Flow Dynamics and Analyte Transfer in a Microfluidic Device for Spatial Two-Dimensional Separations

In the last decade, chip-based separations have become a major area of interest in the field of separation science, especially for the development of “spatial” two-dimensional liquid chromatography (^xLC × ^xLC). In ^xLC × ^xLC, the analytes are first separated by migration to different positions in a first-dimension (¹D) channel and subsequently transferred with the aid of a flow distributor in a perpendicular direction to undergo a second-dimension (²D) separation. In this study, several designs for ²D separations are explored with the aid of computational fluid dynamics simulations. There were several aims of this work, viz. (1) to investigate the possible anomalies arising from the location of analyte bands in the first-dimension channel before transfer to the second dimension induced by the flow distributor, (2) to study the distribution ratio of the analytes across the different outlets of the ¹D channel, and (3) to study the flow behaviour confinement in the flow distributor. In all designs, the simulated absolute flow velocity was not equal in all regions of the ¹D channel. The extreme segments showed higher velocities compared to the central zones. This will eventually influence the migration times (first moments) and the variances (second moments), as confirmed by CFD results. The study has contributed to the understanding of the effects of the peak locations and, ultimately, to progress in spatial 2D-LC separations.