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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 readers, or important in the respective research area. 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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14 pages, 1022 KiB  
Review
Analysis of Volatiles in Food Products
by Małgorzata Starowicz
Separations 2021, 8(9), 157; https://doi.org/10.3390/separations8090157 - 17 Sep 2021
Cited by 29 | Viewed by 7548
Abstract
The evaluation of volatiles in food is an important aspect of food production. It gives knowledge about the quality of foods and their relationship to consumers’ choices. Alcohols, aldehydes, acids, esters, terpenes, pyrazines, and furans are the main chemical groups that are involved [...] Read more.
The evaluation of volatiles in food is an important aspect of food production. It gives knowledge about the quality of foods and their relationship to consumers’ choices. Alcohols, aldehydes, acids, esters, terpenes, pyrazines, and furans are the main chemical groups that are involved in aroma formation. They are products of food processing: thermal treatment, fermentation, storage, etc. Food aroma is a mixture of varied molecules. Because of this, the analysis of aroma composition can be challenging. The four main steps can be distinguished in the evaluation of the volatiles in the food matrix as follows: (1) isolation and concentration; (2) separation; (3) identification; and (4) sensory characterization. The most commonly used techniques to separate a fraction of volatiles from non-volatiles are solid-phase micro-(SPME) and stir bar sorptive extractions (SBSE). However, to study the active components of food aroma by gas chromatography with olfactometry detector (GC-O), solvent-assisted flavor evaporation (SAFE) is used. The volatiles are mostly separated on GC systems (GC or comprehensive two-dimensional GCxGC) with the support of mass spectrometry (MS, MS/MS, ToF–MS) for chemical compound identification. Besides omics techniques, the promising part could be a study of aroma using electronic nose. Therefore, the main assumptions of volatolomics are here described. Full article
(This article belongs to the Section Analysis of Food and Beverages)
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29 pages, 2234 KiB  
Review
Magnetic Ionic Liquids in Sample Preparation: Recent Advances and Future Trends
by Theodoros Chatzimitakos, Phoebe Anagnostou, Ioanna Constantinou, Kalliroi Dakidi and Constantine Stalikas
Separations 2021, 8(9), 153; https://doi.org/10.3390/separations8090153 - 13 Sep 2021
Cited by 12 | Viewed by 3357
Abstract
In the last decades, a myriad of materials has been synthesized and utilized for the development of sample preparation procedures. The use of their magnetic analogues has gained significant attention and many procedures have been developed using magnetic materials. In this context, the [...] Read more.
In the last decades, a myriad of materials has been synthesized and utilized for the development of sample preparation procedures. The use of their magnetic analogues has gained significant attention and many procedures have been developed using magnetic materials. In this context, the benefits of a new class of magnetic ionic liquids (MILs), as non-conventional solvents, have been reaped in sample preparation procedures. MILs combine the advantageous properties of ionic liquids along with the magnetic properties, creating an unsurpassed combination. Owing to their unique nature and inherent benefits, the number of published reports on sample preparation with MILs is increasing. This fact, along with the many different types of extraction procedures that are developed, suggests that this is a promising field of research. Advances in the field are achieved both by developing new MILs with better properties (showing either stronger response to external magnetic fields or tunable extractive properties) and by developing and/or combining methods, resulting in advanced ones. In this advancing field of research, a good understanding of the existing literature is needed. This review aims to provide a literature update on the current trends of MILs in different modes of sample preparation, along with the current limitations and the prospects of the field. The use of MILs in dispersive liquid–liquid microextraction, single drop microextraction, matrix solid-phase dispersion, etc., is discussed herein among others. Full article
(This article belongs to the Special Issue Development and Application of Green or Sustainable Strategies in Analytical Chemistry)
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19 pages, 1396 KiB  
Article
Development of a Simple High-Performance Liquid Chromatography-Based Method to Quantify Synergistic Compounds and Their Composition in Dried Leaf Extracts of Piper Sarmentosum Roxb.
by Rayudika Aprilia Patindra Purba, Siwaporn Paengkoum and Pramote Paengkoum
Separations 2021, 8(9), 152; https://doi.org/10.3390/separations8090152 - 13 Sep 2021
Cited by 20 | Viewed by 3742
Abstract
There is a growing demand to enhance pharmaceutical and food safety using synergistic compounds from Piper sarmentosum Roxb., such as polyphenols and water-soluble vitamins. However, information on standardized analytical methods to identify and quantify these compounds of interest is limited. A reversed-phase high-performance [...] Read more.
There is a growing demand to enhance pharmaceutical and food safety using synergistic compounds from Piper sarmentosum Roxb., such as polyphenols and water-soluble vitamins. However, information on standardized analytical methods to identify and quantify these compounds of interest is limited. A reversed-phase high-performance liquid chromatography with diode-array detection (HPLC-DAD)-based method was developed to simultaneously detect and quantify the amounts of tannin, flavonoid, cinnamic acid, essential oil, and vitamins extracted from P. sarmentosum leaves using methanol, chloroform, and hexane. Commercially and non-commercially-cultivated P. sarmentosum leaves were subjected to seven different drying treatments (shade; sun; air oven at 40 °C, 60 °C, 80 °C, and 100 °C; and freeze-drying) for three consecutive months. Most compounds were detected most efficiently at a detection wavelength of 272 nm. The developed method displayed good detection limits (LOD, 0.026–0.789 µg/mL; LOQ, 0.078–2.392 µg/mL), linearity (R2 > 0.999), precision (%RSD, <1.00), and excellent accuracy (96–102%). All P. sarmentosum leaf extracts were simultaneously tested and analytically compared without time-consuming fractionation. Methanolic plant extracts showed better peak area and retention time splits compared to chloroformic and hexanoic extracts. Differences in synergistic compound composition were dependent on the type of drying treatment but not on cultivation site and time of sampling. Flavonoid was identified as the dominant phytochemical component in P. sarmentosum leaves, followed by the essential oil, cinnamic acid, ascorbic acid, and tannin. Overall, we present a simple and reproducible chromatographic method that can be applied to identify different plant compounds. Full article
(This article belongs to the Special Issue Application of Chromatography and Different Extraction Techniques in Analysis of Polyphenolic Compounds)
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12 pages, 282 KiB  
Article
Analysis of Selected Mycotoxins in Maize from North-West South Africa Using High Performance Liquid Chromatography (HPLC) and Other Analytical Techniques
by Theodora Ijeoma Ekwomadu, Toluwase Adeseye Dada, Stephen Abiola Akinola, Nancy Nleya and Mulunda Mwanza
Separations 2021, 8(9), 143; https://doi.org/10.3390/separations8090143 - 03 Sep 2021
Cited by 17 | Viewed by 2541
Abstract
Contamination of foods by mycotoxins is linked to various health and economic implications. This study evaluated the incidence of mycotoxins in commercial and small-scale maize and evaluated potential health risks for consumers based on South African and international regulations. The sensitivity/specificity of HPLC [...] Read more.
Contamination of foods by mycotoxins is linked to various health and economic implications. This study evaluated the incidence of mycotoxins in commercial and small-scale maize and evaluated potential health risks for consumers based on South African and international regulations. The sensitivity/specificity of HPLC over other analytical methods used was also ascertained. In total, 100 maize samples were analyzed using immuno-affinity column for extraction and clean-up, thin layer chromatography (TLC), HPLC, and enzyme linked immunosorbent assay (ELISA) for quantification. Results revealed that fumonisinB1 was the most contaminant mycotoxin in both small-scale and commercial samples with incidence rates of 100% and 98.6%, respectively. Aflatoxins contamination occurred at incidences of 26.7% in small-scale and 25.0% in commercial samples. Furthermore, ochratoxin A had high incidence rates of 97.8% and 93.0% and ranged from 3.60–19.44 µg/kg and 1.60–9.89 µg/kg, respectively, in small-scale and commercial samples, while ZEA occurred in 50% and 55% of small-scale and commercial samples, respectively. Results demonstrate that maize, especially from small-scale farmers, may contribute to dietary exposure to mycotoxins. Farmers and consumers should be alerted to the dangers of mycotoxins contamination in maize with resultant health risks. Additionally, HPLC method was also found to be more specific for mycotoxin detection than ELISA. Full article
(This article belongs to the Special Issue HPLC: A Key Tool for Analytical Chemistry)
15 pages, 1305 KiB  
Article
Selective Extraction of Platinum(IV) from the Simulated Secondary Resources Using Simple Secondary Amide and Urea Extractants
by Yuki Ueda, Shintaro Morisada, Hidetaka Kawakita and Keisuke Ohto
Separations 2021, 8(9), 139; https://doi.org/10.3390/separations8090139 - 01 Sep 2021
Cited by 10 | Viewed by 2309
Abstract
The recycling of rare metals such as platinum (Pt) from secondary resources, such as waste electronic and electrical equipment and automotive catalysts, is an urgent global issue. In this study, simple secondary amides and urea, N-(2-ethylhexyl)acetamide, N-(2-ethylhexyl)octanamide, and 1-butyl-3-(2-ethylhexyl)urea, which selectively [...] Read more.
