Extraction trace metal

One example, a candidate matrix material of organotin species in marine water, had stability determined by storage for 120 days at 4°C in the dark, at ambient temperature, and exposed to daylight (Quevauviller and Donard 1991). Frequently storage at different temperatures over at least a i-year period are reported. Examples include organochlorine pesticides (OCPs) in BCR CRM 430, where pork fat was stored at -2o°C, -i-20°C, and -r37°C (van der Paauw et al. 1992). Storage at -20°C, -i-20°C, and -i-4o°C was performed for total and methyl Hg in BCR CRMs 463 and 464, tuna fish (Quevauviller et al. 1994), and metals in BCR CRM 600, EDTA and DTPA-extractable trace metal contents in calcareous soil (Quevauviller et al. 1998m). 

Quevauviller Ph, Lachica M, Barahona E, Gomez A, Rauret G, Ure A, Muntau H (1998m) Certified reference material for the quality control of EDTA- and DTPA-extractable trace metal contents in calcareous soil (CRM 600). Fresenius J Anal Chem 360 505-511. 

Long, E.R., MacDonald, D.D., Cubbage, J.C. and Ingersoll, C.G. (1998) Predicting the toxicity of sediment associated trace metals with simultaneously extracted trace metal acid-volatile sulfide concentrations and dry weight-normalized concentrations a critical comparison, Environmental Toxicology and Chemistry 17 (5), 972-974. 

Quevauviller, Ph., Rauret, G., Muntau, H., Rubio, R., Lopez-Sanchez, J.-F., Fiedler, H. and Griepink, B. (1994d) Evaluation of a sequential extraction procedure for the determination of extractable trace metal contents in sediment. Fresenius J. Anal. Chem., 349, 808. 

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). 

Sahuquillo, A., Lopez-Sanchez, J.F., Rubio, R., Rauret, G., Thomas, R.P., Davidson, C.M. and Ure, A.M. (1999) Use of a certified reference material for extractable trace metals to assess sources of uncertainty in the BCR three-stage sequential extraction procedure. Anal. Chim. Acta, 382, 317—327. 

Most of the procedures for extracting trace metals from sea water have been developed with the objective to analytically determine these metals till now, no trace metal including uranium can be economically recovered from sea water. An enrichment of some trace metals in marine organisms will briefly be mentioned as well. 

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. 

The second interlaboratory exercise on extractable trace metals in sediment showed a consequent improvement in comparison with the results of the first exercise. 

Speciation is defined as the process of identifying and quantifying the different defined species, forms or phases present in a material or the description of the amounts and types of these species, forms or phases present . In some cases, it is possible to identify, by using single or sequential extractions, operationally defined determinations which identify groups of metals without clear identification. In this situation, it is possible to refer to, for example, ethylenediaminete-traacetic acid (EDTA)-extractable trace metals. The reasons why speciation is important is that metals and metalloids can be present in many forms, some of which are toxic. 

One of the major hurdles to be surmounted, before the preparation of a reference material certified for extractable trace metal content could be contemplated, was the question of temporal stability. This problem has been studied by Salomons and Scheltens [200] who repeated, in 1987, the sequential extraction analysis of freshwater sediments first carried out in 1975. While those authors were somewhat disappointed in that significant changes did occur in the measured extractable content after 12 years, it is likely that the temporal stability was sufficient for the sediments to be characterized on each occasion in such a way that decisions on the management or use of the sediments would be unchanged. 

The sediment sample used in the second interlaboratory trial was collected in the River Besos, Spain. The material was sampled with a grab, air-dried, then sieved at 63 pm, homogenized and bottled. Homogeneity and stability studies of extractable trace metals were carried out and the material was found to be homogeneous and stable enough to be used in the intercomparison exercise [196]. 

The second interlaboratory exercise on extractable trace metals in sediment showed a consequent improvement in comparison with the results of the first exercise. Furthermore, these collaborative efforts allowed the sequential extraction procedure to be slightly improved by minor amendments. The general noticeable trend was the important decrease in the number of total and accepted sets of values for concentrations in the extract below 10 pgL , which illustrated the difficulties experienced by a number of laboratories in the determination of such concentration levels in these matrices. 

Table 11.22 Coefficients of variation s of the mean of laboratory means of EDTA and DTP A extractable trace metal contents. These data correspond to the results before technical scrutiny...

A series of commercial styrene-divinylbenzene copolymers called Amberlite XAD (Rohm and Haas Co., Philadelphia) has been used as a base to immobilize a variety of complexing agents (269). On XAD-2, tri-/i-octylamine (270), several ferroin-type chromogens (277), and phenylarsonic acid (272) have been used to concentrate and separate several trace species from seawater and fresh water. An EDTA ligand (273) and phenylarsonic acid on XAD-4 can also extract trace metals such as Cr(III), Pb(II), Hg(II), U(VI), Zr(IV), and Zn(II) at the sub-parts-per-billion levels, even in the presence of excess calcium and magnesium if the pH is less than 3.0. 

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