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Separations
Volume 4
Issue 1
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Separations, Volume 4, Issue 1 (March 2017) – 9 articles

Cover Story (view full-size image): For the first time, reversed-phase liquid chromatographic separations of small molecules have been achieved using a graphene oxide nanoparticle (GONP)-modified polystyrene-divinylbenzene polyHIPE capillary column. GONP polyHIPEs were found to have a surface area up to 40% lower than unmodified polyHIPEs, but demonstrated superior analyte adsorption properties. This work indicates the potential offered by GO-polyHIPEs in flow through applications such as adsorption or separation processes. View Paper here.
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11 pages, 235 KB  
Article
Evaluation of Ion Exchange and Sorbing Materials for Their Adsorption/Desorption Performane towards Anthocyanins, Total Phenolics, and Sugars from a Grape Pomace Extract
by Evangelos D. Trikas, Rigini M. Papi, Dimitrios A. Kyriakidis and George A. Zachariadis
Separations 2017, 4(1), 9; https://doi.org/10.3390/separations4010009 - 18 Mar 2017
Cited by 10 | Viewed by 6356
Abstract
Byproducts of winery industries are treated, in many cases, as useless wastes constituting not only a major disposal problem but also not providing any additional profit to the industries. However, these byproducts could be utilized as a source of various phenolic compounds, such [...] Read more.
Byproducts of winery industries are treated, in many cases, as useless wastes constituting not only a major disposal problem but also not providing any additional profit to the industries. However, these byproducts could be utilized as a source of various phenolic compounds, such as anthocyanins, that could be used as nutraceuticals or natural colorants. Nine materials were tested and evaluated for their ability to retain and elute anthocyanins, total phenolics, and sugars from a grape pomace extract. The materials tested were the ion exchange Amberlite IRA 400 Cl−, Lewatit TP 208 and Lewatit TP 260, and the sorbing Chromosorb G-HP, Amberite XAD 2, Zeocros CA 150, Chemviron Carbon, Oasis HLB (hydrophilic-lipophilic balance) and Isolute C8 end-capped (EC). The two materials with the higher anthocyanins recovery rate, Oasis HLB and Isolute C8 (EC), were further examined for their anthocyanin capacities which were calculated as 5.76 mg·cm−3 and 3.06 mg·cm−3 respectively. Furthermore, their behavior pattern towards anthocyanins of various molecular weights was investigated using a liquid chromatography coupled with mass spectrometry (LC-PDA-MS) system. Full article
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11 pages, 1760 KB  
Article
Comparison of Miniaturized and Conventional Asymmetrical Flow Field-Flow Fractionation (AF4) Channels for Nanoparticle Separations
by Zengchao You, Florian Meier and Steffen Weidner
Separations 2017, 4(1), 8; https://doi.org/10.3390/separations4010008 - 18 Mar 2017
Cited by 6 | Viewed by 6262
Abstract
The performance of a miniaturized channel for the separation of polymer and metal nanoparticles (NP) using Asymmetrical Flow Field-Flow Fractionation (AF4) was investigated and compared with a conventional AF4 system. To develop standard separation methods, experimental parameters like cross flow, gradient profile and [...] Read more.
The performance of a miniaturized channel for the separation of polymer and metal nanoparticles (NP) using Asymmetrical Flow Field-Flow Fractionation (AF4) was investigated and compared with a conventional AF4 system. To develop standard separation methods, experimental parameters like cross flow, gradient profile and injection time were varied and optimized. Corresponding chromatographic parameters were calculated and compared. Our results indicate that the chromatographic resolution in the miniaturized channel is lower, whereas significantly shorter analyses time and less solvent consumption were obtained. Moreover, the limit of detection (LOD) and limit of quantification (LOQ) obtained from hyphenation with a UV-detector are obviously lower than in a conventional channel, which makes the miniaturized channel interesting for trace analysis. Full article
(This article belongs to the Special Issue Size Separation Techniques)
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12 pages, 2428 KB  
Article
Analyses of Indole Compounds in Sugar Cane (Saccharum officinarum L.) Juice by High Performance Liquid Chromatography and Liquid Chromatography-Mass Spectrometry after Solid-Phase Extraction
by Jean Wan Hong Yong, Liya Ge, Wei San Wong, Zhen Ma and Swee Ngin Tan
Separations 2017, 4(1), 7; https://doi.org/10.3390/separations4010007 - 15 Mar 2017
Cited by 10 | Viewed by 9998
Abstract
Simultaneous quantitative analysis of 10 indole compounds, including indole-3-acetic acid (IAA, one of the most important naturally occurring auxins) and some of its metabolites, by high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) after solid-phase extraction (SPE) was reported for the [...] Read more.
