Separations

42 pages, 8198 KB

Open AccessReview

NMR Spectroscopy in Complex Mixture Analysis and Structure Elucidation of Natural Products: Rethinking the Need for Separations

by Ioannis P. Gerothanassis

Separations 2026, 13(6), 184; https://doi.org/10.3390/separations13060184 (registering DOI) - 22 Jun 2026

Abstract

Qualitative and quantitative analysis of complex mixtures and structure elucidation is generally impeded by the intrinsic complexity of the NMR spectra and the extensive signal overlap. The conventional approach to characterizing individual metabolites from complex crude extracts of natural products relies on multistep [...] Read more.

Qualitative and quantitative analysis of complex mixtures and structure elucidation is generally impeded by the intrinsic complexity of the NMR spectra and the extensive signal overlap. The conventional approach to characterizing individual metabolites from complex crude extracts of natural products relies on multistep separation workflows employing diverse liquid chromatographic approaches and/or hyphenated techniques, which combine online integration of NMR with separation methods and other forms of spectroscopy. In recent decades, considerable efforts have been devoted to NMR applications in crude extracts without previous separation and isolation of the individual analytes. We present herein a critical overview of several NMR applications using chemical shift ranges of common organic functional groups, which can provide significant resolution advantages under specific experimental conditions. Particular emphasis is placed on: (i) characteristic chemical shift regions of strongly deshielded phenol OH groups, aldehyde CHO groups, hydroperoxide C-O-O-H groups and olefinic protons in conjugated double bonds; (ii) the advantages of using ¹³C chemical shift ranges through 2D ¹H-¹³C HSQC and HMBC experiments of strongly deshielded phenol OH groups, aldehyde CHO groups, hydroperoxide groups, conjugated double bonds, and deshielded aliphatic CH groups; (iii) selective 1D NMR-spin chromatography techniques (1D TOCSY, 1D NOE); (iv) multiple suppression of strong resonances for minor analyte identification and (v) band-selective excitation techniques for minor analyte identification and quantification. The complementary contributions of statistical heterospectroscopy and computational chemical shift prediction are also considered, together with a brief assessment of the NMR experimental parameters and performance characteristics. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Online Conference on Separations (IOCS2025))

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24 pages, 3694 KB

Open AccessArticle

Analysis of the Motion Characteristics of Different Particles Within a Novel Wide Neck Classifier

by Yan Zheng, Yan Li, Dongbo Li and Lujun Wang

Separations 2026, 13(6), 183; https://doi.org/10.3390/separations13060183 (registering DOI) - 22 Jun 2026

Abstract

A novel wide-neck classifier (WNC) was designed to address the problem that thickeners cannot achieve classification prior to flocculation in a single unit. Using the computational fluid dynamics-discrete phase method and PIV experimental method, the reliability of the model was validated. We studied [...] Read more.

A novel wide-neck classifier (WNC) was designed to address the problem that thickeners cannot achieve classification prior to flocculation in a single unit. Using the computational fluid dynamics-discrete phase method and PIV experimental method, the reliability of the model was validated. We studied the motion characteristics of different particles within the novelty-designed WNC. The primary forces acting on coal slime particles in the composite force field were gravity, drag force, pressure gradient force, and virtual mass force. Drag force dominated the classification and sedimentation processes. In contrast, gravity, pressure gradient, and virtual mass forces promoted downward sedimentation but hindered upward overflow. The classification of slime particles in WNC was divided into initial classification after tangential feeding and centrifugal classification in a cone. Both simulation and experimental results demonstrate that, under consistent feed conditions, mineral density significantly affected the distribution of particles at the classification underflow and classification overflow. Among the three minerals, kaolinite has the highest classification effect, followed by quartz, while coal has the lowest classification effect. Full article

(This article belongs to the Section Separation Engineering)

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Graphical abstract

14 pages, 765 KB

Open AccessCommunication

In Situ Anion-Generating Molecularly Imprinted Solid-Phase Extraction Coupled with HILIC-MS/MS for Determination of Metanephrines in Low Volume of Plasma

by Antons Podjava and Artūrs Šilaks

Separations 2026, 13(6), 182; https://doi.org/10.3390/separations13060182 (registering DOI) - 19 Jun 2026

Abstract

Metanephrine (MN) and normetanephrine (NMN) are critical biomarkers for neuroendocrine tumors (pheochromocytoma and paraganglioma). Following our previous development of a molecularly imprinted solid-phase extraction (MISPE) sorbent for urine analysis, this study evaluated MISPE coupled with HILIC-MS/MS for determining metanephrines in human plasma. Unlike [...] Read more.

