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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
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Electrophoresis

  • Publisher: Wiley
  • FAD Code: ECPH
  • CODEN: ELCTDN
  • ISSN: 0173-0835
  • Abbreviation: Electrophoresis
  • DOI Prefix: 10.1002/elps
  • Language: English
  • Comments: Fulltext from 1980 V1

Citations 34

"Combination Of Flow Injection With Electrophoresis Using Capillaries And Chips"
Electrophoresis 2007 Volume 28, Issue 1-2 Pages 33-44
Yonglei Chen, Wenjuan Lü, Xingguo Chen, Professor *, Zhide Hu

Abstract: Technique of combined flow injection CE (FI-CE) integrates the essential favorable merits of FI and CE and can significantly expand the application of CE by utilizing the various on-line sample pretreatments and pre-concentration of Fl. The basic principles, instrumental developments, and applications of the FI-CE system from 2004 to 2006 are reviewed. The recent developments and applications of FI-CE are outlined.

"Online Concentration By Field-amplified Sample Injection In Acidic Buffer For Analysis Of Fangchinoline And Tetrandrine In Herbal Medicine By Flow Injection-micellar Electrokinetic Capillary Chromatography"
Electrophoresis 2005 Volume 26, Issue 23 Pages 4456-4464
Lihong Liu, Xingguo Chen*, Zhide Hu

Abstract: A novel, rapid, and continuous online concentration approach based on field-amplified sample injection for the analysis of fangchinoline and tetrandrine was developed in this paper by combination of flow injection-MEKC. The BGE used was a solution composed of 75 mM H3PO4-triethylamine-2.5% v/v polyoxyethylene sorbitan monolaurate-20% v/v methanol buffer (pH* 5.0). The analytes prepared in 50% v/v aqueous ethanol were used as the test analytes. Sample was injected electrokinetically between plugs of water. When the cations reached the boundary between the water plug and BGE, they slowed down and became concentrated. Thereafter, MEKC was initiated for the separation. This results in 6.8-8.9-fold improvement in concentration sensitivity relative to conventional CE methods. The separation could be achieved within 10 min and sample throughput rate can reach up to 50/h. The repeatability (defined as RSD) was 4.8, 4.4% with peak height evaluation and 3.6, 0.94% with peak area evaluation for TET and FAN, respectively.

"Head-column Field-amplified Sample Stacking In A Capillary Electrophoresis-flow Injection System"
Electrophoresis 2005 Volume 26, Issue 22 Pages 4345-4354
Liuyin Fan, Yuqiao Cheng, Yuqin Li, Hongli Chen, Xingguo Chen*, Zhide Hu

Abstract: A simple, effective, and continuous online concentration method for the sensitive detection of alkaloids applying CE-flow injection analysis with head-column field-amplified sample stacking was developed. A series of samples was continuously introduced into the capillary by electrokinetic means without interrupting the high voltage. A short water plug was introduced by the EOF at the capillary inlet end prior to sample introduction. Under optimum conditions, 15-fold improvement in concentration sensitivity was achieved, giving an LOD of about 0.67 and 0.73 g/mL for ephedrine (E) and pseudoephedrine (PE), respectively. The separation could be achieved within 4 min and sample throughput rate could reach up to 7/h. The repeatability (defined as RSD) was 3.62, 1.51% with peak area evaluation and 1.30, 2.58% with peak height evaluation for E and PE, respectively. This method has been successfully applied to the analysis of commercial pharmaceutical preparations containing E and PE, and the recoveries were 92.3-102.4%.

"A Simple Microfluidic System For Efficient Capillary Electrophoretic Separation And Sensitive Fluorimetric Detection Of DNA Fragments Using Light-emitting Diode And Liquid-core Waveguide Techniques"
Electrophoresis 2005 Volume 26, Issue 19 Pages 3602-3608
Shi-Li Wang, Xiao-Feng Fan, Zhang-Run Xu, Zhao-Lun Fang, Professor *

Abstract: A miniaturized CE system has been developed for fast DNA separations with sensitive fluorimetric detection using a rectangle type light-emitting diode (LED). High sensitivity was achieved by combining liquid-core waveguide (LCW) and lock-in amplification techniques. A Teflon AF-coated silica capillary on a compact 6 x 3 cm baseplate served as both the separation channel for CE separation and as an LCW for light transmission of fluorescence emission to the detector. An electronically modulated LED illuminated transversely through a 0.2 mm aperture, the detection point on the LCW capillary without focusing, and fluorescence light was transmitted to the capillary outlet. To simplify the optics and enhance collection of light from the capillary outlet, an outlet reservoir was designed, with a light transmission window, positioned directly in front of a photomultiplier tube (PMT), separated only by a high pass filter. Automated sample introduction was achieved using a sequential injection system through a split-flow interface that allowed effective release of gas bubbles. In the separation of a X174 HaeIII DNA digest sample, using ethidium bromide as labeling dye, all 11 fragments of the sample were effectively resolved in 400 s, with an S/N ratio comparable to that of a CE system with more sophisticated LIF.

