Methyl benzoate as a non-halogenated extraction solvent for dispersive liquid-liquid microextraction: Application to the preconcentration of copper(II) with 1-nitroso-2-naphthol

Methyl benzoate, whose density is greater than that of water, was used as a non-halogenated extraction solvent for dispersive liquid-liquid microextraction (DLLME). The quantitative extraction of some elements, such as Au(III), Cd(II), Co(II), Fe(III), Ni(II), Pb(II), and Pd(II), was achieved using some traditional extractants, including diethyldithiocarbamate, 1-(2-pyridilazo)-2-naphthol, 8-hydroxyquinoline, and 1-nitroso-2-naphthol (NN) with acetone as a disperser solvent. As a demonstration, the preconcentration of Cu(II) with NN was studied in detail. The Cu(II) in 8 mL of a sample solution was rapidly and quantitatively extracted at pH 7 using 80 mu L of methyl benzoate containing 1 mmol L-1 of NN; in this system, no disperser solvent was needed. After centrifugation, the extracted Cu(II) in a sedimented phase could be determined by electrothermal atomic absorption spectrometry. The detection limit was 2.3 ng L-1 (three times the standard deviation of the blank values, n = 8) as the Cu(II) concentration in 8 mL of the sample solution. The proposed method was applicable to the determination of Cu(II) in some water samples, including tap water, ground water, and snow-melted water without any interference.