title: Mixed-mode reversed-phase and ion-exchange monolithic columns for micro-HPLC.
abstract: This paper describes the fabrication of RP/ion-exchange mixed-mode monolithic materials for capillary LC. Following deactivation of the capillary surface with 3-(trimethoxysilyl)propyl methacrylate (gamma-MAPS), monoliths were formed by copolymerisation of pentaerythritol diacrylate monostearate (PEDAS), 2-sulphoethyl methacrylate (SEMA) with/without ethylene glycol dimethacrylate (EDMA) within 100 microm id capillaries. In order to investigate the porous properties of the monoliths prepared in our laboratory, mercury intrusion porosimetry, SEM and micro-HPLC were used to measure the monolithic structures. The monolithic columns prepared without EDMA showed bad mechanical stability at high pressure, which is undesirable for micro-HPLC applications. However, it was observed that the small amount (5% w/w) of EDMA clearly improved the mechanical stability of the monoliths. In order to evaluate their application for micro-HPLC, a range of neutral, acidic and basic compounds was separated with these capillaries and satisfactory separations were obtained. In order to further investigate the separation mechanism of these monolithic columns, comparative studies were carried out on the poly(PEDAS-co-SEMA) monolithic column and two other monoliths, poly(PEDAS) and poly(PEDAS-co-2-(methacryloyloxy)ethyl-trimethylammonium methylsulphate (METAM)). As expected, different selectivities were observed for the separation of basic compounds on all three monolithic columns using the same separation conditions. The mobile phase pH also showed clear influence on the retention time of basic compounds. This could be explained by ion-exchange interaction between positively charged analytes and the negatively charged sulphate group.
authors.affiliation: Pharmaceutical Sciences Research Division, King's College London, London, UK.
authors.forename: Zhengjin
authors.initials: Z
authors.lastname: Jiang
authors.forename: Norman W
authors.initials: NW
authors.lastname: Smith
authors.forename: Paul D
authors.initials: PD
authors.lastname: Ferguson
authors.forename: Mark R
authors.initials: MR
authors.lastname: Taylor
mesh_terms: D000179:Acrylates / Q000737:chemistry; D000639:Amitriptyline / Q000032:analysis; D000814:Aniline Compounds / Q000032:analysis; D002851:Chromatography, High Pressure Liquid / Q000295:instrumentation / Q000379:methods; D002852:Chromatography, Ion Exchange / Q000295:instrumentation* / Q000379:methods; D004110:Diltiazem / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007659:Ketones / Q000032:analysis; D008689:Methacrylates / Q000737:chemistry; D008832:Microchemistry / Q000295:instrumentation; D015394:Molecular Structure; D010316:Particle Size; D010636:Phenols / Q000032:analysis; D011084:Polycyclic Aromatic Hydrocarbons / Q000032:analysis; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry; D016062:Porosity; D011719:Pyrazines / Q000032:analysis; D011803:Quinine / Q000032:analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013228:Stearates / Q000737:chemistry; D013499:Surface Properties; D013997:Time Factors; D014700:Verapamil / Q000032:analysis
chemical_list: D000179:Acrylates; D000814:Aniline Compounds; D007659:Ketones; D008689:Methacrylates; D010636:Phenols; D011084:Polycyclic Aromatic Hydrocarbons; D011108:Polymers; D011719:Pyrazines; D013228:Stearates; C531048:pentaerythritol diacrylate monostearate; D000639:Amitriptyline; C004919:ethylene dimethacrylate; D011803:Quinine; D014700:Verapamil; D004110:Diltiazem; C529625:2-sulfoethyl methacrylate; C023650:aniline