"Separation And Determination Of Four Active Anthraquinones In Chinese Herbal Preparations By Flow Injection-capillary Electrophoresis"
Electrophoresis 2005 Volume 26, Issue 15 Pages 2999-3006
Lihong Liu, Liuyin Fan, Hongli Chen, Xingguo Chen, Professor, Zhide Hu

Abstract: A simple, rapid, and accurate method for the separation and determination of physcion, chrysophanol, aloe-emodin, and emodin in Rhubarb, Juemingzi, and Chinese herbal preparations was developed by combination of flow injection-capillary zone electrophoresis for the first time. The analysis was carried out using an unmodified fused-silica capillary (75 mm x 50 m ID x 375 m OD, effective separation length of 48 mm) and direct ultraviolet detection at 254 nm. By a series of optimization, the sample solvent consisted of NaOH (100 mmol/L) and ACN (1:1 v/v), and a running buffer composed of 15 mmol/L sodium borate - 12.5 mmol/L sodium dihydrogen phosphate - 42% v/v ACN (pH 10.1) was applied for the separation of the four anthraquinones. The separation was rapid and highly reproducible, with complete resolution of all four compounds within 6 min. The sample throughput rate could reach up to 12 per h. The repeatability (defined as relative standard deviation) was 4.45, 4.44, 4.34, 0.61% with peak height evaluation and 1.62, 0.89, 2.49, 2.19% with peak area evaluation for physcion, chrysophanol, aloe-emodin, and emodin, respectively.
Physcion Chrysophanol Aloe-emodin Emodin Chinese Spectrophotometry Electrophoresis Interface

"Development Of A New Hybrid Technique For Rapid Speciation Analysis By Directly Interfacing A Microfluidic Chip-based Capillary Electrophoresis System To Atomic Fluorescence Spectrometry"
Electrophoresis 2005 Volume 26, Issue 11 Pages 2261-2268
Feng Li, Dong-Dong Wang, Xiu-Ping Yan*, Jin-Ming Lin*, Rong-Guo Su

Abstract: This paper represents the first study on direct interfacing of microfluidic chip-based capillary electrophoresis (chip-CE) to a sensitive and selective detector, atomic fluorescence spectrometry (AFS) for rapid speciation analysis. A volatile species generation technique was employed to convert the analytes from the chip-CE effluent into their respective volatile species. To facilitate the chip-CE effluent delivery and to provide the necessary medium for subsequent volatile species generation, diluted HCl solution was introduced on the chip as the makeup solution. The chip-CE-AFS interface was constructed on the basis of a concentric tube-in-tube design for introducing a KBH4 solution around the chip effluent as sheath flow and reductant for volatile species generation as well. The generated volatile species resulting from the reaction of the chip-CE effluent and the sheath flow were separated from the reaction mixture in a gas-liquid separator and swept into the AFS atomizer by an argon flow for AFS determination. Inorganic mercury (Hg(II)) and methylmercury (MeHg(I)) were chosen as the targets to demonstrate the performance of the present technique. Both mercury species were separated as their cysteine complexes within 64 s. The precision (relative standard deviation, RSD, n = 5) of migration time, peak area, and peak height for 2 mg L-1 Hg(II) and 4 mg L-1 MeHg(I) (as Hg) ranged from 0.7 to 0.9%, 2.1 to 2.9%, and 1.5 to 1.8%, respectively. The detection limit was 53 and 161 µg L-1 (as Hg) for Hg(II) and MeHg(I), respectively. The recoveries of the spikes of mercury species in four locally collected water samples ranged from 92 to 108%.

"Microautosamplers For Discrete Sample Injection And Dispensation"
Electrophoresis 2005 Volume 26, Issue 9 Pages 1807-1813
Chun-Wei Huang, Gwo-Bin Lee*

Abstract: Microfluidic systems show considerable potential for use in the continuous reaction and analysis of biosamples for various applications, such as drug screening and chemical synthesis. Typically, microfluidic chips are externally connected with large-scale autosamplers to inject specific volumes of discrete samples in the continuous monitoring and analysis of multiple samples. This paper presents a novel microelectromechanical system (MEMS)-based autosampler capable of performing the discrete injection and dispensation of variable-volume samples. This microdevice can be integrated with other microfluidic devices to facilitate the continuous monitoring and analysis of multiple biosamples. By means of electroosmotic focusing and switching controlled by the direct application of electric sources on specific fluid reservoirs, a precise sample volume can be injected into the specified outlet port. Fluorescence dye images verify the performance of the developed device. An injection-and-washing scheme is developed to prevent cross-contamination during the continuous injection of different samples. This approach renders feasible the injection of several discrete samples using a single microchip. Compared to its large-scale counterparts, the developed microautosampler is compact in size, has low fabrication costs, is straightforward to control, and most importantly, is readily integrated with other microfluidic devices (e.g., microcapillary electrophoresis chips) to form a microfluidic system capable of the continuous monitoring and analysis of bioreactions. The proposed microautosampler could be promising towards realizing the micrototal analysis system (µ-TAS) concept.

