1
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De Silva M, Opallage PM, Dunn RC. Investigation of induced electroosmotic flow in small-scale capillary electrophoresis devices: Strategies for control and reversal. Electrophoresis 2024. [PMID: 39054801 DOI: 10.1002/elps.202400107] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2024] [Revised: 07/02/2024] [Accepted: 07/17/2024] [Indexed: 07/27/2024]
Abstract
Electroosmotic flow (EOF) is the bulk flow of solution in a capillary or microchannel induced by an applied electric potential. For capillary and microchip electrophoresis, the EOF enables analysis of both cations and anions in one separation and can be varied to modify separation speed and resolution. The EOF arises from an electrical double layer at the capillary wall and is normally controlled through the pH and ionic strength of the background buffer or with the use of additives. Understanding and controlling the electrical double layer is therefore critical for maintaining acceptable repeatability during method development. Surprisingly, in fused silica capillaries at low pH, studies observe an EOF even though the capillary surface should be neutralized. Previous work has suggested the presence of an "induced electroosmotic flow" from radial electric fields generated across the capillary wall due to the separation voltage and grounded components external to the capillary. Using thin-wall (15 µm) fused silica separation capillaries to facilitate the study of radial fields, we show that the EOF mobility depends on both the separation voltage and the location of external grounds. This is consistent with the induced EOF model, in which radial electric fields embed positive charges at the capillary walls to create an electrical double layer. The magnitude of the effect is characterized and shown to have long-range influences that are difficult to completely null by moving grounded components away from the separation capillary. Instead, active EOF control using externally applied potentials or a passive approach using a negative separation voltage are discussed as two possible methods for controlling the induced EOF. Both methods can reverse the EOF and improve the resolution and peak efficiency in amino acid separations.
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Affiliation(s)
- Miyuru De Silva
- Department of Chemistry, Ralph N. Adams Institute for Bioanalytical Chemistry, University of Kansas, Lawrence, Kansas, USA
| | - Prabhavie M Opallage
- Department of Chemistry, Ralph N. Adams Institute for Bioanalytical Chemistry, University of Kansas, Lawrence, Kansas, USA
| | - Robert C Dunn
- Department of Chemistry, Ralph N. Adams Institute for Bioanalytical Chemistry, University of Kansas, Lawrence, Kansas, USA
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2
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Štěpánová S, Andris E, Gutten O, Buděšínský M, Dejmek M, Břehová P, Rulíšek L, Kašička V. Acidity constants and protonation sites of cyclic dinucleotides determined by capillary electrophoresis, quantum chemical calculations, and NMR spectroscopy. Electrophoresis 2024; 45:687-705. [PMID: 38059733 DOI: 10.1002/elps.202300232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2023] [Revised: 11/11/2023] [Accepted: 11/18/2023] [Indexed: 12/08/2023]
Abstract
Cyclic dinucleotides (CDNs) are important second messengers in bacteria and eukaryotes. Detailed characterization of their physicochemical properties is a prerequisite for understanding their biological functions. Herein, we examine acid-base and electromigration properties of selected CDNs employing capillary electrophoresis (CE), density functional theory (DFT), and nuclear magnetic resonance (NMR) spectroscopy to provide benchmark pKa values, as well as to unambiguously determine the protonation sites. Acidity constants (pKa) of the NH+ moieties of adenine and guanine bases and actual and limiting ionic mobilities of CDNs were determined by nonlinear regression analysis of the pH dependence of their effective electrophoretic mobilities measured by CE in aqueous background electrolytes in a wide pH range (0.98-11.48), at constant temperature (25°C), and constant ionic strength (25 mM). The thermodynamic pKa values were found to be in the range 3.31-4.56 for adenine and 2.28-3.61 for guanine bases, whereas the pKa of enol group of guanine base was in the range 10.21-10.40. Except for systematic shifts of ∼2 pKa, the pKa values calculated by the DFT-D3//COSMO-RS composite protocol that included large-scale conformational sampling and "cross-morphing" were in a relatively good agreement with the pKas determined by CE and predict N1 atom of adenine and N7 atom of guanine as the protonation sites. The protonation of the N1 atom of adenine and N7 atom of guanine in acidic background electrolytes (BGEs) and the dissociation of the enol group of guanine in alkaline BGEs was confirmed also by NMR spectroscopy.