The recycling of rare metals such as platinum (Pt) from secondary resources, such as waste electronic and electrical equipment and automotive catalysts, is an urgent global issue. In this study, simple secondary amides and urea, N-(2-ethylhexyl)acetamide, N-(2-ethylhexyl)octanamide, and 1-butyl-3-(2-ethylhexyl)urea, which selectively extract Pt(IV) from a simulated effluent containing numerous metal ions, such as in an actual hydrometallurgical process, were synthesized and achieved efficient Pt(IV) stripping using only water. Comparison of Pt(IV) extraction behavior with a tertiary amide without N–H moieties suggests that the secondary amides and urea extractants effectively use hydrogen bonding to the hexachloroplatinate anion by N–H moieties. Examining the conditions for the third phase formation revealed that the secondary amide extractant with the longest alkyl chain can be used in the extraction process for a long time without forming any third phase, despite its lower Pt(IV) extraction capacity. The practical trial with simple compounds developed in this study should contribute to the development of Pt separation and purification processes. Full article
(This article belongs to the Section Analysis of Energies)
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13 pages, 2386 KiB  
Article
Development of Green and Efficient Extraction Methods of Quercetin from Red Onion Scales Wastes Using Factorial Design for Method Optimization: A Comparative Study
by Heba-Alla H. Abd-ElSalam, Mohammed Gamal, Ibrahim A. Naguib, Medhat A. Al-Ghobashy, Hala E. Zaazaa and M. Abdelkawy
Separations 2021, 8(9), 137; https://doi.org/10.3390/separations8090137 - 29 Aug 2021
Cited by 22 | Viewed by 5066
Abstract
Waste resulting from edible plants is considered one of the best sources of valuable phytochemicals. A promising approach for using these appreciated wastes is extracting precious medically important constituents, for example, free quercetin. Two new cost-effective and green extraction methods are introduced in [...] Read more.
Waste resulting from edible plants is considered one of the best sources of valuable phytochemicals. A promising approach for using these appreciated wastes is extracting precious medically important constituents, for example, free quercetin. Two new cost-effective and green extraction methods are introduced in the present study: ultrasound-assisted glycerol extraction (UAGE) and microwave-assisted extraction (MAE). These extraction protocols are optimized using factorial design to define the highest yield of extraction, and HPLC-UV at 370 nm was used as a method of yield analysis. Quercetin remained stable during the whole process in both extraction protocols. A standard addition technique was performed to quantify quercetin in different extracts and eliminate the matrix effect. In UAGE and MAE, extraction yields were 16.55 ± 0.81 and 27.20 ± 1.55 mg/1g from red onion scales on a dry base, respectively. The amount of quercetin extracted using MAE was superior to UAGE in terms of time and yield. A greenness assessment of the offered studies compared to previously published relevant extraction methods was performed using the analytical eco-scale assessment method (ESA) and national environmental methods index (NEMI). MAE showed to be a greener method with a higher ESA score and a greener NEMI pictogram. Full article
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10 pages, 1115 KiB  
Article
Quantification of Histidine-Containing Dipeptides in Dolphin Serum Using a Reversed-Phase Ion-Pair High-Performance Liquid Chromatography Method
by Momochika Kumagai, Sanae Kato, Nanami Arakawa, Mika Otsuka, Takahisa Hamano, Nobuyuki Kashiwagi, Akira Yabuki and Osamu Yamato
Separations 2021, 8(8), 128; https://doi.org/10.3390/separations8080128 - 23 Aug 2021
Cited by 5 | Viewed by 2760
Abstract
The quantification of histidine-containing dipeptides (anserine, carnosine, and balenine) in serum might be a diagnostic tool to assess the health condition of animals. In this study, an existing reversed-phase ion-pair high-performance liquid chromatography (HPLC)–ultraviolet detection method was improved and validated to quantify serum [...] Read more.
The quantification of histidine-containing dipeptides (anserine, carnosine, and balenine) in serum might be a diagnostic tool to assess the health condition of animals. In this study, an existing reversed-phase ion-pair high-performance liquid chromatography (HPLC)–ultraviolet detection method was improved and validated to quantify serum anserine, carnosine, and balenine levels in the dolphin. The serum was deproteinized with trichloroacetic acid and directly injected into the HPLC system. Chromatographic separation of the three histidine-containing dipeptides was achieved on a TSK–gel ODS-80Ts (4.6 mm × 150 mm, 5 µm) analytical column using a mobile phase of 50 mmol/L potassium dihydrogen phosphate (pH 3.4) containing 6 mmol/L 1-heptanesulfonic acid and acetonitrile (96:4). The standard curve ranged from 0.1 µmol/L to 250 µmol/L. The average accuracy of the intra- and inter-analysis of anserine, carnosine, and balenine was 97–106%. The relative standard deviations of total precision (RSDr) of anserine, carnosine, and balenine in dolphin serum were 5.9%, 4.1%, and 2.6%, respectively. The lower limit of quantification of these compounds was 0.11–0.21 µmol/L. These results indicate that the improved method is reliable and concise for the simultaneous determination of anserine, carnosine, and balenine in dolphin serum, and may be useful for evaluation of health conditions in dolphins. Furthermore, this method can also be applied to other biological samples. Full article
(This article belongs to the Special Issue Separations in Biomedical Analysis)
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18 pages, 2428 KiB  
Article
Supercritical Carbon Dioxide Extraction, Antioxidant Activity, and Fatty Acid Composition of Bran Oil from Rice Varieties Cultivated in Portugal
by Tânia I. Pinto, José A. Coelho, Bruna I. Pires, Nuno R. Neng, José M. Nogueira, João C. Bordado and José P. Sardinha
Separations 2021, 8(8), 115; https://doi.org/10.3390/separations8080115 - 05 Aug 2021
Cited by 12 | Viewed by 2915
Abstract
Bran of different rice cultivars produced in Portugal were used to study supercritical carbon dioxide extraction conditions of rice bran oil (RBO) and evaluate and compare antioxidant activity and fatty acid composition of the different rice bran varieties. The effect of plant loading [...] Read more.
Bran of different rice cultivars produced in Portugal were used to study supercritical carbon dioxide extraction conditions of rice bran oil (RBO) and evaluate and compare antioxidant activity and fatty acid composition of the different rice bran varieties. The effect of plant loading (10–20 g), CO2 flow rate (0.5–1.5 L/min), pressure (20–60 MPa), and temperature (40–80 °C) was studied. The amount of oil extracted ranged from 11.72%, for Ariete cultivar, to 15.60%, for Sirio cultivar. The main fatty acids components obtained were palmitic (13.37%–16.32%), oleic (44.60%–52.56%), and linoleic (29.90%–38.51%). Excellent parameters of the susceptibility to oxidation of the oils were obtained and compare. RBO of Ariete and Gladio varieties presented superior DPPH and ABTS radical scavenging activities, whereas, Minima, Ellebi, and Sirio varieties had the lowest scavenging activities. Moreover, the oil obtained towards the final stages of extraction presented increased antioxidant activity. Full article
(This article belongs to the Special Issue Spectroscopic, Chromatographic, and Chemometric Techniques Applied in Food Products Characterization)
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11 pages, 1379 KiB  
Article
Development of a Modified QuEChERS Procedure for the Isolation of Pesticide Residues from Textile Samples, Followed by GC–MS Determination
by Svetlana Hrouzková and Agneša Szarka
Separations 2021, 8(8), 106; https://doi.org/10.3390/separations8080106 - 23 Jul 2021
Cited by 9 | Viewed by 2298
Abstract
Due to the use of pesticides during cotton production and/or textile storage, it is necessary to assure textile and clothing safety in order to improve the protection of human health. In this work, an efficient method was established for a multiresidue determination of [...] Read more.
