The retention behavior of a small molecule pharmaceutical compound and one of its degradants in reversed-phase liquid chromatography (RPLC) using aqueous/MeOH or aqueous/ACN mobile phases with elevated pressures and column temperatures mimicking the conditions encountered in very high pressure liquid chromatography (VHPLC) was studied. MeOH and ACN are commonly used organic modifiers in RPLC. Many thermodynamic studies and molecular simulations have been performed for investigation of the effects of aqueous/MeOH and aqueous/ACN solutions on the selectivity and the retention mechanisms of RPLC. These studies suggest that the differences in the bulk and the local (around solute) solution structures between MeOH/Water and ACN/Water mixtures significantly affect the retention process and, in turn, chromatographic selectivity. Studies on the temperature dependence of the structure of these mixtures in mobile and stationary phases are also reported. The effects of MeOH- or ACN-containing mobile phases on the retention behaviors of a non-ionizable pharmaceutical compound and a zwitterionic degradant were examined as a function of the column inlet pressure (600-10000 psi) and column temperature (30-80 �C). Both compounds show a similar trend in the relationship of retention factor vs. change of pressure in both mobile phase systems, with steeper slopes observed in MeOH/Water system. As for the relationship between the retention factor and the column temperature, a remarkable contrast between retention in the two mobile phase systems was observed for the zwitterion. The significantly different retention behaviors of these compounds has a direct impact on the comparability of the retention times of the compounds during method conversion and transfer from regular HPLC to VHPLC and vice versa in pharmaceutical analysis. Work is ongoing to attempt to elucidate the cause, e.g. conformation and solvation of the analyte, changes in the stationary phase, or ionization of the analytes.

Chromatographic behaviors of a non-ionizable pharmaceutical compound and a zwitterionic degradant in methanol and acetonitrile containing mobile phases under very high pressure liquid chromatography conditions

246th National Meeting (2013)

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