Preparation of SiO 2 /Nb 2 O 5 /ZnO mixed oxide by sol–gel method and its application for adsorption studies and on-line preconcentration of cobalt ions from aqueous medium Kristiany Moreira Diniz a , Felipe Augusto Gorla a , Emerson Schwingel Ribeiro b , Marcela Betta Olimpio do Nascimento b , Rodrigo José Corrêa b , César Ricardo Teixeira Tarley a,c,⇑ , Mariana Gava Segatelli a a Universidade Estadual de Londrina (UEL), Departamento de Química, Centro de Ciências Exatas, Rodovia Celso Garcia Cid, PR 445, Km 380, 86057-970 Londrina, PR, Brazil b Universidade Federal do Rio de Janeiro (UFRJ), Instituto de Química, 21941-909 Rio de Janeiro, RJ, Brazil c Instituto Nacional de Ciência e Tecnologia (INCT) de Bioanalítica, Universidade Estadual de Campinas (UNICAMP), Instituto de Química, Departamento de Química Analítica, Cidade Universitária Zeferino Vaz s/n, 13083-970 Campinas, SP, Brazil highlights  A new material (SiO 2 /Nb 2 O 5 /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. article info Article history: Received 3 September 2013 Received in revised form 10 November 2013 Accepted 12 November 2013 Available online 20 November 2013 Keywords: Cobalt Water and food samples SiO 2 /Nb 2 O 5 /ZnO Preconcentration FAAS abstract A new Nb 2 O 5 /ZnO mixed oxide dispersed in a silica matrix (i.e., SiO 2 /Nb 2 O 5 /ZnO) was synthesized via sol– gel method and used as an adsorbent of cobalt ions (Co 2+ ). 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 Co 2+ ions (16.0 mL, pH 7.4) at a high flow rate (8.0 mL min 1 ) onto a mini-column packed with the adsor- bent (200 mg). The analyte was then eluted with 1.0 mol L 1 HCl and transported toward the FAAS detec- tor. Linear calibration range was obtained from 0.96 up to 150.0 lgL 1 , with a limit of detection of 0.28 lgL 1 . The precision of method, estimated as relative standard deviation of ten replicate measure- ments of 30 and 150 lgL 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. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Cobalt has long been used in manufacturing process of alloys, batteries, magnetic and stainless steels, catalysts and pigments. The exposition to this element at high levels can cause nausea, reproductive problems, hypertension (high blood pressure), pul- monary diseases and hyperglycemia (high blood sugar) [1,2]. On the other hand, at low concentrations, cobalt is an essential element for human health, as a constituent of vitamin B 12 , and its insufficient intake from food can lead to anemia and weight loss [3]. Taking into account growing industrial activities, there is evi- dence to suggest that cobalt levels in air, water and soils have in- creased worldwide [4]. Therefore, cobalt monitoring in food and in the environment is of paramount importance. Nevertheless, due to great variability of matrix from sample to sample and the low concentration of this element, there is an increasing need to develop simple, selective and sensitive methods for a reliable anal- ysis. Electrothermal atomic absorption spectrometry (ETAAS) and inductively coupled plasma–mass spectrometry (ICP–MS) are very sensitive analytical techniques for detection of metal ions, but still suffer from the high acquisition and maintenance costs. Therefore, 1385-8947/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2013.11.027 ⇑ Corresponding author at: Universidade Estadual de Londrina (UEL), Departa- mento de Química, Centro de Ciências Exatas, Rodovia Celso Garcia Cid, PR 445, Km 380, 86057-970 Londrina, PR, Brazil. Tel.: +55 43 3371 4366; fax: +55 43 3371 4286. E-mail address: ctarleyquim@yahoo.com.br (C.R.T. Tarley). Chemical Engineering Journal 239 (2014) 233–241 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej