Elements bioavailability parameters

On the basis of the preceding discussion, it should be obvious that ultratrace elemental analysis can be performed without any major problems by atomic spectroscopy. A major disadvantage with elemental analysis is that it does not provide information on element speciation. Speciation has major significance since it can define whether the element can become bioavailable. For example, complexed iron will be metabolized more readily than unbound iron and the measure of total iron in the sample will not discriminate between the available and nonavailable forms. There are many other similar examples and analytical procedures that must be developed which will enable elemental speciation to be performed. Liquid chromatographic procedures (either ion-exchange, ion-pair, liquid-solid, or liquid-liquid chromatography) are the best methods to speciate samples since they can separate solutes on the basis of a number of parameters. Chromatographic separation can be used as part of the sample preparation step and the column effluent can be monitored with atomic spectroscopy. This mode of operation combines the excellent separation characteristics with the element selectivity of atomic spectroscopy. AAS with a flame as the atom reservoir or AES with an inductively coupled plasma have been used successfully to speciate various ultratrace elements. 

Cadmium speciation in the soil solution may well play a role in its bioavailability. An element s bioavailability is reported to be a function of at least three parameters (Brummer, 1986) ... 

Operationally defined RMs in which the assigned or certified values are directly linked to the applied method. These materials involve parameters that are associated with a certain properties, e.g., leachable or mobilizable fractions of elements from soils and/or bioavailable fractions, or an activity (e.g., enzymatic activity). The values are defined by the applied method following a very strict analytical protocol (e.g., a standardized method). 

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