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Affiliation(s)
- Sille Štěpánová
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Prague, Czech Republic
| | - Erik Andris
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Prague, Czech Republic
| | - Ondrej Gutten
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Prague, Czech Republic
| | - Miloš Buděšínský
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Prague, Czech Republic
| | - Milan Dejmek
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Prague, Czech Republic
| | - Petra Břehová
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Prague, Czech Republic
| | - Lubomír Rulíšek
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Prague, Czech Republic
| | - Václav Kašička
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Prague, Czech Republic
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3
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Nowak PM, Biel I, Kózka G, Klag M, Woźniakiewicz M. Influence of pH measurement inaccuracy on the values of acidity constant determined on the basis of electrophoretic and thermophoretic data. Microchem J 2022. [DOI: 10.1016/j.microc.2022.107689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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4
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The First Online Capillary Electrophoresis-Microscale Thermophoresis (CE-MST) Method for the Analysis of Dynamic Equilibria-The Determination of the Acidity Constant of Fluorescein Isothiocyanate. Molecules 2022; 27:molecules27155010. [PMID: 35956959 PMCID: PMC9370695 DOI: 10.3390/molecules27155010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Revised: 08/02/2022] [Accepted: 08/04/2022] [Indexed: 11/18/2022] Open
Abstract
This article presents the first successful application of a capillary electrophoresis-microscale thermophoresis tandem technique (CE-MST) for determining the values of equilibrium constant, realized by connecting online the CE and MST instruments using a fused-silica capillary. The acid-base dissociation of fluorescein isothiocyanate, expressed by the acidity constant value (pKa), was used as a model. The measurement procedure consisted of introducing a mixture containing the analyte and a deliberately added interferent into the CE capillary, electrophoretic separation of the analyte from the interferent, the detection of the analyte with a CE-integrated detector, detection with a MST detector, and then stopping the flow temporarily by turning off the voltage source to conduct the thermophoretic measurement. The analysis of migration times, peak areas and MST responses obtained concurrently for the same sample allowed us to determine the pKa value using three independent methods integrated within one instrumentation. The analyte was effectively separated from the interferent, and the acidity values turned out to be consistent with each other. An attempt was also made to replace the standard commercial CE instrument with a home-made portable CE setup. As a result, the similar pKa value was obtained, at the same time proving the possibility of increasing cost efficiency and reducing energy consumption. Overall, the CE-MST technique has a number of limitations, but its unique analytical capabilities may be beneficial for some applications, especially when sample separation is needed prior to the thermophoretic measurement.
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5
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Šolínová V, Štěpánová S, Jančařík A, Klívar J, Šámal M, Stará IG, Chocholoušová JV, Vacek J, Starý I, Kašička V. Nonaqueous capillary electrophoresis and quantum chemical calculations applied to investigation of acid-base and electromigration properties of azahelicenes. Electrophoresis 2021; 43:696-707. [PMID: 34933403 DOI: 10.1002/elps.202100331] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Revised: 12/06/2021] [Accepted: 12/16/2021] [Indexed: 11/07/2022]
Abstract
Nonaqueous capillary electrophoresis (NACE) using methanol (MeOH) as a solvent of the BGEs and quantum mechanical density functional theory (DFT) have been applied to determine the thermodynamic acidity (ionization) constants (pKa ) of mono- and diaza[5]helicenes, mono- and diaza[6]helicenes, and their dibenzo derivatives in MeOH and water. First, the mixed acidity constants, p K a , MeOH mix , of ionogenic pyridinium groups of azahelicenes and their derivatives in MeOH were obtained by nonlinear regression analysis of pH dependence of their effective electrophoretic mobilities. The effective mobilities were measured by NACE in a large series of methanolic BGEs within a wide conventional pH range (pHMeOH 1.6-12.0) and at ambient temperature (21-26°C) in a home-made CE device. Prior to mixed acidity constant calculation, the effective mobilities were corrected to reference temperature (25°C) and constant ionic strength (25 mM). Then, the mixed acidity constants were recalculated to the thermodynamic acidity constants pKa,MeOH by the Debye-Hückel theory of nonideality of electrolyte solutions. Finally, from the methanolic thermodynamic pKa,MeOH values, the aqueous thermodynamic p K a , H 2 O constants were estimated using the empirical relations between methanolic and aqueous acidity constants derived for structurally related pyridine derivatives. Depending on the number and position of the nitrogen atoms in their molecules, the analyzed azahelicenes were found to be weak to moderate bases with methanolic pKa,MeOH in the range 2.01-8.75 and with aqueous p K a , H 2 O in the range 1.67-8.28. The thermodynamic pKa,MeOH obtained by the DFT calculations were in a good agreement with those determined experimentally by NACE.
