Ionic interactions techniques

An understanding of the chemical behaviour of the element can aid in the choice of appropriate techniques and methods, the application of which would not disrupt the interaction of the element with associated constituents. For example, in the study of aluminium some relevant information may include its amphoteric nature, its ability to form predominantly ionic complexes, its tendency to form hydroxides, and the stability of aluminium complexes formed with biological ligands. It is clear that in order to maintain the ionic interactions the pH, ionic strength and, of lesser importance, the ionic composition of the medium used for sample preparation should be similar to that found in vivo. In addition, highly charged surfaces should not come into contact with the sample. 

Solid-phase extraction (SPE) is a purification technique based on the extraction of a compound (or a mixture of compounds) from a solution through absorption on a solid support The main physical principles involved in the extraction process are ionic interactions between acidic and basic species, and polar and/or nonpolar... 

Kelly and Leyden10 studied the interaction of APTS with silica gel by thermometric enthalpy titration. This technique provides information regarding kinetic and thermodynamic parameters, which govern the reactivity of immobilized functional groups. They found that 26% of the APTS molecules were irreversibly bonded to the silica surface and attributed this stability to ionic interactions. Both values are equal within experimental error. 

Size exclusion chromatography (SEC, also known as gel permeation chromatography) is a method of separating compounds of different molecular masses and sizes. Because steric interactions between analytes and the stationary phase are relatively weak, unstable forms of metals can be separated from more stable complexes and from adducts stabilized by ionic interactions. Unfortunately, the process of sorption and ionic interactions between the investigated substances and the stationary phase can decrease metal recovery by as much as 50 % these interactions are also responsible for the instability of retention times [146]. The separation can be performed both in the aqueous environment and in the presence of organic solvents. Because the technique is not selective, it is utilized primarily as the first stage of multidimensional chromatography [147]. 

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