Application of a Sequential Extraction Procedure to Calcareous Soil Samples: Preliminary Studies

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Abstract
The localization of trace metals in soils is usually performed by sequential extraction procedures. Our purpose was to study the fractioning of copper in calcareous soils, in order to predict its mobility, using the extraction procedure proposed by Tessier et al. This preliminary study is devoted to the improvements of this method applied to calcareous soil samples. First, it was necessary to assess the experimental conditions allowing the complete solubilisation of the different compartments involved in the extraction procedure with their appropriate reagent (acetic acid-sodium acetate and carbonates, iron hydroxide and hydroxylamine, organic matter and hydrogen peroxide, fluorhydric-perchloric acid and residual fraction). The complete solubilisation of each compartment was tested by measuring the residual phase. Secondly, it was necessary to study the analytical protocol for the determination of copper with electrothermal atomic absorption; an improvement of this determination was particularly necessary for the reagent used for the exchangeable fraction (sodium acetate at pH = 8.5). According to the experimental results, the quality (repeatability, concordance of the sum of fractions with the total content of copper determined with independent measurement) of the proposed protocol seems to be quite good. Some results of the fractioning of copper in calcareous soil samples are given; these samples are characterised by a high value of copper in the residual fraction corresponding to a poor availability of this element.