title: Amine-phenyl multi-component gradient stationary phases.
abstract: Continuous multi-component gradients in amine and phenyl groups were fabricated using controlled rate infusion (CRI). Solutions prepared from either 3-aminopropyltriethoxysilane (APTEOS) or phenyltrimethoxysilane (PTMOS) were infused, in a sequential fashion, at a controlled rate into an empty graduated cylinder housing a vertically aligned thin layer chromatography (TLC) plate. The hydrolyzed precursors reacted with an abundance of silanol (SiOH) groups on the TLC plates, covalently attaching the functionalized silane to its surface. The extent of modification by phenyl and amine was determined by the kinetics of each reaction and the exposure time at each point along the TLC plate. The local concentrations of phenyl and amine were measured using diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy, respectively. The profile of the multi-component gradients strongly depended on the order of infusion, the direction of the gradient and the presence of available surface silanol groups. A slightly higher amount of phenyl can be deposited on the TLC plate by first modifying its surface with amine groups as they serve as a catalyst, enhancing condensation. Separation of water- and fat-soluble vitamins and the control of retention factors were demonstrated on the multi-component gradient TLC plates. Uniformly modified and single-component TLC plates gave different separations compared to the multi-component gradient plates. The retention factors of the individual vitamins depended on the order of surface modification, the spotting end, and whether the multi-component gradients align or oppose each other.
authors.affiliation: Department of Chemistry, Virginia Commonwealth University, Richmond, VA 23284-2006, United States.
authors.forename: Veeren C
authors.initials: VC
authors.lastname: Dewoolkar
authors.affiliation: McMaster University, Hamilton, Ontario, Canada.
authors.forename: Balamurali
authors.initials: B
authors.lastname: Kannan
authors.affiliation: Department of Chemistry, Virginia Commonwealth University, Richmond, VA 23284-2006, United States.
authors.forename: Kayesh M
authors.initials: KM
authors.lastname: Ashraf
authors.affiliation: Department of Chemistry, Kansas State University, Manhattan, KS 66506-0401, United States. Electronic address: higgins@ksu.edu.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Higgins
authors.affiliation: Department of Chemistry, Virginia Commonwealth University, Richmond, VA 23284-2006, United States. Electronic address: mmcollinson@vcu.edu.
authors.forename: Maryanne M
authors.initials: MM
authors.lastname: Collinson
mesh_terms: D002855:Chromatography, Thin Layer / Q000379:methods*; D017646:Organosilicon Compounds / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D011437:Propylamines; D012821:Silanes / Q000737:chemistry*; D012997:Solvents; D014815:Vitamins / Q000302:isolation & purification; D014867:Water
chemical_list: D017646:Organosilicon Compounds; D011437:Propylamines; D012821:Silanes; D012997:Solvents; D014815:Vitamins; D014867:Water; C410706:phenyltrimethoxysilane; C477625:amino-propyl-triethoxysilane
keywords: Functionally graded surfaces; Gradient; Organoalkoxysilanes; Planar chromatography; Silane chemistry; Sol–gel