"On-line Hyphenation Of Capillary Electrophoresis With Flame-heated Furnace Atomic Absorption Spectrometry For Trace Mercury Speciation"
Electrophoresis 2005 Volume 26, Issue 3 Pages 661-667
Yan Li, Yan Jiang, Xiu-Ping Yan

Abstract: Capillary electrophoresis (CE) was directly interfaced to flame-heated furnace atomic absorption spectrometry (FHF-AAS) via a laboratory-made thermospray interface for nanoliter trace element speciation. The CE-FHF-AAS interface integrated the superiorities of stable CE separation, complete sample introduction, and continuous vaporization for AAS detection without the need of extra external heat sources and any post-column derivation steps. To demonstrate the usefulness of the developed hybrid technique for speciation analysis, three environmentally significant and toxic forms of methylmercury (MeHg), phenylmercury (PhHg), and inorganic mercury (Hg(II)) were taken as model analytes. Baseline separation of the three mercury species was achieved by CE in a 60 cm long x 75 µm inner diameter fused-silica capillary at 20 kV and using a mixture of 100 mM boric acid and 10% v/v methanol (pH 8.30) as running electrolyte. The precision (relative standard deviation, RSD, n = 7) of migration time, peak area and peak height for the mercury species at 500 %micro;g L-1 (as Hg) level were in the range of 0.9-1.2%, 1.5-1.9%, and 1.4-2.0%, respectively. The detection limit (S/N = 3) of three mercury species was 3.0 ± 0.15 pg (as Hg), corresponding to 50.8 ± 2.4 µg L-1 (as Hg) for 60 nL sample injection, which was almost independent on specific mercury species. The developed hybrid technique was successfully applied to the speciation analysis of mercury in a certified reference material (DORM-2, dogfish muscle).

"The Combination Of Flow Injection With Electrophoresis Using Capillaries And Chips"
Electrophoresis 2004 Volume 25, Issue 23-24 Pages 3962-3969
Xingguo Chen, Liuyin Fan, Zhide Hu

Abstract: The combined flow injection capillary electrophoresis (FI-CE) system that integrates the essential favorable merits of FI and CE, can significantly expand the application scope of CE by exploring the various on-line sample pretreatments and pre-concentration of FI. The principle behind this technique, some innovative designs of the split-flow interface, as well as novel applications to a variety of analytical problems, are reviewed and discussed. Some salient features and unique advantages of this technique are outlined.
Review Microfluidic Interface

"Autonomous Protein Sample Processing On-chip Using Solid-phase Microextraction, Capillary Force Pumping, And Microdispensing"
Electrophoresis 2004 Volume 25, Issue 21-22 Pages 3778-3787
Lars Wallman*, Simon Ekström, György Marko-Varga, Thomas Laurell, Johan Nilsson

Abstract: A capillary force filling microsystem consisting of a chip-integrated solid-phase microextraction (SMEC) array and a microdispenser for sample purification and trace enrichment of peptides is described. The microextraction array was loaded with solid-phase media (50 m Poros R2 beads) for purification and enrichment of proteomic samples. Samples bound to the SMEC were eluted in a volume of 200 nL. A piezo-electric microdispenser was docked to the array and the samples bound to the SMEC were eluted in a volume of 200 nL using capillary forces. The purified and enriched samples were dispensed onto the matrix-assisted laser desorption/ionization (MALDI) target, providing quality data from samples in the picomolar range. The nanoproteomic platform was compared to corresponding commercial preparation protocols, showing higher mass spectrometry (MS) signal intensities for peptides generated from an -casein digest. The platform was also elvaluated with regards to two-dimensional (2-D) gel-derived protein digests from both fibroblast and epithelial target cells.

"A Simple Mechanism For Reliable Particle Sorting In A Microdevice With Combined Electroosmotic And Pressure-driven Flow"
Electrophoresis 2004 Volume 25, Issue 21-22 Pages 3720-3729
Robert Johann*, Philippe Renaud

Abstract: Selective transport and sorting of particles in microfluidic devices by electroosmosis is complicated due to superposition of uncontrolled hydrodynamic pressure contributions on the electroosmotic force. In this paper, we present a microfluidic concept for the reliable and simple separation and sorting of particles in a microchip by electroosmosis combined with pressure-driven flow. The presented device allows fluid quantities to be switched and particles to be sorted within a channel manifold using only a single power supply with fixed voltage and an electric switch. Consequently, chip operation and fluid switching procedure are greatly simplified compared to a situation, in which several independent power sources are used for flow balancing, as is the common procedure. With the triple-T channel design presented, backpressure flow disturbing the electrokinetic fluid and particle separation process is eliminated by introducing controlled opposed hydrodynamic flow of buffer from side channels. This pressure-driven flow is generated on-chip by setting up differences in the reservoir pressures in a defined manner. A detailed flow analysis based on the equivalence of fluid flow and electric current is performed and the conditions for reliable chip function are worked out.

"High-resolution DNA Separation In Microcapillary Electrophoresis Chips Utilizing Double-L Injection Techniques"
Electrophoresis 2004 Volume 25, Issue 21-22 Pages 3652-3659
Lung-Ming Fu, Che-Hsin Lin*

Abstract: An experimental and numerical investigation into the use of high-resolution injection techniques to separate DNA fragments within electrophoresis microchips is presented. The principal material transport mechanisms of electrokinetic migration, fluid flow, and diffusion are considered, and several variable-volume injection methods are discussed. A detailed analysis is provided of a double-L injection technique, which employs appropriate electrokinetic manipulations to reduce sample leakage within the microchip. The leakage effect in electroosmotic flow (EOF) is investigated using a sample composed of rhodamine B and Cy3 dye. Meanwhile, the effects of sample leakage in capillary electrophoresis (CE) separation are studied by considering the separation of 100-base pairs (bp) DNA ladders and HaeIII-digested X-174 DNA samples. The present experimental and simulation results indicate that the unique injection system employed in the current microfluidic chip has the ability to replicate the functions of both the conventional cross-channel and the shift-channel injection systems. Furthermore, applying the double-L injection method to these two injection systems is shown to reduce sample leakage significantly. The proposed microfluidic chip and double-L injection technique developed in this study have an exciting potential for use in high-resolution, high-throughput biochemical analysis applications and in many other applications throughout the micrototal analysis systems field.

