method were applied to design the experiments and find out the optimum conditions. four factors entitled concentration of hydrogel, hcl, tmk and kcl (to study the salting out effect) were investigated. at the optimum conditions, the analytical characteristics of the method (e.g., limit of detection, linear range, relative standard deviation) were obtained. linearity was obeyed in the range of 5-200 ng ml-1 of hg(ii) with a correlation coefficient of 0.987. the detection limit of the method was 1 ng ml-1 for hg(ii) ion. relative standard deviation (rsd) for 7 replicate determinations of complex mercury with thio micher's ketone was 3.37%. the interference effect of some anions and cations was also investigated.