Combining Different Stationary-Phase Chemistries to Improve the Selectivity of Impurity Profiling Methods

Abstract

To improve the selectivity of challenging separations, a possible solution is the modulation of the stationary phase through serial coupling of different columns having different chemistries. Such an approach is interesting when each column used for a tandem setup results in distinct critical peak pairs. For impurity profiling methods, gradient elution mode is preferred. However, in gradient mode, the order of the coupled columns may result in different selectivities. In addition, the length of the individual columns may also impact the separation quality. The aim of this work was to study the possibilities of serial column coupling for impurity profiling methods. Various C8, C18, cyano, and phenyl phases were tested and compared. An algorithm was used to investigate peak migration through tandem columns, considering both the length and order of the individual column segments. As an example, amlodipine impurity profiling was considered to illustrate the benefit of serial column coupling. We also draw attention to the fact that common column tests are not always helpful because they do not declare anything about the compounds of our interest. Oftentimes, it is more informative and less time-consuming to run one or a few linear gradient experiments by injecting the sample of interest.