"Determination Of Inorganic Ions Using Microfluidic Devices"
Electrophoresis 2004 Volume 25, Issue 21-22 Pages 3602-3624
Christopher J. Evenhuis, Rosanne M. Guijt, Miroslav Macka, Paul R. Haddad

Abstract: The separation and detection of inorganic ions on microfluidic devices has received little attention since the 'lab-on-a-chip' concept has revolutionised the field of electrokinetically driven analysis. This review presents a summary and discussion of the published literature on inorganic analysis using microfluidic devices and includes sections on electromigration separation methods, namely isotachophoresis (ITP), capillary electrophoresis (CE), and hyphenated ITP-CE, together with a brief account of flow injection analysis. The review concludes with the authors' perspective on future directions for inorganic analysis on microfluidic devices.

"Direct Automatic Determination Of Biogenic Amines In Wine By Flow Injection-capillary Electrophoresis-mass Spectrometry"
Electrophoresis 2004 Volume 25, Issue 20 Pages 3427-3433
Bricio Santos, Bartolomé M. Simonet, Angel Ríos, Miguel Valcárcel

Abstract: A capillary electrophoresis-electrospray mass spectrometry (CE-ESI-MS) method for the separation and determination of nine biogenic amines is proposed. Operational variables, such as the voltage, temperature, sheath liquid composition, flow-rate, and MS parameters, were optimized. Samples are injected in the hydrodynamic mode into a 75 cm x 50 m ID coated capillary and separated by using 25 mM citric acid at pH 2.0. Heptylamine is used as internal standard. The experimental setup includes a flow manifold coupled to the CE system for automatic insertion of samples into the CE vials. The proposed method allows amines to be determined with limits of detection from 0.018 to 0.09 g mL-1 and relative standard deviation (RSD) values from 2.4% to 5.0% (except 6.8% for histamine). The method was successfully used to determine biogenic amines in red and white wines.

"Continuous On-line Derivatization And Selective Separation Of D-aspartic Acid By A Capillary Electrophoresis System With A Continuous Sample Introduction Interface"
Electrophoresis 2004 Volume 25, Issue 18-19 Pages 3163-3167
Liuyin Fan, Yuqiao Cheng, Hongli Chen, Lihong Liu, Xingguo Chen*, Zhide Hu

Abstract: A rapid and selective method is described for the separation of D-aspartic acid (D-Asp) using a continuous on-line derivatization system coupled to capillary electrophoresis (CE). D-Asp was derivatized using o-phthaldialdehyde/N-acetyl-L-cysteine (OPA/NAC). By on-line derivatization, amino acid enantiomers were automatically and reproducibly converted to the UV-absorbing diastereomer derivatives which were separated by capillary zone electrophoresis (CZE) in the presence of 10 mmol/L -cyclodextrin (-CD). Under the investigated separation conditions, D-Asp is resolved from L-aspartic acid (L-Asp) and other amino acids in a standard mixture of amino acids. The separation could be achieved within 4 min and the sample throughput rate can reach up to 16 h-1. The repeatability (defined as relative standard deviation, RSD) was 3.21%, 3.58% with peak area evaluation and 3.72%, 4.03% with peak height evaluation for L-Asp and D-Asp.

"Separation Of Proteins On Surface-modified Poly(dimethylsiloxane) Microfluidic Devices"
Electrophoresis 2004 Volume 25, Issue 17 Pages 3024-3031
Yue-Hua Dou, Ning Bao, Jing-Juan Xu, Fei Meng, Hong-Yuan Chen *

Abstract: Separation and detection of proteins have been realized on nonionic surfactant-modified poly(dimethylsiloxane) (PDMS) microfabricated devices with end-column amperometric detection. The hydrophobic PDMS channels are turned into hydrophilic ones after being modified with Brij35 and facilitate the separation of proteins. The coating can remarkably reduce the adsorption of large protein molecules and is stable in the range of pH 6-12. The detection of proteins in such channels needs less rinsing time and thus efficiency is raised. Even large molecules of proteins can also be detected with better reproducibility and enhanced plate numbers. The relative standard deviation (RSD) of the migration time for glucose oxidase (GOD) is 2.2% (n = 19). Separation of GOD and myoglobin has been developed in modified channels. Predominant operational variables, such as the coating conditions, the concentration of surfactant and buffer, are studied in detail.Digital Object Identifier (DOI)10.1002/elps.200405986 About DOI

"On-line Preconcentration For Capillary Electrophoresis-atomic Fluorescence Spectrometric Determination Of Arsenic Compounds"
Electrophoresis 2004 Volume 25, Issue 12 Pages 1837-1842
Xue-Bo Yin*

