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 material (SiO2/Nb2O5/ZnO) was prepared.
• The life time of adsorbent was very high.
• A preconcentration factor of 26 times was achieved.
• The method provides low limit of detection and low sample consumption.

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 m2 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 μg L−1, with a limit of detection of 0.28 μg L−1. The precision of method, estimated as relative standard deviation of ten replicate measurements of 30 and 150 μg 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.