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Green Approach for Ultratrace Determination of Divalent Metal Ions and Arsenic Species Using Total-Reflection X‑ray Fluorescence Spectrometry and Mercapto-Modified Graphene Oxide Nanosheets as a Novel Adsorbent Rafal Sitko,*,† Paulina Janik,† Beata Zawisza,† Ewa Talik,‡ Eva Margui,§ and Ignasi Queralt∥ †
University of Silesia, Institute of Chemistry, Szkolna 9, 40-006 Katowice, Poland University of Silesia, Institute of Physics, Uniwersytecka 4, 40-007 Katowice, Poland § Department of Chemistry, University of Girona, Campus Montilivi, 17071 Girona, Spain ∥ Laboratory of X-ray Analytical Applications, Institute of Earth Sciences Jaume Almera, CSIC, Solé Sabarís s/n, 08028 Barcelona, Spain ‡
S Supporting Information *
ABSTRACT: A new method based on dispersive microsolid phase extraction (DMSPE) and total-reflection X-ray fluorescence spectrometry (TXRF) is proposed for multielemental ultratrace determination of heavy metal ions and arsenic species. In the developed methodology, the crucial issue is a novel adsorbent synthesized by grafting 3mercaptopropyl trimethoxysilane on a graphene oxide (GO) surface. Mercapto-modified graphene oxide (GO-SH) can be applied in quantitative adsorption of cobalt, nickel, copper, cadmium, and lead ions. Moreover, GO-SH demonstrates selectivity toward arsenite in the presence of arsenate. Due to such features of GO-SH nanosheets as wrinkled structure and excellent dispersibility in water, GO-SH seems to be ideal for fast and simple preconcentration and determination of heavy metal ions using methodology based on DMSPE and TXRF measurement. The suspension of GO-SH was injected into an analyzed water sample; after filtration, the GO-SH nanosheets with adsorbed metal ions were redispersed in a small volume of internal standard solution and deposited onto a quartz reflector. The high enrichment factor of 150 allows obtaining detection limits of 0.11, 0.078, 0.079, 0.064, 0.054, and 0.083 ng mL−1 for Co(II), Ni(II), Cu(II), As(III), Cd(II), and Pb(II), respectively. Such low detection limits can be obtained using a benchtop TXRF system without cooling media and gas consumption. The method is suitable for the analysis of water, including high salinity samples difficult to analyze using other spectroscopy techniques. Moreover, GO-SH can be applied to the arsenic speciation due to its selectivity toward arsenite.
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analytical chemistry is paid to the development of precise, sensitive, and selective methods for the sample treatment. The most commonly employed techniques for the preconcentration/separation of trace elements include liquid−liquid extraction and, most of all, solid-phase extraction (SPE) due to its low cost, low consumption of organic solvents, and rapid phase separation. Moreover, this technique can be easily combined with different spectroscopy techniques in offline and online modes. Suitable selection of adsorbent is crucial to ensure quantitative retention of the trace elements and, in some cases, selective retention.5 The most popular adsorbents used in SPE are silica, activated carbon, cellulose, chelating resins, and polyurethane foams. In recent years, nanosized materials have
he determination of trace metal ions in the samples of different matrices is a subject of great interest. For this purpose, the modern laboratory offers several sensitive and selective analytical techniques, such as flame and electrothermal atomic absorption spectrometry (FAAS and ETAAS), totalreflection X-ray fluorescence spectrometry (TXRF), inductively coupled plasma atomic emission spectrometry (ICP-OES), and inductively coupled plasma mass spectrometry (ICP-MS).1,2 However, the direct determination of extremely low concentrations of metal ions by most spectroscopy techniques can be difficult. These limitations usually result from the insufficient sensitivity of these techniques and matrix interferences. Therefore, a preliminary preconcentration and separation of trace and ultratrace metal ions from a complex matrix are usually required.3,4 Unfortunately, sample preparation is considered the most time-consuming and error-prone step of the analytical process. Therefore, the great attention of modern © XXXX American Chemical Society
Received: January 22, 2015 Accepted: February 23, 2015
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DOI: 10.1021/acs.analchem.5b00283 Anal. Chem. XXXX, XXX, XXX−XXX
Article
Analytical Chemistry
p.a.), ammonium hydroxide solution (25%, p.a.), potassium permanganate (p.a.), sodium nitrite (p.a.), and hydrogen peroxide (30%, p.a.) were from Avantor Performance Materials Poland S.A. (Gliwice, Poland). Standard solutions were diluted with high purity water obtained from Milli-Q system (Millipore, Molsheim, France). Certified reference material BCR-610 (groundwater) was obtained from The Institute for Reference Materials and Measurements of Joint Research Centre (Geel, Belgium), LGC6016 (estuarine water) from LGC-Standards (Teddington, U.K.). TXRF analysis was performed using a portable spectrometer S2 PICOFOX (Bruker AXS Microanalysis GmbH, Berlin, Germany). The spectrometer is equipped with tungsten target X-ray tube of maximum power 50 W, Si drift detector (10 mm2,