Abstract: An on-line pre-concentration method was developed for capillary electrophoresis (CE) with hydride generation-atomic fluorescence spectrometric (HG-AFS) detection of arsenite, arsenate, dimethylarsenic acid, and monomethylarsenic acid. These arsenic species were negatively charged in the sample solution with high pH. When the potential was applied to the electrophoretic capillary, the negatively charged analyte ions moved faster and stacked at the boundary of sample and CE buffer with low pH. So, high sample pH in combination with low buffer pH allowed the injection of large sample volumes (1100 nL). Comparison of the pre-concentration of analyte solution, prepared with doubly deionized water and that prepared with lake or river water, indicated that pre-concentration was independent on the original matrix. With injection of 1100 nL sample, an enrichment factor of 37-50-fold was achieved for the four species. Detection limits for the four arsenic species ranged from 5.0 to 9.3 g L-1. Precisions (RSDs, n = 5) were in the range of 4.9-6.7% for migration time, 4.7-11% for peak area, and 4.3-7.1% for peak height, respectively. The recoveries of the four species in locally collected water solution spiked with 0.1 g mL-1 (as As) ranged from 83 to 109%.

"A Flow Injection-capillary Electrophoresis System With High-voltage Contactless Conductivity Detection For Automated Dual Opposite End Injection"
Electrophoresis 2004 Volume 25, Issue 1 Pages 35-42
Pavel Kubáň, Petr Kubáň, Peter C. Hauser, Vlastimil Kubáň*

Abstract: The system comprises two flow injection-capillary electrophoresis interfaces into which the opposite ends of the separation capillary are inserted. The electrolyte solution flows through both interfaces by use of hydrostatic pressure. The injection of the samples into the electrolyte flow is accomplished by a rotary-type chromatographic valve at the grounded side and by a pinch-valve injector at the high-voltage side that provides sufficient isolation from the high electric field. The system allows a fully automated dual-injection sequence of samples from both capillary ends and simultaneous electrophoretic separation of anions and cations in the samples. The analytes are detected by a high-voltage contactless conductometric detector positioned approximately in the middle of the separation capillary. The parameters of the system were evaluated. The repeatability of the flow injection-capillary electrophoresis system for the simultaneous determination of anions and cations was evaluated for ten consecutive injections and relative standard deviation (RSD) values for peak areas were better than 1.0%. The sample throughput for total ionic analysis was estimated to be 25 samples per hour. The system was used for automated simultaneous analysis of anions and cations in various real samples. Using a short separation capillary, rapid total ionic analysis in less then 1 min is demonstrated.

"Microfluidic Systems In Proteomics"
Electrophoresis 2003 Volume 24, Issue 21 Pages 3533-3562
Niels Lion, Tatiana C. Rohner, Loïc Dayon, Isabelle L. Arnaud, Eugen Damoc, Nikolay Youhnovski, Zhi-Yong Wu, Christophe Roussel, Jacques Josserand, Henrik Jensen, Joël S. Rossier, Michael Przybylski, Hubert H. Girault*

Abstract: We present the state-of-the-art in miniaturized sample preparation, immunoassays, one-dimensional and multidimensional analyte separations, and coupling of microdevices with electrospray ionization-mass spectrometry. Hyphenation of these different techniques and their relevance to proteomics will be discussed. In particular, we will show that analytical performances of microfluidic analytical systems are already close to fulfill the requirements for proteomics, and that miniaturization results at the same time in a dramatic increase in analysis throughput. Throughout this review, some examples of analytical operations that cannot be achieved without microfluidics will be emphasized. Finally, conditions for the spreading of microanalytical systems in routine proteomic labs will be discussed.

"Capillary Electrophoresis - Electrospray Ionization - Mass Spectrometry For The Characterization Of Natural Organic Matter: An Evaluation With Free Flow Electrophoresis-off-line Flow Injection Electrospray Ionization-mass Spectrometry"
Electrophoresis 2003 Volume 24, Issue 17 Pages 3057-3066
Philippe Schmitt-Kopplin, Antonius Kettrup

Abstract: The separation of Suwannee River natural organic matter (NOM) with capillary zone electrophoresis hyphenated to electrospray ionization-mass spectrometry (CZE-ESI-MS) is presented. The obtained electropherograms and signal distributions are comparable to the mobility distributions obtained with more classical UV detection. A direct comparison of the results was possible with free-flow electrophoresis (FFE), which allows an upscaling of the CZE method and the analysis of the collected fractions in an off-line modus with flow-injection electrospray ionization-mass spectrometry (FI-ESI-MS). The changes of the m/z distributions with mobility are very similar with both methods and show a decrease of the m/z with increasing electrophoretic mobility in the humic hump at alkaline pH; superimposed on this hump a low-molecular-weight fraction migrates at lower mobility. The analysis of benzene carboxylic acids, glycerrhycic acid as well as oligomers of polystyrene sulfonic acid and polyacrylic acid additionally illustrates possible fragmentation, formation of adducts and multiplicity of the charges of the molecules prior to MS detection. These hardly controllable difficulties add a challenge to the interpretation of the obtained m/z distributions of NOM in terms of charge and mass distributions of molecules present in the NOM mixture.

