BCR procedure

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. 

For quality control, the residue from step 3 has to be digested in aqua regia ( step 4 ) and the cumulative amount of metal extracted [i.e. 2(step 1 + step 2 + step 3 + step 4 )] is compared with the pseudototal amount of metal obtained by aqua regia digestion of a separate 1-g soil sample. In the modified BCR procedure, a 0.5 M hydroxylamine hydrochloride solution at pH 1.5 is applied in step 2. 

In those cases where there are any doubts about the feasibility of producing a sufficiently homogeneous and stable reference material, a feasibility study might be needed. For this study, an extra amount of material is needed. Questions regarding the best way of preparing the sample, the stability of the material, or the fitness for purpose might justify the inclusion of a feasibility study in the project. In the BCR projects, it is common practice to have a feasibility study, which usually has as the sole purpose of assessing the performance of the laboratories in the collaborative study in relation to the certification of the reference material. The feasibility study allows the participants to fine-tune their equipment, their methods, and their procedures in view of the characterization measurements. In each of these cases, a considerable extra number of samples is needed. 

Using a newly developed, transversely heated graphite atomizer and D2-back-ground correction (for details see Sections 2.2 and 4.3), Cd, Pb and Cr were determined in cement and river sediment samples. Of the various calibration approaches applied the best results, also in comparison with wet chemical procedures, were achieved with calibration curves constructed by means of different BCR CRMs with different analyte concentrations and usually n = to individual intakes (Nowka and Muller 1997). 

Standards, Measurements and Testing Programme, EU (formerly BCR) Standard Operating Procedure Society of Plastic Engineers (Brookfield, CT)... 

Ho M.D., Evans G.J. Operational speciation of cadmium, copper, lead and zinc in the NIST standard reference materials 2710 and 2711 (Montana soil) by the BCR sequential extraction procedure and flame atomic absorption spectrometry. Anal Commun 1997 34 353-364. 

Whalley C, Grant A. Assessment of the phase selectivity of the European Community Bureau of Reference (BCR) sequential extraction procedure for metals in sediment. Anal. Chim. Acta 1994 291 287-295. 

Fernandez E, Jimenez R, Lallena AM, Aguilar J. Evaluation of the BCR sequential extraction procedure applied for two unpolluted Spanish soils. Environ. Pollut. 2004 131 355-364. 

Davidson CM, Duncan AL, Littlejohn D, Garden LM. A critical evaluation of the three-stage BCR sequential extraction procedure to assess the potential mobility and toxicity of heavy metals in industrially-contaminated land. Anal. Chim. Acta 1998 363 45-55. 

Mossop KF, Davidson CM. Comparison of original and modified BCR sequential extraction procedures for the fractionation of copper, iron, lead, manganese and zinc in soils and sediments. Anal. Chim. Acta 2003 478 111-118. 

To determine Sb in marine sediments by ETAAS, a direct method was developed based on quantitating the analyte in the liquid phase of the slurries (prepared directly in autosampler cups). The variables influencing the extraction of Sb into the liquid phase and the experimental setup were set after a literature search and a subsequent multivariate optimisation procedure. After the optimisation, a study was carried out to assess robustness. Six variables were considered at three levels each (see Table 2.13). In addition, two noise factors were set after observing that two ions, which are currently present into marine sediments, might interfere in the quantitations. In order to evaluate robustness, a certified reference material was used throughout, BCR-CRM 277 Estuarine Sediment (guide value for Sb 3.5 0.4pgg ). Table 2.13 depicts the experimental setup. 

Much work has been reported on the evaluation of sequential extraction procedures. The three-stage sequential extraction procedure for speciation of heavy metals proposed by the Commission of the European Communities Bureau of References (BCR) was found to be acceptable and reproducible with some modifications [29]. In another study, when applied to real soils and sediments, this (unmodified) BCR method was queried [30]. Lopez-Sanchez et al. [31 ] found that significant results can be obtained when different sequential extraction procedures are used. 

Some work on sediments is reported here in the belief that it may also be useful in the analysis of soil samples. Thus Asikainen and Nikolaides [33] have carried out a sequential extraction study of chromium from contaminated aquifer sediments and found that 65% of the chromium was extractable. Of this amount 25% was exchangeable, 11% was bound to organic matter and 30% was bound to iron and manganese oxide surfaces. Thomas et al. [34] also investigated the use of BCR sequential extraction procedures for river sediments, and found the method to work well. Real et al. [35] improved sequential extraction by optimising microwave heating. 

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). 

In common with other sequential extraction procedures, the BCR scheme suffers from a degree of non-specificity (Whalley and Grant, 1994 Coetzee et d., 1995) and redistribution of analytes during extraction (Raksasataya et d., 1996). Some success in limiting lead redistribution by addition of cryptand 2.2.2 or nitriloacetic acid to the acetic acid in Step 1 has been reported, but the effectiveness of the complexing agent was found to be strongly dependent on the bulk composition of the model soil system studied (Raksasataya et d., 1997). 

Table 10.3 The BCR three-step sequential extraction procedure...

The reference materials currendy certified for metals extractable by a sequential extraction procedure are BCR CRM 601 and BCR CRM 701. The lack of reference materials in this area has prompted many workers to apply sequential extraction to other reference soils and sediments, certified for total metal contents, in an attempt to provide interim data useful in method validation. 

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. 

Rauret, G., Lopez-Sanchez, J.F., Sahuquillo, A., Davidson, C., Ure, A. and Quevauviller, Ph. (1999) Improvement of the BCR 3-step sequential extraction procedure prior to the certification of new sediment and soil reference materials./. Environ. Monit., 1, 57-61. 

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