Column Efficiency Research Articles

Performance evaluation of 2-undecylimidazole/propyl methacrylate bifunctional silica gel for mixed-mode reversed-phase/anion-exchange chromatography

In this work, 2-undecylimidazole (UI) and propyl methacrylate (PMA) dual-functionalized silica gel was prepared and applied as a mixed-mode chromatographic stationary phase. Successful preparation of this stationary phase (SiO2-UI-PMA) was proved through a range of characterization techniques. The chromatographic performance of the obtained SiO2-UI-PMA was investigated for the separation of environmental endocrine disruptors (phthalates, steroid hormones, bisphenols and alkylphenols), sulfonamides and food-borne stimulants in reversed-phase chromatography, as well as for the separation of inorganic anions in anion-exchange chromatography. The effect of column temperature, acetonitrile content, salt concentration and mobile phase pH on retention was studied to explore the separation mechanism, and the results indicated that this stationary phase provided multiple interactions with analytes. Compared with the commercial C18 column, the SiO2-UI-PMA demonstrated more preferable separation ability under the mobile phase conditions with a low content of acetonitrile, thereby acting as a good alternative candidate for the conventional reversed-phase stationary phase in chromatographic analysis. Furthermore, the SiO2-UI-PMA stationary phase exhibited high column efficiency (45 860 plates m−1 for progesterone) even though it was prepared from the non-serviceable silica based chromatographic packing materials.

Exergy Load Distribution Analysis Applied to the Dehydration of Ethanol by Extractive Distillation

This study presents the analysis of the exergy load distribution in a separation process by extractive distillation for ethanol dehydration. The methodology carried out is divided into three parts: the calculation of the flow exergy considering the physical and chemical exergies of the distillation process; the calculation of the primary and transformed exergy contributions considering the consumed exergy; and finally, the overall process efficiency, which shows the real percentage of energy being used in the process. The simulation of an extractive distillation separation system is carried out using Aspen Plus®, from Aspen Tech Version 9. In general, heat transfer processes (heating or cooling) are the ones that generate the greatest exegetic destruction, which is why they must be the operations that must be optimized. As a result of our case study, the local exergy efficiency of the extractive distillation column is 13.80%, which is the operation with the greatest energy loss, and the overall exergy efficiency of the separation system is 30.67%. Then, in order to increase exergy efficiency, a sensitivity analysis is performed with the variation of the azeotrope feed, number of stages, reflux ratio, and solvent feed variation on ethanol purity to reach an overall efficiency of 33.53%. The purity of ethanol is classified as higher than that of the specified, 99.65%.

Submicron Nonporous Silica Particles for Enhanced Separation Performance in pCEC.

Applications of submicron-scale particles are of rising interest in separation science due to their favorable surface-to-volume ratio and their fabrication of highly ordered structures. The uniformly dense packing beds in columns assembled from nanoparticles combined with an electroosmotic flow-driven system has great potential in a highly efficient separation system. Here, we packed capillary columns using a gravity method with synthesized nanoscale C18-SiO2 particles having diameters of 300-900 nm. The separation of small molecules and proteins was evaluated in the packed columns on a pressurized capillary electrochromatography platform. The run-to-run reproducibility regarding retention time and peak area for the PAHs using a column packed with 300 nm C18-SiO2 particles were less than 1.61% and 3.17%, respectively. Our study exhibited a systematic separation analysis of small molecules and proteins based on the columns packed with submicron particles combined with the pressurized capillary electrochromatography (pCEC) platform. This study may provide a promising analytical approach with extraordinary column efficiency, resolution, and speed for the separation of complex samples.

