Chromatographic Stationary Phases Research Articles

Synthesis, characterization and application of carbon nanotube-bonded with silica as a high performance liquid chromatography stationary phase

In order to improve the retention ability of anthraquinones and flavonoids on high performance liquid chromatography (HPLC) column and improve chromatographic performance, multi-walled carbon nanotubes (MWCNTs) were bound to the surface of silica spheres via amide bonding using a chemical synthesis method. Three hybrid fillers were prepared by varying the amount of MWCNTs added, and the stationary phases were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The successful preparation of the mixed stationary phases was demonstrated by comparing the changes in the surface of silica spheres before and after bonding and the changes in the absorption peaks of specific functional groups. The mixed stationary phases were filled in the empty column of the HPLC. The results of this study indicate that the columns can be prepared by CNTs@SiO2 to improve or broaden the chromatographic performance of the stationary phase and obtain better separation of the compounds. This thesis provides an idea for improving chromatographic performance with a view to playing a better role in the application of compound separation.

Long-Term Fluorescence Behavior of CdSe/ZnS Quantum Dots on Various Planar Chromatographic Stationary Phases.

Nanoparticles, particularly quantum dots (QDs), are commonly used for the sensitive detection of various objects. A number of target molecules may be determined using QDs sensing systems. Depending on their chemical nature, physicochemical properties, and spatial arrangement, QDs can selectively interact with given molecules of interest. This can be performed in complex systems, including microorganisms or tissues. Efficient fluorescence enables low exposure of QDs and high sensitivity for detection. One disadvantage of quantum dots fluorophores is fluorescence decay. However, for given applications, this property may be an advantage, e.g., for highly sensitive detection based on correlation images in the time domain. This experimental work deals with the measurement of fluorescence decay of Lumidot TMCdSe/ZnS (530 nm) quantum dots. These nanoparticles were transferred to the surface of various planar chromatographic stationary phases. Fluorescence of formed spots was recorded at room temperature over a long period of time, namely 15.7824 × 105 min (three years). The resulting signal profiles in the time domain were analyzed using classical approach (luminescence model comparison involving different mathematical models).Moreover, fluorescence behavior on different TLC/HPTLC supports was investigated using multivariate statistics (principal component analysis, PCA). Eight planar chromatographic stationary phases were investigated, including cellulose, octadecylsilane, polyamide, silica gel and aluminium oxide in different forms (TLC and HPTLC types). The presented research revealed significantly different and non-linear long-term QDs behavior on these solids. Two different fluorescence signal trajectories were recorded, including typical signal decay after QDs application to the plates and long-term intensity increase. This was particularly visible for given planar chromatographic adsorbents, e.g., cellulose or octadecylsilane. To the author’s knowledge, these findings were not reported before using the stationary chromatographic phases, and enable the design of future experiments toward sensing of low molecular mass chemicals using, e.g., advanced quantification approaches. This may include signal processing computations based on correlation images in the time domain. Additionally, the reported preliminary data indicates that the investigated nanoparticles can be applied as efficient and selective fluorophores. This was demonstrated on micro-TLC plates where separated bioactive organic substances quenching from cyanobacteria extracts were sensitively detected. The described detection protocol can be directly applied for different planar chromatographic systems, including paper-based microfluidic devices, planar electrophoresis and/or miniaturized microfluidic chip devices.

Capillary Gas Chromatographic Separation Performances of a Tetraphenyl Porphyrin Stationary Phase

Tetraphenyl porphyrin (TPP) has enormous potential for use as gas chromatography stationary phases because it has a distinctive extended π–π conjugated coplanar structure and a range of interesting properties such as a good solubility in dichloromethane, high melting point, and good thermal stability. In this work, a TPP column was successfully prepared using a static method. The column was nonpolar and had a high efficiency. The chromatographic selectivity of the TPP column was assessed. The TPP column showed superiority retention and higher resolution for alicyclic, aromatic molecules through ring matching and π-π stacking interaction comparable to HP-5MS column. The unique mechanisms through which the TPP column retained polychlorinated biphenyls allowed the peak pair of 2,2ʹ,5-trichlorobiphenyl and 4,4ʹ-dichlorobiphenyl to be resolved better on the TPP column than the HP-5MS column. The TPP column was thermally stable even at 260°C for 2 h and gave results of a high degree of precision (run-to-run and column-to-column) with relative standard deviations <0.05% and <4.96%, respectively. The results indicated that porphyrin derivatives will be useful gas chromatography stationary phases.

