Aqueous Liquid Chromatography Research Articles

Per aqueous liquid chromatography of Radix hedysari polysaccharides and Au nanoparticles co-functionalized stationary phase and its application in the determination of iridoids and phenylethanols

BackgroundHydrophilic Interaction Liquid Chromatography (HILIC) is an outstanding strategy for the challenging analysis of hydrophilic and polar components. Nevertheless, analysis under HILIC mode typically consumes 70%–95 % acetonitrile with the disadvantage of high analytical costs, being environmentally unfriendly and causing biohazards, which is not in line with the concept of green chromatography. Research has shown that Per Aqueous Liquid Chromatography (PALC) simultaneously emphasizes efficient analytical performance for hydrophilic analytes and green analytical concepts. The development of new PALC stationary phases with superior performance is necessary. ResultsIn this paper, silanized silica was sequentially subjected to esterification reaction, polymerization reaction and covalent bonding through five steps to obtain SiO2-RHP-AuNPs material, which was prepared as a novel stationary phase for PALC. Comprehensive characterization of the materials by means of Fourier transform infrared spectroscopy, Transmission scanning electron microscope, Elemental analysis and Thermogravimetric analysis showed the successful bonding of the functionalized groups on the original silica. The polymeric stationary phase based on Radix hedysari polysaccharide and Au nanoparticles had higher density of hydroxyl and ester functionalized groups. The Au nanoparticles upgraded their mesoporous structure and thermal stability, providing exceptional chromatographic performance and selectivity for chromatographic analysis. The influence of mobile phase water content, salt concentration, pH and column temperature on the retention behavior was evaluated. The novel Column was found to exhibit a dual mechanism of hydrophobic interactions/ion exchange interactions in a mobile phase with high water content. Significance and noveltyThe separation efficiency and selectivity of SiO2-RHP-AuNPs columns for synthetic pigments and organic acids in PALC mode were superior to those of commercial HILIC and C18 columns. In addition, a method for the determination of seven active ingredients in Fructus Ligustri Lucidi by SiO2-RHP-AuNPs column in PALC mode was developed. The method had good stability, reproducibility and accuracy, which was capable of realizing the quality evaluation of Chinese Materia Medicas.

Automated, Transferable, and Ethanol-Free Radiosynthesis of [11C]Butanol.

Cerebral blood flow and blood-brain barrier permeability assessment are crucial hemodynamic parameters to measure under neurological conditions. In conjunction with positron emission tomography (PET), oxygen-15-labeled water has emerged as a gold standard for measuring cerebral perfusion; however, at higher flow rates, [15O]water extraction becomes nonlinear. In such a scenario, freely diffusible [11C]butanol can provide a truer estimate. Radiosyntheses of [11C]butanol reported to date are protracted, are not automated, or require ethanol in the final formulation. By using a flow-based, captive solvent approach on a commercially available radiosynthesizer, we automated and reduced the synthesis time to 28 min. Forgoing cartridge-based purification for an aqueous high-performance liquid chromatography method, we obtained high purity [11C]butanol in ethanol-free phosphate buffered saline in sufficient yields for clinical PET studies. We here report our expedited, automated, and ethanol-free radiosynthesis of [11C]butanol along with preliminary imaging of a porcine subject.

Preparation of ionic gel-modified stationary phase for RPLC/HILIC/IC separation and its application in per aqueous liquid chromatography

In this study, we synthesized and employed an ionic gel-functionalized silica stationary phase for high-performance liquid chromatography. The successful fabrication of the stationary phase was confirmed through attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), zeta-potential measurements, and elemental analysis (EA). Comparative performance evaluation against a commercial column demonstrated the prepared column's effectiveness in the mixed mode of reversed-phase liquid chromatography (RPLC), hydrophilic interaction liquid chromatography (HILIC), and ion chromatography (IC). Moreover, the stationary phase exhibited exceptional retention repeatability in per aqueous liquid chromatography, showcasing its potential as an environmentally friendly analytical method. Mechanistic investigations unveiled multiple solute-stationary phase interactions, including π-π interactions, hydrogen bonding, and ion exchange. Finally, we applied the developed stationary phase for the precise detection of preservatives in carbonated beverages and jelly, achieving high levels of accuracy and recovery rates.

