Four-step Extraction Procedure Research Articles

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

The European directive 2000/53/EC limits the use of Cr(VI) in vehicle manufacturing. Although a maximum of 2g 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.

Mobilization of Antimony and Arsenic in Soil and Sediment Samples – Evaluation of Different Leaching Procedures

This study aims to evaluate the performance of different leaching schemes with respect to the mobilization of antimony and arsenic from polluted samples collected at different sites in Mansfeld District, Germany. Besides the elution by water the leaching by artificial acidic rain and by two different schemes of sequential extraction were employed for estimation of the mobilization of antimony and arsenic. The samples were characterized by X-ray fluorescence analysis for their total concentration of metalloids, metals and main constituents. It was found that both antimony and arsenic show little mobilization with de-ionized water as well as artificial acidic rain in single step batch procedures (≤ 0.13% of the total content). Although the percentage leached is very low, the concentrations in the resulting solutions are of ecotoxicological relevance. BCR procedure indicate a very strong binding of Sb and of As in the samples. Less than 20% of the total content can be leached in sum in all leaching steps, of it most under strongly oxidizing conditions. This scheme seems not suitable for a detailed investigation of possible mobilization processes under environmental conditions for the metalloids under investigation. The four-step extraction procedure by Wenzel et al. gives a more detailed pattern of the binding of antimony and arsenic. This procedure was found to be a suitable scheme for evaluating the possible mobilization processes from the samples contaminated by ore processing waste, especially by change through other ions or under reducing conditions.

The polypeptides of adenovirus IX. Partial purification of early proteins and observations on late proteins of type 5 adenovirus

The identification and partial purification of adenovirus type 5 (Ad 5)-induced early proteins were achieved. Mock- and virus (high multiplicity)-infected HeLa cells were labeled for 90 min with [ 35S]- or [ 3H]methionine at 5 hr after infection in the presence of cytosine arabinoside. Labeled polypeptides from these cells were sequentially fractionated with a four-step extraction procedure: (1) 10 m M NaCl, (2) 1.7 M NaCl, (3) 2% Triton X-100, and (4) 6 M urea plus 2% Triton X-100. At each step, polypeptides from mock-infected and infected cell fractions were analyzed by DEAE-Sephadex chromatography and sodium dodecyl sulfate-polyacrylamide-gel electrophoresis (SDS-disc-PAGE) followed by autoradiography. Six virus-induced early proteins were discerned: El, 42K (E1A), E2, E2A, E2B, and E3. Polypeptides of Ad 5 virions and top components and polypeptides induced at the late stage of adenovirus type 5 infection were analyzed by SDS-PAGE. They were similar to the polypeptide constituents of adenovirus type 2 (Ad 2), except that the hexon and fiber of type 5 had mobilities in polyacrylamide (PA) different from those of type 2. The results eliminate the possibility that polypeptides taking part in Ad 5 morphogenesis differ greatly from those of Ad 2.