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Affiliation(s)
- Veronika Šolínová
- Institute of Organic Chemistry and Biochemistry, The Czech Academy of Sciences, Czech Republic
| | - Sille Štěpánová
- Institute of Organic Chemistry and Biochemistry, The Czech Academy of Sciences, Czech Republic
| | - Andrej Jančařík
- Institute of Organic Chemistry and Biochemistry, The Czech Academy of Sciences, Czech Republic
| | - Jiří Klívar
- Institute of Organic Chemistry and Biochemistry, The Czech Academy of Sciences, Czech Republic
| | - Michal Šámal
- Institute of Organic Chemistry and Biochemistry, The Czech Academy of Sciences, Czech Republic
| | - Irena G Stará
- Institute of Organic Chemistry and Biochemistry, The Czech Academy of Sciences, Czech Republic
| | | | - Jaroslav Vacek
- Institute of Organic Chemistry and Biochemistry, The Czech Academy of Sciences, Czech Republic
| | - Ivo Starý
- Institute of Organic Chemistry and Biochemistry, The Czech Academy of Sciences, Czech Republic
| | - Václav Kašička
- Institute of Organic Chemistry and Biochemistry, The Czech Academy of Sciences, Czech Republic
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Nowak PM, Mitoraj M, Sagan F, Wietecha-Posłuszny R. Differentiation of isomeric metabolites of carbamazepine based on acid-base properties; Experimental vs theoretical approach. J Chromatogr A 2021; 1651:462275. [PMID: 34090055 DOI: 10.1016/j.chroma.2021.462275] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Revised: 05/14/2021] [Accepted: 05/18/2021] [Indexed: 01/01/2023]
Abstract
Metabolism of carbamazepine is complex and leads to the three isomeric derivatives whose occurrence is dependent on the type of sample material. Their unambiguous differentiation is overall important. In this work, the qualitative analysis of 2-hydroxycarbamazepine, 3-hydroxycrbamazepine and carbamazepine-10,11-epoxide was attempted for the first time using capillary zone electrophoresis, based on the models linking electrophoretic mobility with pKa value determining the acidity of the hydroxyl groups. For this purpose, pKa values were determined using electrophoretic and theoretical methods, and then the compliance of the obtained mobility models with the measured values was analyzed. Despite the slight difference in acidity (0.3-0.4 pH unit), the obtained results prove that the correct identification of the metabolites under consideration, and reliable prediction of the selectivity of their separation, are possible on the basis of experimentally determined pKa values, even with highly simplified methods assuming the lack of certain data. However, it is important to choose the optimal pH value, which should be close to pKa. On the other hand, worse results were obtained for the theoretically determined mobilities, which differed significantly from the experimental values. An attempt was also made to explain the acidity of hydroxycarbamazepines and the associated thermodynamic parameters - deprotonation enthalpy and entropy, with respect to their structure. The lack of intramolecular hydrogen bonds and the significant contribution of entropic effects stabilizing the protonated form seems to be significant. The higher pKa value for CBZ-2-OH probably results from the stronger effect of the energetically unfavorable organization of solvent dipoles due to ionization.