Due to the use of pesticides during cotton production and/or textile storage, it is necessary to assure textile and clothing safety in order to improve the protection of human health. In this work, an efficient method was established for a multiresidue determination of 33 pesticides covering several pesticide classes such as organochlorine, organophosphate, pyrethroides, triazines, etc., in textiles by modified QuEChERS and followed by gas chromatography–mass spectrometry. Optimal conditions were selected, including the amount of the sample, type of the extraction solvent and cleaning up sorbents, until the method was finally validated. Sufficient accuracy and precision were presented by the method using spiked samples between 10 and 250 μg/kg, while recoveries from 70 to 120% and an RSD < 20% for all the pesticides were obtained; the limits of quantification were below 5 μg/kg for all studied pesticides. The presented method showed high separation efficiency with minimal sample and sorbent consumption. The validated method was successfully applied to the analysis of real samples and proved to be applicable to routine analyses. Full article
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18 pages, 2747 KiB  
Article
Detailed Group-Type Characterization of Plastic-Waste Pyrolysis Oils: By Comprehensive Two-Dimensional Gas Chromatography Including Linear, Branched, and Di-Olefins
by Hang Dao Thi, Marko R. Djokic and Kevin M. Van Geem
Separations 2021, 8(7), 103; https://doi.org/10.3390/separations8070103 - 16 Jul 2021
Cited by 28 | Viewed by 5200
Abstract
Plastic-waste pyrolysis oils contain large amounts of linear, branched, and di-olefinic compounds. This makes it not obvious to determine the detailed group-type composition in particular to the presence of substantial amounts of N-, S-, and O-containing heteroatomic compounds. The thorough evaluation of different [...] Read more.
Plastic-waste pyrolysis oils contain large amounts of linear, branched, and di-olefinic compounds. This makes it not obvious to determine the detailed group-type composition in particular to the presence of substantial amounts of N-, S-, and O-containing heteroatomic compounds. The thorough evaluation of different column combinations for two-dimensional gas chromatography (GC × GC), i.e., non-polar × polar and polar × non-polar, revealed that the second combination had the best performance, as indicated by the bi-dimensional resolution of the selected key compounds. By coupling the GC × GC to multiple detectors, such as the flame ionization detector (FID), a sulfur chemiluminescence detector (SCD), a nitrogen chemiluminescence detector (NCD), and a mass spectrometer (MS), the identification and quantification were possible of hydrocarbon, oxygen-, sulfur-, and nitrogen-containing compounds in both naphtha (C5–C11) and diesel fractions (C7–C23) originating from plastic-waste pyrolysis oils. Group-type quantification showed that large amounts of α-olefins (36.39 wt%, 35.08 wt%), iso-olefins (8.77 wt%, 9.06 wt%), and diolefins (4.21 wt%, 4.20 wt%) were present. Furthermore, oxygen-containing compounds (alcohols, ketones, and ethers) could be distinguished from abundant hydrocarbon matrix, by employing Stabilwax as the first column and Rxi-5ms as the second column. Ppm levels of sulfides, thiophenes, and pyridines could also be quantified by the use of selective SCD and NCD detectors. Full article
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13 pages, 1737 KiB  
Article
Automated Solid Phase Extraction of Cd(II), Co(II), Cu(II) and Pb(II) Coupled with Flame Atomic Absorption Spectrometry Utilizing a New Sol-Gel Functionalized Silica Sorbent
by Natalia Manousi, Abuzar Kabir, Kenneth G. Furton, George A. Zachariadis and Aristidis Anthemidis
Separations 2021, 8(7), 100; https://doi.org/10.3390/separations8070100 - 08 Jul 2021
Cited by 16 | Viewed by 3123
Abstract
In this study a simple and sensitive on-line sorbent extraction platform coupled with flame atomic absorption spectrometry for trace metals determination was developed. The system utilized for the first time a novel sol-gel thiocyanatopropyl functionalized silica as adsorbent for metal’s separation and preconcentration. [...] Read more.
In this study a simple and sensitive on-line sorbent extraction platform coupled with flame atomic absorption spectrometry for trace metals determination was developed. The system utilized for the first time a novel sol-gel thiocyanatopropyl functionalized silica as adsorbent for metal’s separation and preconcentration. The main factors affecting the performance of the on-line system were investigated and optimized. The effect of potential interfering species that occur naturally in environmental and biological samples, as well as some toxic elements, was evaluated. Under optimum conditions the enhancement factors ranged between 73 and 152 for the target analytes. The LODs of the proposed methods were 0.15 μg L−1 for Cd(II), 0.5 μg L−1 for Co(II), 0.5 μg L−1 for Cu(II) and 1.9 μg L−1 for Pb(II) for 120 s preconcentration time. The relative standard deviation values for all elements were less than 3.8%, indicating good method precision. Moreover, the sol-gel thiocyanatopropyl functionalized silica-packed microcolumns exhibited limited flow resistance and excellent packing reproducibility. Finally, the proposed method was utilized for the analysis of environmental and biological samples. Full article
(This article belongs to the Special Issue Nanomaterials in Green Analytical Chemistry)
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32 pages, 3550 KiB  
Review
Molecularly Imprinted Polymers for Dispersive (Micro)Solid Phase Extraction: A Review
by G. D. Thilini Madurangika Jayasinghe and Antonio Moreda-Piñeiro
Separations 2021, 8(7), 99; https://doi.org/10.3390/separations8070099 - 06 Jul 2021
Cited by 19 | Viewed by 4694
Abstract
The review describes the development of batch solid phase extraction procedures based on dispersive (micro)solid phase extraction with molecularly imprinted polymers (MIPs) and magnetic MIPs (MMIPs). Advantages and disadvantages of the various MIPs for dispersive solid phase extraction and dispersive (micro)solid phase extraction [...] Read more.
The review describes the development of batch solid phase extraction procedures based on dispersive (micro)solid phase extraction with molecularly imprinted polymers (MIPs) and magnetic MIPs (MMIPs). Advantages and disadvantages of the various MIPs for dispersive solid phase extraction and dispersive (micro)solid phase extraction are discussed. In addition, an effort has also been made to condense the information regarding MMIPs since there are a great variety of supports (magnetite and magnetite composites with carbon nanotubes, graphene oxide, or organic metal framework) and magnetite surface functionalization mechanisms for enhancing MIP synthesis, including reversible addition-fragmentation chain-transfer (RAFT) polymerization. Finally, drawbacks and future prospects for improving molecularly imprinted (micro)solid phase extraction (MIMSPE) are also appraised. Full article
(This article belongs to the Special Issue Molecularly Imprinted Polymers: Selective Extraction Materials for Sample Preparation)
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13 pages, 1926 KiB  
Article
Formation of Humic-Like Substances during the Technological Process of Lignohumate® Synthesis as a Function of Time
by Olga Yakimenko, Andrey Stepanov, Svetlana Patsaeva, Daria Khundzhua, Olesya Osipova and Oleg Gladkov
Separations 2021, 8(7), 96; https://doi.org/10.3390/separations8070096 - 03 Jul 2021
Cited by 10 | Viewed by 2628
Abstract
The composition, structure, and biological activity of humic-like substances (HLS) synthesized in the process of lignosulfonate conversion for the production of the humic product Lignohumate® (LH) were examined. It is shown that during the hydrolytic-oxidative process, the transformation of raw material and [...] Read more.
The composition, structure, and biological activity of humic-like substances (HLS) synthesized in the process of lignosulfonate conversion for the production of the humic product Lignohumate® (LH) were examined. It is shown that during the hydrolytic-oxidative process, the transformation of raw material and accumulation of HLS occur. Data on the chemical (elemental content, functional groups, FTIR) and spectral (absorbance and fluorescence) parameters and biological activity (in phytotest) combined with PCA show that the LH samples can be divided into three groups, depending on the duration of synthesis: initial raw material (0-time sample); “young” HLS (15–30 min), and “mature” HLS in 45–120 min of treatment. During the first 30 min, reactions similar to the ones that occur during lignin humification in nature take place: depolymerization, oxidative carboxylation, and further polycondensation with the formation and accumulation of HLS. After 45–60 min, the share of HLS reaches a maximum, and its composition stabilizes. Biological activity reaches a maximum after 45–60 min of treatment, and at that stage, the further synthesis process can be stopped. Further processing (up to 2 h and more) does not provide any added value to the humic product. Full article
(This article belongs to the Special Issue Research Progress on Extraction and Characterization of Humus)
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18 pages, 3235 KiB  
Article
Effect of Ultrasound-Assisted Extraction Parameters on Total Polyphenols and Its Antioxidant Activity from Mango Residues (Mangifera indica L. var. Manililla)
by Anahí J. Borrás-Enríquez, Elizabeth Reyes-Ventura, Socorro J. Villanueva-Rodríguez and Lorena Moreno-Vilet
Separations 2021, 8(7), 94; https://doi.org/10.3390/separations8070094 - 30 Jun 2021
Cited by 23 | Viewed by 3659
Abstract
Manililla is a mango variety whose residues contain bioactive compounds such as polyphenols and flavonoids, with high added value. The use of environmentally friendly extraction technology would be of great relevance; hence, this study aimed to evaluate the effect of solvent relation, sonication [...] Read more.