"Multiple Injection Techniques For Microfluidic Sample Handling"
Electrophoresis 2003 Volume 24, Issue 17 Pages 3026-3032
Lung-Ming Fu, Ruey-Jen Yang*, Gwo-Bin Lee, Yu-Jen Pan

Abstract: This paper presents an experimental and numerical investigation into electrokinetic focusing flow injection for bioanalytical applications on 1 x N (i.e., 1 sample inlet port and N outlet ports) and M x N (i.e., M sample inlet ports and N outlet ports) microfluidic chips. A novel device is presented which integrates two important microfluidic phenomena, namely electrokinetic focusing and valveless flow switching within multiported microchannels. The study proposes a voltage control model which achieves electrokinetic focusing in a prefocusing sample injection system and which allows the volume of the sample to be controlled. Using the developed methods, the study shows how the sample may be prefocused electrokinetically into a narrow stream prior to being injected continuously into specified outlet ports. The microfluidic chips presented within this paper possess an exciting potential for use in a variety of techniques, including high-throughput chemical analysis, cell fusion, fraction collection, fast sample mixing, and many other applications within the micrototal analysis systems field.

"Determination Of Myo-inositol Phosphates In Food Samples By Flow Injection-capillary Zone Electrophoresis"
Electrophoresis 2003 Volume 24, Issue 12-13 Pages 2092-2098
Bartolomé M. Simonet, Angel Ríos, Félix Grases, Miguel Valcárcel

Abstract: A capillary electrophoresis (CE) method with indirect photometric detection was developed to identify and quantify myo-inositol phosphates in food samples. A flow-injection (FI) system including a micro-column containing anionic exchange resin was used for the solid-phase extraction of the myo-inositol phosphates with a view to their pre-concentration. The FI system was automatically coupled to CE equipment via a mechanical interface. The overall analysis time was shortened by incorporating an FI system for myo-inositol hexakisphosphate monitoring. The limit of detection for myo-inositol phosphates as determined by FI-CE ranged from 11 to 26 mol/L and the coefficient of variation from 3.9 to 5.0%. On the other hand, the limit of detection and coefficient of variation for myo-inositol hexakisphosphate as monitored by the FI system were 75 mol/L and 2.9%, respectively. The proposed method was successfully applied to a variety of food samples with recoveries ranging from 96.0 to 107.7% and the precision from 3.9 to 7.9%. Based on the results, the content of myo-inositol hexakisphosphate in nuts was two or three times higher than that in legumes.

"Flow Injection-capillary Electrophoresis System With Contactless Conductivity Detection And Hydrostatic Pressure Generated Flow. Application To The Quantitative Analysis Of Inorganic Anions In Water Samples"
Electrophoresis 2003 Volume 24, Issue 12-13 Pages 1935-1943
Pavel Kubáň, Petr Kubáň, Vlastimil Kubáň*

Abstract: A simple and inexpensive flow injection-capillary electrophoresis (FI-CE) system with contactless conductivity detection (CCD) for automated quantitative analysis of chloride, nitrate, and sulfate in various water samples is demonstrated. A glass bottle containing the background electrolyte that is raised above the FI-CE interface generates a pulse-free, highly reproducible flow of the electrolyte through the FI-CE interface. The system operates at a flow rate of 300 Lmin-1 with an injection volume of only 4 L. The repeatability of peak areas (n = 18) was better than 0.81% RSD and the sample throughput was 90 samples per hour using the background electrolyte containing 12 mM L-histidine adjusted to pH 4.00 with acetic acid. The limits of detection were better than 125 gL-1 and were comparable to those obtained by conventional CE systems with CCD. Various calibration methods for FI-CE system with electrokinetic injection were tested and their suitability for the analysis of anions in real samples was evaluated.

"On-column Polymer-imbedded Graphite Inlet Electrode For Capillary Electrophoresis Coupled On-line With Flow Injection Analysis In A Poly(dimethylsiloxane) Interface"
Electrophoresis 2003 Volume 24, Issue 11 Pages 1723-1729
Jenny Samskog, Sara K. Bergström, Mats Jönsson, Oliver Klett, Magnus Wetterhall, Karin E. Markides*

Abstract: A method for coupling an electrophoretic driven separation to a liquid flow, using conventional fused-silica capillaries and a soft polymeric interface is presented. A novel design of the electrode providing high voltage to the electrophoretic separation was also developed. The electrode consisted of a conductive polyimide/graphite imbedded coating immobilized onto the capillary electrophoresis (CE) column inlet. This integrated electrode gave the same separation performance as a commonly used platinum electrode. The on-column electrode also showed good electrochemical stability in chronoamperometric experiments. In addition, with this electrode design, the electrode position relative to the inlet end of the CE column will always be constant and well defined. The on-line flow injection analysis (FIA)-CE system was used with electrospray ionization (ESI)-time of flight (TOF)-mass spectrometry detection. The preparation of the PDMS (poly(dimethylsiloxane)) interface for FIA-CE is described in detail and used for initial tests of the on-column polymer-imbedded graphite inlet electrode. In this interface, a pressure-driven liquid flow, a make up CE electrolyte and a CE column inlet meet in a two-level cross (95 m ID) in the PDMS structure, enabling independent flow characterization.

