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Separations
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Recent Advances on Ionic Liquid Uses in Separation Techniques
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Recent Advances on Ionic Liquid Uses in Separation Techniques

A special issue of Separations (ISSN 2297-8739).

Deadline for manuscript submissions: closed (30 November 2020) | Viewed by 30190

Special Issue Editors

Prof. Dr. María José Ruiz-Angel

E-Mail Website
Guest Editor
Departament de Química Analítica, Universitat de Valencia, Valencia, Spain
Interests: secondary equilibria using surfactants and ionic liquids; fundamental studies in HPLC; modelling and optimisation in HPLC; development of analytical methods for pharmaceutical and clinical samples
Prof. Dr. Samuel Carda-Broch

E-Mail Website
Guest Editor
Universitat Jaume I, Departament de Química Física i Analítica, Castelló, Spain
Interests: applied analysis; micellar liquid chromatography; countercurrent chromatography; ionic liquids in chemical analysis

Special Issue Information

Dear Colleagues,

Interest concerning ionic liquids in chemical analysis has grown considerably in the last decade, as evidenced by the large number of publications released every year. Their favourable properties, such as negligible vapour pressure, high thermal stability or unique solvating capability make ionic liquids suitable candidates to be used in numerous applications, especially in the fields of separation techniques. In addition, properties, such as viscosity or water solubility, can be tuned combining the associated anion and cation to modulate their utility. Further, the quest for new ionic liquids has led to the introduction of deep eutectic solvents, which are not exactly ionic liquids but a promising new class of solvents with similar properties. Deep eutectic solvents enable work with non-aqueous biphasic systems and show great promise in the separation of hydrophobic compounds.

All the continued research involving ionic liquids is continuously presented in books and Special Issues such as the one we are presenting here. This Special Issue invites contributions, as original research articles or reviews, on the current advances in and application of ionic liquids in separation techniques, especially focused on chromatography, extraction for sample preparation, or other related techniques.

Prof. Dr. María José Ruiz-Angel
Prof. Dr. Samuel Carda-Broch
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. Separations is an international peer-reviewed open access monthly 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 2600 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

  • Ionic liquids
  • Deep eutectic solvents
  • Liquid chromatography
  • Gas chromatography
  • Capillary electrophoresis
  • Extraction techniques
  • Sample preparation

Published Papers (5 papers)

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Editorial

Jump to: Research, Review

4 pages, 220 KiB  
Editorial
Recent Advances on Ionic Liquid Uses in Separation Techniques
by María José Ruiz-Ángel and Samuel Carda-Broch
Separations 2022, 9(4), 96; https://doi.org/10.3390/separations9040096 - 11 Apr 2022
Cited by 2 | Viewed by 1999
Abstract
Ionic liquids (ILs) are non-molecular solvents; specifically, molten salts with low melting points, often below 100 °C and even below room temperature, thus allowing these solvents to remain liquid [...] Full article
(This article belongs to the Special Issue Recent Advances on Ionic Liquid Uses in Separation Techniques)

Research

Jump to: Editorial, Review

13 pages, 1170 KiB  
Article
Hydrophilic Liquid Chromatography versus Reversed-Phase Liquid Chromatography in the Absence and the Presence of 1-Hexyl-3-methylimidazolium Chloride for the Analysis of Basic Compounds
by Ester Peris-García, Raquel Burgos-Gil, María Celia García-Alvarez-Coque and María José Ruiz-Angel
Separations 2020, 7(2), 30; https://doi.org/10.3390/separations7020030 - 29 May 2020
Cited by 5 | Viewed by 3054
Abstract
In reversed-phase liquid chromatography (RPLC), positively charged basic compounds yield broad and asymmetric peaks, as a result of ionic interactions with free silanols that remain on conventional silica-based columns. Diverse solutions have been proposed to mask the silanophilic activity, which is translated to [...] Read more.
In reversed-phase liquid chromatography (RPLC), positively charged basic compounds yield broad and asymmetric peaks, as a result of ionic interactions with free silanols that remain on conventional silica-based columns. Diverse solutions have been proposed to mask the silanophilic activity, which is translated to an improved peak shape. In this work, the chromatographic performance of hydrophilic interaction liquid chromatography (HILIC) was evaluated as an alternative to the addition of an ionic liquid (IL) to the aqueous-organic mobile phase used with RPLC columns, for the analysis of eight β-adrenoceptor antagonists. ILs change the behavior of RPLC stationary phases owing to adsorption on their surface. Meanwhile, in HILIC, a layer of adsorbed water is formed on the stationary phase surface. The association of cationic basic compounds with the adsorbed additive ions, hydrophilic partitioning on the HILIC columns, and other interactions, give rise to complex retention mechanisms. The chromatographic behavior was examined in terms of retention, elution strength, selectivity, peak shape and resolution, using acetonitrile-water mobile phases buffered at pH 3. Both chromatographic modes, RPLC with added IL and HILIC, proved to be a viable solution to the problem of poor peak shape for basic compounds. Full article
(This article belongs to the Special Issue Recent Advances on Ionic Liquid Uses in Separation Techniques)
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10 pages, 918 KiB  
Article
Estimation of Solute-Stationary Phase and Solute-Mobile Phase Interactions in the Presence of Ionic Liquids
by María José Ruiz-Ángel
Separations 2019, 6(3), 40; https://doi.org/10.3390/separations6030040 - 13 Aug 2019
Cited by 1 | Viewed by 3432
Abstract
The presence of free silanols on alkyl-bonded reversed-phase stationary phases is responsible for broad and asymmetrical peaks when basic drugs are chromatographed with conventional octadecylsilane (C18) columns due to ionic interactions. In the last few years, ionic liquids (ILs) have attracted attention to [...] Read more.
The presence of free silanols on alkyl-bonded reversed-phase stationary phases is responsible for broad and asymmetrical peaks when basic drugs are chromatographed with conventional octadecylsilane (C18) columns due to ionic interactions. In the last few years, ionic liquids (ILs) have attracted attention to reduce this undesirable silanol activity. ILs should be considered as dual modifiers (with a cationic and anionic character), which means that both cations and anions are able to adsorb on the stationary phase, creating a positively or negatively charged layer, depending on the relative adsorption. The accessibility of basic compounds to the silanols is prevented by both the IL cation and anion, improving the peak profiles. A comparative study of the performance of six imidazolium-based ILs, differing in their cation/anions, as modifiers of the chromatographic behavior of a group of ten β-adrenoceptor antagonists, is addressed. Mobile phases containing cationic amines (triethylamine and dimethyloctylamine) were used as a reference for the interpretation of the results. Using a mathematical model based on two chemical equilibria, the association constants between the solutes and modified stationary phase as well as those between solutes and the additive in the mobile phase were estimated. These values, together with the changes in retention and peak shape, were used to obtain conclusions about the retention mechanism, changes in the nature of the chromatographic system, and silanol suppression effect. Full article
(This article belongs to the Special Issue Recent Advances on Ionic Liquid Uses in Separation Techniques)
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Review

