Solving advanced micromachining problems for ultra-rapid and ultra-high resolution on-chip liquid chromatography


De Malsche, Wim (2008) Solving advanced micromachining problems for ultra-rapid and ultra-high resolution on-chip liquid chromatography. thesis.

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Abstract:High-performance liquid chromatography (HPLC) is one of the most versatile separation
techniques available for the analysis of complex samples that are typically encountered in
fields such as environmental monitoring, biology, pharmacy, biochemistry, etc. A distinction
between different HPLC formats can occur in the shape of the stationary phase, which
necessarily displays a selective interaction with the present analytes in order to establish a
separation. The most prevailing format is the packed particulate bed, which generally consists
of functionalized porous spherical particles that are randomly packed in a capillary.
Monolithic media (polymeric or silica) have recently become popular because of the high
permeability combined with reasonable mass transfer characteristics. In this frame it is
important to stress that it is theoretically expected that disorder restrains the performance of a
column. When conceiving the ideal chromatographic format, the achievement of more order
is therefore an interesting route to pursue. A practical realization of this approach was first put
forward in 1998 by prof. Fred Regnier, making use of a microfabricated array of pillars in
glass in capillary electro-chromatography mode, replacing the random particles by very
accurately positioned pillars. Recognizing the potential of the technique, Desmet and coworkers
performed a number of computational fluid dynamics (CFD) to study the fluidic
behaviour of such a pillar array in pressure-driven mode. As the flow-through pores can be
chosen independently of the pillar diameter, optimal designs can be tailored to provide the
optimal combination of flow resistance and plate height. A first device containing non-porous
silicon pillars was then characterized by De Pra et al. in 2005 under non-retaining conditions,
achieving a minimal reduced plate height of 0.2 in a 40 % porosity pillar bed consisting of 10
μm pillars, in agreement with the CFD predictions. Even though this work was an important
trigger in generating interest in this novel format, no separations were demonstrated, hence
keeping the more relevant fluidic behaviour under retentive conditions in the dark.
Item Type:Thesis
Science and Technology (TNW)
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