Application of Nb2O5-SiO2 in pre-concentration and determination of copper and cadmium by flow system with flame atomic absorption spectrometry

The use of niobium (V) oxide, chemically adsorbed on silica gel surface (Nb2O5-SiO2), as an adsorbent in a pre-concentration system for copper (II) and cadmium (II) determination was proposed. The procedure is based on the large ion-exchange capacity for the adsorption of copper (II) and cadmium (II) ions on the mini-column packed with Nb2O5-SiO2, followed by elution with 2.0 mol L-1 nitric acid and determination by flame atomic absorption spectrometry. Chemical and flow variables were optimized. The results demonstrated that the sample solutions containing copper (II) or cadmium (II) in a concentration range of 3.0 to 600.0 mug L-1 and 3.1 to 100.0 mug L-1 respectively, in a solution of pH 5.0 could be determined using a pre-concentration time of 2 min. The enrichment factor when using a sample volume of 10.2 mL and 2 min of pre-concentration was 17.5 and 20.3 for copper (II) and cadmium (II), respectively. The limit of detection for copper (II) and cadmium (II) was 0.5 mug L-1 and 1.0 mug L-1, respectively. The relative standard deviation (RSD) was lower than 1.4% for copper (II) and cadmium (II) when using a concentration of 25.0 mug L-1 for both metals. The method was tolerant to other ions usually present in water samples. Good accuracy was obtained by the analysis of water reference material and environment samples.