Effect of hydrophilic/lipophilic balance on the porogenic properties of non-ionic surfactants for monolith preparation and chromatographic separation

The effect of hydrophilic/lipophilic balance (HLB) of polyoxyethylene ethers of different chain lengths on the microporogenic properties of the Brij surfactants has been studied. The objective of this work is to help better understand the role of each porogen and to set criteria for selecting the proper non-ionic surfactant, based on the HLB value. Seven recipes of different porogen compositions were first prepared and the highest efficiency was achieved using decane/decanol/dodecanol mixture with Brij® 30. Then, four other Brij surfactants covering the entire HLB scale were tested, and the prepared monoliths were characterized by SEM, BET, FT-IR and chromatography. The results showed that increasing the HLB from 9.72 to 18.84 was accompanied by an increase in monolith density and surface areas. The optimum HLB range was found to be 10 to 15. Surfactants of lower HLB formed either nonporous or less efficient columns, while those of higher HLB formed non-permeable columns. Adjusting the HLB was possible by mixing surfactants of different HLB. The prepared monoliths could be used in the isocratic mode with a mobile phase consisting of a mixture of ACN and water (20:80, v/v) at a flow rate of 1.5 μL min−1 to separate five sulfa drugs. The separation results showed that the elution order of the compounds correlated with their lipophilicity, with sulfamerazine (logp = 0.52) being the first to elute, and sulfaquinoxoline (logp=1.70) being the most retained. The asymmetry factors of the separated compounds ranged between 1.18 and 1.25, and the resolution was found to be in the range 2.92−7.80. The prepared monoliths could be also successfully separate a mixture of four different nonsteroidal anti-inflammatory drugs and a mixture of four benzoic acid derivatives. This work assists in optimizing the surfactant-based porogenic mixture to meet the desired porosity, surface area, morphology and chromatographic separation requirements.

Performance of various 3D-printed monolith geometries as an alternative to expanded bed adsorption for protein purification.

Here, we compare the performance of various three-dimensional-printed Monolith Adsorption (PMA) columns designed from a triply periodic minimal surface geometry, the Schoen gyroid. The structures examined had designed hydraulic diameters between 203 and 458 µm and voidages of 40%-60%. We compare column efficiency, porosity, static binding capacity and dynamic binding capacity for various load volumes and flow rates. The results show that all structures allowed efficient passage of yeast cells (>97%) over a wide range of interstitial velocities (191 to 1911 cm/h) while maintaining a low pressure drop (<0.1 MPa). The structure with a voidage of 40% and a hydraulic diameter of 203 µm showed the best performance in all aspects evaluated. Bovine serum albumin (BSA) recoveries for all structures (27%-91% when the loaded volume was 180 mL) were significantly affected by hydraulic diameter, mean channel wall thickness, velocity and voidage. Moreover, biomass addition resulted in a decrease in BSA recovery, which became more obvious at high velocities. However, this did not lead to a dramatic reduction in saturated binding capacity, significant changes in axial dispersion, or blockage of channels and could be compensated for by recirculation of the feed, even at high velocity. PMA thus potentially provides an appealing alternative to Expanded Bed Adsorption, retaining the latter's advantages, while eliminating fluidization issues and minimizing both processing time and buffer consumption.

Click postsynthesis of microporous organic network@silica composites for reversed-phase/hydrophilic interaction mixed-mode chromatography.

Recently, the good physical and chemical properties, well-defined pore architectures, and designable topologies have made microporous organic networks (MONs) excellent potential candidates in high-performance liquid chromatography (HPLC). However, their superior hydrophobic structures restrict their application in the reversed-phase mode. To solve this obstacle and to expand the application of MONs in HPLC, we realized the thiol-yne "click" postsynthesis of a novel hydrophilic MON-2COOH@SiO2-MER (MER denotes mercaptosuccinic acid) microsphere for reversed-phase/hydrophilic interaction mixed-mode chromatography. SiO2 was initially decorated with MON-2COOH using 2,5-dibromoterephthalic acid and tetrakis(4-ethynylphenyl)methane as monomers, and MER was then grafted via thiol-yne click reaction to yield MON-2COOH@SiO2-MER microspheres (5μm) with a pore size of ~1.3nm. The -COOH groups in 2,5-dibromoterephthalic acid and the post-modified MER molecules considerably improved the hydrophilicity of pristine MON and enhanced the hydrophilic interactions between the stationary phase and analytes. The retention mechanisms of the MON-2COOH@SiO2-MER packed column were fully discussed with diverse hydrophobic and hydrophilic probes. Benefiting from the numerous -COOH recognition sites and benzene rings within MON-2COOH@SiO2-MER, the packed column exhibited good resolution for the separation of sulfonamides, deoxynucleosides, alkaloids, and endocrine-disrupting chemicals. A column efficiency of 27,556 plates per meter was obtained for the separation of gastrodin. The separation performance of the MON-2COOH@SiO2-MER packed column was also demonstrated by comparing with those of MON-2COOH@SiO2, commercial C18, ZIC-HILIC, and bare SiO2 columns. This work highlights the good potential of the thiol-yne click postsynthesis strategy to construct MON-based stationary phases for mixed-mode chromatography.

