Development of silica-based stationary phases for high-performance liquid chromatography

Inhibition of 5-HT alleviates PTSD-like behaviors and promotes hippocampal neuroplasticity by modulating hippocampal autophagy in rats

5-Hydroxytryptamine (5-HT) plays a substantial role in mitigating depression and anxiety. However, the potential effects of 5-HT against posttraumatic stress disorder (PTSD) and its underlying mechanisms remain unclear. Elevated plus maze test evaluates anxiety-related behaviors, and the open field test is used to assess overall activity levels and anxiety. Inflammatory cytokine levels were determined using ELISA. The levels of 5-HT and dopamine were measured using HPLC. mRNA and protein levels were examined by PCR and Western blot, respectively. Rats exposed to single prolonged stress (SPS) exhibited typical PTSD-like phenotypes, with decreased levels of 5-HT in the hippocampus and significant reductions in its downstream targets, brain-derived neurotrophic factor (BDNF) and TrkB. In addition, it was discovered that the autophagy signaling pathway might be involved in regulating hippocampal BDNF in rats exposed to SPS. Subsequent treatment with an intracerebral injection of sh-SERT significantly inhibited anxiety and cognitive dysfunction in rats. Moreover, sh-SERT treatment was observed to substantially reverse the increase in autophagy signaling protein expression and consequently improve the expression of BDNF and TrkB proteins, which had been reduced. The current study demonstrates that sh-SERT exhibits significant anti-PTSD effects, potentially mediated in part through the reduction of cellular autophagy to enhance hippocampal synaptic plasticity.NEW & NOTEWORTHY The study demonstrated that sh-SERT exhibits significant anti-posttraumatic stress disorder (PTSD) effects, potentially mediated in part through the reduction of cellular autophagy to enhance hippocampal synaptic plasticity.

Assessment of Hydrophilicity/Hydrophobicity in Mesoporous Silica by Combining Adsorption, Liquid Intrusion, and Solid-State NMR Spectroscopy

We have developed a comprehensive strategy for quantitatively assessing the hydrophilicity/hydrophobicity of nanoporous materials by combining advanced adsorption studies, novel liquid intrusion techniques, and solid-state NMR spectroscopy. For this, we have chosen a well-defined system of model materials, i.e., the highly ordered mesoporous silica molecular sieve SBA-15 in its pristine state and functionalized with different amounts of trimethylsilyl (TMS) groups, allowing one to accurately tailor the surface chemistry while maintaining the well-defined pore structure. For an absolute quantification of the trimethylsilyl group density, quantitative 1H solid-state NMR spectroscopy under magic angle spinning was employed. A full textural characterization of the materials was obtained by high-resolution argon 87 K adsorption, coupled with the application of dedicated methods based on nonlocal-density functional theory (NLDFT). Based on the known texture of the model materials, we developed a novel methodology allowing one to determine the effective contact angle of water adsorbed on the pore surfaces from complete wetting to nonwetting, constituting a powerful parameter for the characterization of the surface chemistry inside porous materials. The surface chemistry was found to vary from hydrophilic to hydrophobic as the TMS functionalization content was increased. For wetting and partially wetting surfaces, pore condensation of water is observed at pressures P smaller than the bulk saturation pressure p0 (i.e., at p/p0 < 1) and the effective contact angle of water on the pore walls could be derived from the water sorption isotherms. However, for nonwetting surfaces, pore condensation occurs at pressures above the saturation pressure (i.e., at p/p0 > 1). In this case, we investigated the pore filling of water (i.e., the vapor-liquid phase transition) by the application of a novel, liquid water intrusion/extrusion methodology, allowing one to derive the effective contact angle of water on the pore walls even in the case of nonwetting. Complementary molecular simulations provide density profiles of water on pristine and TMS-grafted silica surfaces (mimicking the tailored, functionalized experimental silica surfaces), which allow for a molecular view on the water adsorbate structure. Summarizing, we present a comprehensive and reliable methodology for quantitatively assessing the hydrophilicity/hydrophobicity of siliceous nanoporous materials, which has the potential to optimize applications in heterogeneous catalysis and separation (e.g., chromatography).

