Preconcentration and determination of Pb(ii), Cu(ii) and Cd(ii) ions on octadecyl silica membrane disk modified with 2-mercapto-benzoimidazole by flame atomic absorption spectrometry

Abstract

In the present work, 2-mercapto-benzoimidazole is used as modifier of octadecyl silica membrane disks (C18 disks) for preconcentration of trace amounts of Pb(II), Cu(II) and Cd(II) ions, followed by nitric acid elution and flame atomic absorption spectrometric (FAAS) determination. The system was off-line. The effect of factors influencing the extraction efficiency, i.e., pH of sample solution, amount of ligand, type and volume of eluent, sample solution and eluent flow rates were evaluated and optimized. The optimum pH value was obtained as 6.00. The amount of 3 mg of ligand was obtained as optimum value of sorbent and 5 mL of 2 mol L⁻¹ solution of HNO₃ with flow rate of 10 mL min⁻¹ was obtained as an eluent. Under optimum experimental conditions, the maximum capacity of the membrane disks modified with 3 mg of ligand was found to be 327.8 (±1.6), 245.2 (±1.6) and 211.4 (±1.3) μg for Cu(II), Cd(II) and Pb(II) ions, respectively. The corresponding detection limits were found to be 0.06, 0.14 and 0.18 μg L⁻¹ for Cu(II), Cd(II) and Pb(II) ions, respectively. Also the effect of the presence of some probable interfering ions on the recovery of the target metal ions was investigated under the optimized experimental conditions. The proposed method was successfully applied to the determination of Cu(II), Cd(II) and Pb(II) ions in various real samples such as mineral, spring and snow water samples and also it was used for analyzing these metal ions in spinach, nut and wheat samples. The results show that the recoveries are close to 100%, indicating that this method is suitable for determination of these ions in such samples. The reported method in literature was used for the evaluation of the validity of the proposed method and it showed that there were no statistically significant differences between the results obtained by the proposed method with those obtained using the reported method.