Development and assessment of a miniaturised centrifugal chromatograph for reversed-phase separations in micro-channels (original) (raw)
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Talanta, 2000
A rapid and low-cost means of developing a working prototype for a positive-displacement driven open tubular liquid chromatography (OTLC) analyzer is demonstrated. A novel flow programming and injection strategy was developed and implemented using soft lithography, and evaluated in terms of chromatographic band broadening and efficiency. A separation of two food dyes served as the model sample system. Sample and mobile phase flowed continuously by positive displacement through the OTLC analyzer. Rectangular channels, of dimensions 10 mm deep by 100 mm wide, were micro-fabricated in poly-dimethylsiloxane (PDMS), with the separation portion 6.6 cm long. Using a novel flow programming method, in contrast to electroosmotic flow, sample injection volumes from 0.5 to 10 nl were made in real-time. Band broadening increased substantially for injection volumes over 1 nl. Although underivatized PDMS proved to be a sub-optimal stationary phase, plate heights, H, of 12 mm were experimentally achieved for an unretained analyte with the rectangular channel resulting in a reduced plate height, h, of 1.2. Chromatographic efficiency of the unretained analyte followed the model of an OTLC system limited by mass-transfer in the mobile phase. Flow rates from 6 nl min − 1 up to 200 nl min − 1 were tested, and van Deemter plots confirmed plate heights were optimum at 6 nl min − 1 over the tested flow rate range. Thus, the best separation efficiency, N of 5500 for the 6.6 cm length separation channel, was achieved at the minimum flow rate through the column of 6 nl min − 1 , or 3 ml year − 1. This analyzer is a low-cost sampling and chemical analysis tool that is intended to complement micro-fabricated electrophoretic and related separation devices.
Journal of Separation Science, 2007
The chromatographic characteristics were determined for a set of microfabricated separation channels structured with cylindrical and diamond-shaped pillars with a characteristic size of 5 lm. Channels with different structures and porosities were etched in a silicon wafer using lithographic techniques. The permeability for flow of the channels was shown to increase strongly with the overall porosity. Diamondshaped pillars appeared to yield a slightly higher permeability than cylindrical pillars at the same channel porosity. Compared to packed columns, permeabilities were higher by a factor of up to 5. Band dispersion in the channels was measured with an unretained fluorescent probe compound using a fluorescence microscope. A relatively large variation in the observed plate heights between channels was found, which was mainly attributed to the inaccurate geometry of the structure close to the side walls. Reduced plate heights between 0.2 and 1.0 were obtained. The lowest plate heights were found for channels with low porosity. The chromatographic impedances were calculated and compared to the values for the traditional chromatographic systems. For one of the structured microchannels the impedance was found to be more than ten times lower than for a column packed with nonporous spherical particles. With the data collected, predictions are given on the possibilities in terms of efficiency and speed offered by structured microchannels for pressure-driven separations, taking practical constraints into account.
Journal of Chromatography A, 2003
We present a new stationary phase coating method, yielding a monolayer of densely arrayed porous HPLC beads (d 54 mm) for use in a disposable shear-driven flow LC system. The system is inherently suited for whole-column detection p 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 u5u velocity, shows good agreement with the theoretical expectations, and hence opt constitutes the first full validation of the theory of shear-driven chromatography.
Journal of Chromatography A, 2008
The column technologies play a crucial role in the development of new methods and technologies for the separation of biological samples containing hundreds to thousands compounds. This review focuses on the development of monolithic technology in micro-column formats for biological analysis, especially in capillary liquid chromatography, capillary electrochromatography and microfluidic devices in the past 5 years (2002)(2003)(2004)(2005)(2006)(2007) since our last review in 2002 on monoliths for HPLC and CEC . The fabrication and functionalization of monoliths were summarized and discussed, with the aim of presenting how monolithic technology has been playing as an attractive tool for improving the power of existing chromatographic separation processes. This review consists of two parts: (i) the recent development in fabrication of monolithic stationary phases from direct synthesis to post-functionalization of the polymer-and silica-based monoliths tailoring the physical/chemical properties of porous monoliths; (ii) the application of monolithic stationary phases for one-and multi-dimensional capillary liquid chromatography, fast separation in capillary electro-driven chromatography, and microfluidic devices.
Journal of Chromatography A, 2008
A set of monolithic capillary columns for liquid chromatography, synthesized according to a recently developed protocol which uses methyltrimethoxysilane (MTMS) as a sole precursor, is characterised by various chromatographic tests to assess its physico-chemical properties. The new stationary phase material shows a hydrophobicity (assessed on the basis of methylene selectivity) comparable to commercial C8 columns. The MTMS-based columns exhibit a reduced affinity towards planar molecules such as PAHs, compared to C18 modified columns, which can be explained by a retention mechanism that is more governed by adsorption rather than partitioning. In comparison to commercial products an only moderate silanol activity was observed, even without any endcapping procedure applied. Selectivity between hydrophobic test compounds showed to be uniform between the columns investigated in this study, whereas retention factors differed up to 20% (batch-to-batch reproducibility) between columns produced under the same conditions. For most of the materials investigated in this study, size exclusion towards even only slightly larger molecules such as triphenylene was observed. It was demonstrated that inclusion of a micelle-forming detergent such as Brij in the synthetic protocol could partially overcome this problem.