Manililla is a mango variety whose residues contain bioactive compounds such as polyphenols and flavonoids, with high added value. The use of environmentally friendly extraction technology would be of great relevance; hence, this study aimed to evaluate the effect of solvent relation, sonication time and amplitude on the ultrasound-assisted extraction of total polyphenols in Manililla mango residues (peel, endocarp and kernel) and antioxidant activity. An experimental design 23 with a central point was used to evaluate the curvature behavior of the process variables. Conventional maceration was used as a control. The better conditions were obtained at the central point using 50% ethanol in water, 60% amplitude and 20 min of sonication time. We obtained values of up to 1814 mg GAE/100 g, 469 mg GAE/100 g and 672 mg GAE/100 g of total polyphenols and 1228 mg QE/100 g, 653 mg QE/100 g and 880 mg QE/100 g of total flavonoids for peel, endocarp and kernel, respectively. Mangiferin was quantified in ultrasound-assisted extraction at 150 mg/g in peel and 0.025 mg/g in the kernel, but it was not detectable in maceration. An antioxidant capacity of 87%, 14% and 83% inhibition for peel, endocarp and kernel, respectively, were obtained. Peel and kernel were the residues with higher potential as extraction material, while endocarp was not. Full article
(This article belongs to the Special Issue Analytical Methods and Application of Separation Techniques in Food Science)
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26 pages, 999 KiB  
Review
Analytical Methods for Extraction and Identification of Primary and Secondary Metabolites of Apple (Malus domestica) Fruits: A Review
by Maria Assunta Acquavia, Raffaella Pascale, Luca Foti, Giuseppe Carlucci, Laura Scrano, Giuseppe Martelli, Monica Brienza, Donatella Coviello, Giuliana Bianco and Filomena Lelario
Separations 2021, 8(7), 91; https://doi.org/10.3390/separations8070091 - 25 Jun 2021
Cited by 25 | Viewed by 5535
Abstract
Apples represent a greater proportion of the worldwide fruit supply, due to their availability on the market and to the high number of existing cultivar varieties and apple-based products (fresh fruit, fruit juice, cider and crushed apples). Several studies on apple fruit metabolites [...] Read more.
Apples represent a greater proportion of the worldwide fruit supply, due to their availability on the market and to the high number of existing cultivar varieties and apple-based products (fresh fruit, fruit juice, cider and crushed apples). Several studies on apple fruit metabolites are available, with most of them focusing on their healthy properties’ evaluation. In general, the metabolic profile of apple fruits strongly correlates with most of their peculiar characteristics, such as taste, flavor and color. At the same time, many bioactive molecules could be identified as markers of a specific apple variety. Therefore, a complete description of the analytical protocols commonly used for apple metabolites’ characterization and quantification could be useful for researchers involved in the identification of new phytochemical compounds from different apple varieties. This review describes the analytical methods published in the last ten years, in order to analyze the most important primary and secondary metabolites of Malus domestica fruits. In detail, this review gives an account of the spectrophotometric, chromatographic and mass spectrometric methods. A discussion on the quantitative and qualitative analytical shortcomings for the identification of sugars, fatty acids, polyphenols, organic acids, carotenoids and terpenes found in apple fruits is reported. Full article
(This article belongs to the Section Analysis of Natural Products and Pharmaceuticals)
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19 pages, 3385 KiB  
Article
Automated Screening and Filtering Scripts for GC×GC-TOFMS Metabolomics Data
by Seo Lin Nam, A. Paulina de la Mata and James J. Harynuk
Separations 2021, 8(6), 84; https://doi.org/10.3390/separations8060084 - 15 Jun 2021
Cited by 11 | Viewed by 2900
Abstract
Comprehensive two-dimensional gas chromatography mass spectrometry (GC×GC-MS) is a powerful tool for the analysis of complex mixtures, and it is ideally suited to discovery studies where the entire sample is potentially of interest. Unfortunately, when unit mass resolution mass spectrometers are used, many [...] Read more.
Comprehensive two-dimensional gas chromatography mass spectrometry (GC×GC-MS) is a powerful tool for the analysis of complex mixtures, and it is ideally suited to discovery studies where the entire sample is potentially of interest. Unfortunately, when unit mass resolution mass spectrometers are used, many detected compounds have spectra that do not match well with libraries. This could be due to the compound not being in the library, or the compound having a weak/nonexistent molecular ion cluster. While high-speed, high-resolution mass spectrometers, or ion sources with softer ionization than 70 eV electron impact (EI) may help with some of this, many GC×GC systems presently in use employ low-resolution mass spectrometers and 70 eV EI ionization. Scripting tools that apply filters to GC×GC-TOFMS data based on logical operations applied to spectral and/or retention data have been used previously for environmental and petroleum samples. This approach rapidly filters GC×GC-TOFMS peak tables (or raw data) and is available in software from multiple vendors. In this work, we present a series of scripts that have been developed to rapidly classify major groups of compounds that are of relevance to metabolomics studies including: fatty acid methyl esters, free fatty acids, aldehydes, alcohols, ketones, amino acids, and carbohydrates. Full article
(This article belongs to the Section Chromatographic Separations)
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14 pages, 3732 KiB  
Article
Occurrence of Selected Known or Suspected Endocrine-Disrupting Pesticides in Portuguese Surface Waters Using SPME-GC-IT/MS
by José Vera, Virgínia Cruz Fernandes, Luísa Correia-Sá, Catarina Mansilha, Cristina Delerue-Matos and Valentina F. Domingues
Separations 2021, 8(6), 81; https://doi.org/10.3390/separations8060081 - 07 Jun 2021
Cited by 10 | Viewed by 2242
Abstract
A multiresidue analytical methodology based on a solid-phase microextraction (SPME), followed by gas chromatography-ion trap mass spectrometry (GC–IT/MS), has been developed for trace analysis of 20 known or suspected endocrine-disrupting pesticides. The SPME conditions are optimized considering several key parameters to obtain the [...] Read more.
A multiresidue analytical methodology based on a solid-phase microextraction (SPME), followed by gas chromatography-ion trap mass spectrometry (GC–IT/MS), has been developed for trace analysis of 20 known or suspected endocrine-disrupting pesticides. The SPME conditions are optimized considering several key parameters to obtain the maximum sensitivity. After the optimization, the method validation is performed, and the limits of detection (ranged from 2–150 ng/L) and the coefficient of determination (above 0.990) of studied compounds are determined for all the analytes. A robust sampling of twenty sampling points of surface water samples from the north and center of Portugal is performed, and the validated methodology is applied. In total, 20 compounds from four chemical families (13 organochlorine, 1 organophosphorus, 2 dicarboximide, and 4 pyrethroids) are studied, and the pesticides most frequently detected are eight organochlorine pesticides (α-, β-HCHs, lindane, HCB, o,p′-DDT, p,p′-DDE, p,p′-DDD, α-endosulfan), cypermethrin, and vinclozolin. Full article
(This article belongs to the Special Issue Analytical Methods for the Determination of Emerging Contaminants)
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26 pages, 6239 KiB  
Article
Experimental and Theoretical Research on Pressure Drop Changes in a Two-Stage Air Filter Used in Tracked Vehicle Engine
by Tadeusz Dziubak and Grzegorz Boruta
Separations 2021, 8(6), 71; https://doi.org/10.3390/separations8060071 - 21 May 2021
Cited by 15 | Viewed by 4057
Abstract
The effect of mineral dust in the air sucked in by an engine on accelerated component wear and reduction in performance was presented. The necessity to use two-stage air filters (multicyclone-paper insert) for military vehicles was shown. The results showed that placing an [...] Read more.
The effect of mineral dust in the air sucked in by an engine on accelerated component wear and reduction in performance was presented. The necessity to use two-stage air filters (multicyclone-paper insert) for military vehicles was shown. The results showed that placing an air filter in the path of the air entering the engine causes an additional pressure drop (air filter resistance increase), which leads to engine power decrease and increased fuel consumption. An analysis of model filter beds’ pressure drop changes (depending on bed parameters, aerosol flow parameters, and dust content) was carried out. It was revealed that it is very difficult to model changes in pressure drop in filter beds for actual conditions that appear during vehicle operation. The air filter pressure drop measurement results of more than 20 tracked vehicles operating in variable air dust concentration conditions were presented. The forms of selected regression models of the “life curve” type, best suited to the actual changes in air filters pressure drop as a function of the vehicle mileage, were determined. Significant differences were found between the same model values for different units of the tested vehicles. The quality of forecasting pressure drop value by selected functions was assessed by extrapolating them to the value of the next measurement and comparing the forecast and actual value. It was found that for the performed experiment, sufficiently good results of experimental data approximation and forecasting were obtained for a simple linear model. Full article
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25 pages, 1967 KiB  
Review
Advanced Analytical Approaches for the Analysis of Polyphenols in Plants Matrices—A Review
by Elena Roxana Chiriac, Carmen Lidia Chiţescu, Elisabeta-Irina Geană, Cerasela Elena Gird, Radu Petre Socoteanu and Rica Boscencu
Separations 2021, 8(5), 65; https://doi.org/10.3390/separations8050065 - 12 May 2021
Cited by 20 | Viewed by 5471
Abstract
Phenolic compounds are plants’ bioactive metabolites that have been studied for their ability to confer extensive benefits to human health. As currently there is an increased interest in natural compounds identification and characterization, new analytical methods based on advanced technologies have been developed. [...] Read more.
