Editor's Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to authors, or important in this field. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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Article
Enhanced Photocatalytic Activity of CuWO4 Doped TiO2 Photocatalyst Towards Carbamazepine Removal under UV Irradiation
Separations 2021, 8(3), 25; https://doi.org/10.3390/separations8030025 - 26 Feb 2021
Cited by 5
Abstract
Abatement of contaminants of emerging concerns (CECs) in water sources has been widely studied employing TiO2 based heterogeneous photocatalysis. However, low quantum energy yield among other limitations of titania has led to its modification with other semiconductor materials for improved photocatalytic activity. [...] Read more.
Abatement of contaminants of emerging concerns (CECs) in water sources has been widely studied employing TiO2 based heterogeneous photocatalysis. However, low quantum energy yield among other limitations of titania has led to its modification with other semiconductor materials for improved photocatalytic activity. In this work, a 0.05 wt.% CuWO4 over TiO2 was prepared as a powder composite. Each component part synthesized via the sol-gel method for TiO2, and CuWO4 by co-precipitation assisted hydrothermal method from precursor salts, underwent gentle mechanical agitation. Homogenization of the nanopowder precursors was performed by zirconia ball milling for 2 h. The final material was obtained after annealing at 500 °C for 3.5 h. Structural and morphological characterization of the synthesized material has been achieved employing X-ray diffraction (XRD), Fourier transform infra-red (FTIR) spectroscopy, Brunauer–Emmett–Teller (BET) N2 adsorption–desorption analysis, Scanning electron microscopy-coupled Energy dispersive X-ray spectroscopy (SEM-EDS), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV-Vis diffuse reflectance spectroscopy (UV-vis DRS) for optical characterization. The 0.05 wt.% CuWO4-TiO2 catalyst was investigated for its photocatalytic activity over carbamazepine (CBZ), achieving a degradation of almost 100% after 2 h irradiation. A comparison with pure TiO2 prepared under those same conditions was made. The effect of pH, chemical scavengers, H2O2 as well as contaminant ion effects (anions, cations), and humic acid (HA) was investigated, and their related influences on the photocatalyst efficiency towards CBZ degradation highlighted accordingly. Full article
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Article
Pigments Content (Chlorophylls, Fucoxanthin and Phycobiliproteins) of Different Commercial Dried Algae
Separations 2020, 7(2), 33; https://doi.org/10.3390/separations7020033 - 11 Jun 2020
Cited by 10
Abstract
Algae are a complex, polyphyletic group of organisms, affordable and naturally rich in nutrients, but also valuable sources of structurally diverse bioactive substances such as natural pigments. The aim of this work was to evaluate the polar and non-polar pigment contents of different [...] Read more.
Algae are a complex, polyphyletic group of organisms, affordable and naturally rich in nutrients, but also valuable sources of structurally diverse bioactive substances such as natural pigments. The aim of this work was to evaluate the polar and non-polar pigment contents of different commercial dried algae (brown: Himanthalia elongata, Undaria pinnatifida, Laminaria ochroleuca; red: Porphyra spp.; and a blue-green microalga: Spirulina spp.). The pigment extraction was carried out using different solvents (100% methanol, 100% methanol acid free, 100% ethanol, 90% acetone, N,N-dimethylformamide, dimethyl sulfoxide-water (4:1, v/v) and pH 6.8 phosphate buffer), selected according to their affinity for each class of pigments. Acetone proved to be an efficient solvent to extract chlorophylls from brown and red algae, but not from Spirulina spp. Porphyra spp. presented considerably higher levels of all pigments compared to brown algae, although Spirulina spp. presented significantly higher (p < 0.05) levels of chlorophylls, carotenoids and phycobiliproteins, compared to all macroalgae. The content of fucoxanthin extracted from the three brown algae was highly correlated to the carotenoid content. Within this group, Himanthalia elongata presented the highest fucoxanthin/total carotenoids ratio. Although the yield of extraction depended on the solvent used, the algae studied herein are an interesting source of pigments of great value for a wide range of applications. Full article
(This article belongs to the Special Issue Extraction and Isolation of Natural Products)
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Review

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Review
Analysis of Monoclonal Antibodies by Capillary Electrophoresis: Sample Preparation, Separation, and Detection
Separations 2021, 8(1), 4; https://doi.org/10.3390/separations8010004 - 04 Jan 2021
Cited by 7
Abstract
Therapeutic monoclonal antibodies (mAbs) are dominating the biopharmaceutical field due to the fact of their high specificity in the treatment of diverse diseases. Nevertheless, mAbs are very complex glycoproteins exhibiting several macro- and microheterogeneities that may affect their safety, quality, and efficacy. This [...] Read more.
