Displacement chromatography methods development

The latter system is used at TRU, while the SRL development program demonstrated the suitability of displacement chromatography. Both methods appear to be satisfactory. Until now, and for the foreseeable future, the quantity of transcurium elements has been too small to justify any process other than elution development for the final separation. 

Methods development for displacement chromatography has been previously described for a Langmuirian system using a graphical approach which employs the adsorption isotherms for the displacer and the various components... 

FIGURE 12 Flow sheet for methods development in displacement chromatography. 

Rhee et al. developed a theory of displacement chromatography based on the mathematical theory of systems of quasi-linear partial differential equations and on the use of the characteristic method to solve these equations [10]. The h- transform is basically an eqmvalent theory, developed from a different point of view and more by definitions [9]. It is derived for the stoichiometric exchemge of ad-sorbable species e.g., ion exchange), but as we have discussed, it can be applied as well to multicomponent systems with competitive Langmuir isotherms by introducing a fictitious species. Since the theory of Rhee et al. [10] is based on the use of the characteristics and the shock theories, its results are comprehensive e.g., the characteristics of the components that are missing locally are supplied directly by this theory, while in the /i-transform they are obtained as trivial roots, given by rules and definitions. 

The set of equations 15.34 and 15.35, along with the equilibrium isotherms given by Eqs. 15.36,15.37, and 15.39 for the two compoimds was solved by the method of characteristics, using a method previously developed and apphed to nonlinear isocratic elution, gradient elution and displacement chromatography [41,42]. 

Figure 3.2 Three major methods in chromatography. The commonest form of chromatography involves the introduction of a small volume of sample onto a column and is known as zonal chromatography. Movement down the column is effected by the mobile phase, which may be simply a solvent (A) allowing partition of the test molecules between the stationary and mobile phases. Alternatively, the mobile phase may be a solvent containing solute molecules (B), which actively displace test molecules from the stationary phase. A less frequently used method known as frontal separation (C) does not involve a separate mobile phase but a large volume of the sample is allowed to pass through the column and as the various components separate, concentration fronts develop and their movement can be monitored.

The 2D approach to separation offers not only a great increase in separation power over one-dimensional (ID) methods, but also greater versatility. We have noted that 2D separation requires the use of pairs of ID displacements. If N kinds of ID displacements can be employed, then N2 different pairwise combinations can be found for 2D use. For example, dozens of 2D methods can be envisioned that use a field-flow fractionation (FFF) mechanism these methods fall in four categories in which a given FFF mechanism can be combined with (1) another FFF subtechnique, (2) a form of chromatography, (3) an applied field (e.g., electrical), and (4) bulk flow displacement [20]. For separations generally, literally thousands of kinds of 2D separation systems are possible, although only a handful have been developed [8]. 

For separations involving large amounts of Am, Cm, or rare earths, displacement development provides a satisfactory first-cycle separation and yields Am and Cm products and a transcurium element fraction suitable for final separation by elution development. However, alternative methods for the first cycle (removal of the bulk of the lighter actinides and rare earths) are available besides displacement development chromatography, these include solvent extraction and the LiCl-anion exchange system. 

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