Sediments sequential extraction/CRMs

Quevauviller, Ph., Rauret, G., L6pez-Sanchez, J.-F., Rubio, R., Ure, A. and Muntau, H. (1997d) Certification of trace metal extractable contents in a sediment reference material (CRM 601) following a three-step sequential extraction procedure. Sci. Total Environ., 205, 223. 

Sediment obtained from several sites in Lake Flumendosa, Italy, was collected, homogenised and, following a certification campaign, became available as BCR CRM 601 lake sediment certified for its extractable trace metal contents -sequential extraction (Quevauviller et d., 1997). In sediment CRM 601, concentrations of extractable Cd, Cr, Ni, Pb and Zn are certified in Step 1, but only Cd, Ni and Zn in Step 2, and Cd, Ni and Pb in Step 3. Indicative values are also given for extractable Cu in Step 1 and Pb in Step 2 (European Commission, 1997). The long-term stability of the extractable trace metal content of the reference material was recently demonstrated in a European intercomparison exercise (Lopez-Sanchez, 1998). 

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. 

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. 

European Commission (1997) The certification of the extractable contents (mass fractions) of Cd, Cr, Ni, Pb and Zn in sediment following a three-step sequential extraction procedure (CRM 601). Report EUR, EN 17554, ISBN 92-828-0127-6. 

Owing to the likelihood of the many sources of pitfalls which may occur, a programme was launched, aiming to harmonise sequential extraction schemes for the determination of extractable trace metals in sediment which consisted in two interlaboratory studies followed by a certification campaign on extractable trace metals in a sediment candidate reference material, CRM 601. 

While this CRM was considered of high added value, improvements were deemed necessary for achieving a better comparability of data, using the three-step sequential extraction step. A further project has, therefore, started very recently to improve this scheme (without major modifications) and produce other CRMs (sediment and possibly soil). 

Table 2 A sequential extraction scheme for trace metal speciation in sediments. The first three steps relate to the standardized sequential extraction method applicable to BCR CRM 601 ...

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