Wall Of Capillary Column Research Articles

Enantiomeric Separation by Capillary Electro chromatography with a Novel β-cyclodextrin-hyperbranched Carbosilane–silica Polymer Coating

A new type of β-cyclodextrin-modified hyperbranched carbosilane (β-CD@HBC) stationary phase was synthesized by combining hyperbranched carbosilane with the -OH group of β-cyclodextrin, and then the β-CD@HBC was used as astationary phase to fix it on the inner wall of capillary column, application in chiral drug separation. The chromatographic behaviour of the stationary phase was studied. The preliminary test results showed that the β-CD@HBC coated OT column has the ability to separate a variety of enantiomers, such as clenbuterol, ibuprofen, enrofloxacin, hlorpheniramine, isoproterenol hydrochloride, epinephrine, Phenylalanine, and Ketoprofen. The β-CD@HBC coated OT column has good repeatability and stability. The relative standard deviations (RSD) between runs, between days, and between columns were less than 1.5%, 1.86%, and 4.83%, respectively. This paper shows that hyperbranched polymers have great potential and advantages in the application of capillary electrochromatography for chiral separation.

Flow-Through Atmospheric Pressure-Atomic Layer Deposition Reactor for Thin-Film Deposition in Capillary Columns.

We demonstrate the development of a new atmospheric pressure-atomic layer deposition(AP-ALD) system to coat the inner walls of capillary columns for gas chromatography (GC). Unlike traditional ALD, this reactor operates at near-atmospheric pressure and addresses the challenges of depositing thin films inside capillaries, which include long pump down times, deposition in high-aspect-ratio materials, and temperature control. We show ALD of alumina in 5 and 12 m capillaries (0.53 mm ID) via sequential half reactions of trimethylaluminum and water. Our system yields pinhole-free, uniform thin films. It includes small witness chambers for witness silicon shards before and after the capillary. An engineering flow/transport analysis of the device is provided. Our ALD alumina thin films are characterized by spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy. Alumina film growth achieved is 1.4-1.5 Å/cycle, which is consistent with previously reported results. Film thickness measurements by SE on witness shards of silicon and by TEM at both ends of the capillary are in good agreement. A capillary column coated with alumina is used to separate different gases by GC, although the retention times of gases are essentially the same as with an untreated fused silica capillary. This successful deposition of ALD alumina in long capillaries opens the door for other possible ALD coatings, including hybrid organic-inorganic coatings, using the 450+ ALD precursors available today.

Preparation of covalently bonded liposome capillary column and its application in evaluation of drug membrane permeability

Two liposomes, including 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) + 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (PE) + cholesterol (Chol) (DSPC/PE/Chol liposomes) and soybean lecithin (SPC) + PE + Chol (SPC/PE/Chol liposomes), were prepared and fixed on the inner wall of capillary column by using the adhesion of polydopamine (PDA) membrane and the cross-linking property of glutaraldehyde (GA). The immobilized liposome capillary column (ILCC) has good repeatability and stability based on the electrophoretic mobility of analyte. A CE method based on the immobilized liposome capillary column chromatography (ILCCC) was successfully developed to study the retention behavior of drugs on ILCC, and the logarithm of retention factor (log k) of neutral and ionic drugs were determined. The results show that the log k measured by the ILCCC based on two liposomes have a good linear fitting (R2 = 0.86). Moreover, the linear relationship between ILCCC system and other related research systems (octanol-water system and immobilized artificial membrane (IAM)) was analyzed, and the results indicate that SPC/PE/Chol ILCCC, DSPC/PE/Chol ILCCC and IAM systems have good fitting results, R2 values are 0.86 and 0.78, respectively. In addition, the normalization coefficients of ILCCC and IAM systems obtained by the linear free energy relationship (LFER) analysis are close and the d value is small. In short, the ILCCC is a simple and feasible method for studying drug membrane permeability.

Covalent organic framework TpPa-1 as stationary phase for capillary electrochromatographic separation of drugs and food additives.

Because of unique properties like permanent porosity, low density and large surface area, covalent organic frameworks are attractive microporous materials as stationary phase for CEC. Among them, COF-TpPa-1 possesses extraordinary chemical stability and common features of covalent organic frameworks. So, COF-TpPa-1 could be a promising material as stationary phase to enhance separation selectivity and tolerate the acid or alkaline electrochromatographic separation conditions. Here, we report the preparation of COF-TpPa-1 modified capillary column by in situ growth for electrochromatographic separation. The immobilization of COF-TpPa-1 on the inner wall of capillary column was confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction. The fabricated COF-TpPa-1 modified capillary column indicated good resolution for the separation of neutral analytes, nonsteroidal anti-inflammatory drugs and food additives in open-tubular CEC mode. Compared with bare capillary column, the COF-TpPa-1 modified capillary column improved separation selectivity remarkably for tested analytes, including hydrophobic, π-π and hydrogen bond interactions. Besides, the prepared capillary column showed excellent repeatability and stability. The intraday, interday and column-to-column relative standard deviations of migration time for neutral analytes were less than 3.54%. This work shows enamine-linked covalent organic frameworks have great potential as stationary phases in CEC.

