Highly selective determination of trace quantities of Hg(II) in water samples by spectrophotometric and inductively coupled plasma-optical emission spectrometry methods after cloud point extraction

A cloud-point extraction method for preconcentration of ultra-trace quantities of mercury ions as a prior step to its determination by spectrophotometry is presented and discussed. Cloud-point extraction was carried out using [1-(2-ethoxy phenyl)-3-(2-chloro phenyl)] triazene (EOCT) as the chelating agent and Triton X-114 as the non-ionic surfactant. The preconcentrated mercury was then determined spectrophotometrically by measuring the absorbance of the surfactant rich phase at 366 nm and also by measuring the emission intensities in the ICP-OES signals at 253.7 nm. Linearity was obeyed in the range of 8.0–150.0 ng mL−1 and 20–200 ng mL−1 by ICP-OES and spectrophotometry, respectively. The variable affecting the combined preconcentration-emission and absorption methods have been evaluated and optimized. Under the optimum condition, the detection limit of 1.03 ng mL−1 and 5.46 ng mL−1 were achieved using ICP-OES and UV-vis, respectively. The results in this paper will show using spectrophotometric method after cloud-point extraction can be an appropriate method for determining of mercury concentration at the ppb level in place of ICP-OES which is too costly a method. The interference effect of some anions and cations was also tested. Finally, the proposed method was successfully used for determination of Hg(II) in some real samples.