Open Tubular Columns Research Articles

An Ultra-Trace Analysis Technique for SF6 Using Gas Chromatography with Negative Ion Chemical Ionization Mass Spectrometry.

Sulfur hexafluoride (SF6) is widely used as a tracer gas because of its detectability at low concentrations. This attribute of SF6 allows the quantification of both small-scale flows, such as leakage, and large-scale flows, such as atmospheric currents. SF6's high detection sensitivity also facilitates greater usage efficiency and lower operating cost for tracer deployments by reducing quantity requirements. The detectability of SF6 is produced by its high molecular electronegativity. This property provides a high potential for negative ion formation through electron capture thus naturally translating to selective detection using negative ion chemical ionization mass spectrometry (NCI-MS). This paper investigates the potential of using gas chromatography (GC) with NCI-MS for the detection of SF6. The experimental parameters for an ultra-trace SF6 detection method utilizing minimal customizations of the analytical instrument are detailed. A method for the detection of parts per trillion (ppt) level concentrations of SF6 for the purpose of underground ventilation tracer gas analysis was successfully developed in this study. The method utilized a Shimadzu gas chromatography with negative ion chemical ionization mass spectrometry system equipped with an Agilent J&W HP-porous layer open tubular column coated with an alumina oxide (Al2O3) S column. The method detection limit (MDL) analysis as defined by the Environmental Protection Agency of the tracer data showed the method MDL to be 5.2 ppt.

Open-tubular CEC with a new triethanolamine bonded stationary phase for biomolecule separation.

This study describes the preparation and electrochromatographic application of a new open-tubular capillary column with triethanolamine functionalized stationary phase. The stationary phase was synthesized by in situ grafting polymerization with 3-chloro-2-hydroxypropylmethacrylate based reactive monomer, and followed triethanolamine functionalization. The different 3-chloro-2-hydroxypropylmethacrylate contents on the separation efficiency were studied. The results indicated that the 3-chloro-2-hydroxypropylmethacrylate content (e.g., 15.3v/v%) on the inner surface of the capillary was very important for final preparation of the polymer stationary phase. The electrochromatographic characterization of the stationary phase was performed using alkylbenzene derivatives. The pH effect on the electroosmotic flow was also investigated. The open tubular column functionalized with triethanolamine allowed to operate in the anodic electroosmotic flow mode in the system. With anodic electroosmotic flow mode, favorable separations of the amino acids and the nucleosides were successfully achieved with high column efficiens ranging from 142000 to 257000 plates/m. Good repeatability was gained with relative standard deviation of the migration time and peak areas less than 2.2% for run to run (n=5) and less than 3.2% day to day (n=3). Furthermore, real sample applicability of this column to the separation of amino acids in white tea sample was demonstrated.

A System Map for the Ionic Liquid Stationary Phase 1,9-Di(3-vinylimidazolium)nonane Bis(trifluoromethylsulfonyl)imide

The solvation parameter model is used to characterize the retention properties of the ionic liquid stationary phase 1,9-di(3-vinylimidazolium)nonane bis(trifluoromethylsulfonyl)imide (SLB-IL100) over the temperature range 60–200 °C. The results are presented in the form of a system map comprising a continuous plot of the system constants of the solvation parameter model determined at 20 °C intervals as a function of column temperature. The ionic liquid stationary phase is a cohesive, polar solvent with significant hydrogen-bonding capability. It differs from polar siloxane-based and poly(ethylene glycol) stationary phases by being a moderate hydrogen-bond acid and is shown to possess separation properties that are not duplicated in a comprehensive database of system constants for commercially available open-tubular columns.

An Open Tubular CEC Column of Excellent Separation Efficiency for Proteomic Analysis

E-mail: wjcheong@inha.ac.krReceived May 25, 2014, Accepted June 18, 2014Key Words : CEC capillary column, Open tubular, Molecular imprinted polymer, Tryptic digest, High sepa-ration efficiencyProteomics aims to understand complex biological systemsby analyzing protein expression, protein function, proteinmodifications and protein interactions.

Open tubular lab-on-column/mass spectrometry for targeted proteomics of nanogram sample amounts.