A minireview on covalent organic frameworks as stationary phases in chromatography

Advances in the design of novel porous materials open new avenues for the development of chromatographic solid stationary phases. Covalent organic frameworks (COFs) are promising candidates in this context due to their remarkable structural versatility and exceptional chemical and textural properties. In this minireview, we summarize the main strategies followed in recent years to apply these materials as stationary phases for chromatographic separations. We also comment on the perspectives of this new research field and potential directions to expand the applicability and implementation of COF stationary phases in analytical systems.

Molecularly imprinted polymers in online extraction liquid chromatography methods: Current advances and recent applications

BACKGROUND

One of the primary objectives in green analytical practices is the seamless integration of extraction and separation steps, resulting in the augmentation of both analytical throughput and method performance. Consequently, the exploration of prospective sorbent materials has drawn significant attention in the scientific community, particularly concerning the potential for online procedures. Employing the optimal sorbent material within an automated analytical approach holds the promise of elevating the precision of the analytical evaluation. Molecularly imprinted polymers (MIPs) excel in specific analyte interaction within complex matrices. However, MIPs' full potential was not widely exploring especially for online analytical methodologies.

RESULTS

Here is presented a comprehensive overview of the current applications of MIPs as sorbent materials within integrated and automated separation methodologies applied to diverse matrices including biological, food, and environmental samples. Notably, their primary advantage, as evidenced in the literature, lies in their exceptional selectivity for the target analyte discussed according to the adopted synthesis protocol. Furthermore, the literature discussed here illustrates the versatility of MIPs in terms of modification with one or more phases which are so-called hybrid materials, such as molecularly imprinted monoliths (MIM), the molecularly imprinted ionic liquid polymer (IL-MIP), and restricted access to molecularly imprinted polymer (RAMIP). The reported advantages enhance their applicability in integrated and automated separation procedures, especially to the column switching methods, across a broader spectrum of applications.

SIGNIFICANCE

This revision aims to demonstrate the MIP's potential as a sorbent phase in integrated and automated methods, this comprehensive overview of MIP polymers in integrated and automated separation methodologies can be used as a valuable guide, inspiring new research on developing novel horizons for MIP applications to have their potential emphasized in analytical science and enhanced to the great analytical methods achievement.

The Research Progress of Bioactive Peptides Derived from Traditional Natural Products in China

Traditional natural products in China have a long history and a vast pharmacological repertoire that has garnered significant attention due to their safety and efficacy in disease prevention and treatment. Among the bioactive components of traditional natural products in China, bioactive peptides (BPs) are specific protein fragments that have beneficial effects on human health. Despite many of the traditional natural products in China ingredients being rich in protein, BPs have not received sufficient attention as a critical factor influencing overall therapeutic efficacy. Therefore, the purpose of this review is to provide a comprehensive summary of the current methodologies for the preparation, isolation, and identification of BPs from traditional natural products in China and to classify the functions of discovered BPs. Insights from this review are expected to facilitate the development of targeted drugs and functional foods derived from traditional natural products in China in the future.

Recent development in hydrophilic interaction liquid chromatography stationary materials for glycopeptide analysis

