Electrochromatographic evaluation of a silica monolith capillary column for separation of basic pharmaceuticals

Abstract

A silica-based monolithic capillary column was prepared via a sol-gel process. The continuous skeleton and large through-pore structure were characterized by scanning electron microscopy (SEM). The native silica monolith has been successfully employed in the electrochromatographic separation of b-blockers and alkaloids extracted from traditional Chinese medicines (TCMs). Column efficiencies greater than 250 000 plates/m for capillary electrochromatography (CEC) separation of basic compounds were obtained. It was observed that retention of basic pharmaceuticals on the silica monolith was mainly contributed by a cation-exchange mechanism. Other retention mechanisms including reversed-phase and normal-phase mechanisms and electrophoresis of basic compounds also played a role in separation. A comparison of the differences between CEC and capillary zone electrophoresis (CZE) separation was also discussed.

Preparation of monolithic silica column with strong cation‐exchange stationary phase for capillary electrochromatography

“…The elution order of those analytes is precisely the same as that observed on native silica monolithic column at pH 7.40, but entirely different from that observed in CZE [18], which means that a strong cation-exchange mechanism should be one of the most important factors determining the separation of those analytes. In order to gain a further insight into the retention mechanism on MS-SCX columns, the influence of ionic strength of eluent on the retention factors of five b-blockers was investigated.…”

“…The EOF increases slightly with pH in the latter case, probably due to the dissociation of underivatized silanol groups. This will result in an increase of the cation-exchange capacity, which was supported by the separation of basic drugs on a native monolithic silica column due mainly to a cation-exchange mechanism [18]. The EOF of the MS-SCX is about 1.14610 -4 cm 2 V -1 s -1 , a value that is comparable with that of commercial SCX silica particles [22].…”

“…The extract of Coptis chinensis Franch. was prepared according to procedures reported previously [18].…”

“…Pretreatment of the capillary and formation of monolithic silica inside a capillary were performed by procedures reported elsewhere [18]. (ii) In-situ activation of the monolithic silica was performed by a rehydroxylation process in order to maximize silanol groups on the silica surface.…”

“…is a commonly used traditional Chinese medicine which contains protoberberine alkaloids such as berberine, palmatine, coptisine, epiberberine, jatrorrhizine, and columbamine. It has been demonstrated that the cation-exchange mechanism plays an important role in the separation of these alkaloids on a native silica monolithic column [18]. Moreover, the prepared silica monolithic column with strong cationexchange stationary phase was also used for the separation of the extracted quaternary alkaloids from the root of Coptis chinensis Franch., and a typical electrochromatogram obtained with 12.5 mM phosphate buffer at pH 7.40 is shown in Figure 6.…”