Fused-silica Open Tubular Columns Research Articles

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.

A 3-D open-framework material with intrinsic chiral topology used as a stationary phase in gas chromatography

Compared with liquid chromatography and capillary electrophoresis, the diversity of gas chromatography chiral stationary phases is rather limited. Here, we report the fabrication of Co(D-Cam)1/2(bdc)1/2(tmdpy) (D-Cam = D-camphoric acid; bdc = 1,4-benzenedicarboxylate; tmdpy = 4,4'-trimethylenedipyridine)-coated open tubular columns for high-resolution gas chromatographic separation of compounds. The Co(D-Cam)1/2(bdc)1/2(tmdpy) compound possesses a 3-D framework containing enantiopure building blocks embedded in intrinsically chiral topological nets. In this study, two fused-silica open tubular columns with different inner diameters and lengths, including column A (30 m × 530 μm i.d.) and column B (2 m × 75 μm i.d.), were prepared by a dynamic coating method using Co-(D-Cam)1/2(bdc)1/2(tmdpy) as the stationary phase. The chromatographic properties of the two columns were investigated using n-dodecane as the test compound at 120 °C. The number of theoretical plates (plates/m) of the two metal-organic framework columns was 1,450 and 3,100, respectively. The separation properties were evaluated using racemates, isomers, alkanes, alcohols, and Grob's test mixture. The limit of detection and limit of quantification were found to be 0.125 and 0.417 ng for citronellal enantiomers, respectively. Repeatability (n = 6) showed lower than 0.25 % relative standard deviation (RSD) for retention times and lower than 2.2 % RSD for corrected peak areas. The experimental results showed that the stationary phase has excellent selectivity and also possesses good recognition ability toward these organic compounds, especially chiral compounds.

Infinite dilution activity coefficients, specific retention volumes and solvation thermodynamics of hydrocarbons in C 78H 158 branched alkane solvent

Kováts's retention indices were determined for 60 hydrocarbons by capillary gas–liquid chromatography at temperatures from 373.15 to 433.15 K using fused silica open tubular column coated with 19,24-dioctadecyldotetracontane (C 78H 158) as stationary phase. Gas–liquid equilibrium parameters (specific retention volumes, standard Gibbs energy differences and limiting activity coefficients) were calculated for isoalkanes, cycloalkanes, alkenes, alkynes, aromatics on the basis of absolute retention data of n-alkanes determined by GLC using packed column with the same stationary phase. It was concluded that molecular shape and size have an important effect on limiting activity coefficient values. The standard Gibbs free energy differences of solute transfer were correlated by a Kirchhoff-type temperature function and the thermodynamic parameters of the solvation (partial molar standard enthalpy and entropy differences at reference temperature T * = 403.15 K, furthermore heat capacity differences) were determined. The predictive ability of various entropic models was investigated on the new experimental data of saturated hydrocarbons and it is shown that the modified UNIFAC-FV model, Kannan-FV, represents satisfactorily the presented experimental limiting activity coefficient data of alkanes in size-asymmetric solutions.

Effect of vacuum on the performance of the flame ionization detector used for vacuum-outlet gas chromatography

Vacuum-outlet operation of short fused-silica open tubular columns for gas chromatography provides benefits to analysis speed by increasing the optimum velocity while minimizing the loss in resolution. Vacuum-outlet operation of a column with a gas chromatographic detector necessitates that the detector also be under vacuum. Simple modifications were made to a gas chromatograph–flame ionization detector (GC–FID) for vacuum-inlet and vacuum-outlet operation. The vacuum-inlet system was operated in the splitless mode to allow for efficient sample loading prior to operation at reduced pressures. The goal of FID operation at 100 torr or less was achieved by using oxygen in place of air and optimizing the gas flows under vacuum to maintain a stable flame at pressures as low as 46 torr. An outlet pressure of 85 torr with optimized gas flows allowed for routine operation of the FID without solvent flame-out. It was discovered that the sensitivity is enhanced compared to atmospheric operation over a range of outlet pressures from approximately 200 to 400 torr; however, operation of the FID at the lowest possible pressures decreases the analytical sensitivity due to both the outlet pressure and the absence of helium makeup gas. © 2000 John Wiley & Sons, Inc. J Micro Sep 12: 226–235, 2000

Effect of vacuum on the performance of the flame ionization detector used for vacuum-outlet gas chromatography

Vacuum-outlet operation of short fused-silica open tubular columns for gas chromatography provides benefits to analysis speed by increasing the optimum velocity while minimizing the loss in resolution. Vacuum-outlet operation of a column with a gas chromatographic detector necessitates that the detector also be under vacuum. Simple modifications were made to a gas chromatograph–flame ionization detector (GC–FID) for vacuum-inlet and vacuum-outlet operation. The vacuum-inlet system was operated in the splitless mode to allow for efficient sample loading prior to operation at reduced pressures. The goal of FID operation at 100 torr or less was achieved by using oxygen in place of air and optimizing the gas flows under vacuum to maintain a stable flame at pressures as low as 46 torr. An outlet pressure of 85 torr with optimized gas flows allowed for routine operation of the FID without solvent flame-out. It was discovered that the sensitivity is enhanced compared to atmospheric operation over a range of outlet pressures from approximately 200 to 400 torr; however, operation of the FID at the lowest possible pressures decreases the analytical sensitivity due to both the outlet pressure and the absence of helium makeup gas. © 2000 John Wiley & Sons, Inc. J Micro Sep 12: 226–235, 2000

