Electrokinetic sorting and collection of fractions for preparative capillary electrophoresis on a chip

Abstract

A microfabricated device capable of selecting and collecting multiple components from a mixture separated by capillary electrophoresis (CE) is described. This collection is automated and can be easily controlled by a set of rules defined by an operator, enabling fast and consistent operation. The device consists of an electrokinetically steered fluidic network that can be divided into three sections: a CE part, a fractions distribution region and a set of storage channels. Sample fractions leave the CE channel and are detected in the interfacial region by fluorescence intensity measurements. If an upcoming peak is detected, separation is withheld and the potentials are reconfigured to force the fraction into one of the collection channels, where they become available for further processing or analysis. The sequence of separation and collection is repeated until all the bands of interest are captured. A mixture of three fluorescent dyes (Rhodamine 6G, Rhodamine B and Fluorescein) was used to demonstrate the principle. The components were repeatedly separated by means of CE and pooled in their respective storage channels. In comparison to previous developments, the system presented in this paper offers automatic collection of all fractions in a single run. Furthermore, it is possible to run the system in a repetitive mode for accumulative pooling if more fractionated sample is required.

A continuous-flow, microfluidic fraction collection device

“…Previous examples [11–15, 17] of microfluidic fraction collection devices required that the separation field be withheld while collecting fractions, a potential source of band broadening. Furthermore, in some of these devices, collected fractions were susceptible to cross-contamination by diffusion, since the collected bands were held stationary in close proximity to the common intersection of the collection channels.…”

“…Although the method has the potential to collect more analytes, this multiplexing has not yet been demonstrated. In another example of a fraction collection device, a glass microfluidic chip was used to fractionate the effluent from an electrophoretic separation by switching the electric field from the separation channel to one of four outlet channels [17]. In this way, the analytes in the separation channel stopped while an eluted analyte was sent to one of these outlet channels where it was “parked” while separation recommenced.…”

Continuous fractionation of a two‐component mixture by zone electrophoresis

“…The chip was fabricated using standard microfabrication techniques [20]. The device consisted of two, 1.1 mm thick, borosilicate glass plates.…”

Forced splitting of fractions in CE

“…For example, the high speed of separation, or rather, the high velocity of fractions moving through the separation column, makes precise handling difficult due to the required fast switching of liquid streams. Furthermore, high-volume sample injections, which are preferred for preparative purposes, will decrease separation resolution; this, however, may be solved by performing many consecutive injections and separations in one channel, [27] or performing separations in parallel channels, requiring reproducibility in timing or manufacturing, respectively. Finally, complex channel networks require special electrokinetic valving techniques and a high level of automation and real-time active control of the system are unavoidable.…”