Preparation and evaluation of two silica-based hydrophilic-hydrophobic and acid-base balanced stationary phases via in-situ surface polymerization

Two new hydrophilic-hydrophobic and acid-base balanced liquid chromatographic stationary phases were obtained by using two long-chain monomers including undecylenic acid (UA) and oleic acid (OA) combined with short-chain 4-vinyl pyridine (Py) in-situ polymerized on silica microspheres surfaces, respectively. These two stationary phases can be used for reversed-phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC) modes. Hydrophilic, hydrophobic, acidic and basic analytes can be separated on two new stationary phases in RPLC or HILIC mode. Compared with commercial hydrophobic C18 columns and other HILIC columns, two new stationary phases have excellent selectivity and separation performance in the separation of 9 polycyclic aromatic hydrocarbons, 10 aromatic acids, 10 anilines and 5 oxazolidinones, respectively. This novel polymer-functionalized silica design strategy has opened up new ideas for the future of mixed-mode stationary phases with multiple functions and specificity.

Preparation and characterization of immobilized 5-HT1A receptor stationary phase for high throughput screening of the receptor-binding ligands from complex systems like Curcuma wenyujin Y. H. Chen et C. Ling extract

The incidence of depression has increased significantly during the COVID-19 pandemic. This disease is closely associated with serotonin 1A (5-HT1A) receptor and often treated by complex prescription containing Curcuma wenyujin Y. H. Chen et C. Ling. Therefore, we hypothesized that this herb contains bioactive compounds specially binding to the receptor. However, the rapid discovery of new ligands of 5-HT1A receptor is still challenging due to the lack of efficient screening methods. To address this problem, we developed and characterized a novel approach for the rapid screening of ligands by using immobilized 5-HT1A receptor as the chromatographic stationary phase. Briefly, haloalkane dehalogenase was fused at the C-terminal of 5-HT1A receptor, and the modified 5-HT1A receptor was immobilized on amino-microspheres by the reaction between haloalkane dehalogenase and 6-chlorohexanoic acid linker. Scanning electron microscope and X-ray photo-electron were used to characterize the morphology and element of the immobilized receptor. The binding of three specific ligands to 5-HT1A receptor was investigated by two different methods. Moreover, we examined the feasibility of 5-HT1A receptor colume in high throughput screening of new ligands from complex systems as exemplified by Curcuma wenyujin Y. H. Chen et C. Ling. Gweicurculactone, 2-hydroxy-1-(3,4-dihydroxybenzene)-7-(4′-hydroxybezene)-heptane and curcuminol F were identified as the ligands of 5-HT1A receptor with the binding energies of −7.06 kcal/mol, −7.77 kcal/mol and −5.26 kcal/mol, respectively. Collectively, these results indicated that the immobilized 5-HT1A receptor was capable of screening bioactive compound from complex system, providing an effective methodology for high throughput screening.

Recent Developments of Liquid Chromatography Stationary Phases for Compound Separation: From Proteins to Small Organic Compounds.

Compound separation plays a key role in producing and analyzing chemical compounds. Various methods are offered to obtain high-quality separation results. Liquid chromatography is one of the most common tools used in compound separation across length scales, from larger biomacromolecules to smaller organic compounds. Liquid chromatography also allows ease of modification, the ability to combine compatible mobile and stationary phases, the ability to conduct qualitative and quantitative analyses, and the ability to concentrate samples. Notably, the main feature of a liquid chromatography setup is the stationary phase. The stationary phase directly interacts with the samples via various basic mode of interactions based on affinity, size, and electrostatic interactions. Different interactions between compounds and the stationary phase will eventually result in compound separation. Recent years have witnessed the development of stationary phases to increase binding selectivity, tunability, and reusability. To demonstrate the use of liquid chromatography across length scales of target molecules, this review discusses the recent development of stationary phases for separating macromolecule proteins and small organic compounds, such as small chiral molecules and polycyclic aromatic hydrocarbons (PAHs).

