Octyl-Imidazole/Quaternary Ammonium Bifunctional Bonded Silica Mixed Mode Stationary Phases For The Application Of Compound Drugs

With the development of medical science,the types of drugs are gradually diversified.Compound drugs are becoming more and more popular.Compared with single drug,compound drugs have the advantages of improving drug compliance and efficacy,reducing adverse reactions and drug costs.It plays an increasingly important role in the healthy life of human beings.However,the separation and detection of compound preparations are a big challenge because of their mixed components,complex structures and different properties.High performance liquid chromatography（HPLC）has been widely used in the separation and determination of drugs.However,there are some limitations in the separation of compound drugs by single mode chromatography.Reversed-phase chromatography（RPLC）is the most commonly used chromatographic mode.It has good separation selectivity for hydrophobic compounds,but weak retention for strong polar or ionic compounds.Ion-exchange chromatography（IEC）is often used to separate ionic or dissociatable compounds,but has poor separation selectivity for non-polar compound.Ion pair chromatography（IPC）due to the adding ion pair reagents into the mobile phase,make it has poor compatibility with mass spectrometry and unsuitable for gradient elution,which limits the application of IPC in separation.Mixed-mode chromatography（MMC）is a rapidly developed chromatographic method in recent years.It is based on the interaction between stationary phase and analytes,which can achieve two or more separation mechanisms in the separation process.Compared with single mode chromatography,mixed-mode chromatography has higher selectivity,separation efficiency and column capacity,especially in the separation of complex samples.Among them RP/IEX has attracted much attention due to their high orthogonality and wide application prospects.For RP/IEX,they can be divided into two categories:weak anionic groups,such as pyridine and thiophene,or strong anionic groups,such as quaternary ammonium.The different stationary phase of MMC can be synthesized through chemical bonding by liquid phase method.Toluene is one of the commonly used organic solvent which is harmful to the environment and has a high cost.In our laboratory,vapor deposition method is used in silica gel bonding reaction.This method has advantages in high reaction efficiency,high selectivity,mild reaction conditions and no pollution which has attracted much attention in chemical synthesis.The retention mechanism of MMC and their application of compound drugs need to be further developed.The research contents are described in detail as follows:In the first part,octyl-imidazole（Sil-C₈-Im）and octyl-quaternary ammonium（Sil-C₈-QA）two types stationary phases were prepared by vapor deposition method.Infrared spectroscopy,solid state nuclear magnetic resonance and elemental analysis were used to characterize the two stationary phases qualitatively and quantitatively.The results show that octyl,imidazole and quaternary ammonium are successfully bonded to the surface of silica gel respectively,and the bonding amount of octyl and imidazole on Sil-C₈-Im is 1.68?mol m^-2 and 0.707?mol m^-2,octyl and quaternary ammonium is 2.13?mol m^-2 and 0.77?mol m^-2 respectively on Sil-C₈-QA.The retention behaviors of two stationary phases were compared under different separation modes.It is found that both of the two stationary phases can be used as MMC because of their hydrophobic,hydrophilic and ion exchange mechanism.In the second part,the retention mechanism of two mixed-mode stationary phases were studied.Using benzoic acid homologues as molecular probes,the effects of p H value,ionic strength and solvent strength of mobile phase on the retention were systematic investigated on the two synthesized phases.It was found that Sil-C₈-Im was a p H sensitive stationary phase.Compared with Sil-C₈-QA,the retention of compound on Sil-C₈-Im was greatly affected by p H value.By investigating the influence of ion strength,it is found that both of the two stationary phases have typical―three-point model‖retention mechanism,and the reversed-phase/ion exchange cooperative effect is dominant in the separation process.In the investigation of organic phase strength,it is found that the organic phase strength not only affects the reverse phase retention,but also affects the reverse phase/ion exchange cooperative retention.We found that the selectivity of chromatographic separation can be optimized by changing the composition of mobile phase.In the third part,the synthesized Sil-C₈-Im and Sil-C₈-QA mixed-mode stationary phases were applied in the separation of mixed acidic drugs and compound drugs,the performance was compared with Sil-C₈ phases.It is found that the separation selectivity of acidic drugs on Sil-C₈-Im and Sil-C₈-QA is better because of the mechanism of mixed retention mechanism.At the same time,the results of the application on the three compound preparations demonstrate that MMC can not only improve separation selectivity,but also shorten retention time on the premise of ensuring separation effect.