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Abstract
Isotachophoresis (ITP) is a versatile electrophoretic technique that can be used for sample preconcentration, separation, purification, and mixing, and to control and accelerate chemical reactions. Although the basic technique is nearly a century old and widely used, there is a persistent need for an easily approachable, succinct, and rigorous review of ITP theory and analysis. This is important because the interest and adoption of the technique has grown over the last two decades, especially with its implementation in microfluidics and integration with on-chip chemical and biochemical assays. We here provide a review of ITP theory starting from physicochemical first-principles, including conservation of species, conservation of current, approximation of charge neutrality, pH equilibrium of weak electrolytes, and so-called regulating functions that govern transport dynamics, with a strong emphasis on steady and unsteady transport. We combine these generally applicable (to all types of ITP) theoretical discussions with applications of ITP in the field of microfluidic systems, particularly on-chip biochemical analyses. Our discussion includes principles that govern the ITP focusing of weak and strong electrolytes; ITP dynamics in peak and plateau modes; a review of simulation tools, experimental tools, and detection methods; applications of ITP for on-chip separations and trace analyte manipulation; and design considerations and challenges for microfluidic ITP systems. We conclude with remarks on possible future research directions. The intent of this review is to help make ITP analysis and design principles more accessible to the scientific and engineering communities and to provide a rigorous basis for the increased adoption of ITP in microfluidics.
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Affiliation(s)
- Ashwin Ramachandran
- Department of Aeronautics and Astronautics, Stanford University, Stanford, California 94305, United States
| | - Juan G Santiago
- Department of Mechanical Engineering, Stanford University, Stanford, California 94305, United States
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2
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Chau MK, Arega NG, Nhung Tran NA, Song J, Lee S, Kim J, Chung M, Kim D. Capacitively coupled contactless conductivity detection for microfluidic capillary isoelectric focusing. Anal Chim Acta 2020; 1124:60-70. [PMID: 32534676 DOI: 10.1016/j.aca.2020.05.028] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2019] [Revised: 03/25/2020] [Accepted: 05/09/2020] [Indexed: 12/30/2022]
Abstract
We report capacitively coupled contactless conductivity detection (C4D) of proteins separated by microfluidic capillary isoelectric focusing (μCIEF). To elucidate the evolution of negative conductivity peaks during focusing and seek IEF conditions for sensitive conductivity detection, numerical simulation was performed using a model protein GFP (green fluorescence protein) and hypothetical carrier ampholytes (CAs). C4D was successfully applied to the μCIEF by optimizing assay conditions using a simple and effective pressure-mobilization approach. The conductivity and fluorescence signals of a focused GFP band were co-detected, confirming that the obtained negative C4D peak could be attributed to the actual protein, not the non-uniform background conductivity profile of the focused CAs. GFP concentrations of 10 nM-30 μM was quantified with a detection limit of 10 nM. Finally, the resolving power was analyzed by separating a mixture of R-phycoerythrin (pI 5.01), GFP-F64L (pI 5.48), and RK-GFP (pI 6.02). The conductivities of the three separated fluorescence proteins were measured with average separation resolution of 2.06. We expect the newly developed label-free μCIEF-C4D technique to be widely adopted as a portable, electronics-only protein-analysis tool.
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Affiliation(s)
- Minh Khang Chau
- Department of Mechanical Engineering, Myongji University, Yongin-si, Gyeonggi-do, 17508, South Korea
| | - Nebiyu Getachew Arega
- Department of Mechanical Engineering, Myongji University, Yongin-si, Gyeonggi-do, 17508, South Korea
| | - Nguyen Anh Nhung Tran
- Department of Chemical Engineering, Hongik University, Mapo-gu, Seoul, 04066, South Korea
| | - Jin Song
- Department of Mechanical Engineering, Myongji University, Yongin-si, Gyeonggi-do, 17508, South Korea
| | - Sangmin Lee
- Department of Chemical Engineering, Hongik University, Mapo-gu, Seoul, 04066, South Korea
| | - Jintae Kim
- Department of Electrical Engineering, Konkuk University, Gwangjin-gu, Seoul, 05029, South Korea
| | - Minsub Chung
- Department of Chemical Engineering, Hongik University, Mapo-gu, Seoul, 04066, South Korea
| | - Dohyun Kim
- Department of Mechanical Engineering, Myongji University, Yongin-si, Gyeonggi-do, 17508, South Korea; Natural Science Research Institute, Myongji University, Yongin-si, Gyeonggi-do, 17508, South Korea.