The Preparation of Novel Amino Acid Imidazole Ionic Liquids and Their Application as Stationary Phase for Capillary Gas Chromatographic Separations

AbstractIn this paper, two new amino acid imidazole ionic liquids IL‐3 and IL‐4 were synthesized for the first time, and their separation performance as the stationary phase for capillary gas chromatography (GC) was tested. The statically coated IL‐3 and IL‐4 capillary columns exhibited moderate to high polarity, and achieved the column efficiency of 2242 plates/m and 2487 plates/m respectively determined by n‐octanol at 120 °C. Importantly, the IL‐3 and IL‐4 columns exhibited excellent separation capability for analytes with varying polarity, including n‐alkanes, arenes, esters, alcohols, bromoalkanes, halogenobenzenes, and halogenated anilines. In addition, the IL‐3 and IL‐4 columns presented high selectivity and separation capability for positional, structural and cis‐/trans‐isomers. In particular, they showed high separation performance of the chloroaniline, bromaniline, iodoaniline and xylidine isomers as an important environmental pollutant. The IL‐3 and IL‐4 columns displayed advantageous resolving capability over the commercial HP‐35 column for aromatic amine isomers, and the separation performance of IL‐4 with long carbon chain was better than that of IL‐3. Moreover, it was applied to determine isomer impurities in real samples, and showing huge potential in GC applications. This work demonstrates the potential of the amino acid imidazole ionic liquids as a new type of stationary phase in GC separations.

Rapid and simple determination of organophosphorus pesticides in urine using polydopamine-modified monolithic spin column extraction combined with liquid chromatography–mass spectrometry

The determination of organophosphorus pesticides in urine is useful for evaluating human exposure. In this study, a simple micro-solid-phase extraction method based on a polydopamine-modified monolithic spin column combined with liquid chromatography–mass spectrometry (LC-MS) was developed for the determination of six organophosphorus pesticides (dimethoate, dichlorvos, carbofuran, methidathion, phosalone, and chlorpyrifos) in urine samples. A methacrylate polymer monolithic support was prepared in situ in the spin column, and dopamine solution was repeatedly passed through the monolith matrix via centrifugation to generate a polydopamine layer in the polymeric network. All extraction steps were performed via centrifugation. The monolith exhibited good permeability, which enabled high-flow-rate sample loading and significantly reduced the sample pre-treatment time. The addition of polydopamine significantly improved the extraction efficiency of the monolithic spin column owing to the catechol and amine groups in dopamine, which can enhance hydrogen bonding and π–π stacking. Factors affecting the extraction, including the solution pH, centrifugation speed, and desorption solvent, were investigated to determine the optimal extraction conditions. Under the optimal conditions, the OPP detection limits were 0.02–1.32 µg/L. The relative standard deviations of the single column (n = 5) and column-to-column (n = 3) precision for the extraction method were <11%. The monolithic spin column exhibited high stability and could be used for more than 40 extraction cycles. The recoveries for spiked urine samples were 72.1–109.3% (RSDs: 1.6–7.9%). The developed method was successfully applied to the simple and rapid analysis of organophosphorus pesticides in urine samples.