A novel open tubular nanoproteomic platform featuring accelerated on-line protein digestion and high-resolution nano liquid chromatography mass spectrometry (LC-MS) has been developed. The platform features very narrow open tubular columns, and is hence particularly suited for limited sample amounts. For enzymatic digestion of proteins, samples are passed through a 20 µm inner diameter (ID) trypsin + endoproteinase Lys-C immobilized open tubular enzyme reactor (OTER). Resulting peptides are subsequently trapped on a monolithic pre-column and transferred on-line to a 10 µm ID porous layer open tubular (PLOT) liquid chromatography LC separation column. Wnt/ß-catenein signaling pathway (Wnt-pathway) proteins of potentially diagnostic value were digested+detected in targeted-MS/MS mode in small cell samples and tumor tissues within 120 minutes. For example, a potential biomarker Axin1 was identifiable in just 10 ng of sample (protein extract of ∼1,000 HCT15 colon cancer cells). In comprehensive mode, the current OTER-PLOT set-up could be used to identify approximately 1500 proteins in HCT15 cells using a relatively short digestion+detection cycle (240 minutes), outperforming previously reported on-line digestion/separation systems. The platform is fully automated utilizing common commercial instrumentation and parts, while the reactor and columns are simple to produce and have low carry-over. These initial results point to automated solutions for fast and very sensitive MS based proteomics, especially for samples of limited size.

Preparation and evaluation of open tubular C18-silica monolithic microcartridges for preconcentration of peptides by on-line solid phase extraction capillary electrophoresis

In this study, C18-silica monoliths were synthesized as a porous layer in open tubular capillary columns, to be cut later into microcartridges for the analysis of neuropeptides by on-line solid-phase extraction capillary electrophoresis with UV and MS detection (SPE-CE-UV and SPE-CE-MS). First, several types of C18-silica monolithic (MtC18) microcartridges were used to analyse standard solutions of five neuropeptides (i.e. dynorphin A (1–7), substance P (7–11), endomorphin 1, methionine enkephalin and [Ala]-methionine enkephalin). The MtC18 sorbents were especially selective against endomorphin 1 and substance P (7–11)). The best results in terms of sensitivity and inter-microcartridge reproducibility were achieved with the microcartridges obtained from a 10-cm open tubular capillary column with a thin monolithic coating with large through-pores (1–5μm). Run-to-run repeatability, microcartridge durability, linearity ranges and LODs were studied by MtC18-SPE-CE-MS. As expected due to their greater selectivity, the best LOD enhancement was obtained for End1 and SP (7–11) (50 times with regard to CE-MS). Finally, the suitability of the methodology for analysing biological fluids was tested with plasma samples spiked with End1 and SP (7–11). Results obtained were promising because both neuropeptides could be detected at 0.05μgmL−1, which was almost the same concentration level as for the standard solutions (0.01μgmL−1).

Preparation and electrochromatographic characterization of new chiral β-cyclodextrin poly(acrylamidopropyl) porous layer open tubular capillary columns

A novel chiral stationary phase consisting of an amidopropyltrimethylammonium chloride divinylbenzene (APAT–DVB) polymer containing the chiral selector heptakis(2,3-di-O-acetyl-6-O-sulfo)-β-cyclodextrin (HSβCD) has been employed in porous layer open tubular (PLOT) capillary column format with various conditions evaluated to optimize the polymerization and chiral selector immobilization. Scanning electron microscopy demonstrated a near homogenous longitudinal open path in the column with a polymer film of uniform thickness. IR spectroscopy characterized the functional groups of the polymer and energy-dispersive X-ray spectroscopy provided further evidence of the successful polymer modification with HSβCD. Optimum electrochromatographic separation conditions were elaborated with respect to organic solvent content and pH of the background electrolyte. Colum-to-column and long-term reproducibility was excellent. The effectiveness of the new capillary column was demonstrated with the successful separation of d-and l-aspartic acid, d- and l-tyrosine and d-and l-lysine.

Molecular imprinted polymeric porous layers in open tubular capillaries for chiral separations

A new method has been developed for the preparation of molecular imprinted polymers as porous layers in open tubular (MIP-PLOT) capillary column formats for use in chiral separations by capillary liquid chromatography. The synthesis was based on ‘in-capillary’ ultraviolet (UV) initiated polymerization using light emitting diodes (LEDs) in conjunction with the continuous delivery of the pre-polymerization reagents into the polymerization zone of the capillary using an automated capillary delivery device. The relationships between exposure times, UV-light intensity and polymer layer thickness have been determined, as well as the effects of reagent delivery rate and multiple LED exposures on the layer thickness for various compositions of pre-polymerization mixtures. The polymer surface morphology was investigated by scanning electron microscopy (SEM). The non-steroidal anti-inflammatory drug S-ketoprofen was used as the template for the preparation of the MIP imprinted PLOT coatings. The separation performance with the ketoprofen racemate was investigated by capillary liquid chromatography. In contrast to alternative methods, which require the use of expensive chiral selectors, the described MIP PLOT stationary phases used non-chiral polymer precursors to create enantioselective nano-cavities through molecular self-assembly processes. The described fabrication methods provide a new avenue to tailor-make chiral MIP-PLOT capillary columns for the separation of chiral compounds present in complex or racemic analyte mixtures of chemical and biological origin.

