Elution with Divalent Cations

Metal cations were eluted with eluent containing magnesium perchlorate. The divalent magnesium cation is a more effective eluent than H+ or Na , so lower concentrations are needed. In the range 0.5 mM to 10 mM Mg , the linear plots of log k vs. log [Mg ] for several divalent metal cations gave a slope close to the theoretical value of-1.0 (Table 5.7). 

Several divalent cations were also eluted with eluent containing the ethylenediam-monium- or w-phenylenediammonium 2+ cation. Capacity factors for these and other eluent are summarized in Table 5.8. It can be seen that the 2-v diamine cations are much more efficient than Mg , Na , or H . 

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FIGURE 14.4 Step-by-step isocratic elution of mono- and divalent cations by column-switching. After elution of monovalent cations from CS12A to CSIO, the valves are switched and the order of columns are reversed. (From Rey, M.A. et ah, J. Chromatogr. A, 789, 149, 1997. Copyright 1997. With permission from Elsevier.)... 

The activity was transported to ARCA II with a He(KCl) gas-jet within about 3 s. After deposition on a titanium slider it was dissolved and washed through the 1.6x8 mm column (filled with the cation-exchange resin Aminex A6, 17.5 2 pm) a flow rate of 1 mL/min with 0.1 M HNOj/5-10 4 M HF. 85% of the W elute within 10 s. Neither divalent or trivalent metal ions nor group-4 ions are eluted within the first 15 s. Also the pseudo-homologue uranium, in the form of U022+, is completely retained on the column. 

Goulet et al. (27) describe the immobilizadon of enzymes on divalent cations chelated to bis(carboxymethyl)amino-derivatized agarose. The linkage through Lewis acid-base-type complexes is reversible, because enzymes could be eluted with EDTA. 

Divalent cations such as alkaline-earth metals cannot be eluted with dilute mineral acids, since they exhibit a much higher affinity toward the stationary phase of a strong-acid cation exchanger. However, increasing the acid concentration in the mobile phase is impossible for the following reasons ... 

Alternatively, a strongly conducting eluent may be used. In this case, elution of the solute ions is associated with a negative conductivity change. This indirect detection method is applied to the separation of anions with potassium hydroxide as the eluent [7], A corresponding chromatogram is displayed in Fig. 6-2. This indirect detection method is also utilized in the analysis of mono- and divalent cations, which are eluted by dilute nitric acid or nitric acid/ethylenediamine-mixtures. 

Divalent cations such as alkaline earth metals exhibit a much higher affinity with stationary phase of strong acid cation exchangers and thus cannot be eluted with diluted mineral acids. Therefore, application of another eluent is necessary. 

Preflush the reservoir with slugs of high monovalent cation salinity so that the divalent cations are exchanged from the reservoir clays and eluted through the reservoir ahead of the surfactant slug. 

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