Procedures for the study of chemical species

Five distinct steps can be recognised in the procedures used for the study of the chemical forms of a given element sampling, sample preparation, fractionation, detection and identification. From these arise eight points which should be considered when developing a scheme. 

In the following sections the methods and techniques used for sample collection and pretreatment, fractionation, and detection of metalloid- and metal-containing species will be considered. 

Some of the changes in conditions that could have an adverse effect on the metal-ligand interactions and also lead to denaturation of proteins have already been discussed above. It is therefore essential that especially during the pre-treatment and storage steps changes in these parameters are kept to a minimum. Other factors that may affect the molecular configuration and hence cause the denaturation of biological molecules, have been reviewed by Kauzmann (1959), and Volkin Klibanov (1989). 

Biological systems are a complex mixture of proteins, peptides, amino acids, inorganic complexes and ions. Because the systems are so complex it is virtually impossible to use a single fractionation technique to resolve the various constituents. However, complete resolution of the constituents is not a prerequisite in the study of trace metal bound fractions. Indeed, the extent to which the constituents are to be resolved by the separation technique is determined primarily by the selectivity and sensitivity of the available detection techniques. 

A fractionation technique with low resolution coupled with a highly selective detection may be more powerful than a high resolution separation coupled with a relatively non-se-lective detection. In this regard, techniques that can be used specifically to determine the metal or a class of ligands are preferred to those that measure properties like the UV spectra or refractive index. Only in cases where the metal is associated with two partly unresolved species is the use of two or more fractionation techniques justified. It must be emphasised at this point that the chances of disrupting the metal-ligand association increase as the number of fractionation steps increase. 

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