Determination of neptunium in environmental samples by extraction chromatography after valence adjustment Nicolas Gue ´ rin, Marc-Antoine Langevin, Kenny Nadeau, Charles Labrecque, Alexandre Gagne ´, Dominic Larivi  ere n Laboratoire de radioe´cologie, De´partement de chimie, Universite´ Laval, 1045 Avenue de la Me´decine, Que´bec, QC, Canada G1V 0A6 article info Article history: Received 10 February 2010 Received in revised form 7 April 2010 Accepted 22 June 2010 Keywords: Neptunium(VI) Extraction chromatography UTEVA Alpha spectrometry Inductively coupled plasma mass spectrometry Potassium bromate abstract Neptunium(V) ions are unstable in acid media, which limits their extraction on chromatographic resins. We developed a novel analytical method to measure Np by either a-spectrometry or inductively coupled plasma mass spectrometry (ICP-MS) after extraction chromatography as Np(VI). We investigated the reactivity of various oxidizing reagents, and determined the retention capacity of Np(IV, V, and VI) on various extraction chromatographic supports. A simple method using two UTEVA resins was used to rapidly detect Np in soil and sediment samples. & 2010 Elsevier Ltd. All rights reserved. 1. Introduction The presence of transuranium elements (TRUs, which include neptunium (Np), plutonium (Pu), and americium (Am)), in the environment is an unequivocal signature of anthropogenic contamination, whether from a local source, a more global distribution or from historical pollution (Choiniere et al., 2009; Holm et al., 1992; Knatko et al., 2005; Pavlotskaya et al., 1991). Therefore, actions should be taken towards facilitating their detection in the environment. The recent trends in radioanalytical automation of methodologies for the detection of actinides in the environment are excellent examples of the potential of such approaches for the environmental monitoring of potential con- tamination (Epov et al., 2005; Grate et al., 2008; Lariviere et al., 2007; Peterson et al., 2007). However, the development of radioanalytical strategies aimed at the detection of TRUs is hampered by several issues. First, most isotopes of TRUs are a-emitters, which can only be measured after proper separation from the matrix to reduce spectral and non-spectral interferences, whether the detection is performed by a-spectrometry or inorganic mass spectrometry (Becker, 2005; Vance et al., 1998; Wyse et al., 2001). Second, the typical activity of TRUs in the environment may be below mBq kg 1 levels (Becker, 2005; Donard et al., 2007; Qiao et al., 2009). In order to achieve detection at such levels, pre-concentration of the analytes is required to ensure proper quantification and reasonable counting time (Ivanova et al., 1994). Finally, many TRUs have long half-live (t 1/2 41  10 3 yr) which translates in very low specific radio- activities, which is another reason requiring pre-concentration. Actinides can be challenging both to purify and to detect. Spectral, mass, and/or matrix interferences can hamper detect- ability and quantification (Luisier et al., 2009; Truscott et al., 2001b). Alpha spectrometry is particularly susceptible to matrix- related interferences that can occur when some cations (e.g. Mg 2+ , Ca 2+ ) co-precipitate or electrodeposit simultaneously with the actinide(s) of interest. In addition, spectral overlap can occur, leading to improper actinide identification. For example, 234 U, a naturally occurring uranium isotope with a relatively high abundance (0.0054%) and activity in environmental samples compared to other actinides, can significantly overlap with the spectrum of 237 Np in alpha spectrometry (Heras et al., 2002). In mass spectrometry, 238 U is also very problematic for 237 Np analyses for two reasons: (1) peak tailing (also referred as abundance sensitivity) is frequently observed due to the high abundance of uranium in natural samples and (2) molecular interferences (e.g. 235 U 1 H 2 + , 236 U 1 H + ) can occur (Heras et al., 2002). Both issues lead to an apparent increase in signal at m/z ¼ 237, highlighting the fact Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/apradiso Applied Radiation and Isotopes 0969-8043/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2010.06.021 n Corresponding author. Tel.: + 1 418 656 7250; fax: + 1 418 656 7916. E-mail addresses: Nicolas.guerin.1@ulaval.ca (N. Gue ´ rin), marc-antoine.langevin.1@ulaval.ca (M.-A. Langevin), kenny.nadeau.1@ulaval.ca (K. Nadeau), charles.labrecque.1@ulaval.ca (C. Labrecque), alexandre.gagne.6@ulaval.ca (A. Gagne ´ ), dominic.lariviere@chm.ulaval.ca (D. Larivi  ere). Applied Radiation and Isotopes 68 (2010) 2132–2139