Proposal and investigation of CO2 capture from fired heater flue gases to increase methanol production: A case study

In a petrochemical complex in Iran, for production of 209575 kg of MeOH/h, 154,712 kg/h of flue gas with a CO2 concentration of 10.74 mol% enter the atmosphere through a fired heater. The target of this study is to investigate the effect of using post-combustion CO2 capture technology to reduce carbon dioxide emissions and use it to increase methanol production. In order to, the proposed process was simulated and effect of three different solvents, including piperazine (PZ) 30 wt%, monoethanolamine (MEA) 30 wt%, and a blend of MEA 20 wt %+ PZ 10 wt % were investigated. This study investigated solvent regeneration energy, CO2 absorption rate, energy efficiency, and exergy efficiency of stripper column. Simulation results showed PZ with 93% energy efficiency, 55.45% exergy efficiency of stripper column, CO2 emission intensity equal to 0.01 tCO2/tMeOH and lowest solvent regeneration energy equal to 2.6 GJreb/tCO2 has better performance than the other two solvents. Also, the simulation results showed that blending CO2 output from PZ solvent with syngas increases methanol production by 7.8%. The techno-economic analysis also indicated proposed process is more profitable than original process.

Biogenic silica cycling in the Skagerrak

Dissolved silicate (H4SiO4) is essential for the formation of the opaline skeletal structures of diatoms and other siliceous plankton. A fraction of particulate biogenic silica (bSi) formed in surface waters sinks to the seabed, where it either dissolves and returns to the water column or is permanently buried. Global silica budgets are still poorly constrained since data on benthic bSi cycling are lacking, especially on continental margins. This study describes benthic bSi cycling in the Skagerrak, a sedimentary depocenter for particles from the North Sea. Biogenic silica burial fluxes, benthic H4SiO4 fluxes to the water column and bSi burial efficiencies are reported for nine stations by evaluating data from in-situ benthic landers and sediment cores with a diagenetic reaction-transport model. The model simulates bSi contents and H4SiO4 concentrations at all sites using a novel power law to describe bSi dissolution kinetics with a small number of adjustable parameters. Our results show that, on average, 1100 mmol m-2 yr-1 of bSi rains down to the Skagerrak basin seafloor, of which 50% is released back to overlying waters, with the remainder being buried. Biogenic silica cycling in the Skagerrak is generally consistent with previously reported global trends, showing higher Si fluxes and burial efficiencies than deep-sea sites and similar values compared to other continental margins. A significant finding of this work is a molar bSi-to-organic carbon burial ratio of 0.22 in Skagerrak sediments, which is distinctively lower compared to other continental margins. We suggest that the continuous dissolution of bSi in suspended sediments transported over long distances from the North Sea leads to the apparent decoupling between bSi and organic carbon in Skagerrak sediments.

In-Depth Performance Analysis and Comparison of Monolithic and Particulate Zwitterionic Hydrophilic Interaction Liquid Chromatography Polymer Columns.

The kinetic performance of different zwitterionic hydrophilic interaction liquid chromatography polymer columns is evaluated and compared in-depth. For this purpose, two lab-made monolithic columns, synthesized with different crosslinkers, and a commercial particle packed column are considered. It is found that performance evaluation techniques, such as comparing plate height curves or fitted A-, B- and C-terms, obtained by fitting experimental plate height data to a plate height model, are complicated by the determination of a reliable characteristic length. This is due to the very different morphology of these column types, and the heterogeneity of the monolithic columns. The occurrence of a convective flow through the packed particle column further complicates the interpretation of the obtained fitting parameters, as part of the C-term is wrongfully attributed to the A-term. Therefore, the use of the kinetic plot method is suggested for the comparative evaluation of these columns, as kinetic plots do not require the determination of a characteristic length, nor rely on any fitting parameters. With the kinetic plot method, it is demonstrated that the lab-made monolithic columns outperform the packed particle column for plate counts between 10,000 and 800,000. This is attributed to the higher column efficiency of these columns, due to their small domain and skeleton sizes, and their high permeability, resulting from their high external porosity and the occasional occurrence of preferential flow paths.