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3
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Cieslarova Z, Magaldi M, Barros LA, do Lago CL, Oliveira DR, Fonseca FAH, Izar MC, Lopes AS, Tavares MFM, Klassen A. Capillary electrophoresis with dual diode array detection and tandem mass spectrometry to access cardiovascular biomarkers candidates in human urine: Trimethylamine-N-Oxide and l-carnitine. J Chromatogr A 2019; 1583:136-142. [DOI: 10.1016/j.chroma.2018.10.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Revised: 10/02/2018] [Accepted: 10/06/2018] [Indexed: 02/06/2023]
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4
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Beutner A, Herl T, Matysik FM. Selectivity enhancement in capillary electrophoresis by means of two-dimensional separation or dual detection concepts. Anal Chim Acta 2018; 1057:18-35. [PMID: 30832915 DOI: 10.1016/j.aca.2018.11.042] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Revised: 11/01/2018] [Accepted: 11/19/2018] [Indexed: 12/18/2022]
Abstract
For the identification and quantification of analytes in complex samples, highly selective analytical strategies are required. The selectivity of single separation techniques such as gas chromatography (GC), liquid chromatography (LC), or capillary electrophoresis (CE) with common detection principles can be enhanced by hyphenating orthogonal separation techniques but also by using complementary detection systems. In this review, two-dimensional systems containing CE in at least one dimension are reviewed, namely LC-CE or 2D CE systems. Particular attention is paid to the aspect of selectivity enhancement due to the orthogonality of the different separation mechanisms. As an alternative concept, dual detection approaches are reviewed using the common detectors of CE such as UV/VIS, laser-induced fluorescence, capacitively coupled contactless conductivity (C4D), electrochemical detection, and mass spectrometry. Special emphasis is given to dual detection systems implementing the highly flexible C4D as one detection component. Selectivity enhancement can be achieved in case of complementarity of the different detection techniques.
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Affiliation(s)
- Andrea Beutner
- Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg, Universitaetsstrasse 31, 93053, Regensburg, Germany
| | - Thomas Herl
- Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg, Universitaetsstrasse 31, 93053, Regensburg, Germany
| | - Frank-Michael Matysik
- Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg, Universitaetsstrasse 31, 93053, Regensburg, Germany.
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Kubáň P, Hauser PC. Contactless conductivity detection for analytical techniques: Developments from 2016 to 2018. Electrophoresis 2018; 40:124-139. [PMID: 30010203 DOI: 10.1002/elps.201800248] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Revised: 07/10/2018] [Accepted: 07/10/2018] [Indexed: 01/05/2023]
Abstract
The publications concerning capacitively coupled contactless conductivity detection for the 2-year period from mid-2016 to mid-2018 are covered in this update to the earlier reviews of the series. Relatively few reports on fundamental investigations or new designs have appeared in the literature in this time interval, but the development of new applications with the detection method has continued strongly. Most often, contactless conductivity measurements have been employed for the detection of inorganic or small organic ions in conventional capillary electrophoresis, less often in microchip electrophoresis. A number of other uses, such as detection in chromatography or the gauging of bubbles in streams have also been reported.
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Affiliation(s)
- Pavel Kubáň
- Institute of Analytical Chemistry of the Czech Academy of Sciences, Brno, Czech Republic
| | - Peter C Hauser
- Department of Chemistry, University of Basel, Basel, Switzerland
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Malá Z, Gebauer P. Recent progress in analytical capillary isotachophoresis. Electrophoresis 2018; 40:55-64. [DOI: 10.1002/elps.201800239] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Revised: 07/12/2018] [Accepted: 07/13/2018] [Indexed: 12/30/2022]
Affiliation(s)
- Zdena Malá
- Institute of Analytical Chemistry of the Czech Academy of Sciences; Brno Czech Republic
| | - Petr Gebauer
- Institute of Analytical Chemistry of the Czech Academy of Sciences; Brno Czech Republic
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7
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20th anniversary of axial capacitively coupled contactless conductivity detection in capillary electrophoresis. Trends Analyt Chem 2018. [DOI: 10.1016/j.trac.2018.03.007] [Citation(s) in RCA: 78] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Müller LS, Muratt DT, Molin TRD, Urquhart CG, Viana C, de Carvalho LM. Analysis of Pharmacologic Adulteration in Dietary Supplements by Capillary Zone Electrophoresis Using Simultaneous Contactless Conductivity and UV Detection. Chromatographia 2018. [DOI: 10.1007/s10337-018-3496-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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9
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Enantiomeric separations by capillary electrophoresis: Theoretical method to determine optimum chiral selector concentration. J Chromatogr A 2018; 1539:71-77. [DOI: 10.1016/j.chroma.2018.01.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Revised: 12/18/2017] [Accepted: 01/01/2018] [Indexed: 01/28/2023]
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10
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Liu Y, Wang W, Jia M, Liu R, Liu Q, Xiao H, Li J, Xue Y, Wang Y, Yan C. Recent advances in microscale separation. Electrophoresis 2017; 39:8-33. [DOI: 10.1002/elps.201700271] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2017] [Revised: 08/03/2017] [Accepted: 08/04/2017] [Indexed: 12/14/2022]
Affiliation(s)
- Yuanyuan Liu
- School of Pharmacy; Shanghai Jiao Tong University; Shanghai P. R. China
| | - Weiwei Wang
- School of Pharmacy; Shanghai Jiao Tong University; Shanghai P. R. China
| | - Mengqi Jia
- School of Pharmacy; Shanghai Jiao Tong University; Shanghai P. R. China
| | - Rangdong Liu
- School of Pharmacy; Shanghai Jiao Tong University; Shanghai P. R. China
| | - Qing Liu
- School of Pharmacy; Shanghai Jiao Tong University; Shanghai P. R. China
| | - Han Xiao
- School of Pharmacy; Shanghai Jiao Tong University; Shanghai P. R. China
| | - Jing Li
- Unimicro (shanghai) Technologies Co., Ltd.; Shanghai P. R. China
| | - Yun Xue
- School of Pharmacy; Shanghai Jiao Tong University; Shanghai P. R. China
| | - Yan Wang
- School of Pharmacy; Shanghai Jiao Tong University; Shanghai P. R. China
| | - Chao Yan
- School of Pharmacy; Shanghai Jiao Tong University; Shanghai P. R. China
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