Open-tubular capillary electrochromatography using carboxylatopillar[5]arene as stationary phase.

Pillar[n]arenes have achieved much interest in material chemistry and supramolecular chemistry due to unusual pillar shape structure and high selectivity toward guest. However, pillar[n]arenes have not yet been applied in capillary electrochromatography. This work at first time reports that carboxylatopillar[5]arene is used as a stationary phase in open-tubular capillary electrochromatography. Carboxylatopillar[5]arene not only possess the advantages of pillar[n]arenes but also provide free carboxy groups for immobilizing on the inner wall of capillary column via covalent bonding. The characterization of SEM and FT-IR indicated that carboxylatopillar[5]arene was successfully grafted on the inner wall of capillary. The baseline separation of model analytes including neutral, basic, and acidic compounds, nonsteroidal anti-inflammatory drugs and dansyl-amino acids have been achieved thanks to the electron-rich cavity of carboxylatopillar[5]arene and hydrophobic interactions between the analytes and stationary phase. The intraday, interday, and column-to-column precisions (RSDs) of retention time and peak area for the neutral analytes were all less than 3.34 and 9.65%, respectively. This work indicates that pillar[n]arenes have great potential in capillary electrochromatography as novel stationary phase.

In situ synthesis of the imine-based covalent organic framework LZU1 on the inner walls of capillaries for electrochromatographic separation of nonsteroidal drugs and amino acids

The covalent organic framework LZU1 (Lan Zhou University-1) is one of the imine-based covalent organic frameworks (COFs) that possesses attractive properties such as structural regularity, stability and good porosity. This work reports on the in-situ synthesis of COF-LZU1 on the inner walls of capillary column for open-tubular capillary electrochromatography (OT-CEC). The fused-silica capillary was first modified with 3-aminopropyltriethoxysilane and glutaraldehyde. Epitaxial growth of COF-LZU1 on the inner walls was accomplished by Schiff base reaction. The formation of COF-LZU1 was confirmed by SEM and FT-IR. The COF-LZU1 coating increases the interactions between analytes and coating, which remarkably improves the CEC separation selectivity of neutral analytes, amino acids and nonsteroidal anti-inflammatory drugs. The COF-LZU1-modified column exhibits good stability and repeatability. The precisions (relative standard deviations) for intra-day, inter-day and column-to column are <1.6%, 5.6% and 6.8%, respectively. Hence, the imine-based COFs represent attractive stationary phase for application in CEC separations.

Covalent bonding of homochiral metal-organic framework in capillaries for stereoisomer separation by capillary electrochromatography.

In this work, a [Cu(mal)(bpy)]⋅H2O (mal, L-(-)-malic acid; bpy, 4,4'-bipyridyl) homochiral metal-organic frameworks (MOFs) was synthesized and used for modifying the inner walls of capillary columns by utilizing amido bonds to form covalent links between the MOFs particles and capillary inner wall. The synthesized [Cu(mal)(bpy)]⋅H2 O and MOFs-modified capillary column were characterized by X-ray diffraction, thermogravimetric analysis, particle size distribution analysis, nitrogen absorption characterization, FTIR spectroscopy, SEM, and energy-dispersive X-ray spectroscopy (EDX). The MOFs-modified capillary column was used for the stereoisomer separation of some drugs. The LODs and LOQs of six analytes were 0.1 and 0.25 μg/mL, respectively. The linear range was 0.25-250 μg/mL for ephedrine, 0.25-250 μg/mL for pseudoephedrine, 0.25-180 μg/mL for D-penicillamine, 0.25-120 μg/mL for L-penicillamine, 0.25-180 μg/mL for D-phenylalanine, and 0.25-160 μg/mL for L-phenylalanine, all with R(2) > 0.999. Finally, the MOFs-modified capillary column was applied for the analysis of active ingredients in a real sample of the traditional Chinese medicine ephedra.

