Development and interlaboratory testing of aqueous and lyophilized Cr(III) and Cr(VI) reference materials

Abstract

This work succeeded in developing a reference material for speciation of Cr(III) and Cr(VI) in water. It consisted of a HCO − 3/H 2CO 3 (50 mmol/l) buffer solution containing Cr(III) (40 μg/l) and Cr(VI) (10 μg/l) at pH 6.4. A second reference solution, typical for speciation of Cr(VI) from welding dust, contained Cr(VI) (5 mg/l) at pH 9.6. The parameters to obtain stable solutions were carefully studied. Two formulas were tested: first an aqueous solution kept under a CO 2 blanket in sealed quartz ampoules: this later evolved into a lyophilized version to be reconstituted in the buffer solution at the right pH. The stability studies demonstrated the reliability of the materials, which allowed to organize 2 interlaboratory studies between 7 European laboratories. The results of the intercomparisons confirmed the validity of the methodology for preparing such candidate reference materials for Cr(III)/Cr(VI) speciation.