Phenolic compounds are plants’ bioactive metabolites that have been studied for their ability to confer extensive benefits to human health. As currently there is an increased interest in natural compounds identification and characterization, new analytical methods based on advanced technologies have been developed. This paper summarizes current advances in the state of the art for polyphenols identification and quantification. Analytical techniques ranging from high-pressure liquid chromatography to hyphenated spectrometric methods are discussed. The topic of high-resolution mass spectrometry, from targeted quantification to untargeted comprehensive chemical profiling, is particularly addressed. Structure elucidation is one of the important steps for natural products research. Mass spectral data handling approaches, including acquisition mode selection, accurate mass measurements, elemental composition, mass spectral library search algorithms and structure confirmation through mass fragmentation pathways, are discussed. Full article
(This article belongs to the Special Issue Extraction and Analysis of Plant Active Ingredients)
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26 pages, 1761 KiB  
Article
LC-ESI-QTOF-MS/MS Profiling and Antioxidant Activity of Phenolics from Custard Apple Fruit and By-Products
by Junxi Du, Biming Zhong, Vigasini Subbiah, Colin J. Barrow, Frank R. Dunshea and Hafiz A. R. Suleria
Separations 2021, 8(5), 62; https://doi.org/10.3390/separations8050062 - 09 May 2021
Cited by 14 | Viewed by 4478
Abstract
Custard apple is an edible fruit grown in tropical and subtropical regions. Due to its abundant nutrient content and perceived health benefits, it is a popular food for consumption and is utilized as a medicinal aid. Although some published research had provided the [...] Read more.
Custard apple is an edible fruit grown in tropical and subtropical regions. Due to its abundant nutrient content and perceived health benefits, it is a popular food for consumption and is utilized as a medicinal aid. Although some published research had provided the phenolic compound of custard apple, the comprehensive phenolic profiling of Australian grown custard apple is limited. Hence, this research aimed to evaluate the phenolic content and antioxidant potential by various phenolic content and antioxidant assays, followed by characterization and quantification of the phenolic profile using LC-ESI-QTOF-MS/MS and HPLC-PDA. African Pride peel had the highest value in TPC (61.69 ± 1.48 mg GAE/g), TFC (0.42 ± 0.01 mg QE/g) and TTC (43.25 ± 6.70 mg CE/g), followed by Pink’s Mammoth peel (19.37 ± 1.48 mg GAE/g for TPC, 0.27 ± 0.03 mg QE/g for TFC and 10.25 ± 1.13 mg CE/g for TTC). African Pride peel also exhibited the highest antioxidant potential for TAC (43.41 ± 1.66 mg AAE/g), FRAP (3.60 ± 0.14 mg AAE/g) and ABTS (127.67 ± 4.60 mg AAE/g), whereas Pink’s Mammoth peel had the highest DPPH (16.09 ± 0.34 mg AAE/g), RPA (5.32 ± 0.14 mg AAE/g), •OH-RSA (1.23 ± 0.25 mg AAE/g) and FICA (3.17 ± 0.18 mg EDTA/g). LC-ESI-QTOF-MS/MS experiment successfully characterized 85 phenolic compounds in total, encompassing phenolic acids (20), flavonoids (42), stilbenes (4), lignans (6) and other polyphenols (13) in all three parts (pulp, peel and seeds) of custard apple. The phenolic compounds in different portions of custard apples were quantified by HPLC-PDA, and it was shown that African Pride peel had higher concentrations of the most abundant phenolics. This is the first study to provide the comprehensive phenolic profile of Australian grown custard apples, and the results highlight that each part of custard apple can be a rich source of phenolics for the utilization of custard apple fruit and waste in the food, animal feeding and nutraceutical industries. Full article
(This article belongs to the Special Issue Advances in Food and Biological Samples Analysis)
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19 pages, 759 KiB  
Article
Andean Blueberry of the Genus Disterigma: A High-Resolution Mass Spectrometric Approach for the Comprehensive Characterization of Phenolic Compounds
by Sara Elsa Aita, Anna Laura Capriotti, Chiara Cavaliere, Andrea Cerrato, Benedetta Giannelli Moneta, Carmela Maria Montone, Susy Piovesana and Aldo Laganà
Separations 2021, 8(5), 58; https://doi.org/10.3390/separations8050058 - 02 May 2021
Cited by 21 | Viewed by 2986
Abstract
Wild neotropical blueberries, endemic of Central and South American areas, are promising yet still undisclosed sources of bioactive compounds. Most research studies have addressed wild and cultivated blueberries from Europe and North America, despite the extremely wide variety of wild neotropical species. In [...] Read more.
Wild neotropical blueberries, endemic of Central and South American areas, are promising yet still undisclosed sources of bioactive compounds. Most research studies have addressed wild and cultivated blueberries from Europe and North America, despite the extremely wide variety of wild neotropical species. In the present paper, for the first time, the phenolic composition of Disterigma alaternoides was investigated through ultra-high-performance liquid chromatography coupled to high-resolution mass-spectrometric analysis followed by accurate data analysis and compound validation with a dedicated structure-based workflow. D. alaternoides, which belongs to a closely related genus to that of the common blueberry, grows exclusively in the Andean regions over 2000 above sea level. Thanks to the dedicated analytical platform, 249 phenolic compounds were tentatively identified, including several anthocyanins, flavonoids, phenolic acids, and proanthocyanidins. Thenature and heterogeneity of identified phenolic compounds demonstrate once more the need for a more profound knowledge of such still uncharted matrices. Full article
(This article belongs to the Special Issue Chromatographic Analysis of Biological Samples)
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15 pages, 4552 KiB  
Article
Enhanced Adsorption Capacities of Fungicides Using Peanut Shell Biochar via Successive Chemical Modification with KMnO4 and KOH
by Yong-Gu Lee, Jaegwan Shin, Jinwoo Kwak, Sangwon Kim, Changgil Son, Geon-Youb Kim, Chang-Ha Lee and Kangmin Chon
Separations 2021, 8(4), 52; https://doi.org/10.3390/separations8040052 - 15 Apr 2021
Cited by 14 | Viewed by 2838
Abstract
This study explored the effects of peanut shell biochar (PSB) on the adsorption capacities of fungicides with and without successive chemical modifications, using KMnO4 and KOH (PSBOX-A), in order to provide a valuable understanding of their adsorption mechanisms and behaviors. [...] Read more.
This study explored the effects of peanut shell biochar (PSB) on the adsorption capacities of fungicides with and without successive chemical modifications, using KMnO4 and KOH (PSBOX-A), in order to provide a valuable understanding of their adsorption mechanisms and behaviors. To this end, the physicochemical properties of PSB and PSBOX-A were examined by using the Brunauer–Emmett–Teller method, Fourier transform infrared spectroscopy, and scanning electron microscopy with an energy dispersive X-ray spectrometer. The effects of temperature, ionic strength, and humic acids on the adsorption of fungicides, using PSB and PSBOX-A, were estimated through batch experiments. Furthermore, adsorption kinetics, isotherms, and thermodynamics were studied. The maximum adsorption capacities of fungicides by PSBOX-A were estimated to be more notable (Qmax of carbendazim = 531.2 μmol g−1, Qmax of pyrimethanil = 467.7 μmol g−1, and Qmax of tebuconazole = 495.1 μmol g−1) than PSB (Qmax of carbendazim = 92.6 μmol g−1, Qmax of pyrimethanil = 61.7 μmol g−1, and Qmax of tebuconazole = 66.7 μmol g−1). These findings suggest that successive chemical modification using KMnO4 and KOH could potentially be used to effectively fabricate PSB to remove fungicides in water-treatment processes. Full article
(This article belongs to the Section Environmental Separations)
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14 pages, 1586 KiB  
Review
The Use of Ferrofluids in Analytical Sample Preparation: A Review
by Raúl González-Martín, Adrián Gutiérrez-Serpa and Verónica Pino
Separations 2021, 8(4), 47; https://doi.org/10.3390/separations8040047 - 09 Apr 2021
Cited by 13 | Viewed by 4084
Abstract
Ferrofluids (FFs) constitute a type of tunable magnetic material, formed by magnetic nanoparticles suspended in a liquid carrier. The astonishing magnetic properties of these materials and their liquid nature have led to their extended use in different applications, including fields such as magnetochemistry, [...] Read more.