Protein glycosylation is one of the most important post-translational modifications, and aberrant glycosylation is associated with the occurrence and development of diseases. Deciphering abnormal glycosylation changes can identify disease-specific signatures to facilitate the discovery of potential disease biomarkers. However, glycosylation analysis is challenging due to the diversity of glycans, heterogeneity of glycosites, and poor electrospray ionization of mass spectrometry. To overcome these obstacles, glycosylation is often elucidated using enriched glycopeptides by removing highly abundant non-glycopeptides. Hydrophilic interaction liquid chromatography (HILIC) is widely used for glycopeptide enrichment due to its excellent selectivity and specificity to hydrophilic glycans and compatibility with mass spectrometry. However, the development of HILIC has lagged far behind hydrophobic interaction chromatography, so efforts to further improve the performance of HILIC are beneficial for glycosylation analysis. This review discusses recent developments in HILIC materials and their advanced applications. Based on the physiochemical properties of glycopeptides, the use of amino acids or peptides as stationary phases showed improved enrichment and separation of glycopeptides. We can envision that the use of glycopeptides as stationary phases would definitely further improve the selectivity and specificity of HILIC for glycosylation analysis.

Layer-by-layer coating and chemical cross-linking of multilayer polysaccharides on silica for mixed-mode HPLC application

A facile, controllable and environmentally friendly method for fabricating a novel polysaccharide-silica composite stationary phase (SiO₂@(HA-CS)₁₂) was developed in this report. Two natural polysaccharides (hyaluronan acid and chitosan) were controllably coated on the silica surface using a layer-by-layer assembly technique, and then the polysaccharide shell was chemically cross-linked to improve the stability. The column efficiency of the SiO₂@(HA-CS)₁₂ column reached 74 000 plates per m in HILIC mode and 20 100 plates per m in IEC mode, which indicates great potential for separating polar and charged samples.

Improvement of the froth flotation of LiAlO2 and melilite solid solution via pre-functionalization

In this work froth flotation studies with LiAlO₂ (lithium-containing phase) and Melilite solid solution (gangue phase) are presented. The system was optimized with standard collectors and with compounds so far not applied as collectors. Furthermore, the principle of self-assembled monolayers was introduced to a froth flotation process for the first time resulting in excellent yields and selectivities.

A Molecular Shape Recognitive HPLC Stationary Phase Based on a Highly Ordered Amphiphilic Glutamide Molecular Gel

Chiral glutamide-derived lipids form self-assembled fibrous molecular gels that can be used as HPLC organic phases. In this study, HPLC separation efficiency was improved through the addition of branched amphiphilic glutamide lipids to the side chains of a terminally immobilized flexible polymer backbone. Poly(4-vinylpyridine) with a trimethoxysilyl group at one end was grafted onto the surface of porous silica particles (Sil-VP15, polymerization degree = 15), and the pyridyl side chains were quaternized with a glutamide lipid having a bromide group (BrG). Elemental analysis indicated that the total amount of the organic phase of the prepared stationary phase (Sil-VPG15) was 38.0 wt%, and the quaternization degree of the pyridyl groups was determined to be 32.5%. Differential scanning calorimetric analysis of a methanol suspension of Sil-VPG15 indicated that the G moieties formed a highly ordered structure below the phase transition temperature even on the silica surface, and the ordered G moieties exhibited a gel-to-liquid crystalline phase transition. Compared with a commercially available octadecylated silica column, the Sil-VPG15 stationary phase showed high selectivity toward polycyclic aromatic hydrocarbons, and particularly excellent separations were obtained for geometrical and positional isomers. Sil-VPG15 also showed highly selective separation for phenol derivatives, and bio-related molecules containing phenolic groups such as steroids were successfully separated. These separation abilities are probably due to multiple interactions between the elutes and the highly ordered functional groups, such as the pyridinium and amide groups, on the highly ordered molecular gel having self-assembling G moieties.

Characterization of the new CelerisTM Arginine column: Retentive behaviour through a combination of chemometric tools and potential in drug analysis

