Ultra Traces Analyses Aquitaine, Hélioparc Pau-Pyrénées, 2, avenue du Président Angot, 64053, Pau Cedex 9, France.
Anal Bioanal Chem. 2008 May;391(2):587-97. doi: 10.1007/s00216-008-2051-7. Epub 2008 Apr 12.
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.
欧盟指令 2000/53/EC 限制了车辆制造中六价铬的使用。虽然为关键部件的腐蚀防护涂层，每辆车可允许使用 2 克六价铬，但自 2007 年 7 月以来，除了一些特殊应用外，已禁止使用六价铬。因此，这项工作的目的是开发直接分析程序，用于测定用于螺丝的不同钢涂层中的六价铬。为了提高数据可比性，不是直接用螺丝进行优化，而是对均匀涂覆金属板的工艺进行优化。通过超声处理从金属部件中提取六价铬。测试了两种提取溶液：一种是标准协议中使用的直接水提取溶液，另一种是 pH 值为 8.9 的铵/氨缓冲溶液。根据浓度水平，进一步通过高效液相色谱（HPLC）电感耦合等离子体（ICP）原子发射光谱或 HPLC ICP 质谱法分析提取物中的铬形态。在可能的情况下，还通过固相形态分析技术（X 射线光电子能谱，XPS 和 X 射线吸收近边结构，XANES）对涂层进行直接分析，以验证结果。当使用 pH 值为 8.9 的提取缓冲溶液时，对于由加热油漆组成的涂层样品，该样品包含 Zn、Al 和 Cr，不同分析方法之间得到了非常好的结果。在对同一部分进行重复的四步提取程序后，考虑到达到的表面层深度，与 XPS 和 XANES 结果吻合良好。相比之下，对于由碱性 Zn 层组成的涂层，其中沉积了六价铬和三价铬，只有使用水的提取程序才能检测到六价铬。为了阐明在 pH 值为 8.9 时提取过程中六价铬的还原，研究了 Cr(VI)与涂层中通常存在的不同种类 Zn（金属 Zn 和氧化锌）之间的反应性。结果表明，金属 Zn 迅速还原六价铬，而在存在氧化锌的情况下，这种反应不太明显。因此，对于含有金属 Zn 的涂层，保留了水。