Separating and purifying of Panax notoginseng saponins using a rosin-based polymer-bonded with silica as a high-performance liquid chromatography stationary phase

In this study, methyl methacrylate and fumaropimaric acid tris (ethylene glycol) ester were used as functional monomer and cross-linker, respectively, to prepare a rosin-based polymer-bonded with silica as a high-performance liquid chromatography stationary phase via a coating–bonding method. The produced stationary phase was characterized by thermogravimetric analysis, Fourier transform infrared spectroscopy, and microporous physical adsorption, and the specific surface area and particle size distribution were calculated. The results showed that the stationary phase particles have good sphericity, having a particle size of approximately 4.81 µm, specific surface area of 280 m2·g−1, and average pore diameter of 6.76 nm, and were nontoxic. Further, column evaluation revealed that the produced stationary phase exhibited typical reversed-phase chromatographic behavior, hydrophobicity, good reproducibility and strong steric selectivity. Thus, the resin was used for separating and purifying Panax notoginseng saponins, and the effects of the chromatographic conditions on separating Panax notoginseng saponins were investigated; moreover, the thermodynamic parameters of column separation were studied. Finally, Panax notoginseng saponins purification using the new stationary phase resulted an increase in purity from 45.27% to 85.08%.

Characterization of a highly stable zwitterionic hydrophilic interaction chromatography stationary phase based on hybrid organic-inorganic particles.

We have characterized a sulfobetaine stationary phase based on 1.7 μm ethylene‐bridged hybrid organic–inorganic particles, which is intended for use in hydrophilic interaction chromatography. The efficiency of a column packed with this material was determined as a function of flow rate, demonstrating a minimum reduced plate height of 2.4. The batch‐to‐batch reproducibility was assessed using the separation of a mixture of acids, bases, and neutrals. We compared the retention and selectivity of the hybrid sulfobetaine stationary phase to that of several benchmark materials. The hybrid sulfobetaine material gave strong retention for polar neutrals and high selectivity for methyl groups, hydroxy groups, and configurational isomers. Large differences in cation and anion retention were observed among the columns. We characterized the acid and base stability of the hybrid sulfobetaine stationary phase, using accelerated tests at pH 1.3 and 11.0, both at 70°C. The results support a recommended pH range of 2–10. We also investigated the performance of columns packed with this material for metal‐sensitive analytes, comparing conventional stainless steel column hardware to hardware that incorporates hybrid surface technology to mitigate interactions with metal surfaces. Compared to the conventional columns, the hybrid surface technology columns showed a greatly improved peak shape.

Single-Crystalline Covalent Organic Frameworks as High-Performance Liquid Chromatographic Stationary Phases for Positional Isomer Separation

Vigorously developing new stationary phases to meet the requirements for the separation of positional isomers that have similar physicochemical properties is still an urgent topic in separation science. Herein, a single-crystalline covalent organic framework (COF-300) packed column for the separation of positional isomers in high-performance liquid chromatography (HPLC) was reported for the first time. Benefitting from its regular shape, excellent chemical and thermal stability, microporous feature, and strong hydrophobicity of single-crystalline COF-300, the single-crystalline COF-300-packed column showed excellent resolution for the separation of positional isomers, including nitroaniline, dichlorobenzene, dibromobenzene, diiodobenzene, diethylbenzene, chloronitrobenzene, bromonitrobenzene, and iodonitrobenzene isomers, which cannot be all separated on commercial columns and a polycrystalline COF-300-packed column. Especially, the resolution values for m-/p-diiodobenzene and o-/m-diiodobenzene were 4.45 and 2.53. Moreover, the alkylbenzene, monosubstituted aromatics, polycyclic aromatic hydrocarbons, and the mixture of ethylbenzene and styrene were also baseline separated on the single-crystalline COF-300-packed column. This successful application not only confirmed the great potential of single-crystalline COFs in HPLC separation of positional isomers but also pioneered the utilization of single-crystalline COFs in separation science.

A Numerical Investigation of the Hydrodynamic Dispersion in Novel Chromatographic Stationary Phases

A Numerical Investigation of the Hydrodynamic Dispersion in Novel Chromatographic Stationary Phases

An electron-deficient supramolecular macrocyclic host for the selective separation of aromatics and cyclic aliphatics

Host 1 with an electron-deficient nanometer-sized cavity were synthesized in two steps. Moreover, 1 has been successfully used as a gas chromatographic stationary phase to prepare a packed column for the separation of PhH/Cy and Tol/MCy.

