Column properties and flow profiles of a flat, wide column for high-pressure liquid chromatography

Experimental verification of some theoretical considerations on preparative separation with orthogonal pressurised planar electrochromatography

This paper reports for the first time the coupling of a two-dimensional separation technique known as orthogonal pressurised planar electrochromatography (OPPEC) with on-line UV/VIS detection. It establishes the efficiency characteristic of a planar column used in OPPEC. The studies show that in OPPEC, all separation steps (mixture introduction, separation, and detection) can run successfully as non-separate operation, much like in HPLC, and the planar column has itself good efficiency, ensuring a relatively low plate height value. In its use, some findings of the previously proposed theoretical model concerning optimisation of preparative separation of components with the same electrophoretic mobility are verified - showing that there is a good agreement between theory and experiment. The paper also demonstrates by means of a specific example of separation of a post-reaction mixture obtained after synthesis of valine diastereomers that OPPEC can be a powerful tool used in preparative separation in that it can achieve much higher separation productivity and significantly lower eluent consumption than when using column chromatography techniques.

Experimental and numerical study of band-broadening effects associated with analyte transfer in microfluidic devices for spatial two-dimensional liquid chromatography created by additive manufacturing

Conventional one-dimensional column-based liquid chromatographic (LC) systems do not offer sufficient separation power for the analysis of complex mixtures. Column-based comprehensive two-dimensional liquid chromatography offers a higher separation power, yet suffers from instrumental complexity and long analysis times. Spatial two-dimensional liquid chromatography can be considered as an alternative to column-based approaches. The peak capacity of the system is ideally the product of the peak capacities of the two dimensions, yet the analysis time remains relatively short due to parallel second-dimension separations. Aspects affecting the separation efficiency of this type of systems include flow distribution to homogeneously distribute the mobile phase for the second-dimension (²D) separation, flow confinement during the first-dimension (¹D) separation, and band-broadening effects during analyte transfer from the ¹D separation channel to the ²D separation area. In this study, the synergy between computational fluid dynamics (CFD) simulations and rapid prototyping was exploited to address band broadening during the ²D development and analyte transfer from ¹D to ²D. Microfluidic devices for spatial two-dimensional liquid chromatography were designed, simulated, 3D-printed and tested. The effects of presence and thickness of spacers in the ²D separation area were addressed and leaving these out proved to be the most efficient solution regarding band broadening reduction. The presence of a stationary-phase material in the ¹D channel had a great effect on the analyte transfer from the ¹D to the ²D and the resulting band broadening. Finally, pressure limit of the fabricated devices and printability are discussed.

Centrifugal-driven, reduced-dimension, planar chromatography

A fundamental problem with efficiency in capillary action driven planar chromatography results from diminishing flow rates as development proceeds, giving rise to molecular diffusion related band dispersion for most sample types. Overpressure and electrokinetic means to speed flow have been used successfully in TLC. We explore the use of centrifugal force (CF) to drive flow for reduced-dimension planar platforms (ultra-TLC, low micrometer features, and nano-TLC, nanoscale features). The silicon wafer platforms have two forms of continuous 2D arrays created by either photolithography or metal dewetting followed by deep reactive ion etching and coated with porous SiO₂ . The flow pattern is unusual with co-planar flows above and within the arrays. The effects of parameters such as spin rate, solvent type, and surface character on flow rates is established and can be substantially greater than capillary action flow. Using fluorescent dyes, we investigate retardation factors and chromatographic plate height; the latter falls in the low to sub-micrometer range. To the best of our knowledge, we demonstrate the first analytical separations performed in pillar arrays using CF to augment solvent flow.

Direct Production of Microstructured Surfaces for Planar Chromatography Using 3D Printing

Through optimization of the printing process and orientation, a suitably developed surface area has been realized upon a 3D printed polymer substrate to facilitate chromatographic separations in a planar configuration. Using an Objet Eden 260VS 3D printer, polymer thin layer chromatography platforms were directly fabricated without any additional surface functionalization and successfully applied to the separation of various dye and protein mixtures. The print material was characterized using gas chromatography coupled to mass spectrometry and spectroscopic techniques such as infrared and Raman. Preliminary studies included the separation of colored dyes, whereby the separation performance could be visualized optically. Subsequent separations were achieved using fluorescent dyes and fluorescently tagged proteins. The separation of proteins was affected by differences in the isoelectric point (pI) and the ion exchange properties of the printed substrate. The simple chromatographic separations are the first achieved using an unmodified 3D printed stationary phase.

Construction and initial evaluation of an apparatus for spatial comprehensive two-dimensional liquid-phase separations

Spatial comprehensive two-dimensional chromatography is discussed as a potentially alternative to the conventional column-based approach. In "spatial" separations each analyte ends up in a specific location, rather than being eluted at a specific time. Ultimately, higher peak-capacity-production rates (peak capacity per unit time) may be attained by spatial two- and three-dimensional separations. While low-pressure planar chromatography is well developed, the high-pressure equivalent is still in its infancy. We discuss the requirements for a device for high-pressure spatial two-dimensional chromatography and we describe a possible design. A prototype instrument has been constructed in-house. The preparation of a polymer monolithic separation body and a valve configuration that allows manual sample injection are described. Initial tests of this study included the investigation of the homogeneity of the monolith and the flow profile through the separation body. Furthermore, in order to evaluate the current chromatographic performance of the device, a mixture of dyes was separated in one dimension within 30 s.

Separation of peptides and oligonucleotides using a monolithic polymer layer and pressurized planar electrophoresis and electrochromatography

The rapid separation of mixtures of six peptides using porous polymer monolithic layers in electrophoresis and pressurized planar electrochromatography modes has been achieved. The separations in the former mode were performed on a generic hydrophobic poly(butyl methacrylate-co-ethylene dimethacrylate) layer with no ionizable functionalities and required 2 min. This layer also enabled the separation of three oligonucleotides. The separation in the pressurized planar electrochromatographic mode was carried out using a negatively charged layer prepared via cografting of 2-acrylamido-2-methyl-1-propanesulfonic acid and 2-hydroxyethyl methacrylate on top of the generic hydrophobic monolith and was completed in 1 min.