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Advances and Challenges in Flow Analysis and Capillary Electrophoresis

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Analytical Chemistry".

Deadline for manuscript submissions: closed (30 June 2023) | Viewed by 10248

Special Issue Editors

Centre for Nuclear Energy in Agriculture, University of Sao Paulo, Sao Paulo, Brazil
Interests: flow analysis; spectroanalysis
Center of Nuclear Energy in Agriculture (CENA), University of São Paulo, Piracicaba, Brazil
Interests: flow analysis; green analytical chemistry; spectroanalysis
Special Issues, Collections and Topics in MDPI journals
Department of Analytical Chemistry, Faculty of Chemistry, Jagiellonian University, Kraków, Poland
Interests: capillary electrophoresis; forensic chemistry
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

We are pleased to announce the launch of the Special Issue of Molecules dedicated to “Advances and Challenges in Flow Analysis and Capillary Electrophoresis”.

These analytical techniques are worldwide accepted and have experienced amazing developments in recent years, as they adhere to the current trends of miniaturization, flow regime modification, green analytical chemistry, expert systems, bioanalysis, chemical speciation, etc. Furthermore, the number of analytical methods that can only be accomplished by these techniques has experienced a sharp increase.

In flow analysis (FA), different physicochemical operations, such as extraction, preconcentration, and chemical derivatization are in-line performed in a closed environment. Sample handling is usually fast, cost-effective, safe, efficient and may include sample preparation and hyphenation with chromatography, capillary electrophoresis (CE), and other techniques. Simultaneous determinations and expert systems make FA attractive for large scale assays. Reaction kinetics, multivariate calibrations, and chemometrics are more straightforwardly exploited in view of its inherent mechanization and automation. To promote further improvements, portable detectors, novel sorbents and (nano)materials, image detection, paper (or similar) as a body of liquid movement and 3D-printing technology have been increasingly applied. Portable flow analysers for in situ or in vivo assays are also a reality. Gradient techniques, µLLE, and µSPE innovations adapted to flow conditions have been increasingly exploited.

Capillary electrophoresis or, more generally speaking, the capillary electromigration methods offer a wide variety of applications involving qualitative and quantitative analysis of small and large molecules, as well as physicochemical and thermodynamic studies on various types of equilibria (e.g., acid dissociation constant, binding constants, and lipophobicity). CE can be hyphenated with various types of detection techniques such as spectrophotometry, fluorescence, mass spectrometry, electrochemical systems, and capacitively coupled contactless conductivity detection (C4D). CE is also used to develop inexpensive, portable devices, open-hardware and expert systems, supported with chemometric and artificial intelligence software. Moreover, it can be performed in microchips, which is the important step towards miniaturization of analytical techniques. Finally, CE is recognized as a green analytical technique, as it provides accurate results operating at the limited amount of chemicals, sample, and energy, as well as producing low levels of waste.

We therefore warmly invite members of the FA-CE community to submit their original contributions to this Special Issue. We will be delighted to receive confirmation and proposed title by November 2022.

Dr. Elias A.G. Zagatto
Dr. Fábio Rodrigo Piovezani Rocha
Dr. Michał Woźniakiewicz
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • microfluidics
  • automation
  • miniaturization
  • green analytical chemistry
  • micro-extraction techniques
  • separation and preconcentration
  • calibration
  • speciation
  • capillary electrophoresis
  • chiral analysis, microchip electrophoresis
  • open source hardware

Published Papers (8 papers)