ZIF-8 Assisted Polyacrylamide Functionalized Silica Core-Shell Stationary Phase for Hydrophilic Interaction Liquid Chromatography

A novel ZIF-8 assisted polyacrylamide functionalized silica polar stationary phase was prepared by a facile method of adding ZIF-8 nanoparticles and silica into polyacrylamide (PAM) aqueous solution, and then stirring the mixture until the solution was evaporated absolutely with the help of mechanical agitator. Interestingly, the prepared stationary phase (PAM-Sil@ZIF-8/PAM) showed favorable hydrophilicity, as demonstrated by good separation performance and strong retention ability toward several types of polar compounds, such as amino acids, saccharides, and alkaloids. In addition, PAM-Sil@ZIF-8(50 mg)/PAM showed better separation performance compared with amino-modified silica and Sil/PAM stationary phase due to the addition of ZIF-8. Furthermore, it was demonstrated that the addition of ZIF-8 improved the specific surface area and provided extra interaction sites for the stationary phase and analytes, which is beneficial for the separation of samples. In addition, the column efficiency can reach 7861.9 plates/m for colchicine. Moreover, it exhibited good stability and reproducibility under our operation conditions. In short, a novel stationary phase, which can be used for hydrophilic interaction liquid chromatography, was obtained and proved that the separation performance of polymer modifying silica stationary phase can be greatly improved by the addition of MOF nanoparticles.

Synthesis and evaluation of ginsenosides imprinted polymer-based chromatographic stationary phase.

Molecular imprinting technique has aroused great interest in preparing novel stationary phases, and the resulting materials named molecularly imprinted polymers coated silica packing materials exhibit good performance in separating diverse analytes based on their good characteristics (including high selectivity, simple synthesis, and good chemical stability). To date, mono-template is commonly used in synthesizing molecularly imprinted polymers-based stationary phases. The resulting materials always own the disadvantages of low column efficiency and restricted analytes, and the price of ginsenosides with high purity was very high. In this study, to overcome the weaknesses of molecularly imprinted polymers-based stationary phases mentioned above, the multi-templates (total saponins of folium ginseng) strategy was used to prepare ginsenosides imprinted polymer-based stationary phase. The resulting ginsenosides imprinted polymer-coated silica stationary phase has a good spherical shape and suitable pore structures. Additionally, the total saponins of folium ginseng were cheaper than other kinds of ginsenosides. Moreover, the ginsenosides imprinted polymer-coated silica stationary phase packed column performed well in separation of ginsenosides, nucleosides, and sulfonamides. The ginsenosides imprinted polymer-coated silica stationary phase possesses good reproducibility, repeatability, and stability for seven days. Therefore, a multi-templates strategy for synthesizing the ginsenosides imprinted polymer-coated silica stationary phase is considered in the future. This article is protected by copyright. All rights reserved.

Evaluating the efficiency of stone columns in mitigating liquefaction risks and enhancing soil bearing capacity: A case study

Several processes allow the improvement of soils such as vibrocompaction, stony columns, static horizontal compaction etc. These processes reduce the risk of liquefaction potential and making it possible to build on this type of soil when the space restriction require it. Stone columns are a recognized method of soil improvement, which consists of creating large diameter columns using special vibrators with granular filling materials introduced into the ground. The objective of this work is to evaluate the effectiveness of stone columns, made in a seismic zone containing liquefiable materials, with regards to the reduction of the risk of liquefaction and the improvement of the bearing capacity of the soil. The approach followed is the exploitation of geotechnical investigation tests (CPT Cone Penetration Test), (SPT: Cone Penetration Test, (pressuremeter tests), carried out before and after soil treatment. This study showed that the network of gravelled columns produces an enhanced soil improvement effect by improving the modulus of elasticity of the soil and reducing settlement and the risk of liquefaction after treatment. The process allows for the improvement of the geotechnical characteristics of its soils, making it possible to build infrastructure and development projects in the area.