Celeris^TM Arginine (ARG) is a mixed-mode stationary phase recently released on the market. To characterize its analytical behavior, the retention factors of a pool (n=100, of which 36 neutrals, 26 acids and 38 bases) of pharmaceutically relevant compounds have been measured on this phase over eight percentages (from 10 to 90% v/v) of acetonitrile (MeCN) as organic modifier. The ARG phase exhibited enhanced affinity for the molecules that are in their anionic form at the experimental pH, whilst basic compounds, albeit over a wide range of lipophilicity and pK_a values, were on average poorly retained. To dissect the separation mechanism of the ARG phase, the overall analytical retention has been deconvoluted into the individual contributions of intermolecular forces by a QSPR/ Partial Least Square (PLS)/Block Relevance (BR) analysis tool recently developed by us. For the neutrals, the most relevant blocks were found to be Size, describing the interaction due to the dimension of the molecule, and O, representing the solute's hydrogen bond donor properties. The change in sign from positive to negative of the Size block, which occurs between 10% and 20% MeCN, allowed to visually appreciate the switch in the separation mode from reversed phase to normal phase. Some good statistic models for rationalizing the analytical behaviour of neutrals were developed from VS+ descriptors. However, their performance in modelling the analytical retention of acids was substandard, probably due to the intrinsic inefficacy of VS+ descriptors in handling electric charges. This instance was addressed by a complimentary MLR strategy, which led to successfully model the retention of acids on the ARG column and to shed light into their retention mechanism, which seemed to be substantially driven by electrostatics.

Striped covalent organic frameworks modified stationary phase for mixed mode chromatography

Covalent organic frameworks (COFs) have showed expected potential in chromatographic separation due to unique structure and excellent performance. Nowadays, COF materials applied as chromatographic stationary phases is still in its infancy. Here, we modified COF materials on silica using benzene-1,4,5-tetracarboxylic dianhydride (PMDA) and 1,3,5-tris-(4-aminophenyl)triazine (TAPT) monomers by one-pot synthetic method for performing mixed-mode function, named as SiO₂@COF. Five characterization methods including thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FT-IR), elemental analysis (EA) and powder X-ray diffraction (XRD) verified the morphology, structure characteristics and physicochemical properties of the materials. SiO₂@COF for performing the separation of polar and nonpolar analytes on high performance liquid chromatography (HPLC) achieved the desired results. Retention mechanisms of the constructed SiO₂@COF were researched via observing the effects of mobile phase with retention times. Results exhibited that the prepared stationary phase can provide various interaction modes, including hydrophobic, hydrophilic, hydrogen bonding and π-π interactions. In conclusion, the prepared SiO₂@COF stationary phase can execute mixed-mode separation abilities and show potential for complex samples analysis.

Preparation and evaluation of an ethylenediamine dicarboxyethyl diamido-bridged bis(β-cyclodextrin)-bonded chiral stationary phase for high performance liquid chromatography

An ethylenediamine dicarboxyethyl diacetamido-bridged bis(β-cyclodextrin) was firstly synthesized through the reaction of 6-deoxy-6-amino-β-cyclodextrin (NH₂-CD) with ethylenediaminetetraacetic dianhydride. Then it was bonded onto the surface of silica gel SBA-15 to obtain an ethylenediamine dicarboxyethyl diacetamido-bridged bis(β-CD)-bonded chiral stationary phase (EBCDP). The structures of the bridged bis(β-CD) and EBCDP were characterized by infrared spectroscopy, mass spectrometry, elemental analysis and thermogravimetric analysis, accordingly. The chiral chromatographic performances of EBCDP were systematically evaluated by separating 28 racemic analytes in the reversed-phase or polar organic mode, including eight flavanones, eight bolckers, five dansyl-amino acids, three DL-amino acids and four other common drugs. As a result, the relatively high enantioselectivity of EBCDP was observed in comparison with a native β-CD-CSP (CDSP). All selected analytes were separated on EBCDP, of which 20 analytes had resolutions up to baseline, 2'-hydroxyflavanone and arotinolol had resolutions up to 4.35 and 2.05 in about 30 min, respectively, whereas CDSP only separated 11 analytes with low resolutions (0.55~1.69). Moreover, EBCDP was able to utilize the complexation of the bridging linker (ethylenediamine dicarboxyethyl diamide group, EDTA-based) to realize direct separations of DL-amino acids with a mobile phase containing copper ion (Cu²⁺), which was similar to the chiral ligand exchange chromatography. Unlike the native cyclodextrin with small cavity (~242 ų), the bridged bis(β-CD) combined two β-CD units with a bridging linker, having a well-organized "pseudo-cavity" as an organic whole to encapsulate more analytes, which made EBCDP have broad-spectrum applications in chiral separations.

