Open-tubular Capillary Liquid Chromatography Research Articles

A stationary pseudophase semi-permanent coating for open-tubular capillary liquid chromatography and electrochromatography

We describe the chromatographic and electrochromatographic separation of small neutral and charged analytes using a fused silica capillary with a stationary pseudophase semi-permanent coating of didodecyldimethyl ammonium bromide (DDAB) aggregates. The coating was prepared by flushing the capillary with a DDAB solution that was rinsed out with the mobile phase. Our studies (i.e., electroosmotic flow measurements by capillary electrophoresis, chromatographic retention of a neutral probe and atomic force microscopy) suggested the formation of DDAB patchy admicelle, complete admicelle, or larger aggregates at the solid surface - liquid interface inside the capillary, depending on the concentration of DDAB used in coating the capillary. The analytical figures of merit for open tubular liquid chromatography (OT-LC, pressure driven) and open tubular capillary electrochromatography (OT-CEC, voltage driven) using a capillary coated with 0.5 mM DDAB and mobile phase/background solution of 25 mM borate buffer at pH 9.5 with 10% MeOH were the following: LOD = 3.0–5.0 µg/mL (OT-LC) and 2.5–5.0 µg/mL (OT-CEC); linearity R2 > 0.99 (peak area (OT-LC) and corrected peak area (OT-CEC)), intraday and interday repeatability%RSD < 5% (n = 12) for retention/migration time, peak area (OT-LC) and corrected peak area (OT-CEC). The reversed-phase and anion-exchange property of the stationary pseudophase was studied by the addition of organic solvents and sodium chloride to the mobile phase, respectively. We also demonstrate the increase in the ks of the tested analytes by implementing successive multiple ionic layer (SMIL) coating strategies with DDAB in combination with a cationic and/or anionic polyelectrolyte. The use of a stationary pseudophase coating is potentially an easy alternative way to conduct open-tubular liquid chromatography and electrochromatography.

Recent advances in open tubular capillary liquid chromatography.

This review covers advances and applications of open tubular capillary liquid chromatography (OT-LC) over the period 2007-2018. Under the right conditions OT-LC columns have the potential to offer superior column efficiency, higher overall peak capacity, and higher column permeability compared to packed capillary and monolithic columns. However, such advantages are highly dependent upon column format and dimensions, and to date in liquid chromatography the advantages of open tubular format columns have been most widely discussed and applied in the field of proteomics. In this review we have focused on the wider variety of separation mechanisms and applications which can be achieved following the modification of the inner wall of the capillary with a thin-layer stationary phase. In particular the latest advances in stationary phase development and formation, together with new column formats and dimensions are reviewed. Detection options for OT-LC are also discussed and recent advances in this area highlighted. Finally, this review summarises existing applications of OT-LC and illustrates the future potential for this technique.

Capillary Coated with Graphene and Graphene Oxide Sheets as Stationary Phase for Capillary Electrochromatography and Capillary Liquid Chromatography

Graphene oxide (GO) nanosheets were immobilized onto the capillary wall using 3-aminopropyldiethoxymethyl silane as coupling agent. Graphene coated column (G@column) was fabricated by hydrazine reduction of GO modified column. Scanning electron microscopy (SEM) images provided visible evidence of the GO grafted on the capillary wall. Energy dispersive X-ray spectrometry (EDS) indicated the high coverage of the GO on the capillary wall. The G@column exhibited a pH-dependent electroosmotic flow (EOF) from anode to cathode in the pH range of 3-9 while the graphene oxide coated column (GO@column) showed a constant EOF. Both GO@column and G@column were evaluated for open-tubular capillary electrochromatography (OT-CEC). The GO@column was also evaluated for open-tubular capillary liquid chromatography (OT-CLC). Good separation of the tested neutral analytes on the GO@column was achieved on the basis of a typical reversed-phase behavior. On the contrary, G@column showed poor separation performance because of the strong π-π stacking and hydrophobic interactions between graphene and polyaromatic hydrocarbons. The high coverage of GO improved the column phase ratio which makes the GO@column promising for OT-CLC separation. Five of the major known proteins including three glycoisoforms of ovalbumin in chicken egg white were identified in a single run on the GO@column with phosphate buffer (5 mM, pH 7.0) and an applied voltage of 20 kV. The run-to-run, day-to-day, and column-to-column reproducibilities are evaluated by calculating the relative standard deviations (RSDs) of the EOF in OT-CEC and retention time of naphthalene in OT-CLC, respectively. These RSD values were found to be less than 3%.

