The determination of hexavalent chromium (Cr 6+) in electronic and electrical components and products to comply with RoHS regulations

Abstract

Toxicity of hexavalent chromium (Cr 6+) was focused on with a publication of EU RoHS directive, a novel method to determine hexavalent chromium is developed. It is a combination of energy dispersion X-ray fluorescence spectrometry (EDXRF), spot test, alkali digestion and UV–vis spectrophotometric analysis. First, by EDXRF screening, the presence or absence of element Cr was established. Spot test was followed to identify the valent state of chromium because Cr 6+ and Cr 3+ normally coexist. After alkali digestion, Cr(VI) was separated without an undersired Cr(VI)–Cr(III) interconversions. With a color reagent (DPC) to chelated with Cr(VI), the solution was finally detected by a UV–vis spectrophotometer at a wavelength of 540 nm which is the basis of analyzing Cr(VI) quantitatively. Some parameters affecting analyses were studied. It was found that when pH in the final solution was 2.0, the extraction time was 60 min, the extraction temperature was 90 °C, pH during the extraction process was 7.5–8.5, and a mixed buffer solution (0.5 M K 2HPO 4/0.5 M KH 2PO 4) was added up to 1 ml, colorimetric reagent was added to 2 ml, it is optimal for extraction. Under this condition, interferences from Fe 3+, Pb 2+, Ag +, etc., were overcome. It was also found that the curves are rectilinear in the range of 0–500 μg l −1, the correlation coefficient is up to 0.999924, and the recovery rates are more than 85%, the Cr(III)–DPCO complex can be kept stable for 24 h with a relative humidity (RH) range of 60–90%, and a temperature range of 5–40 °C. So it can be concluded that the proposed method has a good sensitivity and high precision. It is a more convincing and reliable method due to its relative standard deviation (R.S.D.) <1% after six replicate determinations of Cr(VI) in an Fe–Ni alloy sample.