Metanephrine (MN) and normetanephrine (NMN) are critical biomarkers for neuroendocrine tumors (pheochromocytoma and paraganglioma). Following our previous development of a molecularly imprinted solid-phase extraction (MISPE) sorbent for urine analysis, this study evaluated MISPE coupled with HILIC-MS/MS for determining metanephrines in human plasma. Unlike conventional phases, the novel polymer selectively binds analytes as in situ-generated anions via quaternary alkylammonium groups in hydroxide form, ensuring accurate extraction from just 25 µL of plasma. Validated per U.S. FDA guidelines, the assay showed good intra- and interday precision (CV < 10.8%), accuracy (bias < −10.6%) and excellent linearity (R² > 0.99) across pathological ranges (184.3–877.8 ng/L for MN; 174.8–923.0 ng/L for NMN), with low relative standard errors (<6.9%). Excellent selectivity was demonstrated in the presence of structurally close analogs (catecholamines, DOPA and its derivatives). Compared with commercial WCX, the sorbent yielded cleaner extracts, significantly reducing the phospholipid interference. Although lower limits of quantification (92.2 ng/L MN; 87.4 ng/L NMN) slightly exceeded healthy upper thresholds, the method has potential for use in specific clinical scenarios with pronounced biomarker elevations: diagnosis of pheochromocytoma/paraganglioma, monitoring post-treatment metanephrine decline, and tracking tumor-induced hypertensive crises in emergencies. This accessible protocol forms a solid foundation for advanced diagnostics. Full article

(This article belongs to the Section Bioanalysis/Clinical Analysis)

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12 pages, 1580 KB

Open AccessArticle

A Method for Purifying Pseudorabies Virus for Labeling the Neural Circuit by Using Capto^TM Core 700

by Rui Mei, Qinghan Wang, Kangyixin Sun, You Hu, Fuqiang Xu and Fan Jia

Separations 2026, 13(6), 181; https://doi.org/10.3390/separations13060181 - 19 Jun 2026

Abstract

Background: Viral vectors are indispensable tools in gene therapy and neural circuit mapping, offering promising therapeutic strategies for diverse genetic diseases and advancing neuroscience research. To achieve high transduction efficiency while mitigating impurity-induced immunogenicity, the development of viral vectors with improved purity and [...] Read more.

Background: Viral vectors are indispensable tools in gene therapy and neural circuit mapping, offering promising therapeutic strategies for diverse genetic diseases and advancing neuroscience research. To achieve high transduction efficiency while mitigating impurity-induced immunogenicity, the development of viral vectors with improved purity and quality is essential. However, this critical requirement is often unmet by conventional purification methods such as ultracentrifugation, which are time-consuming and frequently result in limited product purity. The pseudorabies virus (PRV) is extensively employed as a viral tool for mapping neural circuits, where improved purity contributes to enhanced accuracy of neural tracing. PRV531 is a retrograde trans-synaptic tracer modified from the PRV Bartha strain, specifically designed to facilitate the precise visualization of hierarchical neural networks. Methods: In this study, we developed a method for the concentration and purification of PRV531 by integrating hollow fiber ultrafiltration (HF) with Capto^TM Core 700 (CC700) chromatography. Initially, to concentrate the viral supernatant, a 500 kDa HF membrane was employed, maintaining a feed flow rate of 80 mL/min, a shear rate ranging from 2000 to 6000 s⁻¹, and a transmembrane pressure (TMP) between 0.5 and 1 bar. Following concentration, the virus underwent purification through CC700 chromatography, operating at linear flow rates ranging from 100 to 300 cm/h. Results: Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) revealed distinct bands consistent with the expected sizes of major PRV structural proteins, each with molecular weights ranging from 25 kDa to 150 kDa, concurrently demonstrating a substantial reduction in host cell proteins (HCPs) contamination. The purified PRV531 achieved a high final infectious titer of 3.55 × 10⁹ PFU/mL, with an overall functional virus recovery of 8.88% from the crude supernatant to the final product. Conclusion: These data demonstrate that TFF combined with CC700 resin can efficiently purify retrograde trans-synaptic PRV tracer. Furthermore, this approach provides a promising strategy for purifying other viral-based tracers that traditionally rely on conventional centrifugation methods. Full article

(This article belongs to the Section Purification Technology)

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17 pages, 5405 KB

Open AccessArticle

Surface Chemical Regulation of Coal Gangue–Rice Husk Biochar for Concurrent Promotion of Hg²⁺ Adsorption and Inhibition of Hg⁰ Production

by Kaikai Zhang, Wen Ye, Shunquan Shi, Jiale Yang, Yuyu Zhang, Ping Hou, Feng Xie, Yujie He, Jinze Zhao and Shaogang Hu

Separations 2026, 13(6), 180; https://doi.org/10.3390/separations13060180 - 18 Jun 2026

Abstract

Mercury (Hg) is a global pollutant that poses a serious threat to ecosystems and human health. Biochar has shown great potential for mercury removal due to its porous structure and abundant surface functional groups. However, redox-active moieties on biochar can reduce adsorbed Hg [...] Read more.