"Simultaneous Determination Of Selenium And Antimony Compounds By Capillary Electrophoresis With Indirect Fluorescence Detection"
Electrophoresis 2002 Volume 23, Issue 17 Pages 2913-2917
Sarah Y. Chang, Hsien-Tsung Chiang

Abstract: Capillary electrophoresis (CE) with indirect fluorescence detection was used to analyze selenium (selenite, selenate, selenomethionine, and selenocystine) and antimony (antimonite and antimonate) compounds. The separation was achieved by CE in 6 min with a 1.2 mm fluorescein solution at pH 9.5. Fluorescein also functioned as a background fluorophore for the indirect detection of these nonfluorescent species. Linearity of more than two orders of magnitude was generally obtained. Precision of migration times and peak areas was less than 1.0% and 7.2%, respectively. The concentration limits of detection (CLODs) was in the mum range. The detection sensitivity was generally dependent upon the transfer ratio (TR, defined as the number of moles of fluorescein ions displaced by one mole of analyte ions) of each species.

"On-line Conversion And Determination Of Artemisinin Using A Flow Injection Capillary Electrophoresis System"
Electrophoresis 2002 Volume 23, Issue 17 Pages 2865-2871
Hong Li Chen, Ke Tai Wang, Qiao Sheng Pu, Xing Guo Chen, Zhi De Hu

Abstract: A novel, rapid, and simple capillary electrophoresis (CE) method has been developed for the determination of antimalarial artemisinin by on-line treatment with alkaline. By on-line reaction, artemisinin was automatically and reproducibly converted to the strongly UV-absorbing compound, Q292, by treating it with 0.20 mol/L NaOH solution for 3 min at 40°C. Analysis was carried out in less than 12 min after conversion of artemisinin in a flow injection (FI) system that was coupled to CE equipment via a split-flow interface cell, and a sampling frequency of 8 h-1 is achievable. The on-line conversion method has been applied to the determination of artemisin n in the traditional Chinese herbal drug Artemisia annua L., and the results are satisfactory.

"Enhanced Detection Of Porphyrins By Capillary Electrophoresis-laser Induced Fluorescence"
Electrophoresis 2002 Volume 23, Issue 11 Pages 1689-1694
Jeremy E. Melanson, Charles A. Lucy

Abstract: A highly sensitive technique for the analysis of urinary porphyrins using capillary electrophoresis (CE) coupled with laser-induced fluorescence (LIF) detection is reported. Separation of mesoporphyrin IX, coproporphyrin, uroporphyrin and the penta-, hexa- and heptacarboxylic acid porphyrins was achieved in 11 min using a 10 mm 2-(N-cyclohexylamino)ethanesulfonic acid (CHES, pH 10) -75 mm sodium dodecyl sulfate (SDS) buffer. Migration time and peak area repeatability were less than 1 and 5% relative standard deviation (RSD), respectively. Limits of detection of 20 pm (2 x 10^-11 m) were achieved employing the recently introduced Nichia violet diode laser for excitation at 400 nm. This represents an enhancement in sensitivity of over two orders of magnitude compared to previous reports. This high sensitivity for urinary porphyrins was demonstrated through the quantification of coproporphyrin and uroporphyrin in urine samples after up to a 100-fold dilution.

"On-chip Enzymatic Assays"
Electrophoresis 2002 Volume 23, Issue 5 Pages 713-718
Joseph Wang

Abstract: This article reviews different possibilities for conducting enzymatic assays on microchip platforms, along with potential advantages, limitations, and selected examples of such biochips. Enzyme-based chips combine the analytical power and reagent economy of microfluidic devices with the selectivity and amplification features of biocatalytic reactions. Lab-on-chip devices thus allow enzymatic assays to be performed more rapidly, easily, and economically. Such assays usually rely on on-chip mixing and reactions (of the substrates and enzymes) in connection to separations (of the substrates or products). The realization of on-chip enzymatic assays thus requires understanding of how enzymatic reactions behave on a small scale and can be interfaced with separation microchips, and how the microfluidics can be tailored to suit the requirements of particular enzymatic assays. The goal is to obtain sufficient reaction times, without compromising the quality of the analytical separation. The versatility of such on-chip enzymatic assays offers great promise for decentralized testing of clinically or environmentally important substrates.

"Comparison Of Aqueous And Nonaqueous Carrier Electrolytes For The Separation Of Penicillin V And Related Substances By Capillary Electrophoresis With UV And Mass Spectrometric Detection"
Electrophoresis 2002 Volume 23, Issue 3 Pages 414-420
Emily F. Hilder, Christian W. Klampfl, Wolfgang Buchberger, Paul R. Haddad

Abstract: A method for the determination of penicillin V together with its impurities and by-products formed during biosynthesis, using capillary electrophoresis (CE) with UV and electrospray-mass spectrometric (ESI-MS) detection is presented. Aqueous and nonaqueous electrolytes containing 20 mm ammonium acetate were investigated to determine their suitability for the separation of these analytes. These carrier electrolytes were optimized with respect to the pH and the solvent/s used (water, methanol, acetonitrile, ethanol and isopropanol) and it was shown that although the nonaqueous electrolytes offered unique separation selectivities, the best results in terms of selectivity and sensitivity were obtained for the aqueous system. Finally, the applicability of this method for the analysis of a mixture representative of a real fermentation broth was demonstrated using an aqueous carrier electrolyte with both UV and ESI-MS detection.