Efficient hydrogen isotopic analysis with Cu–Fe/ZSM-5 zeolite as a cryogenic chromatographic stationary phase

A bimetal-functionalized zeolite of Cu–Fe/ZSM-5 is synthesized as the stationary phase material for an efficient chromatographic analysis of hydrogen gas isotopes.

High selectivity of a novel D–A structured copolymer as a gas chromatographic stationary phase toward aromatic isomers

This work reports a new π-conjugated copolymer with D–A structure (PBDB-T) as the stationary phase for gas chromatography (GC) with high resolving performance towards aromatic isomers of high similarity in structure and properties.

Gas chromatography of essential oil: State-of-the-art, recent advances, and perspectives.

This review is an overview of the recent advances of gas chromatography in essential oil analysis; in particular, it focuses on both the new stationary phases and the advanced analytical methods and instrumentations. A paragraph is dedicated to ionic liquids as gas chromatography stationary phases, showing that, thanks to their peculiar selectivity, they can offer a complementary contribution to conventional stationary phases for the analysis of complex essential oils and the separation of critical pairs of components. Strategies to speed-up the analysis time, thus answering to the ever increasing request for routine essential oils quality control, are also discussed. Last but not least, a paragraph is dedicated to recent developments in column miniaturization in particular that based on microelectromechanical-system technology in a perspective of developing micro-gas chromatographic systems to optimize the energy consumption as well as the instrumentation dimensions. A number of applications in the essential oil field is also included.

Sustainable hydrophilic ultrasmall carbonaceous spheres modified by click reaction for high-performance polymeric ion chromatographic stationary phase

Novel poly(ethylvinylbenzene-divinylbenzene) (EVB-DVB) agglomerated with ultrasmall carbonaceous spheres (UCSs) anion-exchange packings for ion chromatography (IC) were constructed. Hydrophilic UCSs with mean sizes of 62–98 nm were synthesized in quantity by the polydiallyl dimethyl ammonium chloride aided hydrothermal carbonization of fructose. The green strategy based on the thiol-ene click reaction with cysteamine in aqueous system was first designed for the hyperbranched polyquaternary amine (HPA) grafting of UCSs with negligible damage on their monodispersity. The HPA modified UCSs were evenly distributed on sulfonated EVB-DVB substrate to form one uniform layer of functional nanospheres without observable coagulum. Seven typical anions (F−, Cl−, NO2−, Br−, NO3−, SO42- and PO43−) were baseline separated on constructed packing in 5 min with high efficiencies in the range of 44,800–71,100 plates m − 1. The rapid separation of polarizable anions, small organic acids and saccharides could be also accomplished under isocratic elution with competitive peak symmetry and efficiency. Good reproducibility was demonstrated by consecutive injection. Thiosulfate in water reducer was further detected on prepared packing in 4 min with detection limit of 0.04 mg L − 1 (S/N = 3) and good repeatability.

Light-Driven Polarity Switching of the Chromatographic Stationary Phase with Photoreversibility.

Regrettably, conventional chromatographic columns have immutable polarity, resulting in requirements of at least two columns with polarity difference and sophisticated mechanical switching valves, which hinders the development of "micro-smart" multidimensional tandem chromatography. In this work, light-driven polarity switching was realized in a single capillary column based on the reversible trans-cis isomerization of 4-[3-(triethoxysilyl)propoxy]azobenzene as the stationary phase under light irradiation, with the change in dipole moment. As a result, the stationary phase offers precise and dynamic control of polarity based on the cis-trans azobenzene ratio, which depends on irradiation wavelength and time. Thus, the continuous adjustment of polarity enables diversified chromatographic separation modes, for example, step-polarity gradient and polarity-conversion separation modes, taking advantage of the superior freedom of polarity switching in time and spatial dimensions. The photosensitive column also shows good reproducibility of polarity photoreversibility and high separation efficiency. The present study might offer brand new insight into developing miniaturization and intellectualization of multidimensional chromatography via designing smart responsive switching valves or stationary phases, besides mechanical means.

