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

► Reported are new procedures for preparation of isotopic spike solutions of Cr(VI) and Cr(III). ► Solutions prepared from enriched Cr oxides do not cause artefacts in Cr speciation. ► Alkaline melting is applied for preparation of isotopic spike solution of Cr(VI). ► Cr is quantitatively oxidized with air oxygen without use of other oxidizing agents. ► Isotopic spike solutions of Cr(III) are prepared by microwave digestion of Cr oxide.