Cyclodextrin-Modified Gold Nanoparticle Capillary Electrochromatography with Online Sample Stacking for Simultaneous and Sensitive Determination of Aminobenzoic Acid Isomers

A newly-developed method of complete separation and sensitive determination of o-, m-, and p-aminobenzoic acid isomers was achieved by combining open-tubular columns for capillary electrochromatography (OT-CEC) and online sample stacking. In this study, spherical gold nanoparticles were modified by a covalent attachment of mono-6-thio-β-cyclodextrin, and OT-CEC was formed by immobilizing cyclodextrin-modified gold nanoparticles (CD-AuNP) on prederivatized 3-mercaptopropyl-trimethoxysilane fused-silica capillaries. Based on the theory of moving chemical reaction boundary, effects of several important factors such as the pH and concentration of running buffer and the conditions of stacking analytes were optimized. The optimized separations were carried out in 58 mmol/L HAc buffer at pH 3.0 using a capillary coated with CD-AuNP, while the optimized concentration was carried out in 50 mmol/L disodium hydrogen phosphate (pH 9.5). The linear ranges for m-, p-, and o-aminobenzoic acid were from 5.0 × 10−4–0.1, 5.0 × 10−4–0.1 and 1.0 × 10−4–0.1 mmol/L, respectively. And the detection limits (S/N = 3) were as low as 8.22 × 10−5, 8.21 × 10−5, and 3.76 × 10−5 mmol/L for m-, p-, and o-aminobenzoic acid, respectively. The run-to-run, day-to-day, and column-to-column reproducibilities of migration time were satisfactory with relative standard deviation values of less than 4.5 % in all cases. This method was successfully used in determining procaine hydrochloride injection sample with recoveries in the range of 96.1–106.6 % and relative standard deviations less than 5.0 %.

Room temperature fabrication of post-modified zeolitic imidazolate framework-90 as stationary phase for open-tubular capillary electrochromatography

Metal–organic frameworks (MOFs) are attractive as porous stationary phase for open-tubular capillary electrochromatography (OT-CEC) due to their fascinating structures and unusual properties. Here we report a directly covalent bonding approach to prepare uniform and dense MOF film on the inner wall of fused silica capillary at room temperature for OT-CEC. Zeolitic imidazolate framework-90 (ZIF-90) as a model MOF because it not only possesses large surface area and high stability but also provides the free aldehyde groups to bond to the inner surface of capillary via covalent bond. X-ray diffraction, scan electron microscopy, and UV–vis spectrophotometry were used to confirm the bonding of the ZIF-90 to the inner wall of the silica capillary. The ZIF-90 coating not only increased the phase ratio of open-tubular column, but also improved the interactions of tested analytes and the coating. Owing to the porous structure of ZIF-90 and hydrophobic interactions between the analytes and the organic ligands of ZIF-90, three groups of isomers, neutral and basic compounds and nonsteroidal anti-inflammatory drugs were well separated on the ZIF-90 bonded column. The precisions (relative standard deviation, RSD) of retention time, half peak width and peak area for three consecutive runs were 0.3–1.2%, 1.3–6.0% and 1.5–5.2%, respectively. The run-to-run, day-to-day, and column-to-column precisions (RSDs) for the electroosmotic flow of the ZIF-90 bonded column were 0.2%, 0.4%, and 1.9%, respectively. Moreover, the ZIF-90 bonded column could stand more than 230 runs without observable change in the separation efficiency.

Water determination in active pharmaceutical ingredients using ionic liquid headspace gas chromatography and two different detection protocols

A rapid, accurate, precise and versatile analytical method was developed for the detection and quantification of water in solid active pharmaceutical ingredients (APIs). The headspace gas chromatography (HSGC) method utilized an ionic liquid (IL) based open tubular capillary GC column to increase sensitivity and ruggedness of this method. ILs are also utilized as the headspace solvent because of their low vapor pressure, unique physiochemical properties and high thermal stability. This method is not affected by side reactions and solubility problems which are common with Karl Fischer Titration (KFT) methods. Nor is it as limited as weight loss on drying approaches. The ability to use either/both modern thermal conductivity or barrier ion discharge GC detection provides flexibility, different dynamic ranges and sensitivity. The developed method also was shown to be broadly applicable.

