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Desire CT, Arrua RD, Strudwick XL, Kopecki Z, Cowin AJ, Hilder EF. The development of microfluidic-based western blotting: Technical advances and future perspectives. J Chromatogr A 2023; 1691:463813. [PMID: 36709548 DOI: 10.1016/j.chroma.2023.463813] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Revised: 01/11/2023] [Accepted: 01/18/2023] [Indexed: 01/22/2023]
Abstract
Over the past two decades significant technical advancement in the field of western blotting has been made possible through the utilization of microfluidic technologies. In this review we provide a critical overview of these advancements, highlighting the advantages and disadvantages of each approach. Particular attention is paid to the development of now commercially available systems, including those for single cell analysis. This review also discusses more recent developments, including algorithms for automation and/or improved quantitation, the utilization of different materials/chemistries, use of projection electrophoresis, and the development of triBlots. Finally, the review includes commentary on future advances in the field based on current developments, and the potential of these systems for use as point-of-care devices in healthcare.
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Affiliation(s)
- Christopher T Desire
- Future Industries Institute, University of South Australia, GPO Box 2471, Adelaide, SA 5001, Australia
| | - R Dario Arrua
- Future Industries Institute, University of South Australia, GPO Box 2471, Adelaide, SA 5001, Australia
| | - Xanthe L Strudwick
- Future Industries Institute, University of South Australia, GPO Box 2471, Adelaide, SA 5001, Australia
| | - Zlatko Kopecki
- Future Industries Institute, University of South Australia, GPO Box 2471, Adelaide, SA 5001, Australia
| | - Allison J Cowin
- Future Industries Institute, University of South Australia, GPO Box 2471, Adelaide, SA 5001, Australia
| | - Emily F Hilder
- Future Industries Institute, University of South Australia, GPO Box 2471, Adelaide, SA 5001, Australia.
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2
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Zhao C, Ge Z, Song Y, Yang C. Electrokinetically driven continuous-flow enrichment of colloidal particles by Joule heating induced temperature gradient focusing in a convergent-divergent microfluidic structure. Sci Rep 2017; 7:10803. [PMID: 28883550 PMCID: PMC5589950 DOI: 10.1038/s41598-017-11473-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Accepted: 08/22/2017] [Indexed: 12/02/2022] Open
Abstract
Enrichment of colloidal particles in continuous flow has not only numerous applications but also poses a great challenge in controlling physical forces that are required for achieving particle enrichment. Here, we for the first time experimentally demonstrate the electrokinetically-driven continuous-flow enrichment of colloidal particles with Joule heating induced temperature gradient focusing (TGF) in a microfluidic convergent-divergent structure. We consider four mechanisms of particle transport, i.e., advection due to electroosmosis, electrophoresis, dielectrophoresis and, and further clarify their roles in the particle enrichment. It is experimentally determined and numerically verified that the particle thermophoresis plays dominant roles in enrichment of all particle sizes considered in this study and the combined effect of electroosmosis-induced advection and electrophoresis is mainly to transport particles to the zone of enrichment. Specifically, the enrichment of particles is achieved with combined DC and AC voltages rather than a sole DC or AC voltage. A numerical model is formulated with consideration of the abovementioned four mechanisms, and the model can rationalize the experimental observations. Particularly, our analysis of numerical and experimental results indicates that thermophoresis which is usually an overlooked mechanism of material transport is crucial for the successful electrokinetic enrichment of particles with Joule heating induced TGF.
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Affiliation(s)
- Cunlu Zhao
- Key Laboratory of Thermo-Fluid Science and Engineering of MOE, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, 710049, China.
| | - Zhengwei Ge
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore
| | - Yongxin Song
- Department of Marine Engineering, Dalian Maritime University, 1 Linghai Road, Dalian, 116026, China
| | - Chun Yang
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore.
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3
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Novo P, Janasek D. Current advances and challenges in microfluidic free-flow electrophoresis-A critical review. Anal Chim Acta 2017; 991:9-29. [PMID: 29031303 DOI: 10.1016/j.aca.2017.08.017] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2017] [Revised: 08/10/2017] [Accepted: 08/11/2017] [Indexed: 12/30/2022]
Abstract
The research field on microfluidic free-flow electrophoresis has developed vast amounts of devices, methods, applications and raised new questions, often in analogy to conventional techniques from which it derives. Most efforts have been employed on device development and a myriad of architectures and fabrication techniques have been reported using simple proof-of-principle separations. As technological aspects reach a quite mature state, researchers' new challenges include the development of protocols for the separation of complex mixtures, as required in the fields of application. The success of this effort is extremely dependent on the capability to transfer the device's fabrication to an industrial setting as well as to ensure interfacing simplicity, namely at the solutions' supply and collection, and actuation such as electric potential application and temperature control. Other advanced applications such as direct interfacing to downstream systems such as mass spectrometry, integration of sensing and feedback controls will require further development in the laboratory. In this review we provide an overview on the field, from basic concepts, through advanced developments both in the theoretical and experimental arenas, and addressing the above details. A comprehensive survey of designs, materials and applications is presented with particular highlights to most recent developments, namely the integration of electrodes, flow control and hyphenation of microfluidic free-flow electrophoresis with other techniques.
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Affiliation(s)
- Pedro Novo
- Leibniz-Institut für Analytische Wissenschaften - ISAS - e.V., 44227, Otto-Hahn-Str. 6b, Dortmund, Germany
| | - Dirk Janasek
- Leibniz-Institut für Analytische Wissenschaften - ISAS - e.V., 44227, Otto-Hahn-Str. 6b, Dortmund, Germany.
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4
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Wang Z, Ivory C, Minerick AR. Surface isoelectric focusing (sIEF) with carrier ampholyte pH gradient. Electrophoresis 2017; 38:2565-2575. [PMID: 28722147 DOI: 10.1002/elps.201600565] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Revised: 06/16/2017] [Accepted: 07/12/2017] [Indexed: 11/08/2022]
Abstract
Isoelectric focusing (IEF) is a powerful tool for amphoteric protein separations because of high sensitivity, bio-compatibility, and reduced complexity compared to chromatography or mechanical separation techniques. IEF miniaturization is attractive because it enables rapid analysis, easier adaptation to point of care applications, and smaller sample demands. However, existing small-scale IEF tools have not yet been able to analyze single protein spots from array libraries, which are ubiquitous in many pharmaceutical discovery and screening protocols. Thus, we introduce an in situ, novel, miniaturized protein analysis approach that we have termed surface isoelectric focusing (sIEF). Low volume printed sIEF gels can be run at length scales of ∼300 μm, utilize ∼0.9 ng of protein with voltages below 10 V. Further, the sIEF device platform is so simple that it can be integrated with protein library arrays to reduce cost; devices demonstrate reusability above 50 uses. An acrylamide monomer solution containing broad-range carrier ampholytes was microprinted with a Nano eNablerTM between micropatterned gold electrodes spaced 300 μm apart on a glass slide. The acrylamide gel was polymerized in situ followed by protein loading via printed diffusional exchange. A pH gradient formed via carrier ampholyte stacking when electrodes were energized; the gradient was verified using ratiometric pH-sensitive FITC/TRITC dyes. Green fluorescent protein (GFP) and R-phycoerythrin (R-PE) were utilized both as pI markers and to test sIEF performance as a function of electric field strength and ampholyte concentration. Factors hampering sIEF included cathodic drift and pH gradient compression, but were reduced by co-printing non-ionic Synperonic® F-108 surfactant to reduce protein-gel interactions. sIEF gels achieved protein separations in <10 min yielding bands < 50 μm wide with peak capacities of ∼8 and minimum pI differences from 0.12 to 0.14. This new sIEF technique demonstrated comparable focusing at ∼100 times smaller dimensions than any previous IEF. Further, sample volumes required were reduced four orders of magnitude from 20 μL for slab gel IEF to 0.002 μL for sIEF. In summary, sIEF advantages include smaller volumes, reduced power consumption, and microchip surface accessibility to focused bands along with equivalent separation resolutions to prior IEF tools. These attributes position this new technology for rapid, in situ protein library analysis in clinical and pharmaceutical settings.
