Journal of Chromatography A, 1149 (2007) 2–11 State of the art of shear driven chromatography Advantages and limitations Veronika Fekete a,∗ , David Clicq a , Wim De Malsche a,b , Han Gardeniers b , Gert Desmet a a Vrije Universiteit Brussel, Department of Chemical Engineering, Pleinlaan 2, 1050 Brussels, Belgium b MESA+ Research Institute, University of Twente, Enschede, The Netherlands Available online 5 February 2007 Abstract The present paper reports on the experimental difficulties encountered when trying to realize the full potential of shear-driven chromatography in nanochannels. While it theoretically offers the possibility to yield over 10,000 plates per centimetre in a few seconds, the practical realization of this potential requires a detector miniaturisation that is carried to the extreme combined with very high sampling rates. In the present study, a charge coupled device camera and a photomultiplier tube combined with pinhole were tested as detector. Despite the fact that the photomultiplier tube could offer a higher sampling rate and a better sensitivity, the charge coupled device turned out to be better suited for the current set-up because of inevitable problems with the stray-light transported through the glass channel wall. The chemistry of the separation surface was additionally studied getting more homogenous coating, thus higher separation efficiency. Having also carried out a number of mechanical improvements, it is now possible to measure separations at a distance of 8mm downstream from the injection point. This is four times further downstream than ever before while realizing a four components mixture separation in less than 1.5 s, with a plate generation velocity of about 2000–7000 plates per second depending on the sample. © 2007 Elsevier B.V. All rights reserved. Keywords: Shear-driven chromatography; CCD camera; PMT; Plate height; Separation of coumarin dyes; Coating 1. Introduction The principle of shear-driven chromatography, hereafter referred to as SDC, is based on the same separation principle as liquid or gas chromatography. But while the flow in these lat- ter techniques is generated by pressure, SDC uses mechanical forces to propel the mobile phase [1–4]. The simplest way to generate these forces is to drag a flat surface past a second flat surface, held stationary and carrying the retentive layer. Using the two surfaces to delimit a channel that is much wider than deep, the mean flow velocity is simply determined by [5]: u = u wall 2 (1) The fact that this expression is independent of the channel depth or length shows that a simple change of the driving force (mechanical force instead of a pressure or an electrical force) allows to perform chromatographic separations in channels that are much thinner and much longer than previously possible, ∗ Corresponding author. Tel.: +32 2 629 36 17; fax: +32 2 629 32 51. E-mail address: vfekete@vub.ac.be (V. Fekete). and with a mobile phase velocity that is simply dictated by the speed at which the two surfaces are moved past each other. In Ref. [5], it has been shown that the plate height in a flat rectangular channel with a mono-layer coating is given by: H = 2 D m u + 2 30 1 + 7k + 16k 2 (1 + k) 2 u d 2 D m (2) From Eqs. (1) and (2), it can be derived that, if applied to channels with a submicron thickness, the technique theoretically allows achieving extremely small plate heights. Table 1 gives an overview of these values for a number of different velocities and retention factors that are relevant for the experiments performed in the present study. The employed diffusion coefficient values were obtained from Ref. [6]. Taking the values from Table 1 and assuming a channel with length L = 8 mm, it can be calculated that such a channel could yield about 18,600 plates in about 1 s, at least for weakly retained compounds. Such performances are far beyond what is possible with conventional HPLC or ultra-high pressure HPLC. Even 1.5 m non-porous particles operated at a maximum of 2070 bar yield a plate number generation velocity of not more 0021-9673/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2007.01.120