Ferrofluids (FFs) constitute a type of tunable magnetic material, formed by magnetic nanoparticles suspended in a liquid carrier. The astonishing magnetic properties of these materials and their liquid nature have led to their extended use in different applications, including fields such as magnetochemistry, optics, and biomedicine, among others. Recently, FFs have been incorporated as extractant materials in magnetic-driven analytical sample preparation procedures, thus, permitting the development of different applications. FF-based extraction takes advantage of both the magnetic susceptibility of the nanoparticles and the properties of the liquid carrier, which are responsible for a wide variety of interactions with analytes and ultimately are a key factor in achieving better extraction performance. This review article classifies existing FFs in terms of the solvent used as a carrier (organic solvents, water, ionic liquids, deep eutectic solvents, and supramolecular solvents) while overviewing the most relevant analytical applications in the last decade. Full article
(This article belongs to the Special Issue Development of Analytical Methods Based on Microextraction Techniques)
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19 pages, 4600 KiB  
Article
Grafting of Acrylic Membrane Prepared from Fibers Waste for Dyes Removal: Methylene Blue and Congo Red
by Ahmed Labena, Ahmed E. Abdelhamid, Shimaa Husien, Tarek Youssef, Ehab Azab, Adil A. Gobouri and Gehan Safwat
Separations 2021, 8(4), 42; https://doi.org/10.3390/separations8040042 - 01 Apr 2021
Cited by 14 | Viewed by 2656
Abstract
Dyes are a type of pollutant that have been discharged into water streams by various industries and had harmful effects on the environment and human health. Therefore, present work was directed to recycle acrylic fibers waste to be used as an adsorbent to [...] Read more.
Dyes are a type of pollutant that have been discharged into water streams by various industries and had harmful effects on the environment and human health. Therefore, present work was directed to recycle acrylic fibers waste to be used as an adsorbent to exclude dyes such as methylene blue (MB) and Congo red (CR) from dyes-polluted wastewater. Acrylic fibers waste was converted into membrane followed by chemical grafting with p-phenylenediamine monomer to form functional modified membranes. Afterwards, some characterization analyses; Fourier transform-infrared, scanning electron microscope, swelling behavior, and porosity properties were performed for the acrylic fiber grafted membrane (AFGM). For obtaining the best conditions that permit the highest adsorption capacity of the AFGM, some preliminary experiments followed by general full factorial design experiments were displayed. Langmuir, Freundlich isotherms and kinetic studies evaluations were applied. Results revealed that, the adsorption capacities of the AFGM were 61% for Methylene blue and 86% for Congo red that stated the high affinity of the AFGM to the anionic dyes. The reusability of the AFGM membranes in different cycles for 3Rs processes “Removal, Recovery, and Re-use” indicated the efficiency of the AFGM to be used in wastewater treatment. Full article
(This article belongs to the Special Issue Challenges and Trends in the Analysis of Compounds of Emerging Concern)
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14 pages, 289 KiB  
Review
Recent Applications of Solid Phase Microextraction Coupled to Liquid Chromatography
by Carlo Zambonin and Antonella Aresta
Separations 2021, 8(3), 34; https://doi.org/10.3390/separations8030034 - 20 Mar 2021
Cited by 16 | Viewed by 3084
Abstract
Solid phase microextraction (SPME) is one of the most popular sample preparation methods which can be applied to organic compounds allowing the simultaneous extraction and pre-concentration of analytes from the sample matrix. It is based on the partitioning of the analyte between the [...] Read more.
Solid phase microextraction (SPME) is one of the most popular sample preparation methods which can be applied to organic compounds allowing the simultaneous extraction and pre-concentration of analytes from the sample matrix. It is based on the partitioning of the analyte between the extracting phase, generally immobilized on a fiber substrate, and the matrix (water, air, etc.), and has numerous advantages such as rapidity, simplicity, low cost, ease of use and automation, and absence of toxic solvents. Fiber SPME has been widely used in combination with various analytical instrumentation even if most of the work has been done coupling the extraction technique with gas and liquid chromatography (GC and LC). This manuscript presents an overview of the recent works (from 2010 to date) of solid phase microextraction coupled to liquid chromatography (SPME-LC) relevant to analytical applications performed using commercially available fibers or lab-made fibers already developed in previous papers, and to improved instrumental systems and approaches. Full article
14 pages, 10438 KiB  
Review
Ion Mobility–Mass Spectrometry for Bioanalysis
by Xavier Garcia, Maria del Mar Sabaté, Jorge Aubets, Josep Maria Jansat and Sonia Sentellas
Separations 2021, 8(3), 33; https://doi.org/10.3390/separations8030033 - 16 Mar 2021
Cited by 13 | Viewed by 4020
Abstract
This paper aims to cover the main strategies based on ion mobility spectrometry (IMS) for the analysis of biological samples. The determination of endogenous and exogenous compounds in such samples is important for the understanding of the health status of individuals. For this [...] Read more.
This paper aims to cover the main strategies based on ion mobility spectrometry (IMS) for the analysis of biological samples. The determination of endogenous and exogenous compounds in such samples is important for the understanding of the health status of individuals. For this reason, the development of new approaches that can be complementary to the ones already established (mainly based on liquid chromatography coupled to mass spectrometry) is welcomed. In this regard, ion mobility spectrometry has appeared in the analytical scenario as a powerful technique for the separation and characterization of compounds based on their mobility. IMS has been used in several areas taking advantage of its orthogonality with other analytical separation techniques, such as liquid chromatography, gas chromatography, capillary electrophoresis, or supercritical fluid chromatography. Bioanalysis is not one of the areas where IMS has been more extensively applied. However, over the last years, the interest in using this approach for the analysis of biological samples has clearly increased. This paper introduces the reader to the principles controlling the separation in IMS and reviews recent applications using this technique in the field of bioanalysis. Full article
(This article belongs to the Special Issue Advances in Food and Biological Samples Analysis)
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14 pages, 4922 KiB  
Article
Adsorption Characteristics of Phosphate Ions by Pristine, CaCl2 and FeCl3-Activated Biochars Originated from Tangerine Peels
by Changgil Son, Wonyeol An, Geonhee Lee, Inho Jeong, Yong-Gu Lee and Kangmin Chon
Separations 2021, 8(3), 32; https://doi.org/10.3390/separations8030032 - 13 Mar 2021
Cited by 10 | Viewed by 2709
Abstract
This study has evaluated the removal efficiencies of phosphate ions (PO43−) using pristine (TB) and chemical-activated tangerine peel biochars. The adsorption kinetics and isotherm presented that the enhanced physicochemical properties of TB surface through the chemical activation with CaCl2 [...] Read more.
This study has evaluated the removal efficiencies of phosphate ions (PO43−) using pristine (TB) and chemical-activated tangerine peel biochars. The adsorption kinetics and isotherm presented that the enhanced physicochemical properties of TB surface through the chemical activation with CaCl2 (CTB) and FeCl3 (FTB) were helpful in the adsorption capacities of PO43− (equilibrium adsorption capacity: FTB (1.655 mg g−1) > CTB (0.354 mg g−1) > TB (0.104 mg g−1)). The adsorption kinetics results revealed that PO43− removal by TB, CTB, and FTB was well fitted with the pseudo-second-order model (R2 = 0.999) than the pseudo-first-order model (R2 ≥ 0.929). The adsorption isotherm models showed that the Freundlich equation was suitable for PO43− removal by TB (R2 = 0.975) and CTB (R2 = 0.955). In contrast, the Langmuir equation was proper for PO43− removal by FTB (R2 = 0.987). The PO43− removal efficiency of CTB and FTB decreased with the ionic strength increased due to the compression of the electrical double layer on the CTB and FTB surfaces. Besides, the PO43− adsorptions by TB, CTB, and FTB were spontaneous endothermic reactions. These findings demonstrated FTB was the most promising method for removing PO43− in waters. Full article
(This article belongs to the Section Environmental Separations)
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23 pages, 5523 KiB  
Article
Enhanced Photocatalytic Activity of CuWO4 Doped TiO2 Photocatalyst Towards Carbamazepine Removal under UV Irradiation
by Chukwuka Bethel Anucha, Ilknur Altin, Emin Bacaksız, Tayfur Kucukomeroglu, Masho Hilawie Belay and Vassilis N. Stathopoulos
Separations 2021, 8(3), 25; https://doi.org/10.3390/separations8030025 - 26 Feb 2021
Cited by 28 | Viewed by 4271
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
(This article belongs to the Special Issue Detection, Fate and Removal of Contaminants of Emerging Concern in Aqueous Environment)
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21 pages, 3726 KiB  
Article
Immobilized TiO2/ZnO Sensitized Copper (II) Phthalocyanine Heterostructure for the Degradation of Ibuprofen under UV Irradiation
by Chukwuka BethelAnucha, IIknur Altin, Emin Bacaksiz, Ismail Degirmencioglu, Tayfur Kucukomeroglu, Salih Yılmaz and Vassilis N. Stathopoulos
Separations 2021, 8(3), 24; https://doi.org/10.3390/separations8030024 - 26 Feb 2021
Cited by 17 | Viewed by 3720
Abstract
Photocatalytic coatings of TiO2/ZnO/CuPc were developed on stainless steel substrates by subsequent sol gel dip coating for TiO2, spray pyrolysis for ZnO, and spin coating for copper (ii) phthalocyanine (CuPc) deposition. The latter compound was successfully prepared using a [...] Read more.