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32 pages, 2703 KiB  
Review
Role of Ionic Liquids in Composites in Analytical Sample Preparation
by Adrián Gutiérrez-Serpa, Patricia I. Napolitano-Tabares, Jakub Šulc, Idaira Pacheco-Fernández and Verónica Pino
Separations 2020, 7(3), 37; https://doi.org/10.3390/separations7030037 - 6 Jul 2020
Cited by 22 | Viewed by 5692
Abstract
Ionic liquids (ILs) are a group of non-conventional salts with melting points below 100 °C. Apart from their negligible vapor pressure at room temperature, high thermal stability, and impressive solvation properties, ILs are characterized by their tunability. Given such nearly infinite combinations of [...] Read more.
Ionic liquids (ILs) are a group of non-conventional salts with melting points below 100 °C. Apart from their negligible vapor pressure at room temperature, high thermal stability, and impressive solvation properties, ILs are characterized by their tunability. Given such nearly infinite combinations of cations and anions, and the easy modification of their structures, ILs with specific properties can be synthesized. These characteristics have attracted attention regarding their use as extraction phases in analytical sample preparation methods, particularly in liquid-phase extraction methods. Given the liquid nature of most common ILs, their incorporation in analytical sample preparation methods using solid sorbents requires the preparation of solid derivatives, such as polymeric ILs, or the combination of ILs with other materials to prepare solid IL-based composites. In this sense, many solid composites based on ILs have been prepared with improved features, including magnetic particles, carbonaceous materials, polymers, silica materials, and metal-organic frameworks, as additional materials forming the composites. This review aims to give an overview on the preparation and applications of IL-based composites in analytical sample preparation in the period 2017–2020, paying attention to the role of the IL material in those composites to understand the effect of the individual components in the sorbent. Full article
(This article belongs to the Special Issue Recent Advances on Ionic Liquid Uses in Separation Techniques)
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15 pages, 967 KiB  
Review
Recent Advances in Hydrophobic Deep Eutectic Solvents for Extraction
by Amos K. Dwamena
Separations 2019, 6(1), 9; https://doi.org/10.3390/separations6010009 - 12 Feb 2019
Cited by 163 | Viewed by 19714
Abstract
In the over 1,800 articles published since their inception in 2001, most deep eutectic solvents (DES) synthesized have been hydrophilic. The low cost, low toxicity, and bioavailability of DES make the solvent ‘green’ and sustainable for diverse applications. Conversely, the hydrophilicity of DES [...] Read more.
In the over 1,800 articles published since their inception in 2001, most deep eutectic solvents (DES) synthesized have been hydrophilic. The low cost, low toxicity, and bioavailability of DES make the solvent ‘green’ and sustainable for diverse applications. Conversely, the hydrophilicity of DES limits their practical application to only polar compounds, which is a major drawback of the solvent. For the past three years, hydrophobic deep eutectic solvents (HDES) have emerged as an alternative extractive media capable of extracting non-polar organic and inorganic molecules from aqueous environments. Due to the infancy of HDES, for the first time, this mini-review summarizes the recent developmental advances in HDES synthesis, applications, challenges, and future perspectives of the solvent. In the future, it is believed HDES will replace the majority of toxic organic solvents used for analytical purposes. Full article
(This article belongs to the Special Issue Recent Advances on Ionic Liquid Uses in Separation Techniques)
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