title: Estimation of surface desorption times in hydrophobically coated nanochannels and their effect on shear-driven and pressure-driven chromatography.
abstract: The present paper provides a detailed analysis of the analyte-wall adsorption effects in nanochannels, including a random walk study of the analyte-wall collision frequency, and uses these insights to estimate wall desorption times from chromatographic experiments in nanochannels. Using coumarin dye analytes and using a methanol/water mixture buffered at pH 3 in 120-nm deep channels, the surface desorption times on naked fused-silica glass were found to be maximally of the order of 60 to 150 mus, while they were found to be on the order of 100 to 500 mus on a hydrophobically coated wall. These nonzero adsorption and desorption times lead to an additional band broadening when conducting chromatographic separations. Shear-driven flows, requiring a noncoated moving wall and a stationary coated wall, intrinsically turn out to be more prone to this effect than pressure-driven or electro-driven flows for example. The present study also shows that, interestingly, the number of analyte-wall collisions increases with the inverse of the channel depth and not with its second power, as would be expected from the Einstein-Smoluchowski relationship for molecular diffusion.
authors.affiliation: Department of Chemical Engineering, Vrije Universiteit Brussel, 1050, Brussels, Belgium.
authors.forename: Frederik
authors.initials: F
authors.lastname: Detobel
authors.forename: Veronika
authors.initials: V
authors.lastname: Fekete
authors.forename: Wim
authors.initials: W
authors.lastname: De Malsche
authors.forename: Selm
authors.initials: S
authors.lastname: De Bruyne
authors.forename: Han
authors.initials: H
authors.lastname: Gardeniers
authors.forename: Gert
authors.initials: G
authors.lastname: Desmet