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Affiliation(s)
- Zhichao Wang
- Department of Chemical Engineering, Michigan Technological University, Houghton, MI, USA
| | - Cornelius Ivory
- Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA, USA
| | - Adrienne R Minerick
- Department of Chemical Engineering, Michigan Technological University, Houghton, MI, USA
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5
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Abstract
Microfluidics has been undergoing fast development in the past two decades due to its promising applications in biotechnology, medicine, and chemistry. Towards these applications, enhancing concentration sensitivity and detection resolution are indispensable to meet the detection limits because of the dilute sample concentrations, ultra-small sample volumes and short detection lengths in microfluidic devices. A variety of microfluidic techniques for concentrating analytes have been developed. This article presents an overview of analyte concentration techniques in microfluidics. We focus on discussing the physical mechanism of each concentration technique with its representative advancements and applications. Finally, the article is concluded by highlighting and discussing advantages and disadvantages of the reviewed techniques.
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Affiliation(s)
- Cunlu Zhao
- Key Laboratory of Thermo-Fluid Science and Engineering of MOE, School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China
- Correspondence: (C.Z.); (C.Y.); Tel.: +86-29-8266-3222 (C.Z.); +65-6790-4883 (C.Y.)
| | - Zhengwei Ge
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore;
| | - Chun Yang
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore;
- Correspondence: (C.Z.); (C.Y.); Tel.: +86-29-8266-3222 (C.Z.); +65-6790-4883 (C.Y.)
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6
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Zhou H, Li G, Yao S. A droplet-based pH regulator in microfluidics. LAB ON A CHIP 2014; 14:1917-1922. [PMID: 24745036 DOI: 10.1039/c3lc51442k] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In this paper, we develop a strategy to form on-demand droplets with specific pH values. The pH control is based on electrolysis of water in microfluidics, and the produced hydrogen and hydroxyl ions are separated and confined in individual containers during the droplet generation, triggered by a pressure pulse. By tuning the applied voltages and pressure pulses, we can control on demand the pH value in a droplet.
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Affiliation(s)
- Hongbo Zhou
- Department of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Hong Kong, China.
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7
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Wright P, Noirel J, Ow SY, Fazeli A. A review of current proteomics technologies with a survey on their widespread use in reproductive biology investigations. Theriogenology 2012; 77:738-765.e52. [DOI: 10.1016/j.theriogenology.2011.11.012] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2011] [Revised: 11/08/2011] [Accepted: 11/11/2011] [Indexed: 12/27/2022]
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8
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Chantiwas R, Park S, Soper SA, Kim BC, Takayama S, Sunkara V, Hwang H, Cho YK. Flexible fabrication and applications of polymer nanochannels and nanoslits. Chem Soc Rev 2011; 40:3677-702. [PMID: 21442106 PMCID: PMC4773912 DOI: 10.1039/c0cs00138d] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Fluidic devices that employ nanoscale structures (<100 nm in one or two dimensions, slits or channels, respectively) are generating great interest due to the unique properties afforded by this size domain compared to their micro-scale counterparts. Examples of interesting nanoscale phenomena include the ability to preconcentrate ionic species at extremely high levels due to ion selective migration, unique molecular separation modalities, confined environments to allow biopolymer stretching and elongation and solid-phase bioreactions that are not constrained by mass transport artifacts. Indeed, many examples in the literature have demonstrated these unique opportunities, although predominately using glass, fused silica or silicon as the substrate material. Polymer microfluidics has established itself as an alternative to glass, fused silica, or silicon-based fluidic devices. The primary advantages arising from the use of polymers are the diverse fabrication protocols that can be used to produce the desired structures, the extensive array of physiochemical properties associated with different polymeric materials, and the simple and robust modification strategies that can be employed to alter the substrate's surface chemistry. However, while the strengths of polymer microfluidics is currently being realized, the evolution of polymer-based nanofluidics has only recently been reported. In this critical review, the opportunities afforded by polymer-based nanofluidics will be discussed using both elastomeric and thermoplastic materials. In particular, various fabrication modalities will be discussed along with the nanometre size domains that they can achieve for both elastomer and thermoplastic materials. Different polymer substrates that can be used for nanofluidics will be presented along with comparisons to inorganic nanodevices and the consequences of material differences on the fabrication and operation of nanofluidic devices (257 references).
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Affiliation(s)
- Rattikan Chantiwas
- Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA
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9
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Koval D, Kašička V, Cottet H. Analysis of glycated hemoglobin A1c by capillary electrophoresis and capillary isoelectric focusing. Anal Biochem 2011; 413:8-15. [DOI: 10.1016/j.ab.2011.01.048] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2009] [Revised: 01/29/2011] [Accepted: 01/31/2011] [Indexed: 11/30/2022]
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Cologna SM, Russell WK, Lim PJ, Vigh G, Russell DH. Combining isoelectric point-based fractionation, liquid chromatography and mass spectrometry to improve peptide detection and protein identification. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2010; 21:1612-1619. [PMID: 20537905 PMCID: PMC2927729 DOI: 10.1016/j.jasms.2010.04.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2010] [Revised: 03/17/2010] [Accepted: 04/14/2010] [Indexed: 05/29/2023]
Abstract
The off-line coupling of an isoelectric trapping device termed membrane separated wells for isoelectric focusing and trapping (MSWIFT) to mass spectrometry-based proteomic studies is described. The MSWIFT is a high capacity, high-throughput, mass spectrometry-compatible isoelectric trapping device that provides isoelectric point (pI)-based separations of complex mixtures of peptides. In MSWIFT, separation and analyte trapping are achieved by migrating the peptide ions through membranes having fixed pH values until the peptide pI is bracketed by the pH values of adjacent membranes. The pH values of the membranes can be tuned, thus affording a high degree of experimental flexibility. Specific advantages of using MSWIFT for sample prefractionation include: (1) small sample volumes (approximately 200 microL), (2) customized membranes over a large pH range, (3) flexibility in the number of desired fractions, (4) membrane compatibility with a variety of solvents systems, and (5) resulting fractions do not require sample cleanup before MS analysis. Here, we demonstrate the utility of MSWIFT for mass spectrometry-based detection of peptides in improving dynamic range and the reduction of ion suppression effects for high-throughput separations of tryptic peptides.