Mercury (Hg) is a global pollutant that poses a serious threat to ecosystems and human health. Biochar has shown great potential for mercury removal due to its porous structure and abundant surface functional groups. However, redox-active moieties on biochar can reduce adsorbed Hg²⁺ to volatile Hg⁰, leading to secondary mercury dispersion. To suppress this reduction, this study proposes a strategy of co-pyrolyzing coal gangue with rice husk to prepare composite biochars (RHB/CG), leveraging the abundant metal oxides in coal gangue to tailor the surface chemistry of biochar. The materials were characterized by FTIR, Raman, and XRD; static adsorption, mercury speciation analysis, and kinetic experiments were conducted. The results show that coal gangue incorporation significantly enhances the Hg²⁺ adsorption capacity of biochar, with the equilibrium adsorption capacity calculated by the pseudo-second-order kinetic model, increasing from 20.6 mg/g for pristine RHB to 38.7 mg/g for RHB/CG-1:1. More importantly, RHB/CG composites effectively suppress the reduction of Hg²⁺ to Hg⁰, and the amount of Hg⁰ accumulated in the system is 57.1% lower than that of pristine RHB. Mechanistic studies reveal that coal-gangue-derived basic functional groups (e.g., C–O–C, Si–O–M) inhibit reduction via sequestering Hg²⁺ through coordination and disruption of electron transfer pathways. PHREEQC simulations (pe = 6.0) confirm the decreased tendency of Hg²⁺ reduction to Hg⁰ with increasing pH, in good agreement with the experimental results showing reduced Hg²⁺ reduction. The corresponding results provide a green and sustainable solution for mercury-contaminated water and soil remediation. Full article

(This article belongs to the Special Issue Advanced Materials for Heavy Metal Adsorption in Wastewater Treatment)

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40 pages, 14798 KB

Open AccessReview

From Capture to Conversion: Advances and Challenges in Integrated CO₂ Capture and Utilization for Industrial Decarbonization

by Peng Bian, Qinchen Meng, Xianyin Yu, Jinou Han, Zhichen Zeng and Xudong Wang

Separations 2026, 13(6), 179; https://doi.org/10.3390/separations13060179 - 18 Jun 2026

Abstract

Amid growing pressure to reduce carbon emissions, carbon capture, utilization, and storage (CCUS) has become an important pathway toward deep decarbonization. However, the conventional separated “capture–release–conversion” process suffers from high energy consumption and system complexity, which severely limits its large-scale application. Integrated CO [...] Read more.

Amid growing pressure to reduce carbon emissions, carbon capture, utilization, and storage (CCUS) has become an important pathway toward deep decarbonization. However, the conventional separated “capture–release–conversion” process suffers from high energy consumption and system complexity, which severely limits its large-scale application. Integrated CO₂ Capture and Utilization (ICCU), which enables the capture, activation, and conversion of CO₂ within a single system, has attracted widespread attention because it can effectively reduce intermediate energy-intensive steps and improve carbon utilization efficiency. This review systematically summarizes recent progress in ICCU technology, with particular emphasis on reaction mechanisms and interfacial coupling characteristics. The performance features of solvent-based chemical absorption and solid-sorbent adsorption, two widely studied capture routes, are summarized, and typical integrated conversion pathways, including reverse water–gas shift, methanation, and dry reforming of methane, are discussed. On this basis, the roles of non-conventional energy-assisted strategies, such as photocatalysis, electrocatalysis, non-thermal plasma, and microwave irradiation, in expanding ICCU systems are further examined, together with their system-level coupling potential in carbon-intensive industries such as steel, cement, and power generation. Finally, the key scientific issues and engineering challenges currently facing ICCU are analyzed from the perspectives of fundamental mechanisms, material design, and system engineering, and future development directions are proposed. This review highlights that elucidating multiscale synergistic mechanisms, developing high-performance dual-function materials, and optimizing system integration are crucial to promoting the industrial application of ICCU technology. Full article

(This article belongs to the Special Issue Recent Advances in Carbon Dioxide Capture, Utilization, and Storage Technology)

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19 pages, 5568 KB

Open AccessArticle

Green Synthesis of Thiourea-Grafted Activated Carbon for Efficient Adsorption of AuCl₄⁻

by Tianyi Chen, Xudong Liu, Yaobin Lai, Jiayi Zan and Xuxia Zhang

Separations 2026, 13(6), 178; https://doi.org/10.3390/separations13060178 - 17 Jun 2026

Abstract

The thiourea grafting method can effectively improve the ability of activated carbon to recover chloroauric acid (AuCl₄⁻). Conventional grafting strategies rely on acyl halide reactions using reagents such as SOCl₂ and CH₂Cl₂, which suffer from [...] Read more.

