Complex formation and extraction by liquid chromatography

In aqueous acidic solutions transition elements and their heaviest homologs undergo the complex formation 

The complex formation is known to increase in the transition element groups with increasing Z. The aim of chemical studies has therefore been to establish whether the transactinides are in line with this trend, or whether deviation from the trend occurs due to strong relativistic effects. 

Experimentally, the complex formation is studied using aqueous chemistry separation techniques liquid-liquid extractions and ion exchange separations (see Section 12a). As a result, the distribution coefficient, Kd, of the extracted complex MLi between organic (or resin) and aqueous phases usually plotted versus the acid concentration is obtained (Fig. 32, for example). The classical definition of is 

For a step-wise process, consecutive constants are used. In the solvent extraction or extraction by ion exchange resins, the expression for Kj is more complicated than Eq. (25) [211], but is still directly proportional to Pi or Ki. In experiments with single atoms, is defined by the retention time indicated by peaks on elution curves as given by Eq. (1), see Section 1.1. Obtained sequences in the Ki values for a studied series of complexes, e.g. for elements of one group, provide the information about relative stabilities of their complexes, i.e., of Pi. 

In aqueous solutions the complex formation is competing with hydrolysis 

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