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Affiliation(s)
| | | | | | | | - David H. Russell
- Address reprint requests to: Professor David H. Russell, Department of Chemistry, Texas A&M University, PO BOX 30012, College Station, TX 77842, Fax: (979) 845-9485, Phone: (979) 845-3345,
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12
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Kaushik V, Cook N, Liang AY, Desai UR, Sidorov V. Chemoselective precipitation of lactose from a lactose/sucrose mixture: proof of concept for a new separation methodology. Supramol Chem 2010. [DOI: 10.1080/10610278.2010.500732] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- Vivek Kaushik
- a Department of Chemistry , Virginia Commonwealth University , Richmond , VA , 23284 , USA
| | - Nicole Cook
- a Department of Chemistry , Virginia Commonwealth University , Richmond , VA , 23284 , USA
| | - Ayie Y. Liang
- b Institute of Structural Biology and Drug Discovery, Virginia Commonwealth University , Richmond , VA , 23298 , USA
| | - Umesh R. Desai
- b Institute of Structural Biology and Drug Discovery, Virginia Commonwealth University , Richmond , VA , 23298 , USA
| | - Vladimir Sidorov
- a Department of Chemistry , Virginia Commonwealth University , Richmond , VA , 23284 , USA
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13
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Du JR, Wei HH. Focusing and trapping of DNA molecules by head-on ac electrokinetic streaming through join asymmetric polarization. BIOMICROFLUIDICS 2010; 4:034108. [PMID: 20838480 PMCID: PMC2937043 DOI: 10.1063/1.3481468] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2010] [Accepted: 07/31/2010] [Indexed: 05/23/2023]
Abstract
In this work, invoking join asymmetric ac polarization using double half-quadrupole electrodes in a symmetric arrangement, we demonstrate a head-on ac electro-osmotic streaming capable of focusing and trapping DNA molecules efficiently. This is manifested by the observation that picomolar DNA molecules can be trapped into a large crosslike spot with at least an order of magnitude concentration enhancement within just half a minute. We identify that the phenomenon is a combined result of the formation of two prefocused DNA jets flowing toward each other, dipole-induced attraction between focused DNA molecules, and dielectrophoretic trap on the spot. With an additional horizontal pumping, we observe that the trap can transform into a peculiar pitchfork streaming capable of continuous collection and long-distance transport of concentrated DNA molecules. We also show that the same electrode design can be used to direct assembly of submicrometer particles. This newly designed microfluidic platform not only has potentials in enhancing detection sensitivity and facilitating functional assembly for on-chip analysis but also provides an added advantage of transporting target molecules in a focused and continuous manner.
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Affiliation(s)
- Jung-Rong Du
- Department of Chemical Engineering and Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan 701, Taiwan
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14
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Wiberg H, Ek P, Ekholm Pettersson F, Lannfelt L, Emmer Å, Roeraade J. Separation and characterization of aggregated species of amyloid-beta peptides. Anal Bioanal Chem 2010; 397:2357-66. [DOI: 10.1007/s00216-010-3839-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2009] [Revised: 03/19/2010] [Accepted: 05/07/2010] [Indexed: 11/28/2022]
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15
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Jain A, Chakraborty S. Interfacial pH-gradient induced micro-capillary filling with the aid of transverse electrodes arrays in presence of electrical double layer effects. Anal Chim Acta 2010; 659:1-8. [DOI: 10.1016/j.aca.2009.11.029] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2009] [Revised: 11/11/2009] [Accepted: 11/13/2009] [Indexed: 10/20/2022]
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16
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Alahmad Y, Thuy Tran N, Duboeuf J, Grégoire A, Rancé I, Taverna M. CZE for glycoform profiling and quality assessment of recombinant human interleukin-7. Electrophoresis 2009; 30:2347-54. [DOI: 10.1002/elps.200800789] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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17
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Hlushkou D, Dhopeshwarkar R, Crooks RM, Tallarek U. The influence of membrane ion-permselectivity on electrokinetic concentration enrichment in membrane-based preconcentration units. LAB ON A CHIP 2008; 8:1153-62. [PMID: 18584092 DOI: 10.1039/b800549d] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
The performance of nanoporous hydrogel microplugs with varying surface charge density is described in concentrating charged analytes electrokinetically in a microfluidic device. A neutral hydrogel plug with a mean pore size smaller than the size of charged analytes acts as a simple size-exclusion membrane. The presence of fixed charges on the backbone of a nanoporous hydrogel creates ion-permselectivity which results in charge-selective transport through the hydrogel. This leads to the development of concentration polarization (CP) in the adjoining bulk electrolyte solutions under the influence of an applied electrical field. CP strongly affects the distribution of the local electrical field strength, in particular, in the vicinity of the hydrogel plug which can significantly reduce the concentration enrichment factors compared to the neutral hydrogel. A theoretical model and simulations are presented, together with experimental data, to explain the interplay of hydrogel or membrane cation-selectivity, electrical field-induced CP, and the distribution of the local electrical field strength with respect to concentration enrichment of negatively charged analytes at the cathodic membrane-solution interface.
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Affiliation(s)
- Dzmitry Hlushkou
- Institut für Verfahrenstechnik, Otto-von-Guericke-Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany
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Strong RA, Liu H, Krull IS, Cho BY, Cohen SA. ADVANTAGES AND LIMITATIONS OF DERIVATIZATION OF PEPTIDES FOR IMPROVED PERFORMANCE AND DETECTABILITY IN CAPILLARY ISOELECTRIC FOCUSING (CIEF). J LIQ CHROMATOGR R T 2007. [DOI: 10.1081/jlc-100100451] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
- Richard A. Strong
- a Department of Chemistry , Northeastern University , 102 Hurtig Building 360 Huntington Avenue, Boston, MA, 02115, U.S.A
| | - Hongji Liu
- a Department of Chemistry , Northeastern University , 102 Hurtig Building 360 Huntington Avenue, Boston, MA, 02115, U.S.A
| | - Ira S. Krull
- b Department of Chemistry , Northeastern University , 102 Hurtig Building 360 Huntington Avenue, Boston, MA, 02115, U.S.A
| | | | - Steven A. Cohen
- c Biotechnology Applications Laboratory , Waters Corporation , 34 Maple Street, Milford, MA, 01757, U.S.A
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19
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Das S, Chakraborty S. Transverse electrodes for improved DNA hybridization in microchannels. AIChE J 2007. [DOI: 10.1002/aic.11144] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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20
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Kim SM, Sommer GJ, Burns MA, Hasselbrink EF. Low-Power Concentration and Separation Using Temperature Gradient Focusing via Joule Heating. Anal Chem 2006; 78:8028-35. [PMID: 17134136 DOI: 10.1021/ac061194p] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We present an experimental study of temperature gradient focusing (TGF) exploiting an inherent Joule heating phenomenon. A simple variable-width PDMS device delivers rapid and repeatable focusing of model analytes using significantly lower power than conventional TGF techniques. High electric potential applied to the device induces a temperature gradient within the microchannel due to the channel's variable width, and the temperature-dependent mobility of the analytes causes focusing at a specific location. The PDMS device also shows simultaneous separation and concentration capability of a mixture of two sample analytes in less than 10 min. An experiment combining Joule heating with external heating/cooling further supports the hypothesis that temperature is indeed the dominant factor in achieving focusing with this technique.