The thiourea grafting method can effectively improve the ability of activated carbon to recover chloroauric acid (AuCl₄⁻). Conventional grafting strategies rely on acyl halide reactions using reagents such as SOCl₂ and CH₂Cl₂, which suffer from instability and high toxicity. Herein, we propose a green grafting strategy for thiourea by activating carboxyl groups with EDC-HCl/NHS in acetonitrile, followed by the amidation reaction to obtain thiourea-modified carbon (AC-NCS). FT-IR and XPS analyses confirm the successful grafting of thiourea onto the activated carbon surface. Compared with pristine activated carbon, the adsorption capacity of AC-NCS is 104.8 mg/g, increased by 5.76 times. Furthermore, it maintains a recovery rate of 84.2% after three cycles. XPS and FT-IR further reveal that adsorption occurs on the thiourea sulfur atoms (C=S) and protonated primary amines(-NH₃⁺), and the recovery of chloroauric acid is achieved through a synergistic “reduction–electrostatic attraction” mechanism. This method reduces the dependence on highly toxic reagents and provides a promising approach for the efficient and green recovery of gold from secondary resources. Full article

(This article belongs to the Special Issue Adsorbent Materials for Wastewater Treatment)

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Graphical abstract

24 pages, 1404 KB

Open AccessArticle

Identification of Key Aroma-Active Compounds in Plum, Jujube, and Grape Extracts via GC×GC-O-TOF-MS, GC-MS, Aroma Recombination and Omission Tests

by Ruiyang Chen, Qinghui Jia, Anzhen Fu, Fan Yang, Yixin Dai, Jingzhe Sun, Liya Liu, Ye Liu and Shuang Bi

Separations 2026, 13(6), 177; https://doi.org/10.3390/separations13060177 (registering DOI) - 16 Jun 2026

Abstract

Fruity natural flavors are widely used in food, cosmetics, and tobacco products, and their flavor profiles directly affect the sensory quality of the final products. However, the volatile organic compound systems in these flavors are highly complex, and severe co-elution among volatile components [...] Read more.

Fruity natural flavors are widely used in food, cosmetics, and tobacco products, and their flavor profiles directly affect the sensory quality of the final products. However, the volatile organic compound systems in these flavors are highly complex, and severe co-elution among volatile components makes effective component resolution a persistent analytical challenge. In this study, comprehensive two-dimensional gas chromatography–olfactometry–time-of-flight mass spectrometry (GC×GC-O-TOF-MS) was employed to separate and identify volatile odor compounds in three natural fruit flavor extracts: plum, jujube, and grape. A total of 113, 103, and 85 volatile odor compounds were identified from the plum, jujube, and grape extracts, respectively. By progressively adjusting the split ratio, aroma extract dilution analysis was performed, leading to the screening of 14, 11, and 32 aroma-active compounds from the three extracts, respectively. Compounds with high flavor dilution factors were subjected to quantitative analysis, and their odor activity values were calculated. Subsequently, omission and recombination experiments were conducted to confirm the key aroma-active compounds in each extract. The results showed that octanal was a key aroma compound shared by the plum and jujube extracts, while ethyl cinnamate was common to both the plum and grape extracts. Through a molecular sensory science approach and utilizing GC×GC-O-TOF-MS chromatographic separation technology, this study provides a reliable analytical platform for aroma characterization in complex samples. It also establishes a critical theoretical and data foundation for precisely identifying key aroma-active components and implementing targeted aroma modulation to enhance the natural flavor quality of fruits. Full article

(This article belongs to the Collection Feature Paper Collection in Section ‘Chromatographic Separations’)

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18 pages, 4299 KB

Open AccessArticle

Breaking Recovery Bottlenecks in Long-Chain Dicarboxylic Acid Extraction: Effect of pH and Solvents

by Priyanka Mondal, Iris Cornet, Inge Noëlle Adrienne Van Bogaert, Anita Buekenhoudt and Kristien De Sitter

Separations 2026, 13(6), 176; https://doi.org/10.3390/separations13060176 - 13 Jun 2026

Abstract

Efficient recovery of long-chain dicarboxylic acids (LCDAs) from aqueous fermentation broths is a key challenge for the industrial development of bio-based LCDA production. This study evaluates liquid–liquid extraction (LLE) as a downstream recovery strategy, comparing physical extraction (PE) and reactive extraction (RE) for [...] Read more.

Efficient recovery of long-chain dicarboxylic acids (LCDAs) from aqueous fermentation broths is a key challenge for the industrial development of bio-based LCDA production. This study evaluates liquid–liquid extraction (LLE) as a downstream recovery strategy, comparing physical extraction (PE) and reactive extraction (RE) for DCA 12, DCA 16, and DCA 18. The novelty of this work lies in demonstrating that LCDA extraction is governed by mechanisms fundamentally different from those of short- and medium-chain dicarboxylic acids. Whereas shorter chain dicarboxylic acids are mainly controlled by dissociation degree, LCDA recovery is strongly influenced by carbon-chain apolarity, low aqueous solubility, and compound losses through agglomeration, precipitation, and/or micellization. PEs enabled the selective recovery of the more hydrophobic DCA 16 and DCA 18 over DCA 12, confirming the dominant role of chain length in LCDA separation. In contrast, RE with Aliquat^®336 maximized total LCDA recovery, achieving extraction efficiencies above 85%, but with reduced selectivity. Validation in autoclaved fermentation broth from UCO feedstock confirmed the potential of Aliquat^®336 in octanol for high LCDA recovery, while revealing lower extraction efficiencies than in model mixtures due to broth matrix complexity. Overall, this study establishes LLE as a promising platform for LCDA recovery and highlights that future downstream process design must balance total recovery, chain-length selectivity, and broth-specific matrix effects. Full article

