Preparation of SiO2/Nb2O5/ZnO mixed oxide by sol-gel method and its application for adsorption studies and on-line preconcentration of cobalt ions from aqueous medium

A new Nb2O5/ZnO mixed oxide dispersed in a silica matrix (i.e., SiO2/Nb2O5/ZnO) was synthesized via sol-gel method and used as an adsorbent of cobalt ions (Co2+). The material presented a high surface area (323 m(2) g(-1)) and the maximum adsorption capacity was found to be 0.518 mg g(-1), determined from the non-linear Langmuir-Freundlich isotherm model. The material was used as a chelating agent free-solid phase extractor (CAF-SPE) in an on-line preconcentration procedure, based on the adsorption of Co2+ ions (16.0 mL, pH 7.4) at a high flow rate (8.0 mL min(-1)) onto a mini-column packed with the adsorbent (200 mg). The analyte was then eluted with 1.0 mol L-1 HCl and transported toward the FAAS detector. Linear calibration range was obtained from 0.96 up to 150.0 mu g L-1, with a limit of detection of 0.281 mu g L-1. The precision of method, estimated as relative standard deviation of ten replicate measurements of 30 and 150 mu g L-1 analyte solutions, was found to be 4.6% and 3.1%, respectively. The reliability of method was verified through the analysis of water and food samples and the accuracy was confirmed by using a certified reference material. (C) 2013 Elsevier B.V. All rights reserved.