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Affiliation(s)
- Sun Min Kim
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2125, USA.
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21
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Horká M, Růzicka F, Holá V, Slais K. Capillary isoelectric focusing of microorganisms in the pH range 2–5 in a dynamically modified FS capillary with UV detection. Anal Bioanal Chem 2006; 385:840-6. [PMID: 16791563 DOI: 10.1007/s00216-006-0508-0] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2005] [Revised: 04/18/2006] [Accepted: 04/21/2006] [Indexed: 10/24/2022]
Abstract
The isoelectric points of many microbial cells lie within the pH range spanning from 1.5 to 4.5. In this work, we suggest a CIEF method for the separation of cells according to their isoelectric points in the pH range of 2-5. It includes the segmental injection of the sample pulse composed of the segment of the selected simple ampholytes, the segment of the bioanalytes and the segment of carrier ampholytes into fused silica capillaries dynamically modified by poly(ethylene glycole). This polymer dissolved in the catholyte, in the anolyte and in the injected sample pulse was used for a prevention of the bioanalyte adsorption on the capillary surface and for the reduction of the electroosmotic flow. Between each focusing run, the capillaries were washed with the mixture of acetone/ethanol to achieve the reproducible and efficient CIEF. In order to trace of pH gradients, low-molecular-mass pI markers were used. The mixed cultures of microorganisms, Escherichia coli CCM 3954, Candida albicans CCM 8180, Candida parapsilosis, Candida krusei, Candida glabrata, Candida tropicalis, CCM 8223, Proteus vulgaris, Klebsiela pneumoniae, Staphylococcus aureus CCM 3953, Streptococcus agalactiae CCM 6187, Enterococcus faecalis CCM 4224 and Staphylococcus epidermidis CCM 4418, were focused and separated by the CIEF method suggested here. This CIEF method enables the separation and detection of the microbes from the mixed cultures within several minutes. The minimum detectable number of microbial cells was less than 10(3).
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Affiliation(s)
- Marie Horká
- Institute of Analytical Chemistry, Academy of Sciences of the Czech Republic, Veverí 97, 61142, Brno, Czech Republic.
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22
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Dhopeshwarkar R, Sun L, Crooks RM. Electrokinetic concentration enrichment within a microfluidic device using a hydrogel microplug. LAB ON A CHIP 2005; 5:1148-54. [PMID: 16175272 DOI: 10.1039/b509063f] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
A simple and efficient approach for concentration of charged molecules in microfluidic devices is described. The functional component of the system is a hydrogel microplug photopolymerized within the main channel of a microfluidic device. When an appropriately biased voltage is applied across the hydrogel, charged analyte molecules move from the source well toward the hydrogel. Transport of the analyte through the hydrogel is slow compared to its velocity in the microfluidic channel, however, and therefore it concentrates at the hydrogel/solution interface. For an uncharged hydrogel, a bias of 100 V leads to a approximately 500-fold enrichment of the DNA concentration within 150 s, while the same conditions result in an enrichment of only 50-fold for fluorescein. Somewhat lower enrichment factors are observed when a negatively charged hydrogel is used. A qualitative model is proposed to account for the observed behavior.
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Affiliation(s)
- Rahul Dhopeshwarkar
- Department of Chemical Engineering, Texas A&M University, Mailstop 3122, College Station, TX 77843-3122, USA
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May EL, Hillier AC. Rapid and Reversible Generation of a Microscale pH Gradient Using Surface Electric Fields. Anal Chem 2005; 77:6487-93. [PMID: 16194117 DOI: 10.1021/ac051014w] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We report a method for the rapid and reversible generation of microscale pH gradients using a spatially varied electric field. A linear gradient in electrochemical potential is produced on an electrode surface consisting of a platinum catalyst layer on indium-tin oxide-coated glass by the application of two different potential values at spatially distinct surface locations. The resulting potential gradient drives the oxidation and reduction of water at different rates along the surface, as dictated by the local applied potential. A nonuniform distribution of pH in the neighboring solution results due to the variation in surface reaction rates. The extent and magnitude of the pH gradient can be controlled by the appropriate selection of applied potential values. In addition, the gradient can be rapidly turned on or off and reversibly switched between various profiles. The size of the pH gradient can be readily modified by changing the dimensions of the electrode and contact pads to allow integration into chip-scale devices. Characteristics of the pH gradient are described, including experimental and theoretical evidence of significant improvement in time response over competing methods for the generation of microscale pH gradients.
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Affiliation(s)
- Erin L May
- Department of Chemical Engineering, Iowa State University, Ames, Iowa 50011, USA
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24
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Busnel JM, Varenne A, Descroix S, Peltre G, Gohon Y, Gareil P. Evaluation of capillary isoelectric focusing in glycerol-water media with a view to hydrophobic protein applications. Electrophoresis 2005; 26:3369-79. [PMID: 16143969 DOI: 10.1002/elps.200500252] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Capillary isoelectric focusing (CIEF) separations are usually performed with neutral coated fused-silica capillaries in aqueous anticonvective media. Glycerol, a very viscous solvent (eta = 945 mPa x s at 25 degrees C), known to help stabilize any kind of proteins and solubilize hydrophobic ones, was tested as an alternative to using commercial gels. Viscosity and electroosmotic mobility were measured as a function of gel or glycerol content in water, and a 30:70 v/v glycerol-water medium appeared as a good compromise for performing CIEF in a bare fused-silica capillary without imposing too high a viscosity. To demonstrate the feasibility of this new CIEF system, a standard mixture of nine model proteins was separated according to their pI with a good agreement between experimental and literature aqueous pIs. Moreover, better resolution was achieved with this system than with the conventional aqueous CIEF system, as two of the model proteins could not be separated in the latter system. Glycerol-water CIEF in bare silica capillary was next applied to the separation of horse radish peroxidase, a complex mixture of protein isoforms. The good concordance with the separation obtained by the conventional CIEF system indicated the adequacy of this new system. Finally, as anticipated from the results obtained for the separation of bacteriorhodopsin, a membrane protein, glycerol-water CIEF performed in bare silica capillary appears to be a promising alternative to conventional aqueous CIEF for hydrophobic protein characterization, under their native form.