Challenges and Advances in the Fabrication of Monolithic Bioseparation Materials and their Applications in Proteomics Research

High-performance liquid chromatography integrated with tandem mass spectrometry (HPLC-MS/MS) has become a powerful technique for proteomics research. Its performance heavily depends on the separation efficiency of HPLC, which in turn depends on the chromatographic material. As the "heart" of the HPLC system, the chromatographic material is required to achieve excellent column efficiency and fast analysis. Monolithic materials, fabricated as continuous supports with interconnected skeletal structure and flow-through pores, are regarded as an alternative to particle-packed columns. Such materials are featured with easy preparation, fast mass transfer, high porosity, low back pressure, and miniaturization, and are next-generation separation materials for high-throughput proteins and peptides analysis. Herein, the recent progress regarding the fabrication of various monolithic materials is reviewed. Special emphasis is placed on studies of the fabrication of monolithic capillary columns and their applications in separation of biomolecules by capillary liquid chromatography (cLC). The applications of monolithic materials in the digestion, enrichment, and separation of phosphopeptides and glycopeptides from biological samples are also considered. Finally, advances in comprehensive 2D HPLC separations using monolithic columns are also shown.

Simultaneous separation and determination of seven chelating agents using high-performance liquid chromatography based on statistics design

We describe an optimization approach to determine simultaneously occurring chelating agents (glycine, malonic acid, citric acid, glycolic acid, lactic acid, DL-malic acid, and ethylenediaminetetraacetic acid) in an electroplating effluent using high-performance liquid chromatography. With chromatography signal area and overall resolution considered as responses, detection conditions were optimized via multiple functions combined with response surface methodology and Plackett-Burman design. Optimized detection conditions were as follows: 15 mmol/L ammonium phosphate buffer (pH 2.5), a 94:6 v/v ratio of ammonium phosphate buffer/acetonitrile, a column temperature of 23.3°C, and a mobile phase flow rate of 1 mL/min. The experimental values conformed to the predicted values and were repeatable (relative standard deviation < 6.4%) and linear (r²  > 0.991) over concentration ranges of 1-100 µmol/L. Moreover, the quantification limit (signal-to-noise ratio = 10) and the detection limit (signal-to-noise ratio = 3) ranged from 0.03 to 0.15 µmol/L and from 0.01 to 0.04 µmol/L, respectively. These results indicate that high-performance liquid chromatography coupled with statistical design may be a simple and rapid method for simultaneously determining multiple chelating agents in electroplating wastewater effectively.

Alkaloid purification using rosin-based polymer-bonded silica stationary phase in HPLC

Alkaloids are important natural products that exhibit a wide spectrum of pharmacological activities. To efficiently separate and purify them, a rosin-based polymer-bonded silica stationary phase in high-performance liquid chromatography was synthesized via the surface radical polymerization of ethylene glycol maleic rosinate acrylate and methacrylic acid onto functionalized silica. The stationary phases, columns, optimization of chromatographic conditions for alkaloids, and thermodynamic behavior of the analytes on the column were fully studied. Under the optimized conditions, the prepared column efficiently purified natural camptothecine, caffeine, and evodiamine with the corresponding purities of 92, 96, and 97%. With this work, we have developed an efficient approach to isolate alkaloids and promoted the research on rosin-based materials in biomedicine and analytical chemistry.