A nitrogen-specific detector for high performance liquid chromatography

We describe a nitrogen-specific detector (NSD) for aqueous mobile phase-based high performance liquid chromatography (HPLC). It is based by means of total hydrophilic organic nitrogen detection. Separated analytes are photooxidized online and converted to nitrate, followed by an ultravilet absorbance detector. It features response dependant on the product of nitrogen number in the molecule and its molar concentration, no matter what is ultravilet-absorbing or not. The HPLC equipped with NSD can quantify nitrogen-containing analytes via a sole standard of potassium nitrate for calibration. This results in identical calibration curve for all nitrogen-containing analytes, obviating individual calibration. The limit of detection of NSD is 4.3 μM N/L, and its linear range is up to 4 mM N/L.

The series of L-lysine-derived gelators-modified multifunctional chromatography stationary phase for separation of chiral and achiral compounds

In this study, using chiral L-lysine as the molecular skeleton, three kinds of L-lysine-derived gelators (GBLB, GBLF and GFLF) were synthesized and then bonded to the surface of silica matrix (5 μm) by amide condensation to prepare a series of multifunctional chromatography stationary phases (GBLB-SiO2, GBLF-SiO2, and GFLF-SiO2) were prepared. The L-lysine-derived gelators not only possess chiral recognition ability, but also can spontaneously form oriented and ordered network structures in liquid medium through the interaction of non-covalent bonding forces such as hydrogen bonding, π-π stacking, and van der Waals forces. The comprehensive effect of multiple weak interaction sites enhances the molecular recognition ability and further improves the separation diversity of different types of compounds on stationary phases. The separation and evaluation of chiral compounds showed that benzoin, 1-phenyl-ethanol, 1-phenyl-propanol and 6-hydroxyflavanone could be separated in normal phase mode (NPLC). The separation of different types of non-chiral compounds, such as sulfonamides, nucleosides, nucleobases, polycyclic aromatic hydrocarbons (PAHs), anilines, and aromatic acids, were achieved in hydrophilic interaction/reversed-phase/ion-exchange mode (HILIC/RPLC/IEC), and the separation of polarized compounds could be performed under the condition of ultrapure water as the mobile phase, which has the typical retention characteristics of per aqueous liquid chromatography (PALC). The effects of organic solvent content, temperature, pH value, and buffer salt concentration on the retention and separation performance of the column were investigated. Comparison of the three prepared columns showed that the separation performance (such as aromatic selectivity) could be improved by increasing the types of functional groups on the surface of the stationary phase and the number of aromatic groups. In a word, the prepared stationary phase have multiple retention properties, can simultaneously separate chiral compounds and various types of achiral compounds. This work provides an idea for developing multifunctional liquid chromatography stationary phase materials, and further expands the application of gelators in separation science.

Preparation and chromatographic evaluation of hydrophilic polymer brushes grafted-silica with post modification of silicon/carbon dots as a green liquid chromatography stationary phase.

Polar stationary phases were prepared by grafting hydrophilic acrylamide (Am) polymer brushes with post modification of carbon dots (CDs) and silicon dots (SiDs) onto SiO2 particles. The prepared stationary phases, SiO2-PAm-CDs, SiO2-PAm-CDs/SiDs, and SiO2-PAm-SiDs, were packed as chromatographic columns, respectively. Using nucleic bases, organic acids, and β-agonists as targetsubstances to investigate the influence of chromatographic conditions on retentionand separation, the packed columns showed the partitioning and adsorption of mixed retention behavior in hydrophilic interaction liquid chromatography mode and successfully separated thepolar compounds. Most importantly, under per aqueous liquid chromatography mode (using 100% water as mobile phase), those columns still had goodseparation ability toward nucleic bases, β-agonist, and organic acids. Because AM isa temperature-sensitive monomer, the resulting van't Hoff curves exhibited a nonlinear relationship, having temperature-responsive chromatographic characteristic under pure water separation. Hence, building on temperature-sensitive characteristics and pure water of separation conditions, the separation selectivity toward hydrophilic compounds greatly improved. Compared with the commercial hydrophilic columns, the efficiency of our developed column had the superior ability in separation and detection of betaine in Goji berry with the enhanced resolution achieved in the proposedgreen separation method(just using pure water as mobile phase).