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Research

10 pages, 1162 KiB  
Communication
Copper (II) Ions Induced Self-Disproportionation of Enantiomers in Capillary Electrophoresis for the Quantification of Atenolol Enantiomers
by Shaoqiang Hu
Molecules 2023, 28(15), 5908; https://doi.org/10.3390/molecules28155908 - 06 Aug 2023
Cited by 2 | Viewed by 855
Abstract
Despite the fact that the self-disproportionation of enantiomers (SDE) has been found for several decades and has been widely used in crystallization, sublimation and chromatography for the purification or separation of nonracemic compounds, the phenomenon of SDE in capillary electrophoresis (CE) has never [...] Read more.
Despite the fact that the self-disproportionation of enantiomers (SDE) has been found for several decades and has been widely used in crystallization, sublimation and chromatography for the purification or separation of nonracemic compounds, the phenomenon of SDE in capillary electrophoresis (CE) has never been reported up to now. Here, a new approach to separate enantiomers in CE based on SDE was demonstrated by introducing copper (II) ions into the separation media. The enantiomers of atenolol interact with copper ions to produce positively charged complexes with different electrophoretic mobilities from the single molecules. The dynamic equilibrium between homo- or heterochiral complexes (associates) and single molecules of atenolol enantiomers supports the manifestation of SDE. Different mobilities of the single molecules and associates, and different distribution of two enantiomers between the single molecules and associates caused by their different concentrations, produce a net difference in electrodriven migration velocities of the two enantiomers. The relative movement of two enantiomers causes a zone depleted in one enantiomer at the rear end of sample segment, giving a trapezoidal CE curve with a step at the end. Quantification of enantiomers is achieved according to the step height. The analysis does not rely on the use of enantiomerically pure chiral selector and the result agrees with that obtained by conventional chiral CE using a chiral selector. Full article
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12 pages, 5452 KiB  
Article
Submicron Nonporous Silica Particles for Enhanced Separation Performance in pCEC
by Qing Liu, Chao Yan and Yan Wang
Molecules 2023, 28(8), 3542; https://doi.org/10.3390/molecules28083542 - 17 Apr 2023
Viewed by 1044
Abstract
Applications of submicron-scale particles are of rising interest in separation science due to their favorable surface-to-volume ratio and their fabrication of highly ordered structures. The uniformly dense packing beds in columns assembled from nanoparticles combined with an electroosmotic flow-driven system has great potential [...] Read more.
Applications of submicron-scale particles are of rising interest in separation science due to their favorable surface-to-volume ratio and their fabrication of highly ordered structures. The uniformly dense packing beds in columns assembled from nanoparticles combined with an electroosmotic flow-driven system has great potential in a highly efficient separation system. Here, we packed capillary columns using a gravity method with synthesized nanoscale C18-SiO2 particles having diameters of 300–900 nm. The separation of small molecules and proteins was evaluated in the packed columns on a pressurized capillary electrochromatography platform. The run-to-run reproducibility regarding retention time and peak area for the PAHs using a column packed with 300 nm C18-SiO2 particles were less than 1.61% and 3.17%, respectively. Our study exhibited a systematic separation analysis of small molecules and proteins based on the columns packed with submicron particles combined with the pressurized capillary electrochromatography (pCEC) platform. This study may provide a promising analytical approach with extraordinary column efficiency, resolution, and speed for the separation of complex samples. Full article
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14 pages, 2536 KiB  
Article
Transparent Cross-Flow Platform as Chemiluminescence Detection Cell in Cross Injection Analysis
by Thachkorn Somboonsuk, Phoonthawee Saetear, Thitirat Mantim, Nuanlaor Ratanawimarnwong, Prapin Wilairat, Nathawut Choengchan and Duangjai Nacapricha
Molecules 2023, 28(3), 1316; https://doi.org/10.3390/molecules28031316 - 30 Jan 2023
Viewed by 1294
Abstract
This work presents the use of a transparent ‘Cross Injection Analysis’ (CIA) platform as a flow system for chemiluminescence (CL) measurements. The CL-CIA flow device incorporates introduction channels for samples and reagents, and the reaction and detection channels are in one acrylic unit. [...] Read more.