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Affiliation(s)
- Paweł Mateusz Nowak
- Jagiellonian University in Kraków, Faculty of Chemistry, Department of Analytical Chemistry, Gronostajowa St. 2, 30-387 Kraków, Poland.
| | - Mariusz Mitoraj
- Jagiellonian University in Kraków, Faculty of Chemistry, Department of Theoretical Chemistry, Gronostajowa St. 2, 30-387 Kraków, Poland
| | - Filip Sagan
- Jagiellonian University in Kraków, Faculty of Chemistry, Department of Theoretical Chemistry, Gronostajowa St. 2, 30-387 Kraków, Poland
| | - Renata Wietecha-Posłuszny
- Jagiellonian University in Kraków, Faculty of Chemistry, Department of Analytical Chemistry, Gronostajowa St. 2, 30-387 Kraków, Poland
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7
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Martínková E, Křížek T, Kubíčková A, Coufal P. Mobilization of electroosmotic flow markers in capillary zone electrophoresis. Electrophoresis 2021; 42:932-938. [PMID: 33570209 DOI: 10.1002/elps.202000301] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2020] [Revised: 02/05/2021] [Accepted: 02/05/2021] [Indexed: 11/11/2022]
Abstract
UV-absorbing neutral substances are commonly used as markers of mean electroosmotic flow in capillary electrophoresis for their zero electrophoretic mobility in an electric field. However, some of these markers can interact with background electrolyte components and migrate at a different velocity than the electroosmotic flow. Thus, we tested 11 markers primarily varying in their degree of methylation and type of central atom in combination with five background electrolyte cations differing in their ionic radii and surface charge density, measuring the relative electrophoretic mobility using thiourea as a reference marker. Our results from this set of experiments showed some general trends in the mobilization of the markers based on the effects of marker structure and type of background electrolyte cation on the relative electrophoretic mobility. As an example, the effects of an inadequate choice of marker on analyte identification were illustrated in the electrophoretic separation of glucosinolates. Therefore, our findings may help electrophoretists appropriately select electroosmotic flow markers for various electrophoretic systems.
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Affiliation(s)
- Eva Martínková
- Department of Analytical Chemistry, Faculty of Science, Charles University, Prague, Czech Republic
| | - Tomáš Křížek
- Department of Analytical Chemistry, Faculty of Science, Charles University, Prague, Czech Republic
| | - Anna Kubíčková
- Department of Analytical Chemistry, Faculty of Science, Charles University, Prague, Czech Republic
| | - Pavel Coufal
- Department of Analytical Chemistry, Faculty of Science, Charles University, Prague, Czech Republic
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8
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Generalized model of the linear theory of electromigration and its application to electrokinetic chromatography: Capillary zone electrophoretic systems with complex-forming equilibria. J Chromatogr A 2020; 1610:460595. [DOI: 10.1016/j.chroma.2019.460595] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2019] [Revised: 09/27/2019] [Accepted: 09/30/2019] [Indexed: 12/25/2022]
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9
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Acidity constant of pH indicators in the supramolecular systems studied by two CE-based methods compared using the RGB additive color model. Anal Bioanal Chem 2019; 412:577-588. [PMID: 31838556 DOI: 10.1007/s00216-019-02289-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Revised: 10/31/2019] [Accepted: 11/14/2019] [Indexed: 02/07/2023]
Abstract
Acid-base properties of methyl orange, bromocresol green, bromophenol blue, and bromothymol blue were thoroughly investigated in the past due to their application as colorimetric pH indicators. However, it is still unknown how these properties change upon the supramolecular host-guest interactions. Owing to the growing interest in using supramolecular host-guest interactions to reach expected modification of various physicochemical properties of guests, we decided to address this question in the present article. We estimated the shifts of pKa values induced by diverse hosts (cyclodextrins, cucurbiturils, calixarenes, micelles, and serum albumin) and performed a thermodynamic analysis of the selected systems. To make a deeper insight, we confronted the aforementioned dyes with the other kinds of molecules studied by us in the past. In overall, the results obtained demonstrate a large multiplicity of possible pKa behaviors, their poor predictability, and the existence of subtle structure-acidity relationships. In addition, we observed three thermodynamically different mechanisms of pKa alteration. Therefore, more studies are needed to bring closer the promising perspective of a programmable acidity's tuning. Our methodology was based on capillary electrophoresis (CE) applied in two parallel variants: a classical method based on the fitting of a nonlinear function, and an alternative two-value method (TVM), which requires over twice less measurements to estimate pKa. To identify the optimal approach for further studies, both methods were comprehensively compared and discussed based on the RGB additive color model, a user-friendly scale that integrates three primary aspects of an analytical method: analytical performance, green chemistry, and practicality.