The role of the cation and anion in aqueous liquid chromatography with sodium dodecyl sulphate and imidazolium-based ionic liquids as mobile phase reagents

BackgroundIn reversed-phase liquid chromatography, solute retention is primarily influenced by interactions between a nonpolar stationary phase and a moderately polar hydro-organic mobile phase, based on the solute lipophilicity. However, challenges regarding retention and peak tailing can arise due to ionic interactions between positively charged analytes and free silanols present on silica-based stationary phases. To address these challenges, incorporating surfactants and ionic liquids (ILs) into the mobile phase offers an effective solution. These additives synergistically enhance chromatographic performance through electrostatic and lipophilic interactions, which enable fine-tuning of selectivity and improved separation efficiency. ResultsThis study explores the chromatographic behaviour of several basic compounds in aqueous mixtures containing the anionic surfactant sodium dodecyl sulphate (SDS), above its critical micellar concentration, combined with various 1-alkyl-3-methylimidazolium-based ionic liquids (ILs) featuring chloride, tetrafluoroborate, and hexafluorophosphate anions, all without the addition of organic solvents. Specifically, this research investigates the influence of different anion types within the ILs and considers the impact of the IL cations. Analysis of solute peak profiles reveals narrow and symmetrical peaks. By introducing tetrafluoroborate and hexafluorophosphate IL anions into a mobile phase that contains an anionic surfactant, the study sheds light on the interactions occurring within the chromatographic column. This enhanced understanding of the combined effects of surfactants and ILs contributes to refining chromatographic methodologies. SignificanceThis research highlights the importance of carefully selecting the appropriate IL when incorporating it into a micellar mobile phase alongside SDS. This combination results in practical retention times that surpass the performance achieved with either the surfactant or IL alone in the mobile phase. The study particularly emphasises the impact of the IL anion, especially in the absence of SDS and organic solvents. This unveils interactions that are otherwise obscured in micellar and hydro-organic media, providing new insights into chromatographic dynamics.

Retention behavior of nucleosides and nucleobases on a 3 μm undecylenic acid-functionalized silica column in per aqueous liquid chromatography and hydrophilic interaction liquid chromatography separation modes

A 3 μm undecylenic acid-functionalized stationary phase (UAS) was prepared for the separation of nucleosides and nucleobases using per aqueous liquid chromatography (PALC) and hydrophilic interaction liquid chromatography (HILIC). The retention behaviors of nucleosides and nucleobases in PALC and HILIC modes were explored by adjusting parameters such as water content, buffer concentration, pH of the mobile phase and column temperature. The experimental data and separation chromatogram demonstrated that PALC could provide retention comparable to that of HILIC for nucleosides and nucleobases. Comparative studies using diluted adenosine solutions evaluated theoretical plates and peak shape for the same retention factors (between 0.25 and 5.0) in PALC and HILIC. There was no buffer component in the mobile phases used to operate the comparisons. HILIC mode is more efficient for adenosine than PALC mode at low retention factors. It's the exact opposite phenomenon for high retention factors. It is proposed that the mass transfer of adenosine between the UAS, the water-rich layer and the ACN-rich mobile phase in HILIC is relatively slow. Given the significant use of toxic ACN in HILIC, PALC emerges as a safer and more effective alternative for separating nucleosides and nucleobases.

