Correlations between conformational isomerism and chromatographic diastereoselectivity of bis amino amide s-triazine derivatives.

NMR spectroscopy was used to probe the conformational behavior of diastereomeric s-triazine derivatives containing two chiral amino amide substituents, in order to shed light onto the mechanism of chromatographic diastereoselectivity. Utilizing the amino hydrogen signals in the proton NMR spectrum, the population of the conformations caused by rotation about the bond between the amino nitrogen and aromatic carbon atoms could be observed. The population distribution between the three possible conformations was similar but not identical between the two diastereomers, with similar trends being observed for both bis alanine amide and bis valine amide derivatives.

Feasibility of using gravimetry to measure excess adsorption effects of a binary solvent system in a reversed-phase high-performance liquid chromatography column.

A modified method for weighing HPLC columns filled with solvent is described. The method prevents the loss of traces of solvent from within the threads of the column. The method was tested by obtaining the weights of a C18 column filled with 10 different organic solvents, showing a standard deviation on the order of 0.

Water-immiscible solvents as diluents in reversed-phase liquid chromatography.

It has recently been shown that the use of strong organic solvents as diluent is possible in RPLC, provided that the solvent used as diluent is retained more strongly by the column than the analytes in the sample. In this study, the phenomenon was further studied experimentally using several water-immiscible solvents (ethyl acetate, isopropyl acetate, and methyl isobutyl ketone) and several model analyte compounds. In all cases, analyte peak distortion was minimal provided the analyte eluted earlier than the diluting solvent, in contrast to substantial broadening and distortion when the analyte eluted after the diluting solvent.