Photocatalytic coatings of TiO2/ZnO/CuPc were developed on stainless steel substrates by subsequent sol gel dip coating for TiO2, spray pyrolysis for ZnO, and spin coating for copper (ii) phthalocyanine (CuPc) deposition. The latter compound was successfully prepared using a Schiff-based process. The materials and coatings developed were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy with attached energy dispersive spectroscopy (SEM-EDS), UV-Vis spectroscopy, room temperature photoluminescence (RTPL) spectroscopy, H1-nuclear magnetic resonance (1H-NMR) spectroscopy, C13-nuclear magnetic resonance (13C-NMR) spectroscopy, and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS). The as-deposited TiO2/ZnO/CuPc on stainless steel retained in pristine state the structural and morphological/spectroscopic characteristics of its respective components. Estimated energy band gap values were 3.22 eV, 3.19 eV, 3.19 eV for TiO2, ZnO, TiO2/ZnO respectively and 1.60 eV, 2.44 eV, and 2.92 eV for CuPc. The photocatalytic efficiency of the fabricated TiO2/ZnO/CuPc coatings was tested toward ibuprofen (IBF). After 4 h irradiation under 365 nm UV, an increased degradation of about 80% was achieved over an initial 5 mg/L ibuprofen (IBF). This was much higher compared to about 42% and 18% IBF degradation by TiO2/ZnO and TiO2 thin film, respectively. In all cases, the stability of the best-performing photocatalyst was investigated showing a small decline to 77% of IBF degradation after the 5th cycle run. The effect of pH, reactive oxygen species (ROS) probe, shed light on a possible catalytic mechanism that was suggested. Full article
(This article belongs to the Special Issue Detection, Fate and Removal of Contaminants of Emerging Concern in Aqueous Environment)
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20 pages, 2682 KiB  
Article
ESI–LC–MS/MS for Therapeutic Drug Monitoring of Binary Mixture of Pregabalin and Tramadol: Human Plasma and Urine Applications
by Atiah H. Almalki, Nesma A. Ali, Fadwa A. Elroby, Mohamed R. El Ghobashy, Aml A. Emam and Ibrahim A. Naguib
Separations 2021, 8(2), 21; https://doi.org/10.3390/separations8020021 - 13 Feb 2021
Cited by 7 | Viewed by 4102
Abstract
Tramadol (TRM) and pregabalin (PGB) are frequently used in combination for neuropathic pain management. Accordingly, a selective and sensitive high-performance liquid chromatography–electrospray ionization–mass/mass spectrometric (ESI–LC–MS/MS) method is presented for determination of TRM and PGB, whether in pure forms or human biological fluids (plasma/urine), [...] Read more.
Tramadol (TRM) and pregabalin (PGB) are frequently used in combination for neuropathic pain management. Accordingly, a selective and sensitive high-performance liquid chromatography–electrospray ionization–mass/mass spectrometric (ESI–LC–MS/MS) method is presented for determination of TRM and PGB, whether in pure forms or human biological fluids (plasma/urine), using gabapentin (GBP) (IS) as the internal standard. Chromatographic separation was effected in total run time of 2.5 min, on Phenomenex Luna® Omega 1.6 um polar C18 (LC 150 × 2.1 mm) column with a mobile phase of methanol/water (70:30, v/v), 0.1% (v/v) formic acid at a flow rate of 0.3 mL/min. Ionization of the analytes was obtained using electrospray in the positive ion mode (ESI+). The MS/MS detection was performed by monitoring the fragments for TRM, PGB and GBP on a triple quadrupole mass spectrometer. Assay calibration was over the range of 10–1000 ng mL−1 for TRM and PGB with the correlation coefficients over 0.999 in pure form, human plasma and urine spiked with the studied compounds. Validation data showed the inter-run relative standard deviations (RSDs) were less than 4.3% for TRM and 3.8% for PGB, whereas the intra-run RSDs were less than 3.7% for TRM and 3.6% for PGB. The mean extraction recoveries for TRM and PGB were in the ranges of 86.51–93.38% and 86.20–92.42%. This method was successfully performed on real plasma and urine samples taken from neuropathic patients and proved to be an applicable method for routine therapeutic drug monitoring of the proposed drug combination. Full article
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26 pages, 964 KiB  
Article
Influence of Citrus Flavor Addition in Brewing Process: Characterization of the Volatile and Non-Volatile Profile to Prevent Frauds and Adulterations
by Emanuela Trovato, Adriana Arigò, Federica Vento, Giuseppe Micalizzi, Paola Dugo and Luigi Mondello
Separations 2021, 8(2), 18; https://doi.org/10.3390/separations8020018 - 12 Feb 2021
Cited by 12 | Viewed by 3900
Abstract
In the last few years, the flavored beer market has increased significantly. In particular, consumers showed a growing interest in citrus-flavored beers. Citrus fruits contain, among other class of compounds, terpenes and terpenoids and oxygenated heterocyclic compounds. The absence of a specific legislation [...] Read more.
In the last few years, the flavored beer market has increased significantly. In particular, consumers showed a growing interest in citrus-flavored beers. Citrus fruits contain, among other class of compounds, terpenes and terpenoids and oxygenated heterocyclic compounds. The absence of a specific legislation concerning beer flavored production and ingredients reported on the labels makes these beers subject to possible adulterations. Solid phase micro extraction (SPME) followed by gas chromatographic–mass spectrometry (GC-MS) and gas chromatographic-flame ionization detector (GC-FID) analysis of the volatile profile together with the characterization of the oxygen heterocyclic compounds through high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) demonstrated to be a powerful analytical strategy for quality control. In this study, we combined the volatile and non-volatile profiles of “citrus flavored mainstream beers”, in order to evaluate the authenticity and determine markers to prevent food frauds. The changes in the aroma composition of the unflavored types after the addition of peel, or citrus essential oil were also evaluated. The linear retention index (LRI) system was used for both techniques; in particular, its application in liquid chromatography is still limited and represents a novelty. The coupling of the high sensitivity of the HPLC MS/MS method with the LRI system, it has made possible for the first time a reliable identification and an accurate quantification of furocoumarins in citrus-flavored beers. Full article
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50 pages, 957 KiB  
Review
Overview of Sample Preparation and Chromatographic Methods to Analysis Pharmaceutical Active Compounds in Waters Matrices
by Cristina M. M. Almeida
Separations 2021, 8(2), 16; https://doi.org/10.3390/separations8020016 - 09 Feb 2021
Cited by 18 | Viewed by 6905
Abstract
In the environment, pharmaceutical residues are a field of particular interest due to the adverse effects to either human health or aquatic and soil environment. Because of the diversity of these compounds, at least 3000 substances were identified and categorized into 49 different [...] Read more.
