Graphite furnace atomic absorption spectrometric detection of vanadium in water and food samples after solid phase extraction on multiwalled carbon nanotubes Sham Kumar Wadhwa a,b , Mustafa Tuzen a , Tasneem Gul Kazi b , Mustafa Soylak c,n a Gaziosmanpasa University, Faculty of Science and Arts, Chemistry Department, 60250 Tokat, Turkey b National Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro 76080, Pakistan c University of Erciyes, Faculty of Science, Chemistry Department, 38039 Kayseri, Turkey article info Article history: Received 9 April 2013 Received in revised form 4 May 2013 Accepted 10 May 2013 Available online 16 May 2013 Keywords: Solid phase extraction Vanadium 8-hydroxyquinoline Multiwalled carbon nanotubes Atomic absorption spectrometry abstract Vanadium(V) ions as 8-hydroxyquinoline chelates were loaded on multiwalled carbon nanotubes (MWNTs) in a mini chromatographic column. Vanadium was determined by graphite furnace atomic absorption spectrometry (GFAAS). Various analytical parameters including pH of the working solutions, amounts of 8-hydroxyquinoline, eluent type, sample volume, and flow rates were investigated. The effects of matrix ions and some transition metals were also studied. The column can be reused 250 times without any loss in its sorption properties. The preconcentration factor was found as 100. Detection limit (3 s) and limit of quantification (10 s) for the vanadium in the optimal conditions were observed to be 0.012 mgL -1 and 0.040 μgL -1 , respectively. The capacity of adsorption was 9.6 mg g -1 . Relative standard deviation (RSD) was found to be 5%. The validation of the method was confirmed by using NIST SRM 1515 Apple leaves, NIST SRM 1570a Spinach leaves and GBW 07605 Tea certified reference materials. The procedure was applied to the determination of vanadium in tap water and bottled drinking water samples. The procedure was also successfully applied to microwave digested food samples including black tea, coffee, tomato, cabbage, zucchini, apple and chicken samples. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Vanadium(V) is an essential element for living organisms [1]. The estimated daily intake of vanadium ranges from 6 to 18 mg [2]. It can exist in many oxidation states from -1 to +5, but it is most commonly found in the +4 and +5 states. The coexistence of these species depends on pH, redox potential and ionic strength of the aqueous media [3–6]. The toxicity of vanadium(V) is higher than vanadium(IV) [7]. Vanadium mainly enters the environment from natural sources and combustion of fossil fuels, fuel oils and coal. The burning of petroleum fuels and coal releases vanadium into the air, soil and water [8]. V is toxic to living organisms at mg L -1 level [1]. Several analytical techniques such as inductively coupled plasma mass spectrometry, inductively coupled plasma atomic emission spectrometry, and graphite furnace atomic absorption spectrometry have been used for the determination of vanadium concentrations in water, food and environmental samples [9–11]. The determination of trace quantities of vanadium requires the use of sensitive and selective techniques such as graphite furnace atomic absorption spectrometry is an important instrument. The level of vanadium in natural water samples is very low such as mgL -1 [12]. In order to achieve accurate, reliable and sensitive results, separation–enrichment steps are often necessary prior to the analysis of vanadium. Various separation and preconcentration techniques including coprecipitation, cloud point extraction, flotation, solvent extrac- tion, solid phase extraction have been used prior to the determi- nation of vanadium [13–16]. Solid phase extraction of vanadium for preconcentration is preferred to other techniques due to simple application, easy methodology, high preconcentration factor, sen- sitivity and low organic solvent consumption. Carbon nanotubes have become attractive materials for the adsorption of metal ions at trace level because of their structure characteristics with high surface area. The large surface areas make them a promising solid sorbent for preconcentration proce- dures [17–19]. Surface area and density of multiwalled carbon nanotubes used in this work are 600 m 2 g -1 and 2.1 g mL -1 , respectively [17]. Multiwalled carbon nanotubes (MWNTs) and 8-hydroxyquinoline combination was not used for solid phase extraction of vanadium according to our literature survey. In this study, a simple solid phase extraction method was used for the separation and enrichment of vanadium. Various analytical para- meters were optimized prior to graphite furnace atomic absorption Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/talanta Talanta 0039-9140/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.talanta.2013.05.020 n Corresponding author. Tel./fax: +90 352 4374933. E-mail addresses: soylak@erciyes.edu.tr, msoylak@gmail.com (M. Soylak). Talanta 116 (2013) 205–209