Cyclodextrin-dendrimers nanocomposites functionalized high performance liquid chromatography stationary phase for efficient separation of aromatic compounds

In this work, novel cyclodextrin-dendrimers nanocomposites functionalized high performance liquid chromatography stationary phases were developed for efficient separation of aromatic compounds. β-cyclodextrin was grafted onto the surface of silica gel matrix with poly (amidoamine) dendrimers as spacers. Scanning electron microscope, fourier transform infrared spectroscopy, element analysis and Brunner-Emmet-Teller measurement proved the successful grafting of cyclodextrin-dendrimers nanocomposites. The obtained stationary phases showed satisfactory separation effects for alkylbenzenes and benzenesulfonic acid substituents in reverse phase liquid chromatography mode. Weak hydrophilic and ion exchange interactions were also confirmed at the same time. Meanwhile, the effects of dendrimers and cyclodextrin on the chromatography performance were discussed. Separation mechanism of the stationary phases were verified by two-dimensional nuclear magnetic resonance technology, and the result implied that the proposed cyclodextrin-dendrimers nanocomposites functionalized stationary phases have significant prospects for separation and determination of more aromatic compounds in future.

Hydrogel Coating with Temperature Response Retention Behavior and Its Application in Selective Separation of Liquid Chromatography

We reporte the double-layer hydrogel-coated mesoporous silica material as a new stationary phase for liquid chromatography. The method of combining physical coating and chemical coating was to apply hydrogel coating on the surface of silica, and finally, a new type of liquid chromatography stationary phase with in situ coating of the functional hydrogel on silica was obtained. This hydrogel-functionalized liquid chromatography stationary phase also exhibits a certain temperature responsiveness. Experimental results show that this temperature response is mainly due to changes in the hydrogen bonding between the stationary phase and the analyte at different temperatures in the column oven, which leads to changes in retention behavior. The hydrogel-coated mesoporous silica microspheres showed excellent selectivity for many polar analytes. An excellent column efficiency was obtained (139 000 plates/m for terephthalic acid) after optimization of chromatographic conditions. In addition to rapid separation of some analytes, this new hydrogel stationary phase also has certain superiority in chromatographic performance compared with other new excellent liquid chromatography stationary phases functioned by three-dimensional cross-linking systems. The important thing is that this strategy is relatively easy to prepare a new stationary phase with different properties.

Comparison of chromatographic performance of co-grafted silica using octadecene respectively with vinylpyrrolidone, vinylimidazole and vinylpyridine

Three reversed-phase liquid chromatography (RPLC) stationary phases were obtained by using long-chain 1-octadecene (OD) co-grafted with three short-chain monomers, including N-vinylpyrrolidone (NVP), 1-vinylimidazole (VIm) and 4-vinylpyridine (VPy), respectively (noted as Sil@ODNVP, Sil@ODVIm and Sil@ODVPy). Peak broadening phenomenon in RPLC mode which resulted by short-chain was examined carefully. Compared with Sil@ODNVP, both of Sil@ODVIm and Sil@ODVPy had smaller peak width and higher column efficiency in the separation of 10 polycyclic aromatic hydrocarbons (PAHs), 7 alkyl benzenes, 7 aromatic acids, 7 aromatic esters and 9 phenols. In addition, VPy has the strongest ion exchange capacity than other two short-chains. In this case, we can see that VPy and VIm maybe more suitable to be used as functional monomeric modifiers of new chromatographic stationary phases.

Polymerized phosphonium ionic liquid functionalized silica microspheres as mixed-mode stationary phase for liquid chromatographic separation of phospholipids

There is a large and growing demand for the vigorous development of new high performance liquid chromatography stationary phases in order to solve complex phospholipids separation. Herein, phosphonium-based ionic liquid trioctyl(allyl)phosphonium bromide ([P888Allyl]Br) was first synthesized with trioctylphosphine and allyl bromide. With [P888Allyl]Br as the polymerizable monomer, polymerized phosphonium ionic liquid functionalized silica microsphere (PIL@SiO2) was further synthetized via click chemistry reaction. Significantly, based on the inherent amphiphilic nature of the introduced [P888Allyl]Br, the packed PIL@SiO2 column displayed hydrophilic/hydrophobic mixed-mode retention mechanisms. The PIL@SiO2 column can achieve separation of nucleic acid bases and nucleosides, sulfonamides, amides and anilines with excellent selectivity in a shorter separation time. The column efficiency reached 109,700 N/m for 2-iodoacetamide. One of the important characteristics of the PIL@SiO2 column is that both phospholipid classes and species can be efficiently separated via the same column, outperforming that of the commercial amino column. Furthermore, the application potential of the PIL@SiO2 column was further verified via separation of phospholipids extracted from soy lecithin. The proposed PIL@SiO2 column provides a promising candidate for separation of complex phospholipid samples.