Limits of sequential extraction procedures reexamined with emphasis on the role of H+ ion reactivity

In relation to the application of sequential extraction procedures to soil samples or sediments, arise the problems of the non-selectivity of the extractants and the potential for redistribution of trace metals among phases during the extraction, so that these procedures are said to be operational. Our aim was to re-examine these problems by giving a particular attention to the role of H+ ions which are a necessary element of the reactivity of every aqueous reagent, and seem to be one of the main factors to be taken into account in order to explain some of the discrepancies. Some elements explaining the H+ consumption and its relation with final pH will be given and discussed in terms of selectivity and refixation.