Highly selective preconcentration of Cu(II) from seawater and water samples using amidoamidoxime silica

Chemically modified silica containing amidoamidoxime group was studied as a sorbent for solid-phase extraction (SPE) and preconcentration of Cu(II) prior to determination by flame atomic absorption spectrometry (FAAS). The sorbent showed an extremely high selectivity towards Cu(II) in the pH range of 4-6, while the extraction of Pb(II), Cd(II), Ni(II) and Co(II) was low. The adsorption isotherm followed the Langmuir model and the maximum sorption capacity of 0.0163 mmol Cu(II)g(-1) was achieved. In the flow system, Cu(II) was completely retained on a column containing 40 mg of the modified silica at the flow rate of 4.0 mL min(-1) and quantitatively eluted by 5 mL of 1% (v/v) HNO(3). No interference from Na(+), K(+), Mg(2+), Ca(2+), Cl(-) and SO(4)(2-) at 10, 100 and 1000 mg L(-1) was observed. When applied for preconcentration and determination of Cu(II) in tap water, pond water, and seawater, the recoveries were 96, 101, and 95%, respectively, with high precision (% relative standard deviation (R.S.D.)<4) and low method detection limit (9 microg L(-1)).