Porous layer open tubular columns in capillary liquid chromatography

This review covers the latest developments and applications of porous layer open tubular columns in capillary liquid chromatography. Here, the authors provide a concise background on the fundamentals of porous layer open tubular columns, their fabrication and application. Over the past two decades, growing interest in the areas of proteomics and hyphenated LC-MS techniques have played a large part in the development of porous layer structures within capillary formats due to their high permeability, excellent efficiency and exceptional peak capacity. This review gives a brief overview of open tubular columns in general, however, it focuses predominantly on the applications of covalently bonded porous layer open tubular columns in liquid chromatography. Open tubular columns containing non-bonded or electrostatically attached layers will not be discussed in detail.

Infrared photo-initiated fabrication of monolithic porous layer open tubular (monoPLOT) capillary columns for chromatographic applications

Investigation into the development of a fabrication approach for capillary porous layer open tubular (PLOT) chromatographic columns via infrared (IR) photo-initiated polymerisation and the optimisation of the technique is presented in this work.

Novel tentacle-type polymer stationary phase grafted with anion exchange polymer chains for open tubular CEC of nucleosides and proteins.

A novel and simple method for preparation of a tentacle-type polymer stationary phase grafted with polyethyleneimine (PEI) anion exchanger was developed for open tubular capillary electrochromatography (OT-CEC) of nucleosides and proteins. The polymeric stationary phase was prepared using 3-chloro-2-hydroxypropyl methacrylate (HPMA-Cl)-based reactive monomer. The preparation procedure included pretreatment of the capillary inner wall, silanization, insitu graft polymerization with HPMA-Cl and PEI modification. To compare with the tentacle-type capillary column with PEI functionalization, a monolayer capillary column without PEI functionalization was also prepared. The electrochromatographic characterization of the prepared open tubular column was performed using alkylbenzenes. The electroosmotic flow (EOF) with regard to PEI concentrations and the running buffer pH was investigated. The separation conditions of the nucleosides and the proteins were optimized. The modified tentacle-type column with high anion exchange capacity has proven to afford better retention and resolution for the separation of nucleosides and proteins. The PEI functionalization column can also provide long-term stable use for biomolecule separation using a single capillary with relative standard deviation values of retention times of less than 2%. The results indicate that the present method for open tubular capillary preparation with a HPMA-Cl-based reactive monomer is promising for OT-CEC biomolecule separation.

Homochiral metal-organic framework [Zn2(d-Cam)2(4,4′-bpy)]nfor high-resolution gas chromatographic separations

The metal-organic framework (MOF) is a kind of new type self-assembly porous coordination polymer, which possesses many characteristics such as homologic hole, controllable size of cave, high specific surface area, and good chemical stability. In this study, a three-dimensional framework [Zn2(d-Cam)2(4,4′-bpy)]n with large homochiral channel and the orderly arrangement of left- and right-handed helices was used as chiral stationary phases (CSPs) in gas chromatography (GC). [Zn2(d-Cam)2 (4,4′-bpy)]n-coated open tubular column was prepared by a dynamic coating method for high-resolution GC. Some racemates, isomers, linear alkanes, and alcohols are used as the targets for separation. The column coating properties efficiency, polarity, and selectivity were studied. The experimental results show that the stationary phase has outstanding selectivity and also possesses good recognition ability toward these compounds.

Integrated enzyme reactor and high resolving chromatography in "sub-chip" dimensions for sensitive protein mass spectrometry.

Reliable, sensitive and automatable analytical methodology is of great value in e.g. cancer diagnostics. In this context, an on-line system for enzymatic cleavage of proteins, subsequent peptide separation by liquid chromatography (LC) with mass spectrometric detection has been developed using “sub-chip” columns (10–20 μm inner diameter, ID). The system could detect attomole amounts of isolated cancer biomarker progastrin-releasing peptide (ProGRP), in a more automatable fashion compared to previous methods. The workflow combines protein digestion using an 20 μm ID immobilized trypsin reactor with a polymeric layer of 2-hydroxyethyl methacrylate-vinyl azlactone (HEMA-VDM), desalting on a polystyrene-divinylbenzene (PS-DVB) monolithic trap column, and subsequent separation of resulting peptides on a 10 μm ID (PS-DVB) porous layer open tubular (PLOT) column. The high resolution of the PLOT columns was maintained in the on-line system, resulting in narrow chromatographic peaks of 3–5 seconds. The trypsin reactors provided repeatable performance and were compatible with long-term storage.