The impact of lutein-loaded poly(lactic-co-glycolic acid) nanoparticles following topical application: An in vitro and in vivo study.

Antioxidant therapies are of interest in the prevention and management of ocular disorders such as cataracts. Although an active area of interest, topical therapy with antioxidants for the treatment of cataracts is complicated by multiple ocular anatomical barriers, product stability, and solubility. Entrapment and delivery of antioxidants with poly(lactic-co-glycolic acid) nanoparticles is a possible solution to these challenges, however, little is known regarding their effects in vitro or in vivo. Our first aim was to investigate the impact of blank and lutein loaded PLGA nanoparticles on viability and development of reactive oxygen species in lens epithelial cells in vitro. Photo-oxidative stress was induced by ultraviolet light exposure with cell viability and reactive oxygen species monitored. Next, an in vivo, selenite model was utilized to induce cataract formation in rodents. Eyes were treated topically with both free lutein and lutein loaded nanoparticles (LNP) at varying concentrations. Eyes were monitored for the development of anterior segment changes and cataract formation. The ability of nanodelivered lutein to reach the anterior segment of the eye was evaluated by liquid chromatography coupled to mass spectrometry of aqueous humor samples and liquid chromatography coupled to tandem mass spectrometry (targeted LC-MS/MS) of lenses. LNP had a minimal impact on the viability of lens epithelial cells during the short exposure timeframe (24 h) and at concentrations < 0.2 μg LNP/μl. A significant reduction in the development of reactive oxygen species was also noted. Animals treated with LNPs at an equivalent lutein concentration of 1,278 μg /mL showed the greatest reduction in cataract scores. Lutein delivery to the anterior segment was confirmed through evaluation of aqueous humor and lens sample evaluation. Topical treatment was not associated with the development of secondary keratitis or anterior uveitis when applied once daily for one week. LNPs may be an effective in the treatment of cataracts.

Possibilities and Limitations of Aqueous Temperature Responsive Liquid Chromatography in Comprehensive 2D–LC

In theory, comprehensive two-dimensional liquid chromatography (2D-LC) allows for significant enhanced peak capacity compared to one-dimensional high performance LC (1D-HPLC). However, reaching such a separation performance while also obtaining robust, easily implementable, and sensitive methods proves challenging. Because it can hinder the broader use of 2D-LC, there is a need for developing easier, more trouble-free approaches that feature the benefits of LC×LC while not compromising with what can be done with 1D-HPLC. Commercial 2D-LC interfaces are based on two-position multiport valves composed of two loops, which are alternatingly used either to collect the effluent from the first dimension (1D), or to inject their content to the second dimension (2D). This design implies that if large sampling volumes transferred to the second column need to be avoided, a comparatively (much) higher flow rate and broader column i.d. is required for the second column. However, doing so can lead to a loss in sensitivity because of dilution and impractical analytical chromatography as a result of the high flow rates involved. In most LC×LC column combinations, this problem is exacerbated thanks to the high eluotropic strength of transferred loop volumes. However, when the elution strength of the transferred solvent is very small, refocusing the analytes can be obtained, which allows the user to overcome such issues. For example, this is the case when a purely aqueous separation mode is combined with reversed-phase LC (RPLC) in the 1D and 2D, respectively. Temperature responsive LC (TRLC), which is an emerging LC mode requiring only water as the mobile phase and whereby retention is controlled via temperature only, is promising in this context. In this second installment about TRLC, we illustrate the unique benefits of the combination of this separation mode with RPLC in comprehensive 2D-LC. The potential of the approach is shown through the analysis of representative standard mixtures, active pharmaceutical ingredients, synthetic impurities and phenolics in natural products.

