Retention in Porous Layer Pillar Array Planar Separation Platforms

Abstract

This work presents the retention capabilities and surface area enhancement of highly ordered, high-aspect-ratio, open-platform, two-dimensional (2D) pillar arrays when coated with a thin layer of porous silicon oxide (PSO). Photolithographically prepared pillar arrays were coated with 50-250 nm of PSO via plasma-enhanced chemical vapor deposition and then functionalized with either octadecyltrichlorosilane or n-butyldimethylchlorosilane. Theoretical calculations indicate that a 50 nm layer of PSO increases the surface area of a pillar nearly 120-fold. Retention capabilities were tested by observing capillary-action-driven development under various conditions, as well as by running one-dimensional separations on varying thicknesses of PSO. Increasing the thickness of PSO on an array clearly resulted in greater retention of the analyte(s) in question in both experiments. In culmination, a two-dimensional separation of fluorescently derivatized amines was performed to further demonstrate the capabilities of these fabricated platforms.

Preparation and evaluation of mesoporous silica layers on radially elongated pillars

“…Since the group of Regnier first used perfectly ordered pillars as the stationary-phase support structure in chromatography in 1998 [2], pillar array columns (PACs) have been studied intensively by a limited number of research groups [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. A dramatic reduction of the disorder related eddy dispersion or A-term of the van Deemter equation has been consistently demonstrated throughout the past decade, but also the freedom in external porosity, flow-through pore shape and channel depth turned out to be features that can be exploited to further tune and improve the column considerably.…”

“…The use of CNTs is quite unique in the field of chromatography, on the other hand, silica, a traditional material in this field, is often selected as the material of the porous layers prepared by bottom up approaches. The group of Sepaniak employed plasma-enhanced chemical vapor deposition (PECVD) of silica [11,12]. PECVD allows for formation of silica layers in open systems.…”

Recent applications of retention modelling in liquid chromatography

“…The fourth approach for column characterization is the application of semi‐empirical models. In this method, the fit to a model indicates which of the retention mechanisms is dominant, such as mixed‐mode [87], reversed phase [88–90], normal phase [91], but mostly HILIC [92]. In the past years, HILIC has gained popularity, leading to a better understanding of the mechanism and the influence of several parameters (see Section 3.4), which led to the development of many additional HILIC stationary phases.…”

“…With the increasing popularity of HILIC and mixed‐mode separations over the last years, there has been a rise in the number of stationary phases developed for these two separation modes. Most of the developments in RPLC, the workhorse of LC, are either developments of the geometrical shape of the column, such as pillar–array separations or channel shape [89,97] (discussed in Section 3.3.4), or the addition of other separating mechanisms such as ion‐exchange, creating a mixed‐mode separation [88] (discussed in this section). Few new stationary phases for NPLC have been introduced.…”

Centrifugal‐driven, reduced‐dimension, planar chromatography

“…In order to increase the surface area, we added a second level of roughness to the sidewalls, floors, and tops of our pillared substrates via room temperature plasma‐enhanced chemical vapor deposition of porous silicon dioxide (PSO) . The thin layer of PSO (25 nm) was deposited on the wafer surface using a PECVD System 100 Plasma Deposition Tool (Oxford Instruments).…”