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10
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Sajjadi SH, Goharshadi EK, Ahmadzadeh H. Heat dissipation in slab gel electrophoresis: The effect of embedded TiO 2 nanoparticles on the thermal profiles. J Chromatogr B Analyt Technol Biomed Life Sci 2019; 1118-1119:63-69. [PMID: 31029035 DOI: 10.1016/j.jchromb.2019.04.030] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2018] [Revised: 03/13/2019] [Accepted: 04/14/2019] [Indexed: 12/28/2022]
Abstract
Despite the fast development of novel and high-resolution electrophoresis techniques such as capillary-based methods and microfluidic devices, the slab gel electrophoresis is still a popular method for the separation of biomolecules in medicine and biology. It is a low cost and simple method and offers high throughput. However, this technique is limited to low voltages leading to slow separations. Producing the heat during the electrophoresis known as Joule heating inevitably leads to a rise in the gel temperature. For the first time, this work offers a whole gel temperature measurement by using a thermal camera which presents accurate temperature profiles in the gel with a resolution of more than 10 pixel/mm2 and a precision of 0.1 °C. Titania, TiO2, nanoparticles (NPs) were embedded into the polyacrylamide (PA) gel to improve the electrophoretic separation of proteins. By embedding 0.025% w/v TiO2 NPs, heat dissipation increases by 16.5% at applied voltage of 200 V compared with that of PA gel with no embedded TiO2 NPs. The thermal images showed that the composite gel was 2.5 °C in average cooler than PA gel after 15 min of electrophoresis run at 200 V. The maximum separation voltage increased by 30 V in the composite PA/TiO2 gel compared with the pure PA gel. Moreover, the average number of theoretical plates over the 10 protein peaks, as a criterion of separation performance, increased by about 63% at 180 V when TiO2 NPs were included into the gel.
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Affiliation(s)
- Sayyed Hashem Sajjadi
- Chemistry Department, Faculty of Science, Ferdowsi University of Mashhad, Mashhad 9177948974, Iran
| | - Elaheh K Goharshadi
- Chemistry Department, Faculty of Science, Ferdowsi University of Mashhad, Mashhad 9177948974, Iran; Nano Research Center, Ferdowsi University of Mashhad, Mashhad 9177948974, Iran.
| | - Hossein Ahmadzadeh
- Chemistry Department, Faculty of Science, Ferdowsi University of Mashhad, Mashhad 9177948974, Iran
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11
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Cyclodextrin-induced acidity modification of substituted cathinones studied by capillary electrophoresis supported by density functional theory calculations. J Chromatogr A 2018; 1580:142-151. [DOI: 10.1016/j.chroma.2018.10.036] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Revised: 10/08/2018] [Accepted: 10/16/2018] [Indexed: 11/22/2022]
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12
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Konášová R, Koval D, Dytrtová JJ, Kašička V. Comparison of two low flow interfaces for measurement of mobilities and stability constants by affinity capillary electrophoresis–mass spectrometry. J Chromatogr A 2018; 1568:197-204. [DOI: 10.1016/j.chroma.2018.07.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2018] [Revised: 06/28/2018] [Accepted: 07/04/2018] [Indexed: 12/19/2022]
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13
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Woźniakiewicz M, Nowak PM, Gołąb M, Adamowicz P, Kała M, Kościelniak P. Acidity of substituted cathinones studied by capillary electrophoresis using the standard and fast alternative approaches. Talanta 2018; 180:193-198. [DOI: 10.1016/j.talanta.2017.12.025] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Revised: 12/08/2017] [Accepted: 12/11/2017] [Indexed: 11/26/2022]
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14
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Nowak PM, Woźniakiewicz M, Kościelniak P. Flow variation as a factor determining repeatability of the internal standard-based qualitative and quantitative analyses by capillary electrophoresis. J Chromatogr A 2018; 1548:92-99. [PMID: 29559267 DOI: 10.1016/j.chroma.2018.03.026] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2018] [Revised: 03/08/2018] [Accepted: 03/13/2018] [Indexed: 11/30/2022]
Abstract