(This article belongs to the Topic Separation Techniques and Circular Economy)

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21 pages, 9550 KB

Open AccessArticle

Optimization of Ultrasound-Assisted Extraction of Cyclamen purpurascens Mill. Tubers: Box–Behnken Design and UHPLC-ESI-MS/MS Characterization

by Miljana G. Stojanović, Ivan M. Savić, Jovana Vunduk and Ivana M. Savić Gajić

Separations 2026, 13(6), 175; https://doi.org/10.3390/separations13060175 - 12 Jun 2026

Abstract

In contemporary research on natural bioactive compounds, increasing emphasis is placed on the development of efficient and sustainable extraction technologies. This study aimed to develop and optimize an innovative extraction process for wild cyclamen (Cyclamen purpurascens Mill.) tubers to maximize the yield [...] Read more.

In contemporary research on natural bioactive compounds, increasing emphasis is placed on the development of efficient and sustainable extraction technologies. This study aimed to develop and optimize an innovative extraction process for wild cyclamen (Cyclamen purpurascens Mill.) tubers to maximize the yield of total extractives using a Box–Behnken design. The effects of four extraction parameters were evaluated on the system response. A second-order polynomial model accurately described the extraction process, yielding a coefficient of determination of 0.919. The liquid-to-solid ratio was identified as the dominant factor affecting the extraction efficiency compared to the other factors investigated. The optimal extraction conditions were as follows: extraction time of 15.5 min, 13% (v/v) ethanol, liquid-to-solid ratio of 13.5 mL/g, and extraction temperature of 34 °C, resulting in a yield of 53.44%. The optimized process yielded a significant saponin content of 16.19 g/100 g, while the levels of phenolic compounds (132.52 mg GAE/100 g) and flavonoids (12.04 mg QE/100 g) were also quantified. UHPLC–ESI–MS/MS analysis confirmed the presence of triterpene saponins, flavonoids, and terpenoids. DPPH, ABTS⁺, and CUPRAC assays indicated the antioxidant potential of the extract, while the minimum inhibitory concentration assay showed antibacterial activity against Staphylococcus aureus and Escherichia coli. The established chemical profile and observed biological activities provide the basis for further evaluation of wild cyclamen tubers as a source of bioactive secondary metabolites. Full article

(This article belongs to the Special Issue Application of Chromatography in Bioactive Compound Analysis)

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17 pages, 18782 KB

Open AccessArticle

Hydrophobically Modified Anionic Polyacrylamide for Flocculation–Dewatering of Low-Rank Ultrafine Flotation Clean Coal

by Qiming Zhuo, Rong Zou, Xuan Du, Leilei Gao, Hongxiang Xu, Jiushuai Deng, Wenli Liu, He Zhang and Kejia Ning

Separations 2026, 13(6), 174; https://doi.org/10.3390/separations13060174 - 12 Jun 2026

Abstract

Low-rank ultrafine flotation clean coal typically yields filter cake moisture above 20% due to abundant oxygen-containing functional groups and strong surface hydrophilicity. Conventional polyacrylamide (PAM) flocculants are hydrophilic and improve dewatering only by altering cake porosity, not by reducing particle surface hydrophilicity, so [...] Read more.

Low-rank ultrafine flotation clean coal typically yields filter cake moisture above 20% due to abundant oxygen-containing functional groups and strong surface hydrophilicity. Conventional polyacrylamide (PAM) flocculants are hydrophilic and improve dewatering only by altering cake porosity, not by reducing particle surface hydrophilicity, so they remove little adsorbed water. In this study, hydrophobically modified anionic polyacrylamides (HMAPAM) were synthesized by grafting lauryl acrylate onto APAM. FTIR, ¹H NMR, XPS, and SEM confirmed the grafting and progressive enrichment of hydrophobic alkyl chains on the surface. Moderate hydrophobic modification markedly improved solid–liquid separation. HMAPAM-D (APAM/LA = 4.5:0.5) achieved a settling velocity of 0.817 cm/s at 9 mg/L, 50.2% higher than APAM, and reduced filter cake moisture to 16.64% at 1 mg/L under 0.6 MPa versus 19.39% for unmodified APAM. Excessive modification (HMAPAM-E, 4:1) promoted intramolecular self-association, producing heterogeneous flocs and higher filtration resistance that degraded dewatering efficiency. The performance gain stems from hydrophobic association combined with adsorption bridging. These results clarify how hydrophobic group content controls flocculation and dewatering, informing the design of better flocculants for this type of coal slurry. Full article

(This article belongs to the Section Separation Engineering)

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23 pages, 7612 KB

Open AccessArticle

Multi-Objective Optimization of a Cyclone Separator for Improved Separation Efficiency and Reduced Pressure Drop Using CFD and NSGA-II

by Héctor Calvopiña, Wilson Pavón, Kevin Chacha, Eduardo Bazurto, Aleph Salvador Acebo Arcentales and Angel Fabian Moreira Romero

Separations 2026, 13(6), 173; https://doi.org/10.3390/separations13060173 - 10 Jun 2026

Abstract

This study aims to optimize the performance of cyclone separators by simultaneously maximizing separation efficiency and minimizing pressure drop through a CFD-based multi-objective optimization framework. The research objectives are explicitly focused on (i) developing accurate predictive surrogate models for cyclone behavior and (ii) [...] Read more.