This work presents the use of a transparent ‘Cross Injection Analysis’ (CIA) platform as a flow system for chemiluminescence (CL) measurements. The CL-CIA flow device incorporates introduction channels for samples and reagents, and the reaction and detection channels are in one acrylic unit. A photomultiplier tube placed above the reaction channel detects the emitted luminescence. The system was applied to the analysis of (i) Co(II) via the Co(II)-catalyzed H2O2-luminol reaction and (ii) paracetamol via its inhibitory effect on the catalytic activity of Fe(CN)63− on the H2O2-luminol reaction. A linear calibration was obtained for Co(II) in the range of 0.002 to 0.025 mg L−1 Co(II) (r2 = 0.9977) for the determination of Co(II) in water samples. The linear calibration obtained for the paracetamol was 10 to 200 mg L−1 (r2 = 0.9906) for the determination of pharmaceutical products. The sample throughput was 60 samples h−1. The precision was ≤4.2% RSD. The consumption of the samples and reagents was ca. 170 µL per analysis cycle. Full article
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10 pages, 1144 KiB  
Communication
Developed and Validated Capillary Isotachophoresis Method for the Rapid Determining Organic Acids in Children’s Saliva
by Justyna Dobrowolska-Iwanek, Małgorzata Jamka-Kasprzyk, Marcelina Rusin, Paweł Paśko, Sviatoslav Grekh and Anna Jurczak
Molecules 2023, 28(3), 1092; https://doi.org/10.3390/molecules28031092 - 21 Jan 2023
Cited by 2 | Viewed by 1450
Abstract
One of the current challenges facing researchers is the search for alternative biological material, as opposed to routinely and invasively collected (such as blood), as the analysis of the former would provide information about the state of human health, allowing for the diagnosis [...] Read more.
One of the current challenges facing researchers is the search for alternative biological material, as opposed to routinely and invasively collected (such as blood), as the analysis of the former would provide information about the state of human health, allowing for the diagnosis of diseases in their early stages. With the search for disease biomarkers in alternative materials, the development of newer analytical solutions has been observed. This study aims to develop a reliable analytical method using the capillary isotachophoresis technique for the determination of organic acids in children’s saliva, the presence/elevation of which can be used in the future for diagnostic purposes. Organic acids such as formic, lactic, acetic, propionic, and butyric acid, were determined in the saliva of healthy children without carious lesions. The limit of quantification determined in the validation process was found to vary from 0.05 to 1.56 mg/L, the recoveries at the two levels were determined to vary between 90% and 110% for level I, while for level II the corresponding values of 75% and 106% were found; the presentation, expressed as relative standard deviation values (RSD), did not exceed 5%. The parameters determined while validating the results method indicated that the obtained are reliable. The Red–Green–Blue (RGB) additive color model was used for the evaluation of the method. This comparative analysis allowed us to define the color of the method, which expresses whether it meets the given assumptions and requirements. According to the RGB model, the isotachophoresis method developed requires less reagent input, shorter sample preparation times, and results with lower energy consumption. Thus, the subject procedure may provide an alternative, routine tool for determining organic acids in human saliva, to be applied in the diagnosing of diseases of various etiological origins. Full article
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11 pages, 1312 KiB  
Article
A Multi-Pumping Gradient Calibration Module for Potentiometric Determination of Nitrate in Surface Water
by Sławomir Kalinowski, Paweł Kościelniak, Elwira Wierzbicka and Stanisława Koronkiewicz
Molecules 2023, 28(2), 493; https://doi.org/10.3390/molecules28020493 - 04 Jan 2023
Viewed by 1065
Abstract
The novel, automated, multi-pumping flow system (MPFS) for online calibration and determination of nitrate in surface water is presented for the first time. The system was equipped with micropumps of three different nominal volumes (10, 20, and 50 µL). As a result, it [...] Read more.