Measurement of Henry coefficients by capillary columns coated with slightly polar solvents

The specific retention volumes and Henry coefficients measured on packed columns are compared with those calculated via retention indices determined on wall coated open tubular capillary columns. The stationary phase liquids used were derivatives of a branched paraffin, C78H158, where a methyl or ethyl group of the paraffin was replaced by OH, CN, OCH3 and SH groups. The retention indices of a series of molecular probes of varying polarity (aromatics, 1-chloroalkanes, 1-acetoxy-alkanes, 1-alkanols, 2-alkanones) were determined atT=403.15 K on fused-silica open tubular columns prepared by static coating that gave stable and uniform solvent films. After obtaining the absolute data on packed columns forn-alkanes, the specific retention volumes and Henry coefficients of the solutes were calculated. The retention data obtained on both columns showed good agreement.

In situ crosslinked polybutadiene-encapsulated zirconia as a monolithic column for fast solvating gas chromatography

A new monolithic column type was developed by crosslinking polymer-encapsulated packing materials in polymer-coated fused silica open tubular columns in situ using a free radical reaction. A 25 cm×250 μm i.d. PSB-Octyl fused silica capillary column coated with a 0.25-μm film of polyoctylmethylsiloxane was packed with 3% polybutadiene-encapsulated zirconia packing materials (2.5 μm, 250 Å, 30 m2 g−1). The packing material was immobilized using a dynamic crosslinking reaction at 260°C with azo-tert-butane as a free radical initiator. A scanning electron micrograph of the crosslinked packing in the column showed that the particles were interconnected to each other and attached to the capillary wall, forming a monolith. This monolithic column was found to be stable in carbon dioxide mobile phase at 200 atm column inlet pressure and 260°C. The column efficiency, solute retention, and permeability of the monolithic column were similar to those measured for columns freshly packed, but not crosslinked, with the same material under the same conditions. The potential use of these monolithic columns for fast solvating gas chromatography was demonstrated by the rapid separation of a mixture of hydrocarbons. ©1999 John Wiley & Sons, Inc. J Micro Sep 11: 415–420, 1999

Procedure for the determination of retinol and α-tocopherol in poultry tissues using capillary gas chromatography with solvent venting injection

A procedure designed for the determination of retinol (vitamin A) and α-tocopherol (vitamin E) in poultry tissues has been developed. The procedure involves lipid extraction, saponification, solid-phase clean-up and capillary gas chromatography (cGC). Retinol and α-tocopherol were determined separately by cGC–flame ionisation detection using a fused-silica open tubular capillary column, 30 m×0.25 mm I.D. coated with 5% phenylmethylsilicone and with a film thickness of 0.25 μm. Solvent extraction followed by saponification were sufficient to provide a purified extract which was directly analyzed for retinol by cGC in the solvent venting mode. However, in order to accurately determine α-tocopherol by cGC, further purification of the extract by solid-phase extraction was necessary. A silica SPE column was used to remove interfering cholesterol from the extract. α-Tocopherol was analyzed in its derivatized form. Absolute and relative recoveries for both vitamins from spiked samples were evaluated. Absolute and relative recoveries ranging from 80 to 95% were obtained for both compounds. 5α-Cholestane and α-tocopheryl acetate were used as internal standards. Poultry muscle meat and liver tissue were analyzed for their retinol and α-tocopherol content and the peaks detected by cGC were confirmed by cGC–mass spectrometry.

Multiresidue analysis of pesticides in fruits and vegetables by gel permeation chromatography followed by gas chromatography with electron-capture and mass spectrometric detection

A wide range screening method for multiresidue analysis of seventy-seven pesticides (twelve organohalogens, forty-five organonitrogens, eleven organophosphorus and nine pyrethroids) in agricultural products is proposed. Pesticide residues were extracted from crop samples with acetone followed by dichloromethane partitioning. Crop extracts were cleaned-up by gel permeation chromatography equipped with a 10 mm diameter column. Analytical screening was by gas chromatography using long, narrow-bore fused-silica open-tubular columns equipped with electron-capture detection (ECD). Recoveries of majority of pesticides from spiked samples of carrot, melon and tomato at fortification levels of 0.04–0.10 mg/kg ranged from 70 to 108%. The lowest recovery was for chlormephos (51.5%). Limits of detection were less than 0.01 mg/kg for ECD. Confirmation of pesticide identity was performed by gas chromatography-mass spectrometry in selected-ion monitoring mode. The multiresidue procedure was applied in routine crop analysis: a 9-month period data are reported.

Procedure for the determination of eight cholesterol oxides in poultry meat using on-column and solvent venting capillary gas chromatography.

A procedure for the determination of eight relevant cholesterol oxides in poultry meat has been developed. The method consists of the enrichment of cholesterol oxides by means of the combined use of solid-phase fractionation and thin-layer chromatography. Florisil and silica columns of 10 g permitted the handling of the total cholesterol oxides content included in the lipid bulk obtained after the Folch's