Holdback factor

We can use these same mass balance expressions to calculate a term we have previously called a stripping or holdback factor . The holdback factor is the ratio of metal-ion... 

To avoid confusion with the separation factor (Sr ), we will refer to this term as a holdback factor in this discussion. 

Fig. 11. Calculated holdback factor, normalized to Gd=1.0, for (a) lanthanide (solid curves) and Y (dashed curve) complexes with hiba at pH 4.5, and (b) lanthanide (solid curves) and Y (dashed curve) complexes with...

We compared in sect. 3.1 the holdback factors for several carboxylic and aminopolycar-boxylic acids that have been (or could be) used for lanthanide separations. It is clear that among the carboxylic acid eluants, a hydroxide group on the a-carbon atom is necessary for consistent performance across the series. One might expect that the proximity of the OH group creates the possibility of simultaneous coordination of both a carboxylate oxygen and the hydroxide, thus creating a chelate complex of enhanced stability. However... 

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