Development of a New Type of Open Tubular Capillary Liquid Chromatography System Based on Microphase Separation of Mixed Solvents

Abstract This paper describes a new type of open tubular capillary liquid chromatography (OTCLC) which utilizes the microheterogenities and preferential solvation phenomena in organic-water mixed solvents. Several model compounds have been separated by the proposed OTCLC system, and it has been confirmed the separation occurs due to the micro-phase separation of the mobile phase enhanced by salts. The well-known Golay equations were applied to characterize and optimize the OTCLC system.

Toward a Fully Integrated Positive-Pressure Driven Microfabricated Liquid Analyzer

A versatile integrated analyzer with a flow-programmed injection strategy and multiwavelength detection is described with applications toward sampling, flow injection analysis, and capillary separations. Continuous near-real-time sampling is a major benefit of the flow-programmed injection technique. Injection volumes ranging from 250 pL to several microliters were made without electrophoretic flow. Multiwavelength grating light reflection spectroscopy (GLRS) and transmission absorbance spectroscopy were performed simultaneously in a detection volume of 150 pL. The utility of these detection methods for refractive index (RI) and absorbance detection in capillary channels is demonstrated through analysis of salt, indicator, and dyes. GLRS is a unique, selective, and path-length-independent technique for probing RI, absorbance, and other optical properties. A limit of detection (LOD) of 170 microM was achieved for GLRS interferometric detection of FD&C Red #3, which corresponded to 2.6 fmol of analyte in the 150-pL detection volume. A LOD of 2 mM for phosphate buffer, or 3 fmol in the 150-pL detection volume will also be demonstrated. A siloxane coating on the GLRS grating was employed as a sensing layer to probe interactions between the sample and stationary phase. The combined GLRS interferometric response provided insight into both optical and chromatographic properties of samples. Open tubular capillary liquid chromatography with multidimensional multiwavelength detection is demonstrated for the analysis of three food dyes. Separation efficiency, N, of 16,000 was achieved for an unretained dye peak eluting at 12 min. Integration of novel sampling and detection schemes makes this a broadly applicable liquid analyzer.

Study on open tubular capillary affinity liquid chromatography.

A novel mode of affinity chromatography (AC) based on an open tubular capillary column (OTAC) is demonstrated. The OTAC column is prepared by immobilizing Cibacron blue F3GA onto the inner surface of a 50-microm-i.d. capillary column. The AC experiment is performed on a capillary electrophoresis instrument by using its pressure system as the driving force. Bovine serum albumin and lysozyme (Lys) are successfully separated with stepwise gradient elution. The relative standard deviation (RSD) for the elution time of the retained Lys is 0.08%, and good repeatability of its peak area and peak height with an RSD value lower than 2.12% for 10 consecutive runs is observed. The loading capacity and detection limit for the retained Lys are approximately 36 ng and 8.6 ng, respectively. It is also found that the amount of protein adsorbed is unaffected by the flow rate of the loading buffer, and OTAC can be used for the fast determination of biopolymers. Some of the advantages of OTAC over conventional modes of open tubular capillary liquid chromatography are that the detection sensitivity and loading capacity of a sample can be greatly improved, because the relatively large inner diameter of the capillary can be adopted and the whole capillary column can be used to adsorb the solute in OTAC.

