Eluents requirements

Os-191 injected is not decreased for a given dose of Ir-191m. In addition, the larger column volume increases the dead volume of the generator system and thus increases the volume of eluent required to remove the Ir-191m. 

A detailed SMBR model was used in order to optimize the unit with the objective function of minimal eluent requirement under the constraints of full conversion and complete product separation. Due to the reduced cost of these resins, the cost of this process is in fact controlled by the cost of the solvent recovery from the extract and raffinate streams. 

Fig. 6.16. Qualitative impact of changing ion-exchange capacities on eluent requirement.

Fig. 6.17. Optimal ion-exchange capacity and feed concentration with respect to eluent requirement segmentation 3-2-3-2.

For a stoichiometric feed concentration of acetic acid instead, the optimal resin capacity was calculated as 5 mEq g-1, which is the original Amberlyst 15 resin. Further optimization, including also the feed concentration of acetic acid as a decision variable, yielded an eluent requirement of ca. 3 mol methanol per mol methyl acetate for a 5 mEq g-1 resin and 60 40 acetic acid methanol feed stream (Fig. 6.17). 

The steep increase of the eluent requirement with decreasing resin capacity can be investigated in more detail by analyzing the key adsorptive and reaction parameters. 

The key reaction parameter is clearly the reaction rate constant, which increases linearly with the ion-exchange capacity of the resin. Higher reaction rates clearly enhance SMBR efficiency and reduce eluent requirement. 

Not good for high water percentages in eluent, requires volatile mobile phase components... 

In many cases the cost of eluent (i.e. solvent) is not negligible and in some cases it even represents the greatest contribution to the total separation cost. Therefore, it is advisable in these cases to observe the eluent consumption, or better still, the efficiency of eluent-usage during the chromatographic separation. This can be characterized by specific eluent consumption EQ, which means the amount of eluent required to purify a certain amount of product i. 

In a particular partition chromatography column, the volumes of mobile phase, stationary phase, and inert phase are in the ratio A, A/ of 0.20 0.05 0.75 and the HETP is 0.0050 cm. Two substances having partition coefficients of 1.50 and 1.55 are to be separated. Calculate (a) the values for the two substances, (b) the volume of eluent required to bring each of the bands in turn to a point 10.0 cm down a column of total area 1.0 cm, (c) the volume of eluent required to wash all but 0.13% of the leading component from a 30 cm column, and (d) the % of the lagging component that has been removed under the conditions of part c. 

In on-line elution, the kinetic features of the process are much more important than for off-line batch procedures. Weak eluents requiring long equilibrium periods may be used successfully for off-line procedures, but caimot be used for on-line applications, since slow elutions may significantly degrade the enrichment factors and/or the concentration efficiencies. 

Strength of the eluent required for equal retention factors. If a mobile phase with a low conductivity is desired, as in the case of ion chromatography, a resin with a low capacity is preferred. On the other hand, for high retention and high sample capacity, ion exchangers with a high capacity should be used. 

Elution. Elution is necessary if the sorbed ions are required for examination, and were not removed just to facilitate analysis of the effluent. The volume of eluent required depends on both the resin and the nature of the sorbed ions see later for guidelines. 

Since from an ideal point of view polymer solubility and adsorption are not occurring in this chromatographic process, the volume of eluent required for the elution of any macromolecules species must essentially be dependent on chain length and appears to be insensitive to structure (universal calibration). However, this seems to be not always the case (non-exclusion effects). 

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