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Affiliation(s)
- Jean-Marc Busnel
- Laboratory of Electrochemistry and Analytical Chemistry, ENSCP, Paris, France
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25
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Crowley TA, Hayes MA. Analysis of human blood serum using the off-line coupling of capillary isoelectric focusing to matrix-assisted laser desorption/ionization time of flight mass spectrometry. Proteomics 2005; 5:3798-804. [PMID: 16127730 DOI: 10.1002/pmic.200401212] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Off-line coupling of capillary IEF (CIEF) with matrix-assisted laser desorption/ionization mass spectrometry was utilized for the analysis of human blood serum. Serum proteins were initially separated by CIEF, and fractions of the isoelectric separation were eluted sequentially to a MALDI-TOF MS sample target. During pressure elution of the CIEF sample, voltage was maintained across the capillary system utilizing a sheath flow arrangement to minimize band broadening induced by the laminar flow field. Both pI and mass information were obtained from the complex biological sample, similar to traditional 2-DE techniques, and the platform was faster (hours versus days), more automatable, and simpler than 2-DE. The volume of raw sample present in the actual analysis was approximately 100 nL, making this technique well suited for very rare specimens. Additionally, the speed and simplicity of the technology make it an attractive technique for performing initial comparative analyses of complex samples.
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Affiliation(s)
- Timothy A Crowley
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287, USA
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26
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Stastná M, Slais K. Colored pI standards and gel isoelectric focusing in strongly acidic pH. Anal Bioanal Chem 2005; 382:65-72. [PMID: 15900453 DOI: 10.1007/s00216-005-3106-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2004] [Revised: 01/07/2005] [Accepted: 01/12/2005] [Indexed: 10/25/2022]
Abstract
Colored, low molecular weight pI markers have been developed for isoelectric focusing (IEF) in acidic pH range. Their isoelectric points (pIs) were determined by direct measurement of the pH of the focused bands after completion of IEF on polyacrylamide gels. The practicable suitability of the proposed pI markers as pI standards for IEF was tested by applying gel IEF. The acidic pH gradient was created either by commercial synthetic carrier ampholytes or by mixture of simple buffers consisting of acids (non-ampholytes) and ampholytic buffers. By applying simple acids, it was possible to extend the acidic pH range beyond those achievable with commercial synthetic carrier ampholytes. By using an experimental arrangement without electrode electrolyte reservoirs with electrodes creating the fixed end of the gel, the strongly acidic pH gradient was stable even for prolonged focusing time.
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Affiliation(s)
- Miroslava Stastná
- Institute of Analytical Chemistry, Academy of Sciences of the Czech Republic, Veveri 97, 611 42, Brno, Czech Republic.
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27
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Simpson DC, Smith RD. Combining capillary electrophoresis with mass spectrometry for applications in proteomics. Electrophoresis 2005; 26:1291-305. [PMID: 15765477 DOI: 10.1002/elps.200410132] [Citation(s) in RCA: 159] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Mass spectrometry (MS)-based proteomics is currently dominated by the analysis of peptides originating either from digestion of proteins separated by two-dimensional gel electrophoresis (2-DE) or from global digestion; the simple peptide mixtures obtained from digestion of gel-separated proteins do not usually require further separation, while the complex peptide mixtures obtained by global digestion are most frequently separated by chromatographic techniques. Capillary electrophoresis (CE) provides alternatives to 2-DE for protein separation and alternatives to chromatography for peptide separation. This review attempts to elucidate how the most promising CE modes, capillary zone electrophoresis (CZE) and capillary isoelectric focusing (CIEF), might best be applied to MS-based proteomics. CE-MS interfacing, mass analyzer performance, column coating to minimize analyte adsorption, and sample stacking for CZE are considered prior to examining numerous applications. Finally, multidimensional systems that incorporate CE techniques are examined; CZE often finds use as a fast, final dimension before ionization for MS, while CIEF, being an equilibrium technique, is well-suited to being the first dimension in automated fractionation systems.
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28
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Ptolemy AS, Britz-McKibbin P. Single-step analysis of low abundance phosphoamino acids via on-line sample preconcentration with chemical derivatization by capillary electrophoresis. Analyst 2005; 130:1263-70. [PMID: 16096672 DOI: 10.1039/b504480d] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
New strategies for rapid, sensitive and high-throughput analysis of low abundance metabolites in biological samples are required for future metabolomic research. In this report, a direct method for sub-micromolar analyses of phosphoamino acids was developed using on-line sample preconcentration with 9-fluorenylmethyloxycarbonyl chloride (FMOC) derivatization by capillary electrophoresis (CE) and UV detection. Analyte focusing by dynamic pH junction and FMOC labeling efficiency were influenced by several experimental factors including buffer pH, ionic strength, sample injection length and FMOC concentration. About a 200-fold enhancement in concentration sensitivity was achieved under optimal conditions relative to conventional off-line derivatization, as reflected by a detection limit (S/N approximately 3) of 0.1 microM. In-capillary sample preconcentration with chemical labeling by CE offers a unique single-step analytical platform for high-throughput screening of low abundance metabolites without intrinsic chromophores.
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Affiliation(s)
- Adam S Ptolemy
- Department of Chemistry, McMaster University, Hamilton, ON, L8S 4M1, Canada
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29
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Rodemann T, Johns C, Yang WS, Haddad PR, Macka M. Isoelectric Buffers for Capillary Electrophoresis. 2. Bismorpholine Derivative of a Carboxylic Acid as a Low Molecular Weight Isoelectric Buffer. Anal Chem 2004; 77:120-5. [PMID: 15623286 DOI: 10.1021/ac049237u] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A new compound class of synthetic isoelectric buffers is introduced, designed as a small molecule with one fully or prevailingly dissociated acidic group (such as sulfonic or carboxylic) and two partly pronated (buffering) basic amino groups attached onto a hydrophilic UV-transparent backbone. As an example, a new isoelectric compound 2,2-bis(4-morpholinylmethyl)propanoic acid (BMMPA) was synthesized by attaching two morpholine groups onto a molecule of pivalic acid. It was characterized as having an isoelectric point pI = 6.5 and exhibiting satisfactory buffering capacity at the pI. Solutions of BMMPA are transparent down to the low-UV spectral region, thus making it a potentially suitable buffer for a number of separation methods. Its use in capillary electrophoresis was demonstrated in a separation system for indirect photometric detection of anions based on an electrolyte with the anionic dye Orange G as the indirect detection probe and using BMMPA as a buffer. The use of an isoelectric buffering compound brings the advantages of a buffered electrolyte without the concomitant introduction of co-ions that would be detrimental to the indirect detection process. Submicromole per liter limits of detection for a number of inorganic and small organic ions were achieved. Optimal structural properties of the isoelectric buffer with respect to its buffering properties are discussed.
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Affiliation(s)
- Thomas Rodemann
- School of Chemistry, and Australian Centre for Research on Separation Science (ACROSS), School of Chemistry, University of Tasmania, Private Bag 75, Hobart 7001, Tasmania, Australia
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30
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Righetti PG. Determination of the isoelectric point of proteins by capillary isoelectric focusing. J Chromatogr A 2004; 1037:491-9. [PMID: 15214685 DOI: 10.1016/j.chroma.2003.11.025] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Different ways of determining isoelectric points (pI) of proteins in capillary isoelectric focusing are reviewed here. Due to the impossibility of direct pH measurements in the liquid phase, such assessments have to rely on the use of pI markers. Different types of pI markers have been described: dyes, fluorescently labelled peptides, sets of proteins of known pI values. It appears that, perhaps, the best system is a set of 16 synthetic peptides, trimers to hexamers, made to contain each a Trp residue for easy detection at 280 nm. By a careful blend of acidic (Asp, Glu), mildly basic, with pK around neutrality (His), and basic (Lys, Arg) amino acids, it is possible to obtain a series of pI markers with pI values quite evenly distributed along the pH scale, possessing good buffering capacity and conductivity around their pI values and thus focusing as sharp peaks. Another approach to pI determination is the monitoring of the current during mobilization: this allows, with the aid of known pI markers, to calibrate the system with a pI/current graph. Pitfalls and common errors in pI determinations are reviewed here and guidelines given for minimizing such errors in pI estimation.