The novel, automated, multi-pumping flow system (MPFS) for online calibration and determination of nitrate in surface water is presented for the first time. The system was equipped with micropumps of three different nominal volumes (10, 20, and 50 µL). As a result, it was possible to prepare from one standard, directly in a flow system, up to seven standard solutions. Determination of nitrate was conducted in stop-flow conditions and is based on a commercially available ion selective electrode (ISE) application. It was found that the linearity and slope of the calibration graphs depend mainly on the characteristics of the ISE. The obtained results were very repeatable, owing to the high precision of the micro-pumps used. The R.S.D. for the stroke volume of each micro-pump was below 1%. The accuracy of the method was checked through determination of nitrate in surface water samples. The obtained results were compared with those of the reference method (photometric Hach cuvette tests). It was found that, at a 96% confidence level, the difference between the results obtained by the proposed method and the reference method was statistically insignificant. The accuracy of the method was confirmed through the determination of nitrate in Certified Reference Material. The relative deviation (R.D.) of the measured and the certified concentrations was 5%. Full article
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14 pages, 3287 KiB  
Article
Sequential Injection Amperometric System Coupling with Bioreactor for In-Line Glucose Monitoring in Cell Culture Application
by Chanyanut Wongsa, Suruk Udomsom, Apiwat Budwong, Kanokwan Kiwfo, Kate Grudpan and Pathinan Paengnakorn
Molecules 2022, 27(19), 6665; https://doi.org/10.3390/molecules27196665 - 07 Oct 2022
Cited by 4 | Viewed by 1330
Abstract
We proposed a specially designed sequential injection (SI) amperometric system coupling with a bioreactor for in-line glucose monitoring in cell culture. The system is composed of three main parts which are the bioreactor, SI system, and electrochemical detection unit. The bioreactor accommodates six [...] Read more.
We proposed a specially designed sequential injection (SI) amperometric system coupling with a bioreactor for in-line glucose monitoring in cell culture. The system is composed of three main parts which are the bioreactor, SI system, and electrochemical detection unit. The bioreactor accommodates six individual cell culture units which can be operated separately under different conditions. The SI system enables automatic in-line sampling and in-line sample dilution, with a specially designed mixing unit; therefore, it has the benefits of fast analysis time and less contamination risk. The use of 3D-printed microfluidic components, a mixing channel, and a flow cell helped to reduce operational time and sample volume. A disposable screen-printed electrode (SPE), modified with glucose oxidase (GOD), carbon nanotube, and gold nanoparticle, was used for detection. The developed system provided a linear range up to 3.8 mM glucose in cell culture media. In order to work with cell culture in higher glucose media, the in-line sample dilution can be applied. The developed SI system was demonstrated with mouse fibroblast (L929) cell culture. The results show that glucose concentration obtained from the SI system is comparable with that obtained from the conventional colorimetric method. This work can be further developed and applied for in vitro cell-based experiments in biomedical research. Full article
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14 pages, 2071 KiB  
Article
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
by Paweł Mateusz Nowak, Maria Klag, Gabriela Kózka, Małgorzata Gołąb and Michał Woźniakiewicz
Molecules 2022, 27(15), 5010; https://doi.org/10.3390/molecules27155010 - 06 Aug 2022
Cited by 2 | Viewed by 1356
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 [...] Read more.
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. Full article
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9 pages, 1412 KiB  
Communication
Determination of Phenolic Compounds by Capillary Zone Electrophoresis–Mass Spectrometry
by Ruben Szabo and Attila Gaspar
Molecules 2022, 27(14), 4540; https://doi.org/10.3390/molecules27144540 - 16 Jul 2022
Cited by 3 | Viewed by 1226
Abstract
A CZE-MS method was developed for the determination of several phenolic compounds (phenolic acids, flavonoids). Since the analysis of these components necessitates the application of basic conditions for CZE separation and negative ionization mode for MS detection, the simplest choice was to use [...] Read more.
A CZE-MS method was developed for the determination of several phenolic compounds (phenolic acids, flavonoids). Since the analysis of these components necessitates the application of basic conditions for CZE separation and negative ionization mode for MS detection, the simplest choice was to use 0.5 M NH4OH and IPA:water (1:1 v/v%) as the background electrolyte and sheath liquid, respectively. The LOD values ranged between 0.004–1.9 mg/L showing that there are relatively large differences in the ionization (and chemical) features of these compounds. The precision data were better than 0.75 RSD% for migration times and were between 5–8 RSD% for peak areas. In order to test the applicability of the developed method, a honey sample was analyzed. Full article
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