Electrochromatography In Microchips Research Articles

Development of a Mobile Analytical Chemistry Workstation Using a Silicon Electrochromatography Microchip and Capacitively Coupled Contactless Conductivity Detector.

Capillary electrochromatography (CEC) is a separation technique that hybridizes liquid chromatography (LC) and capillary electrophoresis (CE). The selectivity offered by LC stationary phase results in rapid separations, high efficiency, high selectivity, minimal analyte and buffer consumption. Chip-based CE and CEC separation techniques are also gaining interest, as the microchip can provide precise on-chip control over the experiment. Capacitively coupled contactless conductivity detection (C4D) offers the contactless electrode configuration, and thus is not in contact with the solutions under investigation. This prevents contamination, so it can be easy to use as well as maintain. This study investigated a chip-based CE/CEC with C4D technique, including silicon-based microfluidic device fabrication processes with packaging, design and optimization. It also examined the compatibility of the silicon-based CEC microchip interfaced with C4D. In this paper, the authors demonstrated a nanofabrication technique for a novel microchip electrochromatography (MEC) device, whose capability is to be used as a mobile analytical equipment. This research investigated using samples of potassium ions, sodium ions and aspirin (acetylsalicylic acid).

Recent advances in microchip enantioseparation and analysis.

This review summarizes recent developments (over the past decade) in the field of microfluidics-based solutions for enantiomeric separation and detection. The progress in various formats of microchip electrodriven separations, such as MCE, microchip electrochromatography, and multidimensional separation techniques, is discussed. Innovations covering chiral stationary phases, surface coatings, and modification strategies to improve resolution, as well as integration with detection systems, are reported. Finally, combinations with other microfluidic functional units are also presented and highlighted.

Interfacing monolith-based electrochromatography in microchips with inductively coupled plasma mass spectrometry for elemental speciation

This work demonstrated the coupling of monolith-based electrochromatography in microchips with ICP-MS for elemental speciation.

A miniaturized analysis system composed of monolith-based microchip electrochromatography coupled with on-line chemiluminescence detection for amino acids

Miniaturized chemical analysis instruments using micromachining techniques are receiving increasing attention. We presented a compact microchip-based electrochromatography (μCEC)-chemiluminescence (CL) system for the detection of amino acids. Monoliths prepared by in situ photopolymerization in the separation channel of the microchip served as the stationary phase of the μCEC coupled with CL detection. Negative pressure combined with electrokinetic force injection method was utilized for sampling and transporting CL reagents in this system. The amino acids were directly analyzed by enhanced Cu2+ catalyzed activity for luminol-hydrogen peroxide CL reaction as the formation of Cu2+-biomolecule complexes online. Glycine (Gly), Glutamic acid (Glu), Arginine (Arg) and Aspartic acid (Asp) were chosen as model compounds to evaluate the performance of the μCEC-CL system. The results demonstrated that the proposed system offered a number of benefits including miniaturization, significant simplification in operation and instrumentation; what is more, amino acids were directly analyzed without complex labeling procedure.

Carbon nanotube based separation columns for high electrical field strengths in microchip electrochromatography

Electrically insulated carbon nanotube (CNT) based separation columns have been fabricated that can withstand an electrical field strength of more than 2.0 kV cm(-1) without bubble formation from electrolysis. The carbon nanotubes were grown in a pillar array defined by photolithographic patterning of the catalyst layer used for synthesis of the nanotubes. Multiwall carbon nanotubes are inherently electrically conductive and cannot be used as a continuous layer in the microfluidic channels, without short circuiting the electrical field in the separation column, when the field strength is more than a couple of 100 V cm(-1). Here, the carbon nanotubes are grown in an array of hexagonal pillars, where the nanotubes in the individual pillars are not in direct electrical contact with the nanotubes of the adjacent pillars. This makes it possible to increase the electrical field strength from around 100 V cm(-1) to more than 2.0 kV cm(-1) and thereby to use the CNT columns for electrokinetic separations with the high electrical field strengths that are typically used in this application. An electrochromatographic separation of two Coumarin dyes was demonstrated on the CNT column with an acetonitrile content of 90%.

Microchip electrochromatography: the latest developments and applications

This review summarizes recent developments and applications of microchip electrochromatography (microCEC) mainly in the past five years between 2005 and 2009 with a focus on column technologies. In addition, some new improvements in the chip design and fabrication, sample preconcentration, electroosmotic flow control as well as mechanisms that govern electrochromatographic separation are described and reviewed. The features and limitations of several practical aspects of their applications are highlighted.