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Affiliation(s)
- Pier Giorgio Righetti
- Department of Agricultural and Industrial Biotechnology, University of Verona, Strada Le Grazie 15, Verona 37134, Italy.
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31
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Britz-McKibbin P, Terabe S. On-line preconcentration strategies for trace analysis of metabolites by capillary electrophoresis. J Chromatogr A 2003; 1000:917-34. [PMID: 12877205 DOI: 10.1016/s0021-9673(03)00502-8] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Analysis of low concentrations of metabolites is required for new fields of biological research, such as metabolomics. In this review, recent work in our laboratory aimed at developing improved strategies for on-line sample preconcentration of metabolites by capillary electrophoresis (CE) is presented. Dynamic pH junction, sweeping and dynamic pH junction-sweeping represent three complementary methods for electrokinetic focusing of large volumes of sample directly on-capillary. Focusing selectivity and focusing efficiency are two factors that can be used to assess the suitability of each method for different classes of metabolites. Buffer properties can be selected to enhance the focusing of specific types of metabolites based on knowledge of the analyte physicochemical properties. The application of on-line preconcentration CE for trace analysis of metabolites in real samples of interest, such as biological fluids and cellular extracts, is also demonstrated. Under optimum conditions, up to three orders of magnitude increase in concentration sensitivity can be realized for several classes of metabolites, including catecholamines, purines, nucleosides, nucleotides, amino acids, steroids and coenzymes. Recent work on hyphenating on-line preconcentration with multiplexed CE is highlighted as a promising platform for sensitive and high-throughput analyses of metabolites.
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Affiliation(s)
- Philip Britz-McKibbin
- Graduate School of Science, Himeji Institute of Technology, Kamigori, Hyogo 678-1297, Japan.
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32
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Wilson NL, Schulz BL, Karlsson NG, Packer NH. Sequential analysis of N- and O-linked glycosylation of 2D-PAGE separated glycoproteins. J Proteome Res 2002; 1:521-9. [PMID: 12645620 DOI: 10.1021/pr025538d] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A robust method has been developed that allows analysis of both N- and O-linked oligosaccharides released from glycoproteins separated using 2D-PAGE and then electroblotted to PVDF membrane. This analysis provides efficient oligosaccharide profiling applicable to glycoproteomic analysis. The method involves the enzymatic release of N-linked oligosaccharides using PNGase F followed by the chemical release of O-linked oligosaccharides using reductive beta-elimination and analysis using LC-ESI-MS. Oligosaccharides from the major plasma glycoproteins with a pI between 4 and 7 were characterized from the glycoforms of haptoglobin, alpha2-HS-glycoprotein, serotransferrin, alpha1-antitrypsin, and alpha1-antichymotrypsin. It was shown that the separation of protein glycoforms evident in 2D-PAGE is partially due to the combined sialylation of the O-linked and N-linked oligosaccharides. Bi-, tri- and tetra-antennary N-linked structures, which had differing levels of sialylation and fucosylation, were found to be present on the glycoproteins analyzed, together with O-linked oligosaccharides such as mono-, and disialylated T-antigen and a disialylated core type 2 hexasaccharide. In addition, N-linked site-specific information was obtained by MALDI-MS analysis using tryptic digestion after PNGase F release of the oligosaccharides.
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Affiliation(s)
- Nicole L Wilson
- Proteome Systems Ltd., 1/35-41 Waterloo Road, North Ryde, Sydney, NSW 1670, Australia.
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33
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Britz-McKibbin P, Otsuka K, Terabe S. On-line focusing of flavin derivatives using Dynamic pH junction-sweeping capillary electrophoresis with laser-induced fluorescence detection. Anal Chem 2002; 74:3736-43. [PMID: 12175161 DOI: 10.1021/ac025701o] [Citation(s) in RCA: 136] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Simple yet effective methods to enhance concentration sensitivity is needed for capillary electrophoresis (CE) to become a practical method to analyze trace levels of analytes in real samples. In this report, the development of a novel on-line preconcentration technique combining dynamic pH junction and sweeping modes of focusing is applied to the sensitive and selective analysis of three flavin derivatives: riboflavin, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Picomolar (pM) detectability of flavins by CE with laser-induced fluorescence (LIF) detection is demonstrated through effective focusing of large sample volumes (up to 22% capillary length) using a dual pH junction-sweeping focusing mode. This results in greater than a 1,200-fold improvement in sensitivity relative to conventional injection methods, giving a limit of detection (S/N = 3) of approximately 4.0 pM for FAD and FMN. Flavin focusing is examined in terms of analyte mobility dependence on buffer pH, borate complexation and SDS interaction. Dynamic pH junction-sweeping extends on-line focusing to both neutral (hydrophobic) and weakly acidic (hydrophilic) species and is considered useful in cases when either conventional sweeping or dynamic pH junction techniques used alone are less effective for certain classes of analytes. Enhanced focusing performance by this hyphenated method was demonstrated by greater than a 4-fold reduction in flavin bandwidth, as compared to either sweeping or dynamic pH junction, reflected by analyte detector bandwidths <0.20 cm. Novel on-line focusing strategies are required to improve sensitivity in CE, which may be applied toward more effective biochemical analysis methods for diverse types of analytes.
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Affiliation(s)
- Philip Britz-McKibbin
- Department of Material Sciences, Graduate School and Faculty of Science, Himeji Institute of Technology, Kamigori, Hyogo, Japan.
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34
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Abstract
A new technique is described for the concentration and separation of ionic species in solution within microchannels or capillaries. Concentration is achieved by balancing the electrophoretic velocity of an analyte against the bulk flow of solution in the presence of a temperature gradient. With an appropriate buffer, the temperature gradient can generate a corresponding gradient in the electrophoretic velocity, so that the electrophoretic and bulk velocities sum to zero at a unique point, and the analyte will be focused at that point. The technique is demonstrated for a variety of analytes, including fluorescent dyes, amino acids, DNA, proteins, and particles, and is shown to be capable of greater than 10,000-fold concentration of a dilute analyte.
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Affiliation(s)
- David Ross
- Process Measurements Division, National Institute of Standards & Technology, Gaithersburg, Maryland 20899, USA.