This study aims to optimize the performance of cyclone separators by simultaneously maximizing separation efficiency and minimizing pressure drop through a CFD-based multi-objective optimization framework. The research objectives are explicitly focused on (i) developing accurate predictive surrogate models for cyclone behavior and (ii) identifying optimal geometric configurations that balance both performance criteria. The methodology integrates Design of Experiments (DOE), Response Surface Methodology (RSM), and the Non-dominated Sorting Genetic Algorithm II (NSGA-II), using a full factorial design of 25 simulations to construct fourth-order surrogate models. This formulation was strictly necessary to capture the severe non-linearities observed in preliminary CFD runs. These models exhibited high predictive capability, with coefficients of determination (R²) above 0.94. The NSGA-II optimization generated a Pareto-optimal front that clearly describes the trade-off between separation efficiency and pressure drop, enabling systematic decision-making. The selected optimal configuration achieved a separation efficiency of 94.5% and a pressure drop of 194.78 Pa. CFD validation confirmed the robustness of the surrogate models, with relative errors below 1% for efficiency and below 5% for pressure drop. Overall, the results demonstrate that integrating CFD, surrogate modeling, and evolutionary optimization provides a reliable and computationally efficient strategy for cyclone separator design optimization. Full article

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14 pages, 2584 KB

Open AccessArticle

Production of Diol-Modified Column Packing Material and Its Use in Novel HPLC Method for Urea Analysis in Dialysis Process

by Murat Altan and Uğur Şahin

Separations 2026, 13(6), 172; https://doi.org/10.3390/separations13060172 - 10 Jun 2026

Abstract

Dialysis is a widely used and effective method for removing urea from protein solutions, particularly following protein denaturation or solubilization. Due to its small molecular weight (~60 Da), urea can pass through semipermeable membranes, while larger protein molecules are retained. Therefore, the performance [...] Read more.

Dialysis is a widely used and effective method for removing urea from protein solutions, particularly following protein denaturation or solubilization. Due to its small molecular weight (~60 Da), urea can pass through semipermeable membranes, while larger protein molecules are retained. Therefore, the performance of dialyzers in urea removal is critically important. Dialyzer performance is commonly evaluated according to the method specified in the ISO 8637-1 standard, which is based on the measurement of urea concentrations in aqueous solutions before and after dialysis. In this study, a novel diol-modified silica, typically used as a column packing material in HPLC, was synthesized and applied as a new column. Using this column, a new HPLC method combined with a refractive index detector (RID) was developed for the sensitive and accurate determination of urea in aqueous sample solutions. This study is the first to report quantitative urea analysis using a diol-modified column packing material. Method accuracy was evaluated through standard addition-recovery experiments. The method showed recovery values between 99 and 110%, a limit of detection (LOD) of 0.66 mg/L, a limit of quantification (LOQ) of 2.0 mg/L, and a relative standard deviation (RSD) of 4.4%. Full article

(This article belongs to the Section Chromatographic Separations)

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21 pages, 1417 KB

Open AccessReview

Evolution of P Discharge Regulations in China: Necessity Analysis and Advances in Chemical P Removal Technologies for Wastewater Treatment

by Tao Zhang and Yonghong Zhao

Separations 2026, 13(6), 171; https://doi.org/10.3390/separations13060171 - 9 Jun 2026

Abstract

As eutrophication worsens, countries including China, the US, France, Sweden, and South Korea have tightened phosphorus (P) discharge limits for wastewater treatment plants (WWTPs). This paper first reviews China’s evolving P regulations, then classifies P removal technologies into physical, chemical, biological, and combined [...] Read more.

As eutrophication worsens, countries including China, the US, France, Sweden, and South Korea have tightened phosphorus (P) discharge limits for wastewater treatment plants (WWTPs). This paper first reviews China’s evolving P regulations, then classifies P removal technologies into physical, chemical, biological, and combined methods. Analysis of current WWTPs in China shows that biological P removal alone is insufficient, making chemical P removal (CPR) a necessary supplement or primary approach. Thus, the review focuses on CPR technologies: chemical precipitation, ion exchange, adsorption, electrocoagulation, magnetic methods, hybrid biological-chemical methods, and P recovery technologies. For each, the principles, materials, application conditions, advantages, and disadvantages are discussed. This review aims to guide the selection, application, and future research of CPR processes. Full article

(This article belongs to the Section Environmental Separations)

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18 pages, 6486 KB

Open AccessArticle

Rapid Quantification of Low-Level Crystalline Impurities in Dalmelitinib Mesylate Using NIR Spectroscopy and Chemometric Modeling

by Runxi Gui, Xiaogang Lian, Maolin Li, Mingdi Liu, Lina Zhou, Songgu Wu and Qiuxiang Yin

Separations 2026, 13(6), 170; https://doi.org/10.3390/separations13060170 - 9 Jun 2026

Abstract

Accurate measurement and control of impurities are critical for ensuring the quality and therapeutic performance of solid-state pharmaceutical formulations. This study introduces a rapid, minimal sample preparation analytical approach for quantifying low-level dalmelitinib impurities in dalmelitinib mesylate, employing near-infrared (NIR) spectroscopy combined with [...] Read more.