In the environment, pharmaceutical residues are a field of particular interest due to the adverse effects to either human health or aquatic and soil environment. Because of the diversity of these compounds, at least 3000 substances were identified and categorized into 49 different therapeutic classes, and several actions are urgently required at multiple steps, the main ones: (i) occurrence studies of pharmaceutical active compounds (PhACs) in the water cycle; (ii) the analysis of the potential impact of their introduction into the aquatic environment; (iii) the removal/degradation of the pharmaceutical compounds; and, (iv) the development of more sensible and selective analytical methods to their monitorization. This review aims to present the current state-of-the-art sample preparation methods and chromatographic analysis applied to the study of PhACs in water matrices by pinpointing their advantages and drawbacks. Because it is almost impossible to be comprehensive in all PhACs, instruments, extraction techniques, and applications, this overview focuses on works that were published in the last ten years, mainly those applicable to water matrices. Full article
(This article belongs to the Special Issue Challenges and Trends in the Analysis of Compounds of Emerging Concern)
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12 pages, 1317 KiB  
Article
Hydrophilic Interaction Liquid Chromatography to Characterize Nutraceuticals and Food Supplements Based on Flavanols and Related Compounds
by Oscar Vidal-Casanella, Kevin Arias-Alpizar, Oscar Nuñez and Javier Saurina
Separations 2021, 8(2), 17; https://doi.org/10.3390/separations8020017 - 09 Feb 2021
Cited by 9 | Viewed by 3036
Abstract
Purified extracts from different types of berries and medicinal plants are increasingly used as raw materials for the production of nutraceuticals and dietary supplements, mainly due to their high content in bioactive substances. This is, for instance, the case of phenolic compounds such [...] Read more.
Purified extracts from different types of berries and medicinal plants are increasingly used as raw materials for the production of nutraceuticals and dietary supplements, mainly due to their high content in bioactive substances. This is, for instance, the case of phenolic compounds such as flavonoids, which exhibit a wide range of beneficial properties, including antioxidant, anti-inflammatory, antineoplastic and antimicrobial activities. This paper tackles the characterization of several kinds of nutraceuticals based on hydrophilic interaction liquid chromatography (HILIC) with fluorescence detection (FLD). The study focused on the determination of flavanols and related compounds such as condensed tannins. Analytes were recovered by solvent extraction using methanol:water:hydrochloric acid (70:29:1 v:v:v) as the extraction solvent under sonication for 30 min at 55 °C. Experimental design with response surface methodology was used to optimize the HILIC separation to achieve good resolution of the main components, using acetonitrile:acetic acid (99:1 v/v) (solvent A) and methanol:water:acetic acid, (95:3:2 v/v/v) (solvent B) as the components of the mobile phase. For the assessment of the elution gradient, factors under study were solvent B percentage and gradient time. The best conditions were achieved with 10% solvent B as the initial percentage and 30 min of linear gradient to reach 25% solvent B. Principal component analysis and partial least square-discriminant analysis were used to characterize and compare the compositional features of dietary supplements based on both targeted and non-targeted approaches. Results revealed that the sample distribution relied on the oligomeric nature of descriptors. Full article
(This article belongs to the Special Issue Advances in Food and Biological Samples Analysis)
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30 pages, 1376 KiB  
Review
Analysis of Monoclonal Antibodies by Capillary Electrophoresis: Sample Preparation, Separation, and Detection
by Meriem Dadouch, Yoann Ladner and Catherine Perrin
Separations 2021, 8(1), 4; https://doi.org/10.3390/separations8010004 - 04 Jan 2021
Cited by 25 | Viewed by 14374
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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11 pages, 1371 KiB  
Article
LC-MS Phytochemical Screening, In Vitro Antioxidant, Antimicrobial and Anticancer Activity of Microalgae Nannochloropsis oculata Extract
by Adil Farooq Wali, Yusra Al Dhaheri, Jayachithra Ramakrishna Pillai, Ahlam Mushtaq, Padma G. M. Rao, Syed Arman Rabbani, Aimen Firdous, Mohamed Soliman Elshikh and Dunia A. Al Farraj
Separations 2020, 7(4), 54; https://doi.org/10.3390/separations7040054 - 08 Oct 2020
Cited by 28 | Viewed by 5170
Abstract
Nowadays, marine microalgae are recognized to be a considerably novel and rich origin of bioactive moieties utilized in the sectors of nutraceuticals and pharmaceuticals. In the present study, Nannochloropsis oculata extract (AME) was associated with a wide variety of pharmacological studies such as [...] Read more.
Nowadays, marine microalgae are recognized to be a considerably novel and rich origin of bioactive moieties utilized in the sectors of nutraceuticals and pharmaceuticals. In the present study, Nannochloropsis oculata extract (AME) was associated with a wide variety of pharmacological studies such as in vitro antioxidant, antibacterial, and antifungal and anticancer activity (MDA-MB-231) in cancer cells through in vitro models. In the study, the chemical composition and structure of the bioactive compounds found in the AME extract were studied using the LC-MS technique. The results of the anticancer activity showed a decrease in the percentage of cell viability of the MDA-MB-231 cells in a concentration- and time-dependent manner (400 μg/mL at 24 h, 300 μg/mL at 48 h, and 200 μg/mL at 72 h). We have also observed morphological changes in the cells that could be associated with treatment with AME extract. Our observation of the AME extract-treated MDA-MB231 cells under light microscopy showed that when the concentration increased, the number of cells began to decrease. As far as LC-MS analysis is concerned, it showed the presence of the bioactive molecules was terpenoids along with carotenoids, polyphenolic and fatty acids. The result revealed that the AME extract exhibited noteworthy in vitro free radical scavenging potential, with an IC50 value of 52.10 ± 0.85 µg/L in DPPH assay, 122.84 ± 2.32 µg/mL in H2O2 assay and, 96.95 ± 1.68 µg/mL in ABTS assay. The activity was found to be highly significant against bacteria (Gram-positive and negative) and moderately significant against fungal strain with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC)/minimum fungicidal concentration (MFC) values between 15.63 and 500 µg/mL. Full article
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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 - 06 Jul 2020
Cited by 22 | Viewed by 5610
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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14 pages, 896 KiB  
Article
Pigments Content (Chlorophylls, Fucoxanthin and Phycobiliproteins) of Different Commercial Dried Algae
by Catarina Osório, Susana Machado, Juliana Peixoto, Sílvia Bessada, Filipa B. Pimentel, Rita C. Alves and M. Beatriz P. P. Oliveira
Separations 2020, 7(2), 33; https://doi.org/10.3390/separations7020033 - 11 Jun 2020
Cited by 84 | Viewed by 11904
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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20 pages, 3856 KiB  
Review
Hunting Molecules in Complex Matrices with SPME Arrows: A Review
by Jason S. Herrington, German A. Gómez-Ríos, Colton Myers, Gary Stidsen and David S. Bell
Separations 2020, 7(1), 12; https://doi.org/10.3390/separations7010012 - 15 Feb 2020
Cited by 56 | Viewed by 7755
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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27 pages, 1471 KiB  
Review
Evolution of Environmentally Friendly Strategies for Metal Extraction
by Govind Sharma Shyam Sunder, Sandhya Adhikari, Ahmad Rohanifar, Abiral Poudel and Jon R. Kirchhoff
Separations 2020, 7(1), 4; https://doi.org/10.3390/separations7010004 - 06 Jan 2020
Cited by 42 | Viewed by 9448
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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22 pages, 1517 KiB  
Review
Returning to Nature for the Design of Sorptive Phases in Solid-Phase Microextraction
by Gabriela Mafra, María Teresa García-Valverde, Jaime Millán-Santiago, Eduardo Carasek, Rafael Lucena and Soledad Cárdenas
Separations 2020, 7(1), 2; https://doi.org/10.3390/separations7010002 - 29 Dec 2019
Cited by 50 | Viewed by 5374
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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29 pages, 3934 KiB  
Review
Metal–Organic Frameworks as Key Materials for Solid-Phase Microextraction Devices—A Review
by Adrián Gutiérrez-Serpa, Idaira Pacheco-Fernández, Jorge Pasán and Verónica Pino
Separations 2019, 6(4), 47; https://doi.org/10.3390/separations6040047 - 02 Oct 2019
Cited by 75 | Viewed by 10793
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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21 pages, 3923 KiB  
Review
Metal-Organic Frameworks in Green Analytical Chemistry
by Priscilla Rocío-Bautista, Iván Taima-Mancera, Jorge Pasán and Verónica Pino
Separations 2019, 6(3), 33; https://doi.org/10.3390/separations6030033 - 27 Jun 2019
Cited by 79 | Viewed by 11221
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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47 pages, 6339 KiB  
Review
Chromatographic Techniques in the Research Area of Lithium Ion Batteries: Current State-of-the-Art
by Yannick Philipp Stenzel, Fabian Horsthemke, Martin Winter and Sascha Nowak
Separations 2019, 6(2), 26; https://doi.org/10.3390/separations6020026 - 13 May 2019
Cited by 43 | Viewed by 11158
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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22 pages, 1052 KiB  
Review
Total and Free Fatty Acids Analysis in Milk and Dairy Fat
by Gustavo Amores and Mailo Virto
Separations 2019, 6(1), 14; https://doi.org/10.3390/separations6010014 - 05 Mar 2019
Cited by 67 | Viewed by 22283
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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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 160 | Viewed by 19545
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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