Carbon nanotubes as a solid sorbent for the preconcentration of Cr, Mn, Fe, Co, Ni, Cu, Zn and Pb prior to wavelength-dispersive X-ray fluorescence spectrometry Beata Zawisza a,n , Robert Skorek a , Grazyna Stankiewicz b , Rafal Sitko a a Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland b Chemical Analyses Laboratory, Institute for Ferrous Metallurgy, K. Miarki 12-14, 44-100 Gliwice, Poland article info Article history: Received 2 April 2012 Received in revised form 19 July 2012 Accepted 23 July 2012 Available online 31 July 2012 Keywords: Solid-phase extraction coupled to WDXRF Multiwalled carbon nanotubes Trace element preconcentration Natural water analysis abstract The preconcentration of trace elements on multiwalled carbon nanotubes (MWCNTs) followed by a wavelength-dispersive X-ray fluorescence analysis (WDXRF) has been investigated. The proposed preconcentration procedure is based on the sorption of trace elements on MWCNTs dispersed in analyzed solution. After sorption, the MWCNTs with the metal ions were collected onto the filter, and then the preconcentrated elements were determined directly by WDXRF. The preconcentration method was optimized, and in consequence, in order to obtain satisfactory recoveries using 100 mL of samples, the sorption process was performed with 1 mg of MWCNTs within 5 min. Some conditions of the preconcentration process such as the pH of analyte solution, amounts of MWCNTs, the volume of the sample, the contact time between analytes and MWCNTs (stirring time), and the effects of foreign metals are discussed in detail in the paper. Adsorption onto raw and oxidized MWCNTs was also studied. The proposed procedure allows obtaining the detection limits of 0.6, 0.6, 1.0, 0.7, 0.6, 0.5, 0.9 and 1.9 ng mL 1 for Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Pb(II), respectively. The recoveries of determined elements were about 100%. Because the analytes are not eluted from the sorbent before WDXRF analysis, the risk of contamination and loss of analytes is reduced to minimum. Moreover, because the samples are analyzed as a thin layer, the matrix effects can be neglected. The proposed preconcentration method using MWCNTs coupled with WDXRF spectrometry was success- fully applied to determine trace elements in natural water samples. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Several preconcentration methods for determination of trace elements are applied prior to X-ray fluorescence spectrometry (XRF). Because the XRF allows the solid samples to be analyzed, the precipitation and solid phase extraction (SPE) methods are willingly applied [1]. One of the most appropriate method is preconcentration of trace elements via direct precipitation with inorganic reagents such as MnO 2 , Mg(OH) 2 [2] Fe(OH) 3 , CaC 2 O 4 [3] and organic reagents such as thioacetamide [4], 8-hydroxyquinoline [5], dithiocarbamate [6] or more selective sodium 3-hidroxy-4-((1- hidroxy-2-naphtalenyl)azo)-7-nitro-1-naphtalensulfonate (EBT) [7]. The following step of the procedures using the aforementioned organic compounds was the filtration of the formed complexes and the deposition of the solid on the membrane. A simple method for the preconcentration of trace elements is also applied specially prepared filters, such as paraffin-treated cellulose filters [8], the iminodiacetate extraction disk (IED) [9], the filters with zinc sulfide layer [10], impregnated membranes and polymer inclusion mem- branes contained an anionic exchanger, Aliquat 336 [11,12]. There are also known methods using Aliquat 336 in combination with activated carbon [13] or using only activated carbon as a sorbent prior XRF analysis [14]. Carbon nanotubes (CNTs) – another allotropic form of carbon – have been recently applied willingly in analytical chemistry for the preconcentration of trace elements [15]. Both single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) are particularly useful for analytical application because of their unique properties. They are ideal as a solid-phase extraction adsorbent, because of their large specific sorbing sur- face areas and the hexagonal arrays of carbon atoms, which are profitable for strong interaction with organic compounds and metal ions. CNTs are usually used as a sorbent before flame atomic absorption spectrometry (FAAS) [16–18], electrothermal (ET) AAS [19–22], inductively coupled plasma atomic emission spectrometry ICP-OES [23–25]. There are also papers in which Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/talanta Talanta 0039-9140/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.talanta.2012.07.059 n Corresponding author. E-mail address: beata.zawisza@us.edu.pl (B. Zawisza). Talanta 99 (2012) 918–923