Chromium speciation analysis by solid-phase extraction on a high surface area TiO2
The adsorption of Cr3+ and Cr6+ on different metal oxides (MgO, Al2O3, TiO2, ZrO2 and CeO2) with high specific surface areas was studied under different conditions. It was established that SiO2 can be used for selective and quantitative adsorption of Cr3+, whereas, depending on the pH, TiO2 and Al2O3 can selectively adsorb Cr3+ or Cr6+. On the basis of the results obtained, a simple and sensitive method for the selective determination of Cr3+ and Cr6+ in natural water samples using a column solid-phase extraction on a high surface area TiO2 (anatase) was developed. The conditions for quantitative and reproducible preconcentration, elution and subsequent ETAAS determination were established. The retention efficiency is better than 95% for Cr3+ and Cr6+, giving a sensitivity enhancement of 100 for a 100 ml sample volume. The proposed method is characterized by high precision and high reproducibility. The detection limit based on the 3ς criterion is 30 ng l−1 for Cr3+ and 24 ng l−1 for Cr6+.