In situ growth of imine-based covalent organic framework as stationary phase for high-efficiency electrochromatographic separation

Design of the smart stationary phases, which can improve the separation efficiency is an essential work in the capillary electrochromatography (CEC). Owing to good excellent properties, covalent organic frameworks (COFs) have showed promising potential in the area of separation science. Here, a micro- and mesoporous COF TAPB-BTCA with adequate available interaction sites and outstanding mass transfer performance was first exploited as a stationary phase for high-efficiency in capillary electrochromatography. Through in situ growth approach, the COF TAPB-BTCA coated capillary column was facilely prepared at room temperature. The separation ability of the COF TAPB-BTCA coated capillary column was studied. The fabricated column showed high efficiency for the separation of six types of small molecular compounds, including alkylbenzenes, chlorobenzenes, phenols, parabens, vanillin and related phenolic compounds, and non-steroidal anti-inflammatory drugs (NSAIDs). The maximum theoretical plates reached up to 293,363 N/m for phloroglucinol, showing significantly improved column efficiency in comparison to previous reported COFs-based columns. In addition, the mass loadability for methylbenzene was achieved to 1.44 mg/mL. Also, excellent reproducibility and stability were obtained on the COF TAPB-BTCA coated columns. The relative standard deviations of intra-day (n = 3), inter-day (n = 3) and three batch tubes were all less than 2%, and no obvious change was presented in separation performance after the column was used 120 runs. This COF TAPB-BTCA-based stationary phase would be a promising candidate for high-efficiency chromatographic separation.

Separation performance of the calix[8]arene functionalized with polyethylene glycol units for capillary gas chromatography.

In this paper, an amphiphilic calix[8]arene with polyethylene glycol unit branches (C8A-PEG) was synthesized and applied for capillary gas chromatography (GC). The C8A-PEG was coated on the inner wall of a capillary column by a static method with the column efficiency of 3165 plates/m and polar nature. As demonstrated, the C8A-PEG column has excellent physicochemical properties and separation performance since it has π-electron-rich 3D cavity which combines with polar PEG units. Compared with two columns corresponding to the construction units C8A and PEG, the C8A-PEG column shows distinctly advantageous performance for the mixture of 22 components with diverse types. Impressively, it shows satisfactory resolution for positional isomers and cis-/trans- isomers, especially the challenging isomers of toluidine and dimethylaniline. The outstanding distinguishing capability of the C8A-PEG stationary phase is mainly attributed to the abundant molecular recognition interactions, including van der Waals, dipole-dipole, H-bonding and π-π stacking interactions. This work has proved that the new GC stationary phases constructed by different units can complement each other's advantages, improve their physicochemical properties and separation performance, and have broad application prospects in chromatographic analysis.

Determination of 5-methyldeoxycytosine and oxidized derivatives by nano-liquid chromatography with zwitterionic monolithic capillary column

DNA methylation is one of the epigenetic modifications at the 5-carbon of cytosine to form 5-methyl-2′-deoxycytidine (5mdC). In mammalian cells, 5mdC can be transferred to 5-hydroxymethyl-2′-deoxycytidine (5hmdC) by ten-eleven translocation (TET), and 5hmdC is further oxidized to 5-formyl-2′-deoxycytidine (5fodC) and 5-carboxyl-2′-deoxycytidine (5cadC). In the present work, we developed a highly sensitive nano liquid chromatographic method for the determination of 5mC and 5hmC with zwitterionic monolithic capillary column. The conditions for the preparation of zwitterionic monolithic capillary column were systematically optimized. The monolithic capillary column displayed high column efficiency for nucleoside dA (190,000 plates/m) and allowed the baseline separation of 10 standard nucleosides in HILIC mode. The detection sensitivity was improved significantly by using the large volume injection combined with sample stacking onto the head of the column when sample was dissolved in high content organic solvent (ACN: H2O = 97:3). The limit of detection for 5mdC and 5hmdC were determined as 4 nM and 3 nM, respectively, and the corresponding limit of quantification were determined as 12 nM and 10 nM, respectively. Further, the zwitterionic monolithic capillary column can be easily utilized in nano-LC and mass spectrometry coupling for qualitative analysis of 5mdC, 5hmdC, 5fodC and 5cadC in real mouse brain sample. The whole genomic DNA methylation levels in mouse brain sample can be easily determined with UV detection.