Progress in microchip enantioseparations

Advances in microfluidic chips for chiral separations from 2003 to early 2009 are discussed. Microchip-based separation techniques promise higher speed, throughput, portability, less sample and reagent consumption, better environmental compatibility, reduced cost and the prospect of system integration. Microchip electrophoresis is the most promising technique for miniaturized enantioseparations and has been performed with a variety of designs and analytes, however, other formats such as microchip electrochromatography are also gaining in popularity. Microchip fabrication, chemistry and detection issues are critically discussed and highlighted. Integration of enantioseparation techniques into multifunctional microchips are currently a rapidly advancing area of research and methods are discussed that may eventually enable enantioseparations to be the part of a holistic chemical microchip.

Underivatized cyclic olefin copolymer as substrate material and stationary phase for capillary and microchip electrochromatography

We report, for the first time, the use of underivatized cyclic olefin copolymer (COC, more specifically: Topas) as the substrate material and the stationary phase for capillary and microchip electrochromatography (CEC), and demonstrate chromatographic separations without the need of coating procedures. Electroosmotic mobility measurements in a 25 microm id Topas capillary showed a significant cathodic EOF that is pH-dependent. The magnitude of the electroosmotic mobility is comparable to that found in glass substrates and other polymeric materials. Open-tubular CEC was employed to baseline-separate three neutral compounds in an underivatized Topas capillary with plate heights ranging from 5.3 to 12.7 microm. The analytes were detected using UV absorbance at 254 nm, thus taking advantage of the optical transparency of Topas at short wavelengths. The fabrication of a Topas-based electrochromatography microchip by nanoimprint lithography is also presented. The microchip has an array of pillars in the separation column to increase the surface area. The smallest features that were successfully imprinted were around 2 microm wide and 5 microm high. No plasma treatment was used during the bonding, thus keeping the surface properties of the native material. An RP microchip electrochromatography separation of three fluorescently labeled amines is demonstrated on the underivatized microchip with plate heights ranging from 3.4 to 22 microm.

Electrochromatography in microchips packed with conventional reversed‐phase silica particles

This paper shows the applicability of a disposable and inexpensive microfluidic chip for electrochromatographic separations. The chip, recently developed by us for chip-based LC, was fabricated from PDMS incorporating conventional chromatographic RP silica particles (C18) without the use of frits. Three cephalosporin antibiotics were used to demonstrate the applicability of the chip-based chromatographic packing for electrochromatographic determinations. The used sample injection method utilizes hydrodynamic pressure, thereby, reducing the propensity for sample bias during the injection.

Microchip-based electrochromatography: designs and applications

Different techniques and methods of electrochromatography on “lab on a chip” devices are reviewed. Described approaches include open-channel microchip electrochromatography relying on C 8, C 18 and novel gold nanoparticle (GNP) coating of microchannel wall; packed-channel microchip electrochromatography with new ways of automated loading and unloading of conventional octadecylsilica beads; monolith-based microchip electrochromatography with tailored casting of stationary phase at the specific places of microfluidic network and novel photolitographically fabricated collocated monolithic structures. Specific issues related to the microchip electrochromatography, i.e. importance of high aspect ratio of the microchannels in the open-channel electrochromatography or approaches eliminating the wall effect in the monolith-based electrochromatography, are discussed. Various applications for environmental, pharmacological, genomic and proteomic analysis are described. The operation parameters of reviewed microsystems are summarized in easy-to-read tables.

Electrochromatography in microchips: reversed-phase separation of peptides and amino acids using photopatterned rigid polymer monoliths.

A microfabricated glass chip containing fluidic channels filled with polymer monolith has been developed for reversed-phase electrochromatography. Acrylate-based porous polymer monoliths were cast in the channels by photopolymerization to serve as a robust and uniform stationary phase. UV light-initiated polymerization allows for patterning of polymer stationary phase in the microchip, analogous to photolithography, using a mask and a UV lamp for optimal design of injection, separation, and detection manifolds. The monoliths are cast in situ in less than 10 min, are very reproducible with respect to separation characteristics, and allow easy manipulation of separation parameters such as charge, hydrophobicity, and pore size. Moreover, the solvent used to cast the polymer enables electroosmotic flow, allowing the separation channel to be conditioned without need for high-pressure pumps. The microchip was used for separation of bioactive peptides and amino acids labeled with a fluorogenic dye (naphthalene-2,3-dicarboxaldehyde) followed by laser-induced fluorescence detection using a Kr+ ion laser. The microchip-based separations were fast (six peptides in 45 s), efficient (up to 600,000 plates/m), and outperformed the capillary-based separations in both speed and efficiency. We have also developed a method for complete removal of polymer from the channels by thermal incineration to regenerate the glass chips.