A facile approach to undecylenic acid-functionalized stationary phases for per aqueous liquid chromatography

Green chromatography techniques using low-toxic mobile phase are getting increasingly attention in recent years. The core is developing stationary phases that possess adequate retention and separation under the mobile phase of high content water. Using thiol-ene click chemistry, an undecylenic acid-bonded silica stationary phase (UAS) was prepared in a facile manner. Elemental analysis (EA), solid-state 13C NMR spectroscopy and Fourier transform infrared spectrometry (FT-IR) confirmed the successful preparation of UAS. The synthesized UAS was employed for per aqueous liquid chromatography (PALC), which uses little organic solvent during separation. Due to the hydrophilic carboxy, thioether group and hydrophobic alkyl chains of the UAS, various categories of compounds (including nucleobases, nucleosides, organic acids and basic compounds) with different properties can achieve enhanced separation under the mobile phase of high content water compared with commercial C18 and silica stationary phases. Overall, our present UAS stationary phase shows excellent separation ability toward highly polar compounds and meets the requirements of green chromatography.

Preparation and application of sulfated lily polysaccharide bridged polyhedral oligomeric silsesquioxane hybrid organosilicas as stationary phase

Periodic mesoporous organosilicas (PMO) hydrophilic microspheres were synthesized by co-condensation of sulfated polysaccharide from Lilum lancifolium Thunb. bridged silane (SLLTPBS) and polyhedral oligomeric silsesquioxane (POSS) as stationary phase (PMO(SLLTP-POSS)) for per aqueous liquid chromatography (PALC), which would overcome the disadvantages of using a large amount of acetonitrile on the hydrophilic interaction liquid chromatography (HILIC) columns. Average particle size of PMO (SLLTP-POSS) microspheres was 4.9 μm, which was suitable for stationary phase. The retention mechanism of the stationary phase in PALC was mainly hydrophobic interactions and also included some ion-exchange interactions and electrostatic interactions. The acid-base resistance was greatly improved compared to the C18 column. The PMO(SLLTP-POSS) column under PALC mode had increased the resolution when separating some hydrophilic compounds such as eight organic acids and eleven sweeteners compared with the C18 column and HILIC column. The new column was more efficient than the HILIC columns. Additionally, a PALC-triple quadrupole mass spectrometry approach for the simultaneous identification of the eleven sweeteners was developed. The averagere coveries of the eleven compounds were 70.20%–91.33% with the relative standard deviation (RSD) range of 1.74% to 4.27%. The results showed good precision and accuracy of the method.

Aqueous liquid chromatography with mobile phases of sodium dodecyl sulphate and ionic liquid

In conventional reversed-phase liquid chromatography (RPLC) with hydro-organic solvents, basic cationic solutes yield retained, broad, asymmetric peaks, owing to their interaction with free anionic silanols in the stationary phase. RPLC mobile phases to which the anionic surfactant sodium dodecyl sulphate (SDS), or an ionic liquid (IL) are added, have been proposed as solutions, since these additives are able to block the silanol effect thus improving the chromatographic performance. With these additives, it is however necessary to increase the elution strength by adding an organic solvent, such as an alcohol or acetonitrile. A novel aqueous liquid chromatographic mode (in the absence of organic solvent) is here proposed, where the mobile phases contain only a mixture of aqueous solutions of SDS and an IL derived from 1-alkyl-3-methylimidazolium associated to chloride, both environmentally friendly. When these reagents are added, the anionic surfactant adsorbed on the stationary phase is able to attract the cationic solutes, whereas the adsorbed IL cation repels them. The combination of both effects (attraction and repulsion) allows the modulation of retention, by varying the IL/SDS ratio. Given the character of the additives, a type of green liquid chromatography is achieved. In this work, the chromatographic behavior of six basic compounds of pharmaceutical interest, the β-adrenoceptor antagonists acebutolol, atenolol, carteolol, metroprolol, oxprenolol and propranolol, is examined. In order to assess the chromatographic behavior of the mixed mobile phases containing SDS and IL, changes in retention, peak profile and resolution of mixtures of the analytes were explored at varying concentration of the additives.

