title: Monolithic stationary phases with a longitudinal gradient of porosity.
abstract: The duration of the hypercrosslinking reaction has been used to control the extent of small pores formation in polymer-based monolithic stationary phases. Segments of five columns hypercrosslinked for 30-360 min were coupled via zero-volume unions to prepare columns with segmented porosity gradients. The steepness of the porosity gradient affected column efficiency, mass transfer resistance, and separation of both small-molecule alkylbenzenes and high-molar-mass polystyrene standards. In addition, the segmented column with the steepest porosity gradient was prepared as a single column with a continuous porosity gradient. The steepness of porosity gradient in this type column was tuned. Compared to a completely hypercrosslinked column, the column with the shallower gradient produced comparable size-exclusion separation of polystyrene standards but allowed higher column permeability. The completely hypercrosslinked column and the column with porosity gradient were successfully coupled in online two-dimensional liquid chromatography of polymers.
authors.affiliation: Department of Analytical Chemistry, Faculty of Chemical Technology, University of Pardubice, Pardubice, Czech Republic.
authors.forename: Jiří
authors.initials: J
authors.lastname: Urban
authors.affiliation: Department of Analytical Chemistry, Faculty of Chemical Technology, University of Pardubice, Pardubice, Czech Republic.
authors.forename: Tomáš
authors.initials: T
authors.lastname: Hájek
authors.affiliation: The Molecular Foundry, E.O. Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: Frantisek
authors.initials: F
authors.lastname: Svec
keywords: hypercrosslinking; polymer monoliths; polymers; porosity gradient; size-exclusion chromatography