In Situ Synthesis of MIL-100(Fe) in the Capillary Column for Capillary Electrochromatographic Separation of Small Organic Molecules

Because of the unusual properties of the structure, the metal organic frameworks (MOFs) have received great interest in separation science. However, the most existing methods for the applications of MOFs in separation science require an off-line procedure to prepare the materials. Here, we report an in situ, layer-by-layer self-assembly approach to fabricate MIL-100(Fe) coated open tubular (OT) capillary columns for capillary electrochromatography. By a controllable manner, the OT capillary columns with a tailored MIL-100(Fe) coating have been successfully synthesized. The results of SEM, XRD, FT-IR, and ICP-AES indicated that MIL-100(Fe) was successfully grafted on the inner wall of the capillary. Some neutral, acidic and basic analytes were used to evaluate the performance of the MIL-100(Fe) coating OT capillary column. Because of the size selectivity of lattice aperture and hydrophobicity of the organic ligands, three types of analytes were well separated with this novel MIL-100(Fe) coating OT capillary column. For three consecutive runs, the intraday relative standard deviations (RSDs) of migration time and peak areas were 0.4-4.6% and 1.2-6.6%, respectively. The interday RSDs of migration time and peak areas were 0.6-8.0% and 2.2-9.5%, respectively. The column-to-column reproducibility of retention time was in range of 0.6-9.2%. Additionally, the 10 cycles OT capillary column (10-LC) could be used for more than 150 runs with no observable changes on the separation efficiency.

Chiral separation-based ligand exchange by open-tubular capillary electrochromatography

Chiral ligand-exchange enantioseparation of aliphatic and aromatic amino acids was successfully performed using a new open-tubular zwitterionic column with tentacle-type polymer stationary phase. The polymeric stationary phase was prepared using 3-chloro-2-hydroxypropyl methacrylate (HPMA-Cl), a new reactive monomer. The preparation procedure of the open-tubular column included silanization, in situ graft polymerization with HPMA-Cl, and l-histidine (l-His) modification. l-His was used as a chiral ligand-exchange selector and copper(II) as a central ion. Successful enantioseparation of six pairs of amino acid enantiomers was achieved with a buffer of 5mM CuSO4, 20mM (NH4)2SO4 at pH 3.0.

Chiral 3D Open‐Framework Material Ni(D‐cam)(H2O)2 Used as GC Stationary Phase

Metal-organic frameworks (MOFs) have been explored for analytical applications because of their outstanding properties such as high surface areas, flexibility and specific structure features, especially for chromatography application in recent years. In this work, a chiral MOF Ni(D-cam)(H2O)2 with unusual integration of molecular chirality, absolute helicity, and 3-D intrinsic chiral net was chosen as stationary phase to prepare Ni(D-cam)(H2O)2-coated open tubular columns for high-resolution gas chromatographic (GC) separation. Two fused-silica open tubular columns with different inner diameters and lengths, including column A (30 m × 250 µm i.d.) and column B (2 m × 75 µm i.d.), were prepared via a dynamic coating method. The chromatographic properties of the two columns were investigated using n-dodecane as the analyte at 120 °C. The number of theoretical plates (plates/m) of the two metal-organic framework (MOF) columns was 1300 and 2750, respectively. The racemates, isomer and linear alkanes mixture were used as analytes for evaluating the separation properties of Ni(D-cam)(H2O)2-coated open tubular columns. The results showed that the columns offered good separations of isomer and linear alkanes mixture, especially racemates.

The Application of TD/GC/NICI–MS with an Al2O3-PLOT-S Column for the Determination of Perfluoroalkylcycloalkanes in the Atmosphere

A modified method for the quantitative determination of atmospheric perfluoroalkylcycloalkanes (PFCs) using thermal desorption coupled with gas chromatography and detection by negative ion chemical ionization–mass spectrometry was developed. Using an optimized analytical system, a commercially available Al2O3 porous layer open tubular (PLOT) capillary column (30 m × 0.25 mm) deactivated with Na2SO4 was used for separation of PFCs. Improvements in the separation of PFCs, the corresponding identification and the limit of detection of PFCs using this method and column are presented. The method was successfully applied to determine the atmospheric background concentrations of a range of PFCs from a number of samples collected at a rural site in Germany. The results of this study suggest that the method outlined using the Al2O3-PLOT-S capillary column has good sensitivity and selectivity, and that it can be deployed in a routine laboratory process for the analysis of PFCs in the future research work. In addition, the ability of this column to separate the isomers of one of the lower boiling PFCs (perfluorodimethylcyclobutane) and its ability to resolve perfluoroethylcyclohexane offer the opportunity for single-column analysis for multiple PFCs.