Sequential extraction procedures microwave heating

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. 

Real et al. [341] showed that optimising the microwave heating procedure would optimise the results obtained in sequential extraction procedures. 

Campos, E., Barahona, E., Lachica, M. and Mingorabce, M.D. (1998) A study of the analytical parameters important for the sequential extraction procedure using microwave heating for Pb, Zn and Cu in calcareous soils. Anal. Chim. Acta, 369, 235-243. 

Sequential extractions (SSEs) were performed on the surface and subsurface soils, as Summarized in Table 8.2. The first six steps follow the method of Zeien and Briimmer,71 and Briimmer and Herms.72 The residual phase, that is, the phase that remained after step 6, was digested with a two-step microwave procedure. For the first step, 250 mg of sample were added to 4 ml of 65% HN03, 2.5 ml of 32% HC1 and 1 ml of 48% HF, and then heated for 5 min at 150 W and for 15 min at 350 W. For the second step the sample was cooled, and 10 ml of a 6% H3B03 were added and heated for 25 min at 250 W until a pressure of 15 bars was reached. No visible residues were left after this procedure. Extracted Zn was measured by atomic absorption spectrometry (Varian Spectra 220 Fast Sequential). The percentage of total Zn removed in each of the extraction steps is presented in Figure 8.4. The sum of all SSE steps was in good agreement with the total amount determined by XRF (+5%). 

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