Sequential extraction procedures comparing

Badri M.A., Aston S.R. A comparative study of sequential extraction procedures in the geochemical fractionation of heavy metals in estuarine sediments. International Conference Amsterdam, pp 705-708. 1981. 

Recently, a group of experts working under the auspices of the Commission of the European Communities, Community Bureau of Reference (BCR) sought to improve comparability between sequential extraction results obtained by different laboratories, and proposed a simple, three-stage sequential extraction procedure for sediment (Table 10.3) (Ure et d., 1993a, b). The protocol was then refined through two sets of interlaboratory trials (Quevauviller et d., 1994) and studies were conducted to assess whether adequate homogeneity and stability could be achieved to allow certification of a reference material for metals extractable by the procedure (Fiedler et d., 1994). 

Userno, J., Gamero, M., Morillo, J. and Gracia, I. (1998) Comparative study of three sequential extraction procedures for metals in marine sediments. Environ. Int., 24, 487-496. 

This procedure was compared with sequential extractive techniques employing alkaline hydrolysis of dried plant tissue followed by extraction of the acidified mixture with ethyl acetate. Fractions were individually evaluated for phytotoxic properties. Selected fractions from those showing a positive response were analyzed by gas-liquid chromatography. Structural identification and characterization of the individual components in these selected fractions were accomplished by gas chromatography-mass spectrometry. 

Single and sequential extraction schemes have been designed in earlier years and widely used to assess the different retention/release of metals in soil and sediment samples (Tessier et al., 1979 Salomons and Forstner, 1980 Thomas et al., 1980 Meguellati et al., 1987). However, the lack of uniformity in the different procedures used did not allow the results to be compared worldwide or the procedures to be... 

A modified BCR sequential extraction was recommended based on this work, and its performance compared with the original BCR procedure via an interlaboratory trial (Rauret et al, 1999). Improved reproducibility was obtained. A new sediment reference material CRM 701 has been certified for metals extractable by the modified BCR procedure (Pueyo et al., 2001). The modified extraction protocol is given in the Appendix. It is important to emphasise that extractions should be performed exacdy as described if results comparable with other users are to be obtained. 

Perez-Cid et al. (1996) compared Tessier and BCR sequential extractions for the speciation of Cu, Cr, Pb, Ni and Zn in sludge from an urban wastewater treatment plant and found similar performance for the two procedures. Zufiaurre et al. (1998) later demonstrated, using the Tessier method and PCA, that, since most metals in a sludge were bound to oxidisable and residual fractions, bioavailability was likely to be very low. 

Sequential extraction schemes have been designed for the determination of binding forms of trace metals in sediment [21] and increasingly used over the last ten years. The lack of uniformity of these schemes, however, did not allow the results to be compared worldwide or the procedures to be validated which led to critical comments [22]. Indeed, the results obtained e.g. by sequential extraction are operationally defined, i.e. the forms of metals are defined by the determination of extractable elements using a given procedure. Therefore, the significance of the analytical results is related to the extraction scheme used. 

In conclusion, in this work we demonstrate the excellent capabilities of using ASE to extract compounds with antioxidant activity from natural sources as rosemary leaves and the microalga Spirulina platemis. ASE shows several advantages compared with traditional extraction processes such as 1) it is faster (IS min vs 2-24h in traditional extraction procedures) 2) it has less solvent volume consumption (13 ml vs 30>S00 mL/lOg) 3) it is more efficient (less dependant on matrix) and 4) it is automatic and allows sequential extraction of samples. The use of in-vitro assays and CE coupled to both, DAD and ESI-MS allows obtaining information about the biological and chemical properties of the ASE extracts. 

Various sequential dissolution protocols have been developed by different research groups in order to accommodate their types of soils, experimental conditions, and objectives. This makes it difficult to compare the results with different procedures. We compared two SSD procedures for humid zone and arid zone soils, developed by German and Israeli soil scientists, respectively, based on aggressiveness of extractants, their specificity and selectivity, completeness of phase-extraction by each extractant from defined phases and their effects on subsequent fractions. We also appraised the applicability as well as the limitations of each procedure under different conditions. 

Enzyme-linked immunosorbent assay is a heterogenous immunoassay. Reactions involve a solid phase to which components are sequentially presented and successively bound. This method is very effective in the determination of the total alkaloid content. The positive characteristics of this method are the use of non-toxic reagents and basic equipment with low costs, a small sample volume and the ability to measure alkaloids in crude sample extracts. According to the literature, compared with results obtained from GLC, the precision of ELISA for quinolizidine alkaloids is not as high as that of the gas chromatography procedure, but is adequate for plant breeding purposes. The use of enzymes in developing the methods of quinolizidine alkaloids analysis looks likely to increase in the future. 

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