Therapeutic monoclonal antibodies (mAbs) are dominating the biopharmaceutical field due to the fact of their high specificity in the treatment of diverse diseases. Nevertheless, mAbs are very complex glycoproteins exhibiting several macro- and microheterogeneities that may affect their safety, quality, and efficacy. This complexity is very challenging for mAbs development, formulation, and quality control. To tackle the quality issue, a combination of multiple analytical approaches is necessary. In this perspective, capillary electrophoresis has gained considerable interest over the last decade due to the fact of its complementary features to chromatographic approaches. This review provides an overview of the strategies of mAbs and derivatives analysis by capillary electrophoresis hyphenated to ultraviolet, fluorescence, and mass spectrometry detection. The main sample preparation approaches used for mAb analytical characterization (i.e., intact, middle-up/down, and bottom-up) are detailed. The different electrophoretic modes used as well as integrated analysis approaches (sample preparation and separation) are critically discussed. Full article
(This article belongs to the Special Issue Electrophoretic Methodologies for Protein Analysis)
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Review
Role of Ionic Liquids in Composites in Analytical Sample Preparation
Separations 2020, 7(3), 37; https://doi.org/10.3390/separations7030037 - 06 Jul 2020
Cited by 10
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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Review
Hunting Molecules in Complex Matrices with SPME Arrows: A Review
Separations 2020, 7(1), 12; https://doi.org/10.3390/separations7010012 - 15 Feb 2020
Cited by 14
Abstract
Thirty years since the invention and public disclosure of solid phase microextraction (SPME), the technology continues evolving and inspiring several other green extraction technologies amenable for the collection of small molecules present in complex matrices. In this manuscript, we review the fundamental and [...] Read more.
Thirty years since the invention and public disclosure of solid phase microextraction (SPME), the technology continues evolving and inspiring several other green extraction technologies amenable for the collection of small molecules present in complex matrices. In this manuscript, we review the fundamental and operational aspects of a novel SPME geometry that can be used to “hunt” target molecules in complex matrices: the SPME Arrow. In addition, a series of applications in environmental, food, cannabis and forensic analysis are succinctly covered. Finally, special emphasis is placed on novel interfaces to analytical instrumentation, as well as recent developments in coating materials for the SPME Arrow. Full article
(This article belongs to the Special Issue Development of Alternative Green Sample Preparation Techniques)
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Review
Evolution of Environmentally Friendly Strategies for Metal Extraction
Separations 2020, 7(1), 4; https://doi.org/10.3390/separations7010004 - 06 Jan 2020
Cited by 12
Abstract
The demand for the recovery of valuable metals and the need to understand the impact of heavy metals in the environment on human and aquatic life has led to the development of new methods for the extraction, recovery, and analysis of metal ions. [...] Read more.
