Impurity migration

Newly used chiral surfactants often have a low critical micellar concentration, are highly soluble and can be synthesized both in L- and D-forms. This last feature makes it possible to easily change the migration order of the optical isomers, which is very interesting for the determination of the optical pnrity of drugs, where for quantification purposes it is favorable that the chiral impurity migrates before the main component. 

FIGURE 16 Determination of the enantiomeric impurity (migration time = 6.102 min) of an experimental drug. At optimal conditions the detectability can be very good, even with the typical shortcomings of an UV detector in CE. 

When a metal rod is held in an ultrahigh vacuum just beneath its melting point for 2-3 weeks in a high dc current, impurities migrate to the electrodes. Many of the lanthanoids as well as thorium are highly refined by this method, as measured by the high resistivity ratio R3ook/R. 2k ... 

This can be seen in the plot of (half-time of crystallization at a fixed T. ) versus blend composition. The observations agree very well with the findings that the growth rate of the PP sphemlites is almost unaffected while the nuclei density decreases with increasing LDPE content due to impurity migration from PP to the LDPE phase. 

On the basis of thin layer chromatographic analysis, the anaphylactoid properties of thiamine preparations were ascribed by Blum et al. (1974) to an impurity migrating in the neighborhood of pure thiamine. This impurity was postulated to act in the sense of a systemic anaphylactoid substance. Later this product was identified as 2 -demethylthiamine. Further investigations of this compound, however, could not confirm its anaphylactogenic properties in a reproducible manner. 

The immediate aim of the spheromak experiment is to study the qualitative behavior and plasma transport properties of a high temperature spheromak plasma. In order to carry out this goal/ it is necessary to increase the electron temperature high enough to minimize the ambiguity related to atomic/molecular processes and impurity radiation losses (T > 100 -200 eV). The choice of the metallic liner and equi-psi surface approach should also reduce the impurity migration from the core surface. 

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