Temperature Programming in Open Tubular Liquid Chromatography

Abstract We have examined the separation of test mixtures by linear and step temperature gradients in open tubular capillary liquid chromatography, in reverse and normal-phase modes. Separations using temperature gradients with the upper temperature limit of 433 K were compared to isothermal runs in terms of chromatographic efficiency, analysis time and selectivity. When a temperature gradient (363 K to 433 K in 12 min) was utilized in reverse phase separation of chlorobenzenes, a 40% reduction in analysis time, compared to an isothermal separation at 363 K, was accomplished.

Thermo-Optical Spectroscopy: New and Sensitive Schemes for Detection in Capillary Separation Techniques

Abstract Detection is a major problem in the application of Open-Tubular Capillary Liquid Chromatography (OTCLC) and Capillary Electrophoresis (CE) for analyzing very dilute samples, for instance in trace analysis. Thermo-optical Spectroscopy is a new branch of Spectroscopy which allows the detection of samples with low light absorbances (10−8 −10−9 AU) using a few picoliters sample cell. A few attomoles of analyte can be detected in OTCLC or in CE with these techniques. These results are similar to those achieved by Laser-Induced Fluorescence detection in open-tubular capillary tubings. However, many organic substances present a high absorption coefficient and only a few of them provide good quantum yields. The principles of Thermo-optical Spectroscopy are presented in this work. The main thermo-optical methods and their application in OTCLC and CE are also reviewed

Open-tubular liquid chromatography with surfactant-enhanced electroosmotic flow

The velocity of electroosmotic flow in a polymer-coated, reversed-phase fused silica column is enhanced by low concentrations ({mu}M) of cetyltrimethylammonium bromide (CTAB) in the buffer. Open-tubular capillary liquid chromatography (OTCLC) based upon this enhanced flow makes possible the separation of several neutral, geometrical, and positional isomers with greater than baseline resolution (R > 1) in all cases and efficiencies of up to 230,000 plates generated in less than 4 min in a 54-cm column. As little as 5-pL samples can be directly injected, and as low as 0.75 amol of 9-methylanthracene can be detected. This brings to OTCLC the instrumental simplicity of capillary electrophoresis.

Axial-beam on-column absorption detection for open tubular capillary liquid chromatography

Axial-beam on-column absorption detection for open tubular capillary liquid chromatography

Estimation of the instrumental band broadening contribution to the column elution profiles in open tubular capillary liquid chromatography

AbstractIn comparison with conventionally packed HPLC columns, from a theoretical point of view, open capillary liquid chromatography (OTLC) systems offer a number of advantages like high plate numbers and short analysis times. On the other hand, drastic changes have to be made to the instrumentation. In particular, the contribution to band broadening by the chromatographic equipment must be considerably reduced. In the present study an OTLC system was developed and evaluated, which yields satisfactory results for 26 μm i. d. columns. The determination of the contribution of the chromatographic equipment to the total band broadening is discussed.

Signal enhancement in on-column fluorometric detection in open-tubular capillary liquid chromatography

Signal enhancement in on-column fluorometric detection in open-tubular capillary liquid chromatography is reported. Signal enhancement due to the environment effect of the stationary phase was estimated by using equations derived here. The enhancement factor was about 3 for anthracene on the n-octylmethylpolysiloxane stationary phase.

Preparation and Chromatographic Properties of Stationary Phases for Open-Tubular Capillary Liquid Chromatography

Phases octadecylsilanes, resines aliphatiques ou aromatiques, polyimines, phases reticulees, silice modifiee dynamiquement par des ammoniums quaternaires

Axial dispersion in open-tubular capillary liquid chromatography with electroosmotic flow

Axial dispersion in open-tubular capillary liquid chromatography with electroosmotic flow

On-column fluorescence detector for open-tubular capillary liquid chromatography

On-column fluorescence detector for open-tubular capillary liquid chromatography

Dynamically modified silica columns in open-tubular capillary liquid chromatography

Open-tubular liquid chromatography using dynamically modified columns has been investigated. Chromatographic separations are achieved with silica gel as the stationary phase and a mobile phase containing quaternary ammonium bromide as a hydrophobic layer-forming reagent. Parameters that effect the retention of solutes are examined.