Surface Initiated Atom Transfer Radical Polymerization: Access to Three Dimensional Wavelike Polymer Structure Modified Capillary Columns for Online Phosphopeptide Enrichment

Reversible phosphorylation is one of the most important post-translational modifications of proteins and a key regulator of cellular signaling pathways. Specific enrichment of phosphopeptides from proteolytic digests is a prerequisite for large scale identification of protein phosphorylation by mass spectrometry. Online enrichment of phosphopeptides attracts particular interests due to its automated operation, higher throughput and reproducibility, lower sample loss, and contamination. Here, we report a new type of capillary column developed using surface initiated atom transfer radical polymerization (SI-ATRP) for automated online phosphopeptide enrichment. SI-ATRP modification leads to a surface confined growth of three-dimensional wavelike polymer structure on the inner wall of capillary columns and, therefore, results in largely increased surface area. Furthermore, the noncross-linked flexible polymer chains grown by SI-ATRP create a large internal volume that allows phosphopeptides to penetrate into during enrichment and also facilitate the interaction between the numerous functional groups in the polymer chains and target phosphopeptides. Therefore, highly efficient and specific enrichment is achieved even for a low femtomole of phosphopeptides. The loading capacity is increased more than an order of magnitude compared with that obtained using conventional open tubular capillary columns. The SI-ATRP modified capillary column was successful applied in the online phosphoproteomics analysis of HepG2 cell lysate and resulted in 10 times improved phosphopeptide identification than the previously reported number. Finally, the SI-ATRP technique is compatible with a variety of functional monomers, and therefore, versatile potential applications in reverse phase, ion exchange, and affinity chromatography can be expected.

New method for bonding an adsorbent film to the walls of capillary columns

AbstractA new method for immobilisation of an adsorbent on the wall of a capillary column ensures high thermal and mechanical stability of the resulting coating. The method can be applied to a variety of adsorbents of natural or synthetic origin. Its effectiveness is illustrated by results obtained for coating with modified silica or molecular sieve 13X.

Developments in stationary phase technology for gas chromatography

In gas chromatography (GC), the main driver for the separation is the stationary phase, which is deposited on the inside wall of capillary columns. Many developments have taken place in the past 20 years. The stationary phases used in GC are liquid phases, adsorbents and, sometimes, a combination.Adsorbents are widely used and show highly selective separations, especially for gases and volatiles. Adsorbents, such as aluminum oxide and the molecular sieve, have found wide application in GC for hydrocarbon and permanent gases. A new generation of in-situ adsorbents, based on divinylbenzene, silica and carbon, show improved performance with respect to mechanical stability, temperature range and inertness, and they are used for difficult applications where their selectivity is exploited. Unique interactions are obtained with a multi-layer technology, called Lowox.Liquid phases are usually polymers based on polydimethylsiloxane/carborane/glycol/divinylbenzene with different degrees of substitution. Technologies are developed by chemical bonding and cross-linking of such polymers to stabilize liquid phases, making the stationary phase more robust and suitable for trace and high-temperature analysis. Special groups are incorporated to elute basic, acidic, chiral compounds and FAME (fatty acid methyl ester) compounds. The newest technologies allow the inclusion of special stabilizing groups to increase thermal stability for non-polar as well as polar stationary phases; technologies, such as sol gel, allow the in-situ preparation of bonded liquid phase layers.The behavior of these stabilized adsorbents and liquid phases is discussed in detail, as well as their current application.

Study of the Solution in the Synthesis of a Sol−Gel Composite Used as a Chromatographic Phase

Tetraethoxysilane (TEOS) and octyltriethoxysilane (C8-TEOS) were used in the synthesis of an organic−inorganic hybrid glass composite by the sol−gel process. This composite was used as the stationary phase for chromatographic and electrophoretic separations when cast onto the inner walls of capillary columns. To investigate the reactions leading to the final chromatographic material, the hydrolysis and initial condensation reactions of TEOS, C8-TEOS, and the C8-TEOS/TEOS hybrid mixture were studied by 29Si and 1H NMR spectroscopy. The reaction of methyltriethoxysilane (C1-TEOS) and ethyltriethoxysilane (C2-TEOS) were also followed for comparison purposes. The formation of the various silicon species and the degree of substitution on the Si atom in the reactions revealed that TEOS hydrolyzes faster than C8-TEOS when each precursor reacts individually. However, the rate of hydrolysis for C8-TEOS increases when reacting in a C8-TEOS/TEOS (1:1 mole ratio) mixture, driven by the condensation of hydrolyzed TEOS...