Carbon quantum dots–functionalized silica stationary phase for pharmaceutical analysis by a green liquid chromatography mode

Facing the trends of green chemistry, this work tries to find a novel material for per aqueous liquid chromatography (PALC) aiming to reduce the consumption of hazardous reagents. As a kind of green nanomaterials, the chromatographic performance of carbon quantum dots (CQDs) in PALC was rarely studied. Here, hydrophilic CQDs were prepared by a simple hydrothermal method using citric acid and ethylenediamine as carbon sources. The synthesized CQDs with functional groups of amino, carboxyl, and hydroxyl were decorated on silica gels forming a novel Si-CQDs stationary phase. This Si-CQDs column possesses the typical retention feature of PALC. Compounds with different polarities including hydrophobic pesticides, polar sulfonamides, β-adrenoceptor blockers and agonists, as well as hydrophilic nucleosides and bases obtained satisfactory separation on this Si-CQDs column under PALC mode, even better resolution than in hydrophilic interaction liquid chromatography (HILIC) mode. A mixture of four sulfonamides can be separated within 6min using a mobile phase containing only 5% acetonitrile, and the resolution achieves 2.39, 2.13, and 1.83 with an average column efficiency of 1400. For certain compounds, this Si-CQDs column showed better separation performance than commercial SiO2 column, NH2 column, and C18 column. The retention mechanism includes hydrophobic and electrostatic interactions due to the multifunctional groups of CQDs. This Si-CQDs column achieved the rapid detection of residual sulfonamides in milk with simplified sample pretreatment process and the detection of atenolol in commercial atenolol tablets. The developed Si-CQDs column has great prospects in low-cost and environmentally friendly separation and analysis.

An exploration of angiotensin-converting enzyme (ACE) inhibitory peptides derived from gastrointestinal protease hydrolysate of milk using a modified bioassay-guided fractionation approach coupled with in silico analysis

An improved bioassay-guided fractionation was performed to effectively screen angiotensin-I converting enzyme inhibitory (ACEI) peptides from milk protein hydrolysate. The aqueous normal phase liquid chromatography, namely hydrophilic interaction liquid chromatography (HILIC), was used as a format of solid-phase extraction (SPE) short column for the first fractionation, then the HILIC-SPE fraction with the best ACEI activity (IC50 = 61.75 ± 5.74 µg/mL; IC50 = half-maximal inhibitory concentration) was obtained when eluted by 95% acetonitrile + 0.1% formic acid (fraction F1). The best HILIC-SPE fraction was further fractionated using reversed-phase (RP)-SPE short column. The best RP-SPE fraction was obtained when eluted by 20% acetonitrile + 0.1% formic acid (fraction P3) with an ACEI activity of IC50 36.22 ± 1.18 µg/mL. After the 2-step fractionation, the IC50 value of fraction P3 significantly decreased by 8.92-fold when compared with the crude hydrolysate. Several peptides were identified from fraction P3 using liquid chromatography-tandem mass spectrometry. The in silico analysis of these identified sequences based on the BIOPEP database predicted that HLPLPLL (HL-7) was the most active peptide against angiotensin-converting enzyme (ACE). The HL-7 derived from β-casein showed a potent ACEI activity (IC50 value is 16.87 ± 0.3 µM). The contents of HL-7 in the gastrointestinal protease hydrolysate and RP-SPE fraction originated from 1 mg of milk proteins were quantified using a multiple reaction monitoring mode upon liquid chromatography-tandem mass spectrometry analysis to give 19.86 ± 1.14 pg and 14,545.8 ± 572.9 pg, respectively. Besides, the kinetic study indicated that HL-7 was a competitive inhibitor and the result was rationalized using the docking simulation. The study demonstrated an efficient screening of ACEI peptides from commercially available milk powders using a simple SPE process instead of a sophisticated instrument such as HPLC. Moreover, the potent ACEI peptide HL-7 uncovered by this method could be a natural ACE inhibitor.