Experimental- and simulation-based investigations of coupling a mobile phase gradient with a continuous stationary phase gradient

This work seeks to explore and understand the effects of column orientation and degree of modification of continuous stationary phase gradient columns under a mobile phase gradient using both simulations and experiments. Peak parameters such as retention times, peak widths and resolution are obtained for five phenolic compounds on a C₁₈-silica gradient stationary phase. Simulations show that peak widths for the solutes are dependent upon the fractional composition of C₁₈ and orientation of the stationary phase gradient when coupled to a mobile phase gradient. Also, when compared to a simulated uniform mixed-mode column, peak widths reach a minimum on the gradient column with a coverage higher than 50% C₁₈ where the column is oriented to have the C₁₈ dense region at the end. Experimentally, continuous stationary phase gradients were fabricated to have a total C₁₈ composition of 78% of the original uniform column with an exponential profile using a previously described destructive controlled rate infusion method. Under gradient mobile phase conditions, experimental retention times for the gradient column showed a significant increase compared to the original 100% C₁₈ column. Simulations with a similar C₁₈ composition, however, predicted decreased retention times from the original C₁₈ column. A statistical increase in the retention time of protocatechuic acid and decrease in the peak width of tyrosol, caffeic acid, and coumaric acid were noted when the gradient column was oriented to have the C₁₈ dense region located near the detector. Collectively, combining gradients in both the mobile and stationary phases can yield interesting neighboring ligand effects and peak broadening/focusing effects.

Straightforward Immobilization of Phosphonic Acids and Phosphoric Acid Esters on Mesoporous Silica and Their Application in an Asymmetric Aldol Reaction

The combined benefits of moisture-stable phosphonic acids and mesoporous silica materials (SBA-15 and MCM-41) as large-surface-area solid supports offer new opportunities for several applications, such as catalysis or drug delivery. We present a comprehensive study of a straightforward synthesis method via direct immobilization of several phosphonic acids and phosphoric acid esters on various mesoporous silicas in a Dean–Stark apparatus with toluene as the solvent. Due to the utilization of azeotropic distillation, there was no need to dry phosphonic acids, phosphoric acid esters, solvents, or silicas prior to synthesis. In addition to modeling phosphonic acids, immobilization of the important biomolecule adenosine monophosphate (AMP) on the porous supports was also investigated. Due to the high surface area of the mesoporous silicas, a possible catalytic application based on immobilization of an organocatalyst for an asymmetric aldol reaction is discussed.

Column Characterization and Selection Systems in Reversed-Phase High-Performance Liquid Chromatography

Reversed-phase high-performance liquid chromatography (RP-HPLC) is the most popular chromatographic mode, accounting for more than 90% of all separations. HPLC itself owes its immense popularity to it being relatively simple and inexpensive, with the equipment being reliable and easy to operate. Due to extensive automation, it can be run virtually unattended with multiple samples at various separation conditions, even by relatively low-skilled personnel. Currently, there are >600 RP-HPLC columns available to end users for purchase, some of which exhibit very large differences in selectivity and production quality. Often, two similar RP-HPLC columns are not equally suitable for the requisite separation, and to date, there is no universal RP-HPLC column covering a variety of analytes. This forces analytical laboratories to keep a multitude of diverse columns. Therefore, column selection is a crucial segment of RP-HPLC method development, especially since sample complexity is constantly increasing. Rationally choosing an appropriate column is complicated. In addition to the differences in the primary intermolecular interactions with analytes of the dispersive (London) type, individual columns can also exhibit a unique character owing to specific polar, hydrogen bond, and electron pair donor-acceptor interactions. They can also vary depending on the type of packing, amount and type of residual silanols, "end-capping", bonding density of ligands, and pore size, among others. Consequently, the chromatographic performance of RP-HPLC systems is often considerably altered depending on the selected column. Although a wide spectrum of knowledge is available on this important subject, there is still a lack of a comprehensive review for an objective comparison and/or selection of chromatographic columns. We aim for this review to be a comprehensive, authoritative, critical, and easily readable monograph of the most relevant publications regarding column selection and characterization in RP-HPLC covering the past four decades. Future perspectives, which involve the integration of state-of-the-art molecular simulations (molecular dynamics or Monte Carlo) with minimal experiments, aimed at nearly "experiment-free" column selection methodology, are proposed.

