Nico Vervoort

Sub-second liquid chromatographic separations by means of shear-driven chromatography.

Utilizing the concept of shear-driven chromatography, we have been able to realize reversed-phase LC separations in flat rectangular nano-channels coated with a C8 monolayer and being as thin as 100 nm. At this scale, the separation kinetics are strongly enhanced, as is witnessed by the extremely short time (< 0.1 s) needed to separate a mixture of coumarin dyes. The observed plate numbers are still relatively small, because the experiments were conducted in ultra-short columns (< or = 1 mm) and under injection band width-limiting conditions.

Experimental demonstration of the possibility to perform shear-driven chromatographic separations in micro-channels

The possibility to perform shear-driven chromatographic separations in micro-channels is demonstrated, using a novel laser-jet printed microfluidic channel system. The obtained theoretical plate numbers are in fair agreement with the theoretical calculations. Theoretical extrapolations of the separation speeds and detection limits which can be achieved when further miniaturizing the current system are presented as well.

Shear-flow-based chromatographic separations as an alternative to pressure-driven liquid chromatography.

It is only by developing specially designed injection and detection systems that shear-driven chromatography can become a viable alternative to HPLC. In the present paper, a dedicated zero dead-volume injection procedure is presented with which sample volumes can be injected reproducibly in the required picoliter range. In addition, a transversal detection groove system is designed which should allow to perform on-line UV-VIS absorption measurements with path lengths in the millimeter range, with an acceptable theoretical plate loss (only 20% in a 5 cm long channel) and acting as a nearly perfect wave guide.

Experimental Van Deemter plots of shear-driven liquid chromatographic separations in disposable microchannels.

We present a new stationary phase coating method, yielding a monolayer of densely arrayed porous HPLC beads (d(p)=4 microm) for use in a disposable shear-driven flow LC system. The system is inherently suited for whole-column detection through the small voids between the individual particles of the layer. The chromatographic performance of the system has been characterized by performing a series of coumarin dye separation experiments (reversed-phase mode) and by measuring the theoretical plate height as a function of the mobile phase velocity. The resulting Van Deemter curve, yielding a value of about 90,000 plates/m near the u=u(opt) velocity, shows good agreement with the theoretical expectations, and hence constitutes the first full validation of the theory of shear-driven chromatography.

Pushing the miniaturisation of LC with shear-driven flows

SummaryRecently, a novel driving principle for the mobile phase flow in open-tubular chromatographic systems has been proposed to evade the pressure drop limitation of pressure-driven chromatographic systems. The concept, further referred to as shear-driven chromatography (SDC), gives hitherto unachievably large mobile phase velocities through channels with a sub-micron thickness. Applying the SDC-concept in channels with a flat rectangular cross-section (e.g., 100 micrometer wide and only a few hundred nanometer thick), we hope to combine the high separation speed and resolution offered by the small channel thickness with a sufficient mass loadability arising from the large channel width. An attractive feature of the concept is furthermore that all the mobile and stationary phases of conventional LC can be used without any restriction or modification. The concept hence also provides a powerful alternative to CEC.In the present paper, we first focus on some of the theoretical advantages of SDC and we then subsequently present the first series of peak broadening measurements in shear-driven micro-channel flows. These experiments show good agreement with the theoretical expectations and hence represent a (partial) demonstration of the practical realisability of the SDC-concept.