"Determination Of Phenolic Constituents In Citrus Samples By On-line Coupling Of A Flow System With Capillary Electrophoresis"
Electrophoresis 2001 Volume 22, Issue 8 Pages 1553-1560
K. Kanitsar, Lourdes Arce, Angel Ríos, Miguel Valcárcel

Abstract: Phenolic compounds extracted from different citrus were determined. Calibration, extraction, elution, and introduction into the sample vial was carried out automatically by a continuous flow system (CFS) coupled to capillary electrophoresis (CE) equipment via a programmable arm. The only manual operation was the centrifugation of the sample to remove the pulp. The supernatant solutions were introduced into the CFS-CE system. A C-18 minicolumn coupled into the CFS was used to perform cleanup of the samples. The analytes were eluted from the minicolumn using methanol. Quantitative analysis was carried out by the standard addition method. The method presented allows a fast, quantitative, and reproducible determination of six main phenolic compounds in citrus samples, with precision in the range of 3.0-6.5%, expressed as relative standard deviations.
Extraction

"Determination Of Nonsteroidal Anti-inflammatory Drugs In Biological Fluids By Automatic On-line Integration Of Solid-phase Extraction And Capillary Electrophoresis"
Electrophoresis 2001 Volume 22, Issue 3 Pages 484-490
Claudia Mardones, Angel Ríos, Miguel Valcárcel

Abstract: A new, automatic method for the clean-up, pre-concentration, separation, and quantitation of nonsteroidal anti-inflammatory drugs (NSAIDs) in biological samples (human urine and serum) using solid-phase extraction coupled on-line to capillary electrophoresis is proposed. Automatic pretreatment is carried out by using a continuous flow system operating simultaneously with the capillary electrophoresis equipment, to which it is linked via a laboratory-made mechanical arm. This integrated system is controlled by an electronic interface governed via a program developed in GWBasic. Capillary electrophoresis is conducted by using a separation buffer consisting of 20 mM NaHPO4, 20 mM beta -cyclodextrin and 50 mM SDS at pH 9.0, an applied potential of 20 kV and a temperature of 20°C. The analysis time is 10 min and the detection limits were between 0.88 and 1.71 µg mL-1. Automatic clean-up and pre-concentration is accomplished by using a C-18 minicolumn and 75% methanol as eluent. The limit of detection of NSAIDs can be up to 400-fold improved when using sample clean-up. The extraction efficiency for these compounds is between 71.1 and 109.7 µg mL-1 (RSD 2.0-7.7%) for urine samples and from 77.2 to 107.1 µg mL-1 (RSD 3.5-7.1%) for serum samples.

"Isotachophoretic Determination Of Creatinine In Meat And Meat Products"
Electrophoresis 2000 Volume 21, Issue 14 Pages 2848-2850
František Kvasnička, Michal Voldřich

Abstract: A capillary isotachophoretic method (CITP) to determine the creatinine concentration in meat and meat products is described. A clear separation of the creatinine from other components of an acidic extract of sample was achieved within 20 min. Method characteristics (linearity, accuracy, precision and detection limit) were determined. The developed method was successfully applied to analyze real samples and to determine creatinine and creatine content (indirect determination after acidic hot extraction) in meat and meat products.

"Determination Of Chlorophenols In Human Urine Based On The Integration Of On-line Automated Clean-up And Preconcentration Unit With Micellar Electrokinetic Chromatography"
Electrophoresis 1999 Volume 20, Issue 14 Pages 2922-2929
Claudia Mardones, Angel Ríos, Miguel Valcárcel

Abstract: A new method was developed and validated for the determination of chlorophenols in human urine by using micellar electrokinetic chromatography (MEKC) coupled via a mechanic arm to an on-line automatic clean-up and pre-concentration unit for urine samples. Separation is accomplished by using a selective buffer consisting of 15 mM berate, 25 mM phosphate and 100 mM sodium dodecyl sulfate (SDS) at pH 9.1 in addition to a positive power supply of 25 kV at 18°C. The proposed capillary electrophoresis (CE) method allows the separation of 11 chlorophenols within 7 min with a reproducibility as relative standard deviation (RSD) between 2.6% and 7.2%, and limits of detection (LODs) between 0.08 and 0.46 µg/mL for all chlorophenols. Urine samples were previously hydrolyzed with 37% HCl at 80°C for 60 min and then cleaned on a C-18 mini-column. Recoveries ranged from 58% to 103%. The pre-concentration treatment affords limits of determination between 4 and 12 ng/mL for all chlorophenols except pentachlorophenol and 4-chlorophenol, which could not be determined. The overall analysis time, including on-line clean-up, pre-concentration and electrophoretic separation is 20 min per sample.
Optimization

"Separation And Detection Of Amino Acids And Their Enantiomers By Capillary Electrophoresis: A Review"
Electrophoresis 1995 Volume 16, Issue 1 Pages 467-480
Haleem J. Issaq, King C. Chan

Abstract: Since its introduction as an analytical technique capillary electrophoresis has been used for the separation of amino acids and their enantiomers; over 150 studies have been published to date. This review deals with their separation and detection. Amino acids have been resolved using both capillary zone electrophoresis and micellar electrokinetic chromatography. Pre-column derivatization schemes which are employed for the sensitive detection of amino acids are discussed. Criteria for the selection of the pre- or post-column derivatizing agent, chromophore or fluorophore, are presented. Detection systems, direct and indirect, that have been used are given with emphasis on fluorogenic reagents and laser induced fluorescence detection. Also, procedures for the separation of amino acid enantiomers are discussed and illustrated.
Electrophoresis Post-column derivatization Pre-column derivatization Review