Development of analytical procedures for the determination of hexavalent chromium in corrosion prevention coatings used in the automotive industry

Abstract

The European directive 2000/53/EC limits the use of Cr(VI) in vehicle manufacturing. Although a maximum of 2 g of Cr(VI) was authorised per vehicle for corrosion prevention coatings of key components, since July 2007 its use has been prohibited except for some particular applications. Therefore, the objective of this work was to develop direct analytical procedures for Cr(VI) determination in the different steel coatings used for screws. Instead of working directly with screws, the optimisation of the procedures was carried out with metallic plates homogeneously coated to improve the data comparability. Extraction of Cr(VI) from the metallic parts was performed by sonication. Two extraction solutions were tested: a direct water extraction solution used in standard protocols and an ammonium/ammonia buffer solution at pH 8.9. The extracts were further analysed for Cr speciation by high-performance liquid chromatography (HPLC) inductively coupled plasma (ICP) atomic emission spectrometry or HPLC ICP mass spectrometry depending on the concentration level. When possible, the coatings were also directly analysed by solid speciation techniques (X-ray photoelectron spectroscopy, XPS, and X-ray absorption near-edge structure, XANES) for validation of the results. Very good results between the different analytical approaches were obtained for the sample of coating made up of a heated paint containing Zn, Al and Cr when using the extracting buffer solution at pH 8.9. After a repeated four-step extraction procedure on the same portion test, taking into account the depth of the surface layer reached, good agreement with XPS and XANES results was obtained. In contrast, for the coatings composed of an alkaline Zn layer where Cr(VI) and Cr(III) are deposited, only the extraction procedure using water allowed the detection of Cr(VI). To elucidate the Cr(VI) reduction during extraction at pH 8.9, the reactivity of Cr(VI) towards different species of Zn generally present in the coatings (metallic Zn and zinc oxide) was studied. The results showed that metallic Zn rapidly reduces Cr(VI), whereas this reaction is less evident in the presence of zinc oxide. Water was then retained for coatings containing metallic Zn.

Cr(VI) speciation in foods by HPLC-ICP-MS: investigation of Cr(VI)/food interactions by size exclusion and Cr(VI) determination and stability by ion-exchange on-line separations

“…The use of a collision/reaction cell allows the efficient removal of those interferences [28,29], but it can be associated to a loss of sensitivity. The alternative was therefore to increase the chromatographic resolution to separate the Cr isotopes signal from those of the interferences [22].…”

“…A 250-mm-long CS5A column was finally selected because it had already been reported to be efficient for Cr(VI) speciation in different matrices such as corrosion prevention coatings [21] or cements [20]. The elution of Cr(VI) from this column for those inorganic samples was generally achieved with 0.35 M of HNO 3 .…”

“…Indeed, to minimize contamination, losses of chromium species or redox conversion, and to gain specificity, it is now well admitted that the on-line coupling between HPLC and a highly sensitive detector such as ICP MS is the methodology of choice. This coupling has received the most attention for Cr speciation in the last decade in samples like water [15,16], sediments [17], workplace atmospheres [18], cements [19,20], corrosive preventive coatings [21], or materials used in the automotive industry [22].…”

Inductively coupled plasma- and glow discharge plasma-sector field mass spectrometry : Part II. Applications

“…Spectral interferences can be overcome with high mass resolution. 379,380 Van Lierde et al 381 deployed an experimental set-up based on the hyphenation of CE with ICP-SFMS to study the fate of Cr(III), Cr(VI) and Cr species extracted from chromium-tanned leather in simulated sweat with the aim of obtaining a more profound insight into the chronic allergic contact dermatitis that some individuals develop when their skin is in contact with Cr-tanned leather. Interference-free Cr-monitoring was carried out at a mass resolution of 3000.…”

A espectrometria atômica e a determinação de elementos metálicos em material polimérico

“…O estudo mostrou ainda que a escolha adequada do tratamento da amostra é mais importante que a escolha de uma ou outra técnica analítica. 46 Em outro projeto do PERM 47 49 desenvolveram métodos para determinação de Cr total, utilizando a técnica de ICP-MS com quadrupolo. Foi utilizado um sistema aberto de digestão assistida por microondas, com HNO 3 e com uma mistura de HNO 3 e H 2 O 2 para amostras plásticas de assento de automóveis.…”