Deactivation with polymethylhydrosiloxane : A comparative study with capillary gas chromatography and solid-state 29Si nuclear magnetic resonance spectroscopy

Deactivation of fused-silica capillary columns and vitreous silica surfaces with polymethylhydrosiloxanes (PMHS) at temperatures between 240 and 360°C was investigated by gas chromatography (GC) and solid-state 29Si NMR spectroscopy. The influence of temperature, amount of water at the surface and film thickness on the stability and nature of the polymer deactivation layer was studied by solid-state 29Si NMR of the model substrate Cab-O-Sil, a fumed silica. These NMR measurements match the GC results and offer additional information relating to the nature of the deactivating layer at surfaces silylated under various reaction conditions. Differences in the nature and structure of the deactivating film occur when the silica surface is coated with a different thickness. Optimum deactivation is achieved when a few monolayers of densely cross-linked polymers anchored to the silica surface are formed. On top of this thin, rigid layer, longer mobile polymer chains containing unreacted silicon hydride groups are present. After optimum deactivation, the fused-silica capillary column wall shows no interaction with various critical test components as used in GC practice. The deactivating films exhibit good thermal stability and solvent resistance.

Use of peltier thermoelectric devices to control column temperature in high-performance capillary electrophoresis

A temperature control system for high-performance capillary electrophoresis is described utilizing Peltier thermoelectric devices. The thermoelectric devices heat or cool an alumina block which has a high thermal conductivity for efficient heat removal from the external capillary column wall. The heat dissipation characteristics of this device are compared to natural convection and fan cooling by observing the stability of current with time and the dependence of current on applied field. A linear relationship of electroosmotic flow velocity with increasing field is found, indicative of a constant temperature at the inside wall of the capillary. Also, the change in peak shape of horse heart myoglobin as a function of increasing temperature is shown to demonstrate the importance of temperature control in obtaining optimum efficiency.

Loss of water during heat treatment of acid leached glass and fused silica capillary columns

AbstractA study was carried out on the effects of acid leaching of capillary column wall materials. Leaching experiments with glass and fused silica were performed under static and dynamic conditions; moreover, the influence of the temperature was investigated. The amount of water released during different temperature programs was measured with a microwave plasma detector. Different leaching conditions and column wall materials cause considerable variations in water production. These results probably explain the disappointing deactivation efficiency obtained for fused silica and dynamically leached soft glass if HMDS is used. Evidence was found for an increase in surface area due to acid leaching.

Separation of eight epimeric 2-aminoaldohexoses as aminohexitol acetates by gas chromatography and analysis of bacterial heteroglycans containing rare 2-aminoaldohexoses and 2-aminouronic acids

A method has been developed for the separation of all eight of the possible 2-aminohexitols as alditol acetates derived from 2-aminoaldohexoses by gas chromatography on a capillary column wall coated with Poly A-103 (25 m × 0.25 mm I.D.). For the depolymerization of bacterial polysaccharides containing amino sugars or aminouronic acids, we used methanolysis, which resulted in transglycosylated amino sugar methylglycosides and aminouronic acid methylglycoside methyl esters without appreciable destruction. The latter compounds were converted into amino sugar methylglycosides by reduction with sodium borohydride. This step allows differentiation between amino sugars and aminouronic acids. The usefulness of the method is demonstrated on cell wall polysaccharides of Shigella sonnei, Vibrio parahaemolyticus, Micrococcus lysodeikticus and Methanobacterium thermoautotrophicum containing rare aminouronic acids.

Gas chromatography—mass spectrometry of aldoses as O-methoxime, O-2-methyl-2-propoxime and O- n-butoxime pèrtrifluoroacetyl derivatives on OV-225 with methylpropane as ionization agent : I. Pentoses

Pentoses have been identified by gas chromatography—mass spectrometry using chemical ionization by methylpropane of the O-methoxime, O-2-methyl-2-propoxime and O- n-butoxime pertrifluoroacetyl derivatives, separated on a glass capillary column wall coated with OV-225. Each pentose gave two peaks, the syn (Z) and the anti (E) alkoxime. The syn derivatives of O-2-methyl-2-propoximes give shorter retention times than the corresponding derivatives of O-methoximes. The fragmentation patterns are discussed. M + 1 gives the most intense peak.

Quantitative determination of conjugated estrogens in formulations by capillary GLC

A rapid capillary GLC method for the analysis of conjugated estrogen tablets and injectable formulations is described. The method involves the hydrolytic cleavage of the sodium sulfate ester conjugates by sulfatase enzyme. The free phenolic steroids are reacted sequentially with hydroxylamine hydrochloride and N, O-bis(trimethylsilyl)trifluoroacetamide. The resulting dual derivatives are analyzed on a 15-m glass capillary column wall coated with a cyanopropylmethyl silicone phase.