Journal of Chromatography A, 1024 (2004) 129–137 Retention of Cr(III) by high-performance chelation ion chromatography interfaced to inductively-coupled plasma mass spectrometric detection with collision cell Anne P. Vonderheide a , Juris Meija a , Katherine Tepperman b , Alvaro Puga c , Allan R. Pinhas a , J. Christopher States d , Joseph A. Caruso a,∗ a Department of Chemistry, University of Cincinnati, Cincinnati, OH 45221-0172, USA b Department of Biological Sciences, University of Cincinnati, Cincinnati, OH 45221-0006, USA c Department of Environmental Health, University of Cincinnati, Cincinnati, OH 45221-0056, USA d Department of Pharmacology and Toxicology, University of Louisville, Louisville, KY 40292, USA Received 25 August 2003; received in revised form 15 October 2003; accepted 17 October 2003 Abstract High-performance chelation ion chromatography (HPCIC) was employed to retain cationic Cr(III) on an anion-exchange column and hence allow the separation of the two most prevalent forms of chromium, Cr(III) and Cr(VI). A mobile phase of nitric acid was utilized at pH = 1.5; additionally, 2,6-pyridinedicarboxylic acid was used at a concentration of 6 mM. Additives with different structural characteristics were used in an effort to elucidate retention mechanisms. Inductively-coupled plasma mass spectrometry was used for chromium detection. A collision cell was utilized to reduce chloride-based polyatomic ions that may interfere with the detection of Cr(III), and a detection limit study yielded levels in the low part-per-billion range. The newly developed method was applied to the chromatographic analysis of samples of an incubation medium containing Cr(VI) incubated with cell nuclei. © 2003 Elsevier B.V. All rights reserved. Keywords: Retention mechanisms; Collision cell; High-performance chelation ion chromatography; Speciation; Chromium 1. Introduction The two most prominent oxidation states of chromium that exist in nature are Cr(III) and Cr(VI); the intermediate states of +2, +4 and +5 are metastable and rarely encoun- tered. At low pH, Cr(III) is most often found as a hexahy- dro cationic species, Cr(H 2 O) 6 3+ . As the pH is increased, water molecules are successively replaced with hydroxide ions until three ligand substitutions have occurred; at this point, precipitation occurs. Chromium(VI) usually exists as the chromate ion, CrO 4 2- and may possess some degree of protonation depending on the pH. With both trivalent and hexavalent Cr, the species is pH dependent. By noting the cationic nature of Cr(III) and the anionic nature of Cr(VI) in an acidic medium, the difficulties in their chromatographic separation at lower pH become quite apparent. ∗ Corresponding author. Tel.: +1-5135-565858; fax: +1-5135-560142. E-mail address: joseph.caruso@uc.edu (J.A. Caruso). Chromium enters the environment as a component of in- dustrial wastes, such as that produced by the dyeing, tanning and steel industries. This may also occur as a result of the presence of Cr(VI) in artificial fertilizers. Chromium(III) is an essential element because it helps to activate insulin; on the other hand, chromium(VI), which is carcinogenic, has the capability of crossing cell membranes and then is re- duced to Cr(III) in the cell [1–4]. Hence, there is an obvious need for measurement of the two species individually. Several methods to separate the anionic and cationic forms of chromium have been published and a number of re- views summarize these methods [5,6]. Most use a complex- ing agent to impart a negative charge to the chromium(III) and subsequently use an anion-exchange column for sepa- ration. However, due to the fact that complexes of Cr(III), like those of Co(III), are kinetically inert to ligand substi- tution, the chelation procedures typically require high tem- peratures, although speciation analyses generally necessitate that samples be manipulated as little as possible to preserve the nature of the original species [7]. 0021-9673/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2003.10.070