Preconcentration of ultra-trace Cu(ii) and Cd(ii) using SPE based on an alizarin complexone modified silica gel with detection using FAAS and determination of ultra-trace Cu(ii) by the naked eye

Abstract

A new modified silica gel with alizarin complexone has been prepared and proven to act as a promising adsorbent. Ultra trace Cu(II) and Cd(II) can be selectively enriched and separated from rice and water samples by solid phase extraction and detected by FAAS. What is more, 0.003 mol L⁻¹ and 0.25 mol L⁻¹ of HNO₃ can be used as eluent for the gradient elution of Cd(II) and Cu(II), respectively. Cu(II) could be completely separated from Cd(II) and monitored with the naked eye using color agent 5-Br-PADAP. The selectivity of the adsorbent and the effects of solution pH, type and concentration of the eluent, and foreign ions have been investigated and optimized. Under the optimized conditions, the adsorption capacity for Cu(II) and Cd(II) was 0.511 and 0.157 mmol g⁻¹, respectively. Determination of Cu(II) and Cd(II) by FAAS was linear in the range of 1.0–200 µg L⁻¹ and 2.5–100 µg L⁻¹ with a detection limit of 0.21 µg L⁻¹ and 0.46 µg L⁻¹, respectively. Comparing the determination results for Cu(II) and Cd(II) in water and rice using the new method with those detected by ICP-MS, a considerable difference was not observed between the two methods. The method was validated with the certified reference material GBW08511 rice. Moreover, the determination of Cu(II) in the range of 20–120 µg L⁻¹ is sensitive to the naked eye and the determination results are good in agreement with those detected by UV-Visible spectrometry. The proposed method was simple and capable of determining Cu(II) and Cd(II) in real samples accurately.