Accurate measurement and control of impurities are critical for ensuring the quality and therapeutic performance of solid-state pharmaceutical formulations. This study introduces a rapid, minimal sample preparation analytical approach for quantifying low-level dalmelitinib impurities in dalmelitinib mesylate, employing near-infrared (NIR) spectroscopy combined with partial least squares regression (PLSR). To mimic actual manufacturing conditions, a mixture system was designed comprising dalmelitinib mesylate, dalmelitinib impurity, and formulation excipients. Various spectral preprocessing strategies were systematically evaluated, including Savitzky–Golay first derivative (SG1st), Savitzky–Golay second derivative (SG2nd), multiplicative scatter correction (MSC), standard normal variate (SNV), wavelet denoising, wavelet compression, and their combinations. The optimal model was obtained using SG1st combined with wavelet denoising. The resulting PLSR model (7 latent variables) showed good predictive performance, with an R² of 0.99569 and an RMSECV of 0.00315. The limit of detection (LOD) and limit of quantification (LOQ) were 0.234% and 0.708%, respectively, demonstrating applicability for monitoring low-level impurities in pharmaceutical formulations. Method validation demonstrated satisfactory precision (RSD < 3%), accuracy (100.77–102.01%), and stability over 24 h (RSD ≤ 4.75%). Compared with conventional solid-state analytical techniques, the proposed NIR–PLSR framework enables rapid, non-destructive analysis with minimal sample preparation. The combination of derivative preprocessing and wavelet denoising improved extraction of impurity-related spectral information in complex pharmaceutical systems, highlighting the potential of this approach for process analytical technology (PAT) and pharmaceutical quality monitoring. Full article

(This article belongs to the Special Issue Emerging New Technologies in Fundamental and Industrial Crystallization)

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14 pages, 1815 KB

Open AccessArticle

Optimization of Subcritical Water Extraction for Artemisia argyi Leaf Polysaccharides Using a Hybrid RSM–NN–DSA Framework

by Huanping Zhang, Huichao Lv, Xue Gao, Shuhong Wang, Jinhong Song, Yang Jiao and Rongrong Cai

Separations 2026, 13(6), 169; https://doi.org/10.3390/separations13060169 - 8 Jun 2026

Abstract

Subcritical water extraction (SWE) is an eco-friendly and efficient technique for isolating bioactive ingredients from natural products. To improve the extraction yield of Artemisia argyi leaf polysaccharides (AAPs), a three-stage hybrid optimization strategy combining single-factor experiments, response surface methodology (RSM), neural network (NN), [...] Read more.

Subcritical water extraction (SWE) is an eco-friendly and efficient technique for isolating bioactive ingredients from natural products. To improve the extraction yield of Artemisia argyi leaf polysaccharides (AAPs), a three-stage hybrid optimization strategy combining single-factor experiments, response surface methodology (RSM), neural network (NN), and direct search algorithm (DSA) was proposed. Single-factor experiments were used to screen key parameters. A Box–Behnken design (BBD)-based RSM was applied for preliminary optimization. A {3, 5, 1} structured NN was trained using 63 datasets from RSM, and DSA was used to determine the globally optimal process parameters. The optimal conditions were obtained as follows: extraction time 17.72 min, liquid-to-solid ratio 92.83 mL/g, extraction temperature 123.35 °C, stirring speed 1800 r/min, and natural pH. Under these conditions, the experimental AAP extraction yield reached 6.99%, with a relative error of only 1.16% compared with the predicted value of 6.91%. Fourier transform infrared (FT-IR) spectroscopy confirmed that the product exhibited typical polysaccharide structural characteristics. The integrated RSM–NN–DSA framework provides a reliable and high-precision approach for optimizing SWE of plant polysaccharides, showing good potential for industrial applications. Full article

(This article belongs to the Special Issue Isolation and Identification of Biologically Active Natural Compounds)

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20 pages, 4136 KB

Open AccessArticle

Flotation of Spodumene Against Quartz by Punicines

by Stéphanie Mireille Tsanang, Atzin Moran Mendoza, Ali Zgheib, Maximilian Hans Fischer, Annett Wollmann, Ursula E. A. Fittschen, Thomas Schirmer and Andreas Schmidt

Separations 2026, 13(6), 168; https://doi.org/10.3390/separations13060168 - 6 Jun 2026

Abstract

Five pH- and light-switchable punicine derivatives were investigated as collectors in the flotation of spodumene and quartz. At the natural pH of the minerals, the punicine substituted with a C17 alkyl residue showed the best recovery under daylight (>5000 lux), with values up [...] Read more.