Investigation of the effects of solvent-mismatch and immiscibility in normal-phase × aqueous reversed-phase liquid chromatography

Comprehensive two-dimensional liquid chromatography (LC × LC) is an attractive separation technique that allows achieving high peak capacities and information on chemical correlations. Unfortunately, its application in industrial practice is still not widespread due to limiting factors such as complex method development, tedious method optimization and solvent-incompatibility (such as solvent-strength mismatch or immiscibility experienced during fraction transfer).A severe case of solvent-incompatibility is encountered in the comprehensive coupling of normal-phase LC and reversed-phase LC (NPLC × RPLC). NPLC × RPLC is considered a desirable LC × LC system, especially for the characterization of synthetic polymers, due to the high orthogonality of the two retention mechanisms. However, its experimental realization often suffers from solvent-injection effects in the RPLC dimension, such as peak-deformation, peak-splitting, or even unretained elution (“breakthrough”) of sample components. Such a decrease in performance or loss of retention is highly dependent on the types of solvents used.To explore the boundaries of solvent compatibility, we applied large-volume injections (LVI) of reference analytes (e.g. alkyl benzenes; ethoxylate and propoxylate polymers) dissolved in water-immiscible sample solvents, such as dichloromethane, n-hexane, and isooctane in fast water-based gradient RPLC separations (using methanol or acetonitrile as eluent). It was found that, when using highly aqueous initial gradient conditions, hydrophobic sample diluents were retained and eluted during the applied gradient. Depending on the relative retention of the retained diluent and the sample analytes, good chromatograms for LVI of immiscible solvents were obtained, comparable with injections under ideal conditions. The conclusions from injection experiments in aqueous RPLC were verified by coupling an NPLC system with a gradient from isooctane to tetrahydrofuran and an RPLC system with a gradient from water to acetonitrile in an online comprehensive NPLC × RPLC separation of a mixture of propoxylate polymers. The separation provided separation of the polymers based on their number of hydroxyl end-groups (NPLC) and oligomer chain-length (RPLC), without suffering from significant band-broadening effects due to solvent-mismatch upon injection in the second-dimension RPLC system.

Per-Aqueous Liquid Chromatography for the Separation of Polar Compounds-Preparation and Characterization of Poly(ethylene oxide-co-dimethylsiloxane) Based Stationary Phase

Poly(ethylene oxide-co-dimethylsiloxane) was thermally immobilized on silica particles- Si(PEO)-to separate small polar compounds with water-rich mobile phases. Poly(ethylene oxideco- dimethylsiloxane) content on Si(PEO) stationary phase was optimized using a central composite design. Infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis morphologically and structurally characterized the optimized material. Separation of standard test mixtures showed that the Si(PEO) phase had a typical reversed-phase elution order. However, the Si(PEO) phase retained polar compounds better than C18 or aqueous C18 phases under waterrich mobile phases. Under this condition, small changes in the acetonitrile fraction resulted in a marked increase in the retention of some polar drugs on the Si(PEO) phase. A typical condition observed in per aqueous liquid chromatography separations, a more environmentally friendly liquid chromatography approach. On the other hand, hydrophobic compounds showed lower mass transfer rates due to their low solubility in the aqueous mobile phase. Thus, the Si(PEO) phase was more suitable and efficient for separating polar or hydrophilic compounds.

A new ionic liquid bridged periodic mesoporous organosilicas stationary phase for per aqueous liquid chromatography and its application in the detection of biogenic amines