The demand for the recovery of valuable metals and the need to understand the impact of heavy metals in the environment on human and aquatic life has led to the development of new methods for the extraction, recovery, and analysis of metal ions. With special emphasis on environmentally friendly approaches, efforts have been made to consider strategies that minimize the use of organic solvents, apply micromethodology, limit waste, reduce costs, are safe, and utilize benign or reusable materials. This review discusses recent developments in liquid- and solid-phase extraction techniques. Liquid-based methods include advances in the application of aqueous two- and three-phase systems, liquid membranes, and cloud point extraction. Recent progress in exploiting new sorbent materials for solid-phase extraction (SPE), solid-phase microextraction (SPME), and bulk extractions will also be discussed. Full article
(This article belongs to the Special Issue Development of Alternative Green Sample Preparation Techniques)
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Review
Returning to Nature for the Design of Sorptive Phases in Solid-Phase Microextraction
Separations 2020, 7(1), 2; https://doi.org/10.3390/separations7010002 - 29 Dec 2019
Cited by 21
Abstract
Green analytical chemistry principles aim to minimize the negative impact of analytical procedures in the environment, which can be considered both at close (to ensure the safety of the analysts) and global (to conserve our natural resources) levels. These principles suggest, among other [...] Read more.
Green analytical chemistry principles aim to minimize the negative impact of analytical procedures in the environment, which can be considered both at close (to ensure the safety of the analysts) and global (to conserve our natural resources) levels. These principles suggest, among other guidelines, the reduction/minimization of the sample treatment and the use of renewable sources when possible. The first aspect is largely fulfilled by microextraction, which is considered to be among the greenest sample treatment techniques. The second consideration is attainable if natural products are used as raw materials for the preparation of new extraction phases. This strategy is in line with the change in our production system, which is being gradually moved from a linear model (take–make–dispose) to a circular one (including reusing and recycling as key terms). This article reviews the potential of natural products as sorbents in extraction and microextraction techniques from the synergic perspectives of two research groups working on the topic. The article covers the use of unmodified natural materials and the modified ones (although the latter has a less green character) to draw a general picture of the usefulness of the materials. Full article
(This article belongs to the Special Issue Advances in Solid-Phase Microextraction)
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Review
Metal–Organic Frameworks as Key Materials for Solid-Phase Microextraction Devices—A Review
Separations 2019, 6(4), 47; https://doi.org/10.3390/separations6040047 - 02 Oct 2019
Cited by 33
Abstract
Metal–organic frameworks (MOFs) have attracted recently considerable attention in analytical sample preparation, particularly when used as novel sorbent materials in solid-phase microextraction (SPME). MOFs are highly ordered porous crystalline structures, full of cavities. They are formed by inorganic centers (metal ion atoms or [...] Read more.
Metal–organic frameworks (MOFs) have attracted recently considerable attention in analytical sample preparation, particularly when used as novel sorbent materials in solid-phase microextraction (SPME). MOFs are highly ordered porous crystalline structures, full of cavities. They are formed by inorganic centers (metal ion atoms or metal clusters) and organic linkers connected by covalent coordination bonds. Depending on the ratio of such precursors and the synthetic conditions, the characteristics of the resulting MOF vary significantly, thus drifting into a countless number of interesting materials with unique properties. Among astonishing features of MOFs, their high chemical and thermal stability, easy tuneability, simple synthesis, and impressive surface area (which is the highest known), are the most attractive characteristics that makes them outstanding materials in SPME. This review offers an overview on the current state of the use of MOFs in different SPME configurations, in all cases covering extraction devices coated with (or incorporating) MOFs, with particular emphases in their preparation. Full article
(This article belongs to the Special Issue Advances in Solid-Phase Microextraction)
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Review
Metal-Organic Frameworks in Green Analytical Chemistry
Separations 2019, 6(3), 33; https://doi.org/10.3390/separations6030033 - 27 Jun 2019
Cited by 24
Abstract
Metal-organic frameworks (MOFs) are porous hybrid materials composed of metal ions and organic linkers, characterized by their crystallinity and by the highest known surface areas. MOFs structures present accessible cages, tunnels and modifiable pores, together with adequate mechanical and thermal stability. Their outstanding [...] Read more.