The use of migration times and peak areas referred to another sample component - internal standard, brings many benefits in improving reliability of capillary electrophoresis. However, it is quite commonly overlooked that despite relative migration time and peak area ratio are more stable than the absolute values upon alteration in the flow rate, some shift should always be expected. The present work offers a new look at this analytically-important issue. We have derived a simple model allowing to estimate the magnitude of error for the selected pair of molecules of known mobilities upon the given flow alteration. Then, we have confronted the theoretical predictions with the experimental results obtained for the model sample separated in various flow conditions reached by the external pressure manipulation, including several internal standards of different mobilities. A good agreement has been obtained, pointing out that the magnitude of error may be large even for the seemingly "good" internal standards. Several potentially useful means have been tested to address this issue: the use of electrophoretic mobilities and electrophoretic mobility ratios instead migration times in the qualitative analysis, and performing time-correction of peak area ratios, or alternatively, transformation of electropherograms from the time-related scale into the electrophoretic mobility-related scale in the quantitative analysis. We have also considered some additional factors. The results may be of interest for all users dealing with the development and optimization of analytical methods using capillary electrophoresis.
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Affiliation(s)
- Paweł Mateusz Nowak
- Jagiellonian University in Kraków, Faculty of Chemistry, Department of Analytical Chemistry, Gronostajowa St. 2, 30-387 Kraków, Poland.
| | - Michał Woźniakiewicz
- Jagiellonian University in Kraków, Faculty of Chemistry, Department of Analytical Chemistry, Gronostajowa St. 2, 30-387 Kraków, Poland
| | - Paweł Kościelniak
- Jagiellonian University in Kraków, Faculty of Chemistry, Department of Analytical Chemistry, Gronostajowa St. 2, 30-387 Kraków, Poland
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15
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Thermodynamics of acid-base dissociation of several cathinones and 1‐phenylethylamine, studied by an accurate capillary electrophoresis method free from the Joule heating impact. J Chromatogr A 2018; 1539:78-86. [DOI: 10.1016/j.chroma.2018.01.047] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2017] [Revised: 01/17/2018] [Accepted: 01/21/2018] [Indexed: 12/12/2022]
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16
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Nowak PM, Woźniakiewicz M, Gładysz M, Janus M, Kościelniak P. Improving repeatability of capillary electrophoresis-a critical comparison of ten different capillary inner surfaces and three criteria of peak identification. Anal Bioanal Chem 2017; 409:4383-4393. [PMID: 28484810 PMCID: PMC5486911 DOI: 10.1007/s00216-017-0382-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Revised: 04/18/2017] [Accepted: 04/25/2017] [Indexed: 01/30/2023]
Abstract
A poor repeatability of migration times caused by the fluctuations of electroosmotic flow (EOF) is an inherent weakness of capillary electrophoresis. Most researchers endeavor to prevent this problem using relative migration times or various capillary coatings which are expensive and not easy in comparison. Herein, we present an original approach to this problem: we apply a model sample designed to induce significant EOF instability, in order to critically compare ten capillary types with different physicochemical characteristics. Moreover, we accompany capillary modification with the evaluation of various criteria of peak identification: migration time, migration times ratio, and electrophoretic mobility. Our results show a great effectiveness of a dynamic coating in the stabilization of migration times, with the average RSD(%) value reduced from 3.5% (bare silica capillary) down to 0.5%. The good outcomes were also obtained for the surfactant-modified silica and amine capillaries. For the capillaries exhibiting significant instability of EOF, electrophoretic mobility turned out to be a more universal and reliable criterion of peak identification than relative migration time. It can be explained by an intrinsic dependency of migration times ratio on EOF change, which should always be considered during the selection of an internal standard.
