The Retention Behavior of Acidic, Basic and Neutral Pharmaceuticals on the Deactivated Polybutadiene Zirconia Phase

Reversed zirconia-based stationary phases belong among interesting alternatives of widely used RP silica phases. Zirconia displays specific surface properties, which are responsible for a unique retention mechanism. Furthemore, it is necessary especially for acidic analytes to add a strong Lewis base to the mobile phase mainly to improve the separation efficiency. However, commonly recommended strong Lewis base buffers are not volatile and therefore are incompatible with a mass spectrometric detection. A novel RP zirconia-based stationary phase with deactivated Lewis acid sites of zirconia was introduced to enable the use of volatile additives (acetate, formate) despite their low Lewis basicity. It is reported on the influence of surface deactivation on chromatographic behavior of acidic, basic and neutral analytes in this paper. The influence of variables such as pH levels, Lewis base type, its concentration and temperature were studied. The results were compared with the undeactivated stationary phase. In general, around 2.5-fold stronger retention of compounds was observed on the deactivated phase. Moreover, some variances in retention and selectivity were observed for both acidic and basic analytes when using different Lewis bases. For these reasons the properties of deactivated and unmodified phases under the same conditions were partly diverse and consequently the selectivity was similar but not identical.