Preparation and evaluation of maltose modified polymer-silica composite based on cross-linked poly glycidyl methacrylate as high performance liquid chromatography stationary phase

A new maltose modified polymer-silica composite was fabricated and applied as high performance liquid chromatography (HPLC) stationary phase. The cross-linked poly glycidyl methacrylate (pGMA) layer was chemically bonded to the outer surface as well as pore inner surface of silica beads via in-situ polymerization, and then maltose was modified onto the polymer layer via a [3 + 2] "click" reaction. The porous spherical silica (4 μm diameter) with 300 Å pore size was selected as the matrix so that the 3.25 nm-thick polymer layer fabricated on the pore inner surface would not affect its permeability. The typical 'U-shape' retention curves indicated a mixed-mode retention mechanism of the as-synthesized stationary phase. Both polar and non-polar analytes could be well separated on the stationary phase with column efficiency reaching 123809 plates/m for guanosine in hydrophilic interaction liquid chromatography (HILIC) mode and 46808 plates/m for fluorene in reversed-phase liquid chromatography (RPLC) mode, respectively. Nucleotides and their bases were baseline separated with good peak shape without any buffer salt in mobile phase, suggesting the effective shielding of the silanol groups. The packing material also showed excellent chromatographic repeatability with intraday RSDs of the retention time of five nucleosides less than 0.048% (n = 3) and interday RSDs less than 0.33% (n = 7) and great pH stability (from 1.5 to 10.2). Finally, the stationary phase was applied to the separation of ginseng extract.

Investigation of the retention characteristics of a 26-membered aromatic-aliphatic azamacrocycle bonded silica gel stationary phase for high performance liquid chromatography

A 26-membered aromatic-aliphatic azamacrocycle bonded silica gel stationary phase for high performance liquid chromatography was prepared and characterized.

One-step preparation of zirconia coated silica microspheres and modification with d-fructose 1, 6-bisphosphate as stationary phase for hydrophilic interaction chromatography

In this study, ZrO₂ layer coated silica microspheres (ZrO₂/SiO₂) were successfully prepared by a facile one-step surfactant-free hydrothermal route under low pH condition. The synthesized ZrO₂/SiO₂ material was then modified with d-fructose 1, 6-bisphosphate (FDP) to improve the chromatographic separation property of the material. Fused-silica capillary columns were prepared with the modified material for evaluation. Phenolic, nucleobases and alkaloids compounds in hydrophilic interaction chromatographic (HILIC) mode showed symmetrical peaks. The FDP-ZrO₂/SiO₂ stationary phase showed better performance than ZrO₂/SiO₂ packing material and demonstrated great potential for application in HILIC mode.

Functionalities tuned enantioselectivity of phenylcarbamate cyclodextrin clicked chiral stationary phases in HPLC

The mixed chloro- and methyl- functionalities can greatly modulate the enantioselectivities of phenylcarbamate cyclodextrin (CD) clicked chiral stationary phases (CSPs). A comparison study is herein reported for per(4-chloro-3-methyl)phenylcarbamate and per(2-chloro-5-methyl)phenylcarbamate β-CD clicked CSPs (i.e., CCC4M3-CSP and CCC2M5-CSP). The enantioselectivity dependence on column temperature was studied in both normal-phase and reversed-phase mode high performance liquid chromatography (HPLC). The thermodynamic study revealed that the stronger intermolecular interactions can be formed between CCC4M3-CSP and chiral solutes to drive the chiral separation. The higher enantioselectivities of CCC4M3-CSP were further demonstrated with the enantioseparation of 17 model racemates in HPLC.