Capillary liquid chromatography separations using non-porous pillar array columns
Journal of Chromatography A, 2012
We report on a series of explorative experiments wherein a non-porous pillar array column (NP-PAC) is coupled to a commercial capillary LC instrument. The performance of the system was evaluated by both non-retained and retained experiments using several types of samples. In order to minimize interfacing related dispersion, relatively large pillars (d p = 11 m) were defined so that a considerable depth could be achieved (50 m), resulting in an equivalent cylindrical internal diameter of 252 m. Connecting 20 channel tracks of 1 mm wide and 7 cm long by previously developed distributor-based turns, a large channel length (1.4 m) and volume (28 l) could be achieved without compromising the separation performance excessively. Establishing a van Deemter curve under non-retained conditions with off-chip injection and detection, a minimal plate height of 13 m was established, resulting in some 100,000 plates obtained in 30 min. To demonstrate the practical applicability of the NP-PAC, high pressure operation was applied to perform a number of example separations (parabens, phenones, sulfonamides, steroids and BSA digest) during a continuous operation period of 3 months wherein some 500 injections were performed. In the gradient mode, the NP-PAC approach allowed to achieve good to reasonable peak capacities (n p = 100-140 in 50-70 min) and symmetries for both large and small solutes and for both gradient and isocratic separation modes, with figures of merit for the quantification of the peaks in the ppm range, opening more perspectives for microfluidics-based small molecule analysis.
Analytical Chemistry, 1999
An automated liquid nano-separation system has been developed for nano-liquid chromatography (nano-LC) and capillary electrochromatography (CEC) using both isocratic and gradient elution. One fused-silica nanocolumn, typically 75 µm i.d. × 39 cm (25 cm effective packed length), packed with Spherisorb ODS 1, 3 µm particle size, can be used with either technique without having to remove the column upon switching from one mode to the other. The mobile phase is delivered by two reciprocating micro-LC pumps at a flow rate of 30 µL/min to a postinjection splitter that houses the nanocolumn inlet. The splitter is directly connected to a micro-injection valve with a 0.5 µL injection volume. In the CEC mode, pressure is not applied (no restriction on splitter) to the column inlet or outlet and the voltage is continuously applied during sample injection and mobile phase delivery. In the nano-LC mode, the restrictor is coupled to the splitter. Using the same nanocolumn under isocratic conditions, the repeatabilities of retention time and peak area for nano-LC were better than 0.2% and 4%, respectively, and those for CEC were better than 0.6% and 6%, respectively. On average, column efficiency was 57% higher in CEC compared to nano-LC. Gradient elution separations of parabens and polynuclear aromatic hydrocarbons (PAHs) were accomplished by CEC. Capillary electrochromatography (CEC) is an electrokinetic technique that is receiving significant attention in the separation community because of the combination of attractive features of liquid chromatography (LC) and capillary electrophoresis (CE). Combining the selectivity of LC with the high efficiency of CE leads to an exciting technique that will allow separation scientists to drive complex sample characterization, hyphenation, miniatur-ization, and mass spectrometry detection to new frontiers. Recent studies on the optimization of CEC focused on the fabrication of frits 1-3 that are designed to hold the packing material in the separation column, the minimization of air bubble formation in the column, 4,5 and the generation of gradient separations. 6-9 Commonly used frits seem to be those formed by sintering the stationary phase within the column. 3,10 In our laboratory, we have found that frits formed of silanized glass wool work as well as the sintered frits, are much easier to construct, and can be transferred from column to column. 11 Since air bubbles result in loss of current, and thus electroosmotic flow, most CEC separations are accomplished by applying a constant pressure to both the inlet and outlet buffer reservoirs. The application of pressure reduces the risk of air bubble formation in both the packed and unpacked regions of the separation capillary. It is also common to apply pressure to the inlet end of the column, which results in the combination of pressure and electrically driven flows. 1,12-17 Tsuda et al. first reported this combination of flows using microbore
Microfluidic Chromatographic Techniques
Asian Journal of Pharmacy and Life …
With the fundamentals of microscale flow and species transport well developed, the recent trend in microfluidics has been to work towardsthe development of integrated devices which incorporate multiple fluidic, electronic and mechanical components or ...
Journal of Chromatography A, 2003
In-tube solid-phase microextraction (SPME) has successfully been coupled to capillary LC, and further an automated in-tube SPME system has been developed using a commercially available HPLC auto-sampler. However, an open tubular capillary column with a thick film of polymer (stationary phase) is unfavorable because the ratio of the surface area of coating layer contacted with sample solution to the volume of the capillary column is insufficient for mass transfer. A highly efficient SPME column is, therefore, required. We introduced a C -bonded monolithic capillary column that was used for 18 in-tube SPME. The column consisted of continuous porous silica having a double-pore structure. Both the through-pore and the meso-pore were optimized for in-tube SPME, and the optimized capillary column was connected to an HPLC injection valve for characterization. The results demonstrated that the pre-concentration efficiency is excellent compared with the conventional in-tube SPME. The novel method for both introduction and concentration of the samples was effective, satisfactory and suitable for use in the SPME medium.