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35
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Abstract
The present review highlights the mechanisms of action and efficiency of three major classes of dynamic coatings so far adopted in capillary electrophoresis: (i) amines to oligo-amines, (ii) neutral synthetic and natural polymers, and (iii) neutral and zwitter-ionic surfactants. Their merits and efficacy have been explored in depth via a novel quantitation technique consisting of eluting, by frontal analysis, any adsorbed proteinaceous material, which can then be correctly quantified as a peak as it moves in front of the detector window. This is achieved by loading sodium dodecyl sulfate (SDS) micelles onto the cathodic side and migrating them electrophoretically into the capillary lumen, where they efficiently sweep any adsorbed polypeptide material. It is found that a common trend, for all quenchers, is linked to a hydrophobicity scale: the more hydrophobic the inhibitor, the better it minimizes potential interactions of macromolecules with the wall. This seems to be true for all the classes of dynamic modifiers tested. Finally, we describe a novel, dynamic to static quencher: it is a quaternary piperazine, bearing a reactive iodine atom at the end of a butyl tail (N(methyl-N-omega-iodo-butyl),N'-methyl piperazine). This molecule first binds to the wall, at alkaline pH values, via ionic and hydrogen bonds. Once docked onto the wall, the reactive tail forms a covalent link with the silica surface, to which it then remains permanently affixed.
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Affiliation(s)
- P G Righetti
- University of Verona, Department of Agricultural and Industrial Biotechologies, Italy.
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36
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Cabrera CR, Finlayson B, Yager P. Formation of natural pH gradients in a microfluidic device under flow conditions: model and experimental validation. Anal Chem 2001; 73:658-66. [PMID: 11217778 DOI: 10.1021/ac000495a] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A new isoelectric focusing technique has been developed that incorporates natural pH gradient formation in microfluidic channels under flowing conditions. In conjunction, a one-dimensional finite difference model has been developed that solves a system of algebraic-ordinary differential equations that describe the phenomena occurring in the system, including hydrolysis at the electrodes, buffering effects of weak acids and bases, and mass transport due to both diffusion and electrophoresis. A quantitative, noninvasive, optically based method of monitoring pH gradient formation is presented, and the experimental data generated by this method are found to be in good agreement with model predictions. In addition, the model provides a theoretical explanation for initially unexpected experimental results. Model predictions are also shown to match well with experimental results of microfluidic isoelectric focusing of a single protein species. Accounting for the nonuniform velocity profile, characteristic of pressure-driven flow in microfluidic channels, is found to improve predictions of dynamic pH changes close to the electrodes and overall time required to reach steady state, but to reduce the accuracy of dynamic pH change predictions in other regions of the channel.
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Affiliation(s)
- C R Cabrera
- Department of Bioengineering, University of Washington, Seattle 98195, USA.
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37
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38
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Abstract
A novel method for the concentration of bacterial solutions is presented that implements electrokinetic techniques, zone electrophoresis (ZE) and isoelectric focusing (IEF), in a microfluidic device. The method requires low power (< 3e-5 W) and can be performed continuously on a flowing stream. The device consists of two palladium electrodes held in a flow cell constructed from layers of polymeric film held together by a pressure-sensitive adhesive. Both ZE and IEF are performed with carrier-free solutions in devices in which the electrodes are in intimate contact with the sample fluid. IEF experiments were performed using natural pH gradients; no carrier ampholyte solution was required. Experiments performed in buffer alone resulted in significant electroosmotic flow. Pretreatment of the sample chamber with bleach followed by a concentrated solution of cationic detergent effectively suppressed electroosmotic flow.
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Affiliation(s)
- C R Cabrera
- Department of Bioengineering, University of Washington, Seattle 98195, USA.
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39
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Righetti PG, Gelfi C, Bossi A, Olivieri E, Castelletti L, Verzola B, Stoyanov AV. Capillary electrophoresis of peptides and proteins in isoelectric buffers: an update. Electrophoresis 2000; 21:4046-53. [PMID: 11192123 DOI: 10.1002/1522-2683(200012)21:18<4046::aid-elps4046>3.0.co;2-5] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Capillary electrophoresis in acidic, isoelectric buffers is a novel methodology allowing fast protein and peptide analysis in uncoated capillaries. Due to the low pH adopted and to the use of dynamic coating with cellulose derivatives, silanol ionization is essentially suppressed and little interaction of macromolecules with the untreated wall occurs. In addition, due to the low conductivity of quasi-stationary, isoelectric buffers, high-voltage gradients can be applied (up to 800 V/cm) permitting fast peptide analysis with a high resolving power due to minimal diffusional peak spreading. Four such buffers are here described: cysteic acid (Cys-A, pI 1.85), iminodiacetic acid (IDA, pI 2.23), aspartic acid (Asp, pI 2.77) and glutamic acid (Glu, pI 3.22). A number of applications are reported, ranging from food analysis to the study of folding/unfolding transitions of proteins.
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Affiliation(s)
- P G Righetti
- University of Verona, Department of Agricultural & Industrial Biotechnologies, Italy.
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40
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Olivier E, Sebastiano R, Citterio A, Gelfi C, Righetti PG. Quantitation of protein binding to the capillary wall in acidic, isoelectric buffers and means for minimizing the phenomenon. J Chromatogr A 2000; 894:273-80. [PMID: 11100870 DOI: 10.1016/s0021-9673(00)00665-8] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Notwithstanding the use of acidic, amphoteric, isoelectric buffers with isoelectric points (pI) in the pH 2-3 range, adsorption of proteins to the naked silica wall can be non-negligible. Two such buffers have been tested: iminodiacetic acid (IDA; pI 2.23, apparent pH 3.2 in 7 M urea) and aspartic acid (pI 2.77, apparent pH 3.7 in 7 M urea). Three potential quenchers of such interactions have been tested: hydroxyethylcellulose (HEC; number average molecular mass, Mr 27,000), TEPA (tetraethylenepentamine) and a novel, quatemarized piperazine [N(methyl-N-omega-iodobutyl)-N'-methylpiperazine] (Q-Pip), either alone or in binary and ternary mixtures. Human alpha- and beta-globin chains have been used as test proteins in capillary electrophoresis separations. It has been found that mixtures of these compounds are the worst possible remedy. E.g., a ternary mixture comprising 0.5% HEC, 0.5 mM TEPA and 1 mM Q-Pip still leaves behind 4.5% adsorbed protein onto the silica surface in runs in IDA buffer and 7 M urea (pH 3.2). Conversely, 0.5 mM TEPA or 1 mM Q-Pip, when used alone, minimize adsorption down to only 1.8% and 0.5%, respectively. When the same globin chain separations are performed in Asp and 7 M urea (pH 3.7), the situation is much worse: 44% protein is adsorbed in a ternary mixture of 0.5% HEC, 1 mM Q-Pip and 0.5 mM TEPA. However, when used alone, 0.5 mM TEPA and 1 mM Q-Pip reduce globin adsorption to levels of 8% and 5%, respectively. TEPA and Q-Pip are found to be in all cases the best quenchers of protein interaction to naked fused-silica; in addition they exhibit the unique property of smoothing the base-line and giving reproducible runs. The best method for desorbing bound protein was found to be an electrophoretic step consisting in driving sodium dodecylsulphate micelles from the cathodic reservoir.