Simultaneous quantitative analysis of 10 indole compounds, including indole-3-acetic acid (IAA, one of the most important naturally occurring auxins) and some of its metabolites, by high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) after solid-phase extraction (SPE) was reported for the first time. The analysis was carried out using a reverse phase HPLC gradient elution, with an aqueous mobile phase (containing 0.1% formic acid) modified by methanol. Furthermore, a novel SPE procedure was developed for the pre-concentration and purification of indole compounds using C18 SPE cartridges. The combination of SPE, HPLC, and LC-MS was applied to screen for the indole compounds present in sugar cane (Saccharum officinarum L.) juice, a refreshing beverage with various health benefits. Finally, four indole compounds were successfully detected and quantified in sugar cane juice by HPLC, which were further unequivocally confirmed by LC-MS/MS experiments operating in the multiple reaction monitoring (MRM) mode. Full article
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16 pages, 5257 KB  
Review
Recent Advances in Extraction and Stirring Integrated Techniques
by Soledad Cárdenas and Rafael Lucena
Separations 2017, 4(1), 6; https://doi.org/10.3390/separations4010006 - 15 Mar 2017
Cited by 51 | Viewed by 10093
Abstract
The extraction yield of a microextraction technique depends on thermodynamic and kinetics factors. Both of these factors have been the focus of intensive research in the last few years. The extraction yield can be increased by synthesizing and using novel materials with favorable [...] Read more.
The extraction yield of a microextraction technique depends on thermodynamic and kinetics factors. Both of these factors have been the focus of intensive research in the last few years. The extraction yield can be increased by synthesizing and using novel materials with favorable distribution constants (one of the thermodynamic factors) for target analytes. The extraction yield can also be increased by improving kinetic factors, for example, by developing new extraction modes. Microextraction techniques are usually non-exhaustive processes that work under the kinetic range. In such conditions, the improvement of the extraction kinetics necessarily improves the performance. Since the extraction yield and efficiency is related to how fast the analytes diffuse in samples, it is crucial to stir the sample during extraction. The stirring can be done with an external element or can be integrated with the extraction element in the same device. This article reviews the main recent advances in the so-called extraction/stirring integrated techniques with emphasis on their potential and promising approaches rather than in their applications. Full article
(This article belongs to the Special Issue Trends in Microextraction Techniques for Sample Preparation)
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13 pages, 2407 KB  
Article
Graphene Oxide Nanoparticles and Their Influence on Chromatographic Separation Using Polymeric High Internal Phase Emulsions
by Sidratul Choudhury, Emer Duffy, Damian Connolly, Brett Paull and Blánaid White
Separations 2017, 4(1), 5; https://doi.org/10.3390/separations4010005 - 11 Feb 2017
Cited by 9 | Viewed by 6155
Abstract
This work presents the first instance of reversed-phase liquid chromatographic separation of small molecules using graphene oxide nanoparticle-modified polystyrene-divinylbenzene polymeric high internal phase emulsion (GONP PS-co-DVB polyHIPE) materials housed within a 200-µm internal diameter (i.d.) fused silica capillary. The graphene oxide [...] Read more.
This work presents the first instance of reversed-phase liquid chromatographic separation of small molecules using graphene oxide nanoparticle-modified polystyrene-divinylbenzene polymeric high internal phase emulsion (GONP PS-co-DVB polyHIPE) materials housed within a 200-µm internal diameter (i.d.) fused silica capillary. The graphene oxide nanoparticle (GONP)-modified materials were produced as a potential strategy to increase both the surface area limitations and the reproducibility issues observed in monolithic stationary phase materials. GONP PS-co-DVB polyHIPEs were found to have a surface area up to 40% lower than unmodified polymeric high internal phase emulsion (polyHIPE) stationary phases. However, despite having a surface area significantly lower than that of the unmodified material, the GONP-modified polyHIPEs demonstrated superior analyte adsorption properties. Reducing the GONP material did not have any significant impact on elution order or retention factor of the analytes, which was most likely due to low GONP loading attributed to the 250-nm GONPs utilised. The lower surface area of GONP-modified polyHIPEs provided similar separation efficiency and increased repeatability from injection to injection resulting in % relative standard deviations (%RSDs) of less than 0.6%, indicating the potential offered by graphene oxide (GO)-modified polyHIPES in flow through applications such as adsorption or separation processes. Full article
(This article belongs to the Special Issue Monolithic Columns in Separation Sciences)
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2 pages, 280 KB  
Editorial
Acknowledgement to Reviewers of Separations in 2016
by Separations Editorial Office
Separations 2017, 4(1), 4; https://doi.org/10.3390/separations4010004 - 11 Jan 2017
Viewed by 2790
Abstract
The editors of Separations would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2016.[...] Full article
9 pages, 5323 KB  
Article
Numerical Simulation of Fluid Dynamics in a Monolithic Column
by Kazuhiro Yamamoto and Yuuta Tajima
Separations 2017, 4(1), 3; https://doi.org/10.3390/separations4010003 - 11 Jan 2017
Cited by 3 | Viewed by 5241
Abstract
As for the measurement of polycyclic aromatic hydrocarbons (PAHs), ultra-performance liquid chromatography (UPLC) is used for PAH identification and densitometry. However, when a solvent containing a substance to be identified passes through a column of UPLC, a dedicated high-pressure-proof device is required. Recently, [...] Read more.
