Published: November 03, 2011 r2011 American Chemical Society 10492 dx.doi.org/10.1021/es201002g | Environ. Sci. Technol. 2011, 45, 10492–10500 ARTICLE pubs.acs.org/est Evaluation of Hexavalent Chromium Extraction Method EPA Method 3060A for Soils Using XANES Spectroscopy Julien Malherbe,* ,†,‡ Marie-Pierre Isaure, † Fabienne S  eby, § Russell P. Watson, ‡ Pablo Rodriguez-Gonzalez, || Paul E. Stutzman, ^ Clay W. Davis, ‡ Chiara Maurizio, # Nora Unceta, r John R. Sieber, ‡ Stephen E. Long, ‡ and Olivier F. X. Donard † † Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, IPREM, UMR CNRS 5254, Universit  e de Pau et des Pays de l’Adour, H elioparc Pau-Pyr  en ees, 2, avenue Pierre Angot, 64053 Pau Cedex 9, France ‡ Analytical Chemistry Division, Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8391, Gaithersburg, Maryland, 20899, United States § Ultra Traces Analyses Aquitaine (UT2A), H elioparc Pau-Pyr  en ees, 2, avenue Pierre Angot, 64053 Pau Cedex 9, France ) Departamento de Química Física y Analítica, Universidad Oviedo, c/Juli  an Clavería, 8. E-33006, Oviedo, Spain ^ Materials and Construction Research Division, Engineering Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8615, Gaithersburg, Maryland, 20899, United States # CNR-OGG c/o GILDA beamline, European Synchrotron Radiation Facility, 6 rue J. Horowitz, BP 220, 38043 Grenoble, France r Department of Analytical Chemistry, Faculty of Pharmacy, University of the Basque Country, Vitoria-Gasteiz, Spain b S Supporting Information ’ INTRODUCTION For solid samples, few analytical techniques enable direct determination of Cr speciation without converting samples to the liquid state. X-ray absorption near edge structure spectros- copy (XANES) is a technique of choice for environmental samples because it allows quantification of the Cr(VI)/Cr(III) ratio with good sensitivity. For example, a limit of detection around 10 mg/kg has been reported for Cr(VI). 1 This technique relies on the presence of electronic transitions sensitive to the valence, geometry, and distortion of molecules. In the case of Cr, pre-edge features are much more pronounced for Cr(VI) com- pounds, which have a tetrahedral coordination, than for Cr(III) compounds, which mostly have a centrosymmetric octahedral coordination. 2,3 However, this technique is only available in syn- chrotron facilities, and thus, most speciation studies are performed using wet chemistry methods, which are more sensitive, but require an extraction step to dissolve Cr(VI). Extraction is challenging because ideally it should be complete, and interconversion of Cr species (e.g., reduction of Cr(VI) to Cr(III)) must be prevented to avoid under- or overestimation of the Cr(VI) content. Different extracting solutions have been used to perform the extraction of Cr(VI). 4,5 In these studies, the yield of extraction, the possible interconversion of Cr species, and their recoveries were evaluated by spiking soils with exogenous Cr(III) and Cr(VI). The method yielding the best results was obtained using a combination of Na 2 CO 3 and NaOH with continuous swirling and heating at 95 °C. The pH of the Na 2 CO 3 /NaOH mixture Received: March 25, 2011 Accepted: November 3, 2011 Revised: October 6, 2011 ABSTRACT: Hexavalent chromium (Cr(VI)) occurrence in soils is generally determined using an extraction step to transfer it to the liquid phase where it is more easily detected and quantified. In this work, the performance of the most common extraction procedure (EPA Method 3060A) using NaOHÀNa 2 CO 3 solutions is evaluated using X-ray absorption near edge structure spectroscopy (XANES), which enables the quantification of Cr(VI) directly in the solid state. Results obtained with both methods were compared for three solid samples with different matrices: a soil containing chromite ore processing residue (COPR), a loamy soil, and a paint sludge. Results showed that Cr(VI) contents determined by the two methods differ significantly, and that the EPA Method 3060A procedure underestimated the Cr(VI) content in all studied samples. The underestimation is particularly pronounced for COPR. Low extraction yield for EPA Method 3060A was found to be the main reason. The Cr(VI) present in COPR was found to be more concentrated in magnetic phases. This work provides new XANES analyses of SRM 2701 and its extraction residues for the purpose of benchmarking EPA 3060A performance.