| Cloud point extraction(CPE)is a new liquid-liquid extraction which is based on the solubility and cloud point phenomenon of aqueous solutions of surfactants, upon alteration of the experimental conditions such as pH value of solution.The solution is separated into phases,which results in the separation of hydrophobe and hydrophile.CPE is an easy,safe,high efficiency and inexpensive methodology for preconcentration and separation.It has been widely used in the study of life sciences, environment sciences,and the preconcentration and separation of metal elements.Flame atomic absorption spectrometry is one of common methods in analyzing trace elements.Traditional preconcentration method is not satisfactory because of samples with small-volume and metal elements with trace content.Separation and preconcentration procedures prior to trace element determination have been explored to achieve more accurate,reliable and sensitive results and lower detection limits.The CPE method was based on employing Triton X-100 and OP-7 as nonionic surfactant,1-(2-Pyridylazo)-2-Naphthol(PAN)and Ammonium pyrrolidinedithiocar-bamate(APDC)as complexing reagent.The chemical variables affecting the detection process were optimized in the following 3 systems.(1)In PAN—Triton X-100 system,the detection limit of manganese is 7.4ng·mL-1at pH 11.0 under the optimum conditions.(2)In PAN—OP-7 system,the detection limits of manganese,cadmium,nickel, lead,copper and cobalt is 0.011μg·mL-1,6.6ng·mL-1,0.027μg·mL-1,0.066μg·mL-1, 8.5ng·mL-1and 0.026μg·mL-1at pH 11.0,9.0,8.0,8.0,8.0 and 7.0 respectively.The proposed method was applied to the determination of copper in river waters.The standard addition recovery of copper is 100.8%and RSD is 3.36%(n=10).(3)In APDC—OP-7 system,the detection limits of copper and cobalt is 0.013μg·mL-1and 0.052μg·mL-1at pH 5.0 under the optimum conditions.
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