ABSTRACT

C18 HPLC columns are used to analyze individual parts of chemical mixtures. Ion-exchange chromatography (SAX) is a process that allows the separation of ions and polar molecules based on their charge. We have designed a mix-mode HPLC column named as Optimix C18/SAX (2)   made from 5μm high purity spherical silica particles. A special silane with octadecyl chain embedded quaternary amine group is bonded to the silica particles.

The stationary phase can provide two main interactions with analytes: the reverse-phase adsorption and the anion-exchange. Neutral analyte can be retained by reverse-phase adsorption while acidic analyte can be retained by both anion-exchange and reverse-phase adsorption mechanisms.

What should be given more attention is basic analyte. According to our research, it can be retained by the reverse-phase adsorption basically. However, the presence of quaternary amine group indeed affects its chromatography behavior attributed to the ion-exclusion and deactivation of silanol which lead to symmetrical peak. Also the loadability of basic analyte has been enlarged compared to pure C18 stationary phase. We think the reason is that quaternary amine group makes the stationary phase be more hydrophilic so that the analyte can more easily get into the stationary phase.

Conclusions

In our experiment, the Optimix C18 / SAX (2) can provide two main interactions with analytes: the reverse-phase adsorption and the anion-exchange. Neutral analyte can be retained by reverse-phase adsorption while acidic analyte can be retained by both anion-exchange and reverse-phase adsorption mechanisms. We can change the pH of the mobile phase for separation.