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Affiliation(s)
- Paweł Mateusz Nowak
- Faculty of Chemistry, Department of Analytical Chemistry, Jagiellonian University in Kraków, Ingardena St. 3, 30-060, Kraków, Poland.
| | - Michał Woźniakiewicz
- Faculty of Chemistry, Department of Analytical Chemistry, Jagiellonian University in Kraków, Ingardena St. 3, 30-060, Kraków, Poland
| | - Marta Gładysz
- Faculty of Chemistry, Department of Analytical Chemistry, Jagiellonian University in Kraków, Ingardena St. 3, 30-060, Kraków, Poland
| | - Magdalena Janus
- Faculty of Chemistry, Department of Analytical Chemistry, Jagiellonian University in Kraków, Ingardena St. 3, 30-060, Kraków, Poland
| | - Paweł Kościelniak
- Faculty of Chemistry, Department of Analytical Chemistry, Jagiellonian University in Kraków, Ingardena St. 3, 30-060, Kraków, Poland
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17
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Nowak PM, Sagan F, Mitoraj MP. Origin of Remarkably Different Acidity of Hydroxycoumarins—Joint Experimental and Theoretical Studies. J Phys Chem B 2017; 121:4554-4561. [DOI: 10.1021/acs.jpcb.7b01849] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Paweł Mateusz Nowak
- Faculty
of Chemistry, Department of Analytical Chemistry, Jagiellonian University in Kraków, Ingardena 3, 30-060 Kraków, Poland
| | - Filip Sagan
- Faculty
of Chemistry, Department of Theoretical Chemistry, Jagiellonian University in Kraków, Ingardena 3, 30-060 Kraków, Poland
| | - Mariusz Paweł Mitoraj
- Faculty
of Chemistry, Department of Theoretical Chemistry, Jagiellonian University in Kraków, Ingardena 3, 30-060 Kraków, Poland
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Nowak PM, Śpiewak K, Woźniakiewicz M, Kościelniak P. Minimizing the impact of Joule heating as a prerequisite for the reliable analysis of metal‐protein complexes by capillary electrophoresis. J Chromatogr A 2017; 1495:83-87. [DOI: 10.1016/j.chroma.2017.03.028] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Revised: 03/14/2017] [Accepted: 03/16/2017] [Indexed: 11/29/2022]
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Enhancing effectiveness of capillary electrophoresis as an analytical tool in the supramolecular acidity modification. Anal Bioanal Chem 2017; 409:3633-3643. [PMID: 28341986 PMCID: PMC5406438 DOI: 10.1007/s00216-017-0305-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Revised: 03/01/2017] [Accepted: 03/08/2017] [Indexed: 12/15/2022]
Abstract
A strategic modification of acidity (pKa values) by the non-covalent host-guest interactions is one of the most promising concepts in current supramolecular chemistry. This work is aimed at enhancing the effectiveness of capillary electrophoresis (CE) in determination of pKa shifts caused by such interactions and their thermal dependencies crucial in a deep thermodynamic description. We show how to (i) minimize the systematic errors related to Joule heating, (ii) minimize the influence of a voltage ramp time, (iii) speed up pKa shift identification and estimation, (iv) interpret thermal effects related to two overlapped dynamic equilibria, and (v) determine pKa shifts by an alternative spectrophotometric method (CE-DAD). The proposed solutions were implemented to examine the supramolecular pKa shifts of several coumarin derivatives, caused by a variety of structurally different cyclodextrins. It was revealed that a specific host substitution pattern determines the magnitude of apparent pKa shifts. Accordingly, heptakis(2,6-di-O-methyl)-β-cyclodextrin induces the much stronger shifts than both non-methylated-β-cyclodextrin and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin applied at the same concentration. We also show that insofar as the complexation of 4-hydroxycoumarin and its derivative (coumatetralyl) are similarly exothermic, the thermal effects accompanying the deprotonation process are remarkably different for both molecules. The pKa shift induced by complexation with calixarene was also for the first time determined by a CE method. These observations throw a new light on the background of acidity modification and confirm the applicability of CE as an analytical tool.
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