In order to solve the problems of using a large proportion of acetonitrile on the hydrophilic interaction liquid chromatography (HILIC) columns that was not environmentally friendly, and the poor acid and base resistance of traditional bonded silica columns, we reported a novel stationary phase of Au nanoparticles (Au NPs) covalently bonded to ionic liquid (ILs) bridged periodic mesoporous organosilicas (PMO) hydrophilic microspheres (PMO-ILs-Au NPs) for per aqueous liquid chromatography (PALC). The PMO hydrophilic microspheres were prepared by condensation of 1,3-bis(trimethoxysilylpropyl)imidazoliumchloride and 1, 2-Bis (triethoxysilyl) ethane and then modified with Au NPs the surface. The obtained materials were characterized by elemental analysis, FT-IR spectra, scanning electron microscope and transmission electron microscopy. The retention behavior was evaluated by investigating the effect of various chromatographic factors on the retention of different types of solutes. The retention mechanism of the stationary phases in PALC was a mixed type of anion-exchange and hydrophobic interaction. Compared with C18–SiO2 column, the acid and base resistance of the stationary phase were greatly improved. Compared with the HILIC column and C18 column, some hydrophilic compounds such as six organic acids and eight biogenic amines were baseline separated with the enhanced resolution of the PMO-ILs-Au NPs column under the PALC mode. The efficiency of the new column was significantly higher than that of the HILIC column. Furthermore, the analysis of PALC-triple quadrupole mass spectrometry was developed for simultaneous detection of eight biogenic amines. This method could improve detection efficiency, save reagent and reduce environmental pollution. PALC as a green chromatography analytical method was suitable for the replacement of HILIC.

Purification of linarin and hesperidin from Mentha haplocalyx by aqueous two-phase flotation coupled with preparative HPLC and evaluation of the neuroprotective effect of linarin.

The volatile oil of Mentha haplocalyx is widely used in medicine, food, and cosmetics. However, a large amount of its residue after steam extraction of volatile oil is abandoned, resulting in a waste of resources. The method of aqueous two-phase flotation coupled with preparative high-performance liquid chromatography was established for the separation and purification of nonvolatile active compounds from Mentha haplocalyx for the first time. The parameters of the two-phase aqueous flotation were optimized. Under the optimal conditions including flotation solvent PEG 1000 aqueous solution (1:1, w/w), pH 5, (NH4 )2 SO4 concentration of 350 g/L in aqueous phase, N2 flow rate of 20 mL/min, and flotation time of 20 min, the flotation efficiency of linarin, hesperidin, and didymin was 82.24, 76.38, and 89.33%, respectively. The linarin and hesperidin with the high purities of 95.8 and 97.2%, respectively, were obtained by using preparative high performance liquid chromatography. The neuroprotective effect of linarin against H2 O2 -induced oxidative stress in rat hippocampal neurons was investigated. The experimental result indicated that linarin could alleviate H2 O2 -induced oxidative stress. The work indicated that the combination of aqueous two-phase flotation and preparative high performance liquid chromatography is a feasible and practical method for the purification of nonvolatile active substances from Mentha haplocalyx, which would provide a reference process for the comprehensive utilization of M. haplocalyx. Especially, linarin might be used as a good source of natural neuroprotectants.

Preparation and application of Au nanoparticles-decorated SO3H-cofunctionalized silica stationary phase for per aqueous liquid chromatography

Au nanoparticles (Au NPs)-decorated SO3H-cofunctionalized porous silica particles was prepared as a novel mixed-mode stationary phase and used in Per aqueous liquid chromatography (PALC) mode. The obtained stationary phase was characterized by elemental analysis, FT-IR spectra, and transmission electron microscopy. To evaluate the retention behavior, the effect of a variety of chromatographic factors on the retention of different types of solutes was investigated. The obtained column exhibited a hydrophobic interaction/cation-exchange mixed-mode retention mechanism, and a typical PALC characteristic was observed in water-rich mobile phases. When the particle size of Au NPs was 10–20 nm, the analytes had a sharp peak shape and the column pressure was also moderate. Compared with the hydrophilic interaction liquid chromatography (HILIC) and C18 column, some hydrophilic compounds such as six monosaccharides were baseline separated with the enhanced resolution of the obtained column under the PALC mode. Moreover, the efficiency of the Au-S/SO3H-SiO2-2 column was significantly higher than that of the HILIC column. PALC mode was a green annlysis method and suitable for the replacement of hydrophilic interaction liquid chromatography.