title: Mixed-mode acrylamide-based continuous beds bearing tert-butyl groups for capillary electrochromatography synthesized via complexation of N-tert-butylacrylamide with a water-soluble cyclodextrin. Part I: Retention properties.
abstract: With the aim to improve the understanding of morphology and efficiency properties, we investigate in this series the impact of the complex formation constant of the hydrophobic monomer with respect to statistically methylated-β-cyclodextrin (Me-β-CD) on the electrochromatographic properties of highly crosslinked amphiphilic mixed-mode acrylamide-based monolithic stationary phases. Based on our previous work on amphiphilic mixed-mode monolithic stationary phases for capillary electrochromatography (CEC) using N-(1-adamantyl)acrylamide (Ad-AAm) as hydrophobic monomer that forms an extremely strong water-soluble inclusion complex with Me-β-CD, we now selected N-tert-butylacrylamide (NTBA) as hydrophobic monomer forming an inclusion complex with Me-β-CD with a much lower value of the formation constant. Mixed-mode monolithic stationary phases are synthesized by in-situ free radical copolymerization of cyclodextrin-solubilized N-tert-butylacrylamide, a water soluble crosslinker (piperazinediacrylamide), a hydrophilic neutral monomer (methacrylamide), and a negatively charged monomer (vinylsulfonic acid) in aqueous medium in bind silane pre-treated fused silica capillaries. The synthesized monolithic stationary phases have both hydrophobic and hydrophilic moieties and can be employed in the reversed-phase mode, in the normal-phase mode, in a mixed-mode or in the hydrophilic interaction liquid chromatography (HILIC) mode (depending on the composition of the mobile phase and on the properties of the solute). Morphology and retention properties of this new type of stationary phase are compared to those reported in our previous series. With a homologues series of alkylphenones it is confirmed that the hydrophobicity (methylene selectivity αmeth) of the stationary phase is strongly dependent on the type of hydrophobic monomer employed. The studies reveal a significant influence of the formation constant of the involved host-guest inclusion complex on the morphology (i.e., the domain size) of the produced monoliths.
authors.affiliation: Al al-Bayt University, Faculty of Science, Department of Chemistry, 25113 Mafraq, Jordan.
authors.forename: Ayat Allah
authors.initials: AA
authors.lastname: Al-Massaedh
authors.affiliation: University of Marburg, Department of Chemistry, Hans-Meerwein-Straße, D-35032 Marburg, Germany. Electronic address: pyellu@staff.uni-marburg.de.
authors.forename: Ute
authors.initials: U
authors.lastname: Pyell
mesh_terms: D020106:Acrylamide / Q000737:chemistry*; D000178:Acrylamides / Q000737:chemistry*; D053801:Capillary Electrochromatography / Q000295:instrumentation* / Q000379:methods*; D057927:Hydrophobic and Hydrophilic Interactions; D009682:Magnetic Resonance Spectroscopy; D010636:Phenols / Q000032:analysis; D058105:Polymerization; D012822:Silicon Dioxide / Q000737:chemistry; D012995:Solubility; D014867:Water / Q000737:chemistry*; D047392:beta-Cyclodextrins / Q000737:chemistry*
chemical_list: D000178:Acrylamides; D010636:Phenols; D047392:beta-Cyclodextrins; D014867:Water; D020106:Acrylamide; D012822:Silicon Dioxide; C031215:betadex; C115287:tert-butylacrylamide
keywords: Acrylamide-based monolithic stationary phase; Capillary electrochromatography; Cyclodextrin; Hydrophilic interaction liquid chromatography; Mixed-mode retention; Retention mechanism