Separation behavior of basic compounds on unbonded silicon oxynitride and silica high-performance liquid chromatography stationary phases with reversed-phase eluents

Unbonded silicon oxynitride and silica high-performance liquid chromatography stationary phases have been evaluated and compared for the separation of basic compounds of differing molecular weight, pK_a , and log D using aqueous/organic mobile phases. The influences of percentage of organic modifier, buffer pH, and concentration in the mobile phase on base retention were investigated on unbonded silicon oxynitride and silica phases. The results confirmed that unbonded silicon oxynitride and silica phases demonstrated excellent separation performance for model basic compounds and both the unbonded phases examined possessed a hydrophobic/adsorption and ion-exchange character. The silicon oxynitride stationary phase exhibited high hydrophilicity compared with silica with a reversed-phase mobile phase. An ion-exclusion-type mechanism becomes predominant for the separation of three aimed bases on the silicon oxynitride column at pH 2.8. Different from silicon oxynitride stationary phase, no obvious change for the retention time of three model bases on silica stationary phase at pH 2.8 can be observed.

Recent development in liquid chromatography stationary phases for separation of Traditional Chinese Medicine components

Traditional Chinese Medicine (TCM) is an ancient medical practice which has been used to prevent and cure diseases for thousands of years. TCMs are frequently multi-component systems with mainly unidentified constituents. The study of the chemical compositions of TCMs remains a hotspot of research. Different strategies have been developed to manage the significant complexity of TCMs, in an attempt to determine their constituents. Reversed-phase liquid chromatography (RPLC) is still the method of choice for the separation of TCMs, but has many problems related to limited selectivity. Recently, enormous efforts have been concentrated on the development of efficient liquid chromatography (LC) methods for TCMs, based on selective stationary phases. This can improve the resolution and peak capacity considerably. In addition, high-efficiency stationary phases have been applied in the analysis of TCMs since the invention of ultra high-performance liquid chromatography (UHPLC). This review describes the advances in LC methods in TCM research from 2010 to date, and focuses on novel stationary phases. Their potential in the separation of TCMs using relevant applications is also demonstrated.

Glucaminium ionic liquid-functionalized stationary phase for the separation of nucleosides in hydrophilic interaction chromatography

A glucaminium-based ionic liquid stationary phase was prepared via facile epoxy-amine reaction and subsequent quaternization. Successful immobilization of glucaminium-based ionic liquid onto silica surface was validated by elemental analysis and infrared spectroscopy. The new stationary phase was evaluated for the separation of nucleosides in hydrophilic interaction liquid chromatography (HILIC). Effects of various factors, such as acetonitrile concentration, salt concentration, pH value, as well as column temperature, on the chromatographic behavior toward nucleosides were studied in detail. The results indicated that this new stationary phase can be used for separation of water-soluble polar substances in HILIC mode. The retention of solutes on the stationary phase was influenced by a mixed-mode retention mechanism with a combination of adsorptive and partitioning interactions.

Imidazolium embedded C8 based stationary phase for simultaneous reversed-phase/hydrophilic interaction mixed-mode chromatography

A new imidazolium embedded C8 based stationary phase (SIL-MPS-VOL) was facilely prepared by two steps and characterized by Fourier transform infrared spectrometry and thermogravimetric analysis. Due to the introduction of quaternary imidazolium group to the traditional C8 stationary phase, the developed SIL-MPS-VOL column demonstrated both reversed-phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC) retention mechanisms. A series of hydrophobic and hydrophilic test samples, including benzene homologues, anilines, positional isomers, nucleosides and nucleotides, were used to evaluate the developed SIL-MPS-VOL stationary phase. A rapid separation time, high separation efficiency and planar selectivity were achieved, compared with the commercially available C8 column. Moreover, the developed stationary phase was further used to detect and separate of melamine in powdered infant formula and high polar component of secondary metabolites of Trichoderma, and improved separation efficiency was achieved, indicating the potential merits of the developed SIL-MPS-VOL stationary phase for simultaneous separation of complex hydrophobic and hydrophilic samples with high selectivity.