Metal-organic frameworks (MOFs) are porous hybrid materials composed of metal ions and organic linkers, characterized by their crystallinity and by the highest known surface areas. MOFs structures present accessible cages, tunnels and modifiable pores, together with adequate mechanical and thermal stability. Their outstanding properties have led to their recognition as revolutionary materials in recent years. Analytical chemistry has also benefited from the potential of MOF applications. MOFs succeed as sorbent materials in extraction and microextraction procedures, as sensors, and as stationary or pseudo-stationary phases in chromatographic systems. To date, around 100 different MOFs form part of those analytical applications. This review intends to give an overview on the use of MOFs in analytical chemistry in recent years (2017–2019) within the framework of green analytical chemistry requirements, with a particular emphasis on possible toxicity issues of neat MOFs and trends to ensure green approaches in their preparation. Full article
(This article belongs to the Special Issue Development of Alternative Green Sample Preparation Techniques)
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Review
Chromatographic Techniques in the Research Area of Lithium Ion Batteries: Current State-of-the-Art
Separations 2019, 6(2), 26; https://doi.org/10.3390/separations6020026 - 13 May 2019
Cited by 23
Abstract
Lithium ion batteries (LIBs) are widely used in numerous application areas, including portable consumer electronics, medicine, grid storage, electric vehicles and hybrid electric vehicles. One major challenge during operation and storage is the degradation of the cell constituents, which is called aging. This [...] Read more.
Lithium ion batteries (LIBs) are widely used in numerous application areas, including portable consumer electronics, medicine, grid storage, electric vehicles and hybrid electric vehicles. One major challenge during operation and storage is the degradation of the cell constituents, which is called aging. This phenomenon drastically reduces both storage lifetime and cycle lifetime. Due to numerous aging effects, originating from both the individual LIB cell constituents as well as their interactions, a wide variety of instruments and methods are necessary for aging investigations. In particular, chromatographic methods are frequently applied for the analysis of the typically used liquid non-aqueous battery electrolytes based on organic solvents or ionic liquids. Moreover, chromatographic methods have also been recently used to investigate the composition of electrode materials. In this review, we will give an overview of the current state of chromatographic methods in the context of LIB cell research. Full article
(This article belongs to the Special Issue Analytic Techniques for Lithium Ion Batteries Analysis)
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Review
Total and Free Fatty Acids Analysis in Milk and Dairy Fat
Separations 2019, 6(1), 14; https://doi.org/10.3390/separations6010014 - 05 Mar 2019
Cited by 20
Abstract
Dairy fat is one of the most complex natural fats because of its fatty acid (FA) composition. Ruminant dairy fat contains more than 400 different FA varying in carbon chain length, and degree, position and configuration of unsaturation. The following article reviews the [...] Read more.
Dairy fat is one of the most complex natural fats because of its fatty acid (FA) composition. Ruminant dairy fat contains more than 400 different FA varying in carbon chain length, and degree, position and configuration of unsaturation. The following article reviews the different methods available to analyze FA (both total and free) in milk and dairy products. The most widely used methodology for separating and analyzing dairy FA is gas chromatography, coupled to a flame ionization detector (CG-FID). Alternatively, gas chromatography coupled to a mass spectrometer (GC-MS) is also used. After lipid extraction, total FA (TFA) are commonly converted into their methyl esters (fatty acid methyl esters, FAME) prior to chromatographic analysis. In contrast, free FA (FFA) can be analyzed after conversion to FAME or directly as FFA after extraction from the product. One of the key questions when analyzing FAME from TFA is the selection of a proper column for separating them, which depends mainly on the objective of the analysis. Quantification is best achieved by the internal standard method. Recently, near-infrared spectroscopy (NIRS), Raman spectroscopy (RS) and nuclear magnetic resonance (NMR) have been reported as promising techniques to analyze FA in milk and dairy products. Full article
(This article belongs to the Special Issue Separation Techniques for Dairy Analysis)
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Review
Recent Advances in Hydrophobic Deep Eutectic Solvents for Extraction
Separations 2019, 6(1), 9; https://doi.org/10.3390/separations6010009 - 12 Feb 2019
Cited by 57
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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