Spherical silica particles decorated with graphene oxide nanosheets as a new sorbent in inorganic trace analysis Rafal Sitko a, *, Beata Zawisza a , Ewa Talik b , Paulina Janik a , Grzegorz Osoba a , Barbara Feist a , Ewa Malicka a a University of Silesia, Institute of Chemistry, ul. Szkolna 9, 40-006 Katowice, Poland b University of Silesia, Institute of Physics, ul. Uniwersytecka 4, 40-007 Katowice, Poland H I G H L I G H T S G R A P H I C A L A B S T R A C T  Graphene oxide (GO) covalently bonded to the spherical silica.  Very stable sorbent for SPE of metal ions.  Excellent contact with solution due to the softness and flexibility of GO nanosheets.  Several adsorption–elution cycles without any loss of adsorptive prop- erties.  High adsorption capacity due to the wrinkled structure of GO nanosheets. A R T I C L E I N F O Article history: Received 13 March 2014 Received in revised form 5 May 2014 Accepted 10 May 2014 Available online 20 May 2014 Keywords: Solid-phase extraction Preconcentration Graphene Solid sorbent Nanomaterial Flame atomic absorption spectrometry A B S T R A C T Graphene oxide (GO) is a novel material with excellent adsorptive properties. However, the very small particles of GO can cause serious problems is solid-phase extraction (SPE) such as the high pressure in SPE system and the adsorbent loss through pores of frit. These problems can be overcome by covalently binding GO nanosheets to a support. In this paper, GO was covalently bonded to spherical silica by coupling the amino groups of spherical aminosilica and the carboxyl groups of GO (GO@SiO 2 ). The successful immobilization of GO nanosheets on the aminosilica was confirmed by scanning electron microscopy and X-ray photoelectron spectroscopy. The spherical particle covered by GO with crumpled silk wave-like carbon sheets are an ideal sorbent for SPE of metal ions. The wrinkled structure of the coating results in large surface area and a high extractive capacity. The adsorption bath experiment shows that Cu(II) and Pb(II) can be quantitatively adsorbed at pH 5.5 with maximum adsorption capacity of 6.0 and 13.6 mg g 1 , respectively. Such features of GO nanosheets as softness and flexibility allow achieving excellent contact with analyzed solution in flow-rate conditions. In consequence, the metal ions can be quantitatively preconcentrated from high volume of aqueous samples with excellent flow- rate. SPE column is very stable and several adsorption–elution cycles can be performed without any loss of adsorptive properties. The GO@SiO 2 was used for analysis of various water samples by flame atomic absorption spectrometry with excellent enrichment factors (200–250) and detection limits (0.084 and 0.27 ng mL 1 for Cu(II) and Pb(II), respectively). ã 2014 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +48 32 3591556; fax: +48 32 2599978. E-mail address: rafal.sitko@us.edu.pl (R. Sitko). http://dx.doi.org/10.1016/j.aca.2014.05.014 0003-2670/ ã 2014 Elsevier B.V. All rights reserved. Analytica Chimica Acta 834 (2014) 22–29 Contents lists available at ScienceDirect Analytica Chimica Acta journal homepa ge: www.elsev ier.com/locate /aca