Five pH- and light-switchable punicine derivatives were investigated as collectors in the flotation of spodumene and quartz. At the natural pH of the minerals, the punicine substituted with a C17 alkyl residue showed the best recovery under daylight (>5000 lux), with values up to 65.0% and 97.8%, and also the highest absolute recovery difference between the two minerals. For pH values of 2 and 12, the punicine collector with a viologen moiety and a C9 alkyl residue shows the best absolute recovery difference, with values of 32.45% and 32.88%, respectively. Studies on the influence of pH, particle size distribution, UV light and darkness, ζ-potential measurements, and IR spectroscopic measurements were carried out to gain insight into the mechanisms. Full article

(This article belongs to the Topic Separation Techniques and Circular Economy)

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20 pages, 3164 KB

Open AccessArticle

Flavor Changes Through the Fermentation Process of Longmen Rice Vinegar

by Yibo Bai, Rui Li, Liman Zheng, Yu Zhang, Huanlu Song, Jing Liu, Weining Huo, Wen Nie and Suyan Wan

Separations 2026, 13(6), 167; https://doi.org/10.3390/separations13060167 - 1 Jun 2026

Abstract

The flavor profile of Longmen rice vinegar directly influences consumer purchase intention, and understanding its variation during fermentation is crucial for final product quality control. In this study, the flavor dynamics during the fermentation of Longmen rice vinegar were systematically investigated. Sensory evaluation [...] Read more.

The flavor profile of Longmen rice vinegar directly influences consumer purchase intention, and understanding its variation during fermentation is crucial for final product quality control. In this study, the flavor dynamics during the fermentation of Longmen rice vinegar were systematically investigated. Sensory evaluation indicated that acidity increased significantly during the acetic acid fermentation stage, while alcoholic and fermented odors decreased continuously. Instrumental analysis identified 129 volatile compounds, predominantly esters, alcohols, and acids. Based on relative odor activity value (r-OAV) analysis, acetic acid, 3-methylbutyl acetate, 2,3-butanedione, benzeneacetaldehyde, phenethyl alcohol, ethyl acetate, 2-phenylethyl acetate, ethyl 4-methyl-pentanoate, 3-methyl-1-butanol, and 3-methylbutanal were determined to be the major contributors to the overall aroma. Orthogonal partial least-squares discriminant analysis (OPLS-DA) further screened 21 key differential compounds. Significant variations in organic acid and amino acid contents during fermentation were also observed. Correlation analysis revealed relationships between key aroma compounds and organic, as well as amino, acids. These findings establish a foundation for monitoring flavor dynamics during the fermentation of Longmen rice vinegar. Full article

(This article belongs to the Special Issue Design and Optimization of Extraction/Separation Processes for Natural Products)

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22 pages, 1711 KB

Open AccessArticle

Chemical and Sensory Differences Among Coffee Beverages Brewed by Traditional Moka, Espresso, and Kamira, a Novel Italian Brewing Device

by Giovanna Lo Vecchio, Rosaria Costa, Rossella Vadalà, Laura De Maria, Rita De Pasquale, Giuseppe Tardiolo and Nicola Cicero

Separations 2026, 13(6), 166; https://doi.org/10.3390/separations13060166 - 1 Jun 2026

Abstract

The chemical composition and sensory profile of coffee are influenced by brewing method, namely extraction pressure, temperature, contact time, and equipment. This study compared coffee prepared with a traditional moka pot, a conventional espresso machine, and a novel Italian device (Kamira). Volatile compounds [...] Read more.

The chemical composition and sensory profile of coffee are influenced by brewing method, namely extraction pressure, temperature, contact time, and equipment. This study compared coffee prepared with a traditional moka pot, a conventional espresso machine, and a novel Italian device (Kamira). Volatile compounds were analyzed by headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography–mass spectrometry (GC–MS), leading to the determination of furan (34–42%), pyrrole (4–10%), and pyrazine (13–14%) derivatives. The most abundant fatty acids were palmitic (36–37%), linoleic (40%), and oleic (11%) acids. Physicochemical parameters (total solids, pH, and refractive index) were also measured. Caffeine and chlorogenic acids were quantified by liquid chromatography (HPLC). Differences in chlorogenic acids and volatile compounds were associated with variations in bitterness, acidity, astringency, and aroma intensity. Finally, a trained panel performed sensory evaluation to evaluate the olfactory and flavor attributes of the three types of coffee brews. Significant differences emerged among brewing systems. Espresso showed the highest caffeine content (55.3 ± 4.1 mg/100 g) and total solids (2.61 ± 0.11 g/100 g), together with a stable crema and intense sensory attributes. Moka coffee exhibited a rich aromatic profile but limited crema. The Kamira device produced an abundant crema and a chemical profile partially comparable to espresso. These findings confirm that brewing technology markedly affects coffee composition and sensory perception. Full article

(This article belongs to the Section Analysis of Food and Beverages)

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