As for the measurement of polycyclic aromatic hydrocarbons (PAHs), ultra-performance liquid chromatography (UPLC) is used for PAH identification and densitometry. However, when a solvent containing a substance to be identified passes through a column of UPLC, a dedicated high-pressure-proof device is required. Recently, a liquid chromatography instrument using a monolithic column technology has been proposed to reduce the pressure of UPLC. The present study tested five types of monolithic columns produced in experiments. To simulate the flow field, the lattice Boltzmann method (LBM) was used. The velocity profile was discussed to decrease the pressure drop in the ultra-performance liquid chromatography (UPLC) system. Full article
(This article belongs to the Special Issue Monolithic Columns in Separation Sciences)
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22 pages, 1419 KB  
Review
Nano-Doped Monolithic Materials for Molecular Separation
by Caleb Acquah, Eugene Marfo Obeng, Dominic Agyei, Clarence M. Ongkudon, Charles K. S. Moy and Michael K. Danquah
Separations 2017, 4(1), 2; https://doi.org/10.3390/separations4010002 - 1 Jan 2017
Cited by 21 | Viewed by 9282
Abstract
Monoliths are continuous adsorbents that can easily be synthesised to possess tuneable meso-/macropores, convective fluid transport, and a plethora of chemistries for ligand immobilisation. They are grouped into three main classes: organic, inorganic, and hybrid, based on their chemical composition. These classes may [...] Read more.
Monoliths are continuous adsorbents that can easily be synthesised to possess tuneable meso-/macropores, convective fluid transport, and a plethora of chemistries for ligand immobilisation. They are grouped into three main classes: organic, inorganic, and hybrid, based on their chemical composition. These classes may also be differentiated by their unique morphological and physicochemical properties which are significantly relevant to their specific separation applications. The potential applications of monoliths for molecular separation have created the need to enhance their characteristic properties including mechanical strength, electrical conductivity, and chemical and thermal stability. An effective approach towards monolith enhancement has been the doping and/or hybridization with miniaturized molecular species of desirable functionalities and characteristics. Nanoparticles are usually preferred as dopants due to their high solid phase dispersion features which are associated with improved intermolecular adsorptive interactions. Examples of such nanomaterials include, but are not limited to, carbon-based, silica-based, gold-based, and alumina nanoparticles. The incorporation of these nanoparticles into monoliths via in situ polymerisation and/or post-modification enhances surface adsorption for activation and ligand immobilisation. Herein, insights into the performance enhancement of monoliths as chromatographic supports by nanoparticles doping are presented. In addition, the potential and characteristics of less common nanoparticle materials such as hydroxyapatite, ceria, hafnia, and germania are discussed. The advantages and challenges of nanoparticle doping of monoliths are also discussed. Full article
(This article belongs to the Special Issue Monolithic Columns in Separation Sciences)
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8 pages, 1421 KB  
Article
Simultaneous Determination of Daidzein, Genistein and Formononetin in Coffee by Capillary Zone Electrophoresis
by Feng Luan, Li Li Tang, Xuan Xuan Chen and Hui Tao Liu
Separations 2017, 4(1), 1; https://doi.org/10.3390/separations4010001 - 1 Jan 2017
Cited by 12 | Viewed by 5959
Abstract
Coffee is a favorite and beverage in Western countries that is consumed daily. In the present study, capillary zone electrophoresis (CE) was applied for the separation and quantification of three isoflavones including daidzein, genistein and formononetin in coffee. Extraction of isoflavones from the [...] Read more.
Coffee is a favorite and beverage in Western countries that is consumed daily. In the present study, capillary zone electrophoresis (CE) was applied for the separation and quantification of three isoflavones including daidzein, genistein and formononetin in coffee. Extraction of isoflavones from the coffee sample was carried out by extraction and purification process using ether after the acid hydrolysis with the antioxidant butylated hydroxy-toluene (BHT). The experimental conditions of the CE separation method were: 20 mmol/L Na2HPO4 buffer solution, 25 kV applied voltage, 3 s hydrodynamic injection at 30 mbar, and UV detection at 254 nm. The results show that the three compounds can be tested within 10 min with a linearity of 0.5–50 µg/mL for all three compounds. The limits of detection were 0.0642, 0.134, and 0.0825 µg/mL for daidzein, formononetin and genistein, respectively. The corresponding average recovery was 99.39% (Relative Standard Detection (RSD) = 1.76%), 98.71% (RSD = 2.11%) and 97.37% (RSD = 3.74%). Full article
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