Interference of Sb(III) in the Determination of Hexavalent Chromium in Thermoplastic Matrices

Abstract

Due to the adverse health effects of hexavalent chromium, Cr(VI), pigments and other materials containing Cr(VI) were largely banned for use in electrotechnical products under the EU RoHS Directive [1]. While there are several effective methods to determine the presence of total chromium in electrotechnical plastic matrices, a validated compliance test method that is capable of discerning Cr(VI) from the non-regulated forms of Cr(III) is not yet available. One of the challenges in developing a standardized compliance test for Cr(VI) is the low recovery of Cr(VI) compounds from polymer matrices This study identified antimony trioxide (ATO), a common synergist added to enhance the ignition resistance of brominated flame retardants (BFRs), as a source of matrix interference in the quantitative determination of hexavalent chromium extracted from polymer matrices. ATO reduces hexavalent chromium to trivalent chromium prior to complexation of Cr(VI) with diphenylcarbazide (DPC) leading to false negatives. EDTA was found to be an efficient reagent for Sb(III) complexation, thereby suppressing the reduction of Cr(VI) and enabling quantitative Cr(VI) determination in the presence of ATO.