Preparation of Cr(VI) and Cr(III) isotopic spike solutions from Cr-50 and Cr-53 enriched oxides without the use of oxidizing and/or reducing agents

作者：Novotnik Breda; Zuliani Tea; Martincic Anze; Scancar Janez; Milacic Radmila^*

来源：Talanta, 2012, 99: 83-90.

DOI：10.1016/j.talanta.2012.05.022

• Cr-50 and Cr-53 enriched oxides
• Isotopic spike solutions of Cr-50(VI) and Cr-53(III)
• Alkaline melting
• Microwave assisted digestion
• Anion-exchange fast protein liquid chromatography
• Inductively coupled plasma mass
• Spectrometry

The use of enriched stable isotopes as tracers in speciation procedures by ion-exchange chromatography coupled to ICP-MS enables to follow the oxidation-reduction processes of Cr. The most commonly available Cr stable isotopes are Cr-50 and Cr-53 enriched oxides or metallic Cr. For application of Cr enriched stable isotopes, adequate preparation of isotopic spike solutions is necessary. To ensure that Cr species present in the sample investigated are not compromised, no excess of the reducing neither oxidizing agents should remain in the isotopic spike solutions. Cr(VI) isotopic solutions are mostly prepared by dissolving of Cr oxide in HClO4, followed by the addition of ammonia and H2O2 to quantitatively oxidize Cr, while the excess of H2O2 is removed by boiling or UV irradiation. If traces of H2O2 still remains, such isotopic spike solution may cause artefacts in Cr speciation in the sample investigated. In the present work, new procedure based on alkaline melting of Cr-50 enriched oxide for preparation of pure Cr-50(VI) spike solution was developed. Cr(III) was quantitatively oxidized to Cr(VI) with air oxygen without use of other oxidizing agents. Moreover, the microwave assisted digestion procedure of Cr-53 enriched oxide was applied for preparation of Cr-53(III) spike solution without use of reducing agents. The purity of Cr-50(VI) and Cr-53(III) isotopic spike solutions was verified by the speciation analysis applying hyphenation of anion-exchange FPLC to ICP-MS. Speciation analysis demonstrated suitability of the proposed procedures for preparation of Cr isotopic spike solutions. In addition, the artefacts in Cr speciation, which may be initiated by traces of oxidizing and/or reducing agents present in Cr spike solutions, were demonstrated. The outcomes of our investigation highlighted the importance of the adequate preparation of spike solutions of Cr isotopes that may be used as reliable tracers in the investigations of the oxidation-reduction processes of Cr in wide range of environmentally relevant pH values.

• 出版日期2012-9-15