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Affiliation(s)
- E Olivier
- Department of Agricultural and Industrial Biotechnology, University of Verona, Italy
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41
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Generation of natural pH gradients in microfluidic channels for use in isoelectric focusing. Anal Chem 2000; 72:3745-51. [PMID: 10959958 DOI: 10.1021/ac000237d] [Citation(s) in RCA: 137] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
As a part of an ongoing investigation of the use of isoelectric focusing (IEF) in microfluidic devices, pH gradients were electrochemically formed and optically quantified in microfluidic channels using acid-base indicators. The microchannels consisted of two parallel 40-mm-long electrodes with an interelectrode gap of 2.54 mm; top and bottom transparent windows were separated by 0.2 mm. Gradients in pH were formed as a result of the electrochemical decomposition of water at an applied potential not higher than 2.5 V to avoid generation of gas bubbles. Solutions contained low concentrations of a single buffer. The stability of the pH gradients and their sensitivity to changes in initial conditions were investigated under static (nonflow) conditions. Isoelectric focusing of sample biological analytes, bovine hemoglobin and bovine serum albumin, was performed to illustrate the potential of "microfluidic transverse IEF" for use in continuous concentration and separation systems.
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42
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Shen Y, Berger SJ, Anderson GA, Smith RD. High-efficiency capillary isoelectric focusing of peptides. Anal Chem 2000; 72:2154-9. [PMID: 10815979 DOI: 10.1021/ac991367t] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Several approaches are presently being developed for global proteome characterization that are based upon the analysis of polypeptide mixtures resulting from digestion of (often complex) mixtures of proteins. Improved methods for peptide analysis are needed that provide for sample concentration, higher resolution separations, and direct compatibility with mass spectrometry. In this work, methods for the high-efficiency capillary isoelectric focusing (CIEF) separation of peptides have been developed that provide for simultaneous sample concentration and separation according to peptide isoelectric point. Under typical nondenaturing CIEF conditions, peptides are concentrated approximately 500-fold, and peptides present at < 1 ng/ microL were detectable using conventional UV detection. CIEF separations of peptides provided much faster measurements of isoelectric points compared with conventional isoelectric focusing in gels. Very small differences in peptide isoelectric points (deltapI approximately 0.01) could be resolved, High-efficiency CIEF separations for complex peptide mixtures from tryptic digestion of yeast cytosol fractions were obtained and showed significant improvement over those obtained using capillary zone electrophoresis and packed capillary reversed-phase liquid chromatography.
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Affiliation(s)
- Y Shen
- Pacific Northwest National Laboratory, Richland, Washington 99352, USA
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Verzola B, Gelfi C, Righetti PG. Protein adsorption to the bare silica wall in capillary electrophoresis quantitative study on the chemical composition of the background electrolyte for minimising the phenomenon. J Chromatogr A 2000; 868:85-99. [PMID: 10677082 DOI: 10.1016/s0021-9673(99)01207-8] [Citation(s) in RCA: 128] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A novel method is reported for quantifying protein adsorption to naked silica tubings and for assessing the efficacy of amino quenchers added to the background electrolyte. It consists of flushing a fluorescently-labelled protein (myoglobin) into a capillary equilibrated in Tris-acetate buffer, pH 5.0, until full saturation of the potential adsorbing sites. Desorption is then affected by driving electrophoretically sodium dodecyl sulphate (SDS) micelles into the capillary from the cathodic reservoir: the peak of eluted material is quantified fluorometrically by using a dual laser beam instrument able to read the fluorescein-isothiocyanate-labelled myoglobin at 520 nm and the internal standard (sulphorodamine) at 630 nm. As potential quenchers, a series of monoamines have been investigated (triethylamine, triethanolamine, ethylamine), followed by diamines (putrescine, cadaverine and hexamethonium bromide) and finally by oligoamines [spermidine, spermine and TEPA (tetraethylenepentamine), i.e., a tri- a tetra- and a pentamine, respectively]. Two values of molarities have been derived: a value at 50% (a kind of a dissociation constant) and a value at 90% inhibition of binding of macromolecules to the silica surface. According to these figures of merit, mono- and diamines are rather poor quenchers of interaction with the wall, since the 50% values are of the order of 50-100 mM and the 90% values reach as high as 560 mM. On the contrary, oligoamines, especially spermine and TEPA, are most effective, since the 50% molarities are in the sub-millimolar range and the 90% values are of the order of ca. 1 mM. Figures of merit have also been derived for different washing procedures. Those most commonly adopted in routine practice, i.e., of washing with either 1 M NaOH or with 1 M HCl, or with both, leave behind traces of proteins still bound to the wall, whereas the SDS micelle electrophoretic desorption seems to be 100% effective.
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Affiliation(s)
- B Verzola
- University of Verona, Department of Agricultural and Industrial Biotechnology, Italy
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Abstract
Capillary electrophoresis (CE) offers the analyst a number of key advantages for the analysis of the components of foods. CE offers better resolution than, say, high-performance liquid chromatography (HPLC), and is more adept at the simultaneous separation of a number of components of different chemistries within a single matrix. In addition, CE requires less rigorous sample cleanup procedures than HPLC, while offering the same degree of automation. However, despite these advantages, CE remains under-utilized by food analysts. Therefore, this review consolidates and discusses the currently reported applications of CE that are relevant to the analysis of foods. Some discussion is also devoted to the development of these reported methods and to the advantages/disadvantages compared with the more usual methods for each particular analysis. It is the aim of this review to give practicing food analysts an overview of the current scope of CE.
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Affiliation(s)
- R A Frazier
- Department of Food Science and Technology, The University of Reading, Whiteknights, UK.
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Abstract
This article gives a review of the recent developments in capillary electrophoresis (CE) of peptides. New approaches to the theoretical description of electromigration behavior of peptides are described, and methodological aspects of CE separations of peptides such as selection of separation conditions, sample treatment, suppression of peptide adsorption to the capillary wall and specificities of CE separation modes are discussed. Progress in application of high performance detection schemes, namely laser-induced fluorescence and mass spectrometry, in peptide separations by CE is presented. Applications of different CE techniques, zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography and electrochromatography to peptide analysis, preparation and physicochemical characterization are demonstrated.
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Affiliation(s)
- V Kasicka
- Institute for Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Prague.
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Abstract
This paper provides an overview on the current status of capillary electrophoresis (CE) and capillary electrochromatography (CEC). The focus is largely on the current application areas of CE where routine methods are now in place. These application areas include the analysis of DNA, clinical and forensic samples, carbohydrates, inorganic anions and metal ions, pharmaceuticals, enantiomeric species and proteins and peptides. More specific areas such the determination of physical properties, microchip CE and instrumentation developments are also covered. The application, advantages and limitations of CEC are covered. Recent review articles and textbooks are frequently cited to provide readers with a source of information regarding pioneering work and theoretical treatments.
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Affiliation(s)
- K D Altria
- GlaxoWellcome R&D, Ware, Hertfordshire, UK.
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Separation of peptides in isoelectric cysteic acid buffer and hydro–organic solvents (hexafluoro-2-propanol–urea). J Chromatogr A 1999. [DOI: 10.1016/s0021-9673(99)00215-0] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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