UNE-EN 62321-7-2:2017

This Part of IEC 62321 describes procedures to measure hexavalent chromium, Cr(VI), quantitatively in samples of polymers and electronics. This method employs organic solvent to dissolve or swell the sample matrix, followed by an alkaline digestion procedure to extract Cr(VI) from samples. Studies have shown that organic/alkaline solution is more effective than acidic solution in extracting Cr(VI) from soluble and insoluble samples. Minimal reduction of Cr(VI) to Cr(III) or oxidation of Cr(III) to Cr(VI) occurs under alkaline conditions.For soluble polymers consisting of ABS (Acrylonitrile- butadiene-styrene plastic), PC (Polycarbonate) and PVC (poly(vinyl chloride)), the samples are first dissolved in an appropriate organic solvent and Cr(VI) is then extracted by an alkaline extraction solution. If the identity of the polymer matrix is unknown, a solubility test can be performed by solving a small amount of the sample using an organic solvent. Alternately, infrared spectroscopy (IR) can be performed to identify the bulk polymer.For insoluble/unknown polymers, or electronics, the samples are digested in a toluene/alkaline solution at 150 °C to 160 °C for 2 hours using a heating or microwave device. Then the organic phase in the extracts are separated and carded; the inorganic phase is retained for Cr(VI) analysis.The Cr(VI) concentration in the extract is determined by its reaction under acidic conditions with 1,5-diphenylcarbazide. Cr(VI) is reduced to Cr(III) in the reaction with diphenylcarbazide which is oxidized to diphenylcarbazone. The Cr(III) and diphenylcarbazone further form a red violet-coloured complex in the reaction. The complex solution is measured quantitatively by a colorimeter or a spectrophotometer at 540 nm. Since the stability of Cr(VI) in extracts is not completely understood, the analyses shall be carried out as soon as possible, with a maximum delay of 30 min, after extraction.All potential Cr(VI)-containing samples and reagents used in the method shall be handled with appropriate precautions. Solutions or waste material containing Cr(VI) shall be disposed of properly. For example, ascorbic acid or some other reducing agents can be used to reduce Cr(VI) to Cr(III).