Aligned porous Chitosan/Ti3C2 MXenes monolith as a high-performance fixed-bed separation medium toward globular albumin separation

Designing and tuning macropores into aligned structure is of considerable importance in promoting mass transfer, improving chromatographic performance and enhancing column efficiency. Herein, we have synthesized an innovative aligned porous Chitosan/Ti3C2 MXenes monolith via a facile, versatile and reproducible unidirectional “freeze-casting” method. Typically, the accumulation of Ti3C2 MXenes directs the formation of aligned structure during the unidirectional freezing process and thus aligned macropores are formed by a subsequent freeze-drying process. By various physical characterization, the distribution of aligned macropores, micropores and specific surface area are determined to be 21 μm, 2.53 nm and 103.09 m2·g−1, respectively. In addition, monolith bed permeability is calculated to be 1.94 × 10-12 m2, approximately 10 times than conventional monolith. Batch adsorptive experiments confirm that adsorptive capacities to bovine serum albumin and bovine hemoglobin are remarkably elevated on account of the high affinity of proteins onto those imbedding Ti3C2 MXenes. Meanwhile, continuous mass transfer equation describes the aligned macropores facilitate the film mass transfer factor ([kLa]f) in a separation process thus driving the global mass transfer factor ([kLa]g). It is expected that the aligned porous Chitosan/Ti3C2 MXenes monolith promises great potential for a continuous separation of proteins when a wholesale production is required.

Coupling capillary electrophoresis-electrospray ionization mass spectrometry with sheathless interface for drug analysis

Capillary electrophoresis-mass spectrometry （CE-MS） combines the advantages of capillary electrophoresis， such as the high separation efficiency and low sample consumption， and the high detection sensitivity of mass spectrometry and the ability for providing the structural information for structure elucidation of unknown components. However， the interface technology for coupling capillary electrophoresis and mass spectrometry is still not well resolved. In the present work， we explored the application of the sheathless CE-MS interface which was prepared by gold foil-wrapped CE separation column tip directly as a spray electrode for the analysis of five tyrosine kinase inhibitors， namely sunitinib， imatinib mesylate， gefitinib， dasatinib and erlotinib. This interface integrates separation and electrospray ionization in one capillary， which is easy to manufacture， low in cost， and can be produced in batches. We found that using the nonaqueous CE separation mode can not only achieve baseline separation of five tyrosine kinase inhibitors， but also obtain stable mass spectrometry signals. First， we investigated the effect of the electrolyte solution composition on the separation. The optimized background electrolyte composition was obtained： 2% （v/v） acetic acid and 5 mmol/L ammonium acetate in acetonitrile-methanol （80∶20， v/v）. Under optimized conditions， the five kinase inhibitors could be baseline separated， meantime， the sheathless interface could also maintain stable electrospray for a long time. The relative standard deviation （RSD） values of the intraday and interday repeatability of the analyte retention times were less than 0.5% and 0.8%， respectively， and the RSD value between interface batches is less than 2.6%. Compared with CE-MS with aqueous phase， the separation column efficiency of the five tyrosine kinase inhibitors under nonaqueous phase conditions is higher， the detection sensitivity is higher， and the absolute detection limit reaches amol level. In addition， we evaluated the sheathless interface with various organic acids， such as palaflin A， salvianolic acid C， and rosmarinic acid， as well as hydrophobic macrolide antibiotics， azithromycin， erythromycin， and sporin A， good separation effect and mass spectrometric detection results can be obtained.

A monolithic azacalix[4]pyridine column for high-resolution and high-efficiency pressurized capillary electrochromatographic separation

Herein, a highly stable (NAllyl)4-bridged alyzacalix[4]pyridine monolithic column (nAC4P@capillary) was fabricated by copolymerizing nAC4P with GMA and EDMA into a stationary phase through a simple olefin addition reaction. The physicochemical properties of the prepared materials were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), energy dispersive X-ray (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and elemental analysis (EA). A wide range of analytes with various properties was well separated and demonstrated the synergistic effect of the various interaction sites. The maximum column efficiencies (Nmax) for all the analytes reached 62,368 plates/m, and the relative standard deviations (RSDs) of the daily retention times of alkylbenzenes, measured over six months were all lower than 5.63%. Non-covalent interaction analysis reveals that nAC4P@capillary can effectively combine the advantages of electronic configurations, π-π interactions, CH-π interactions, O–H…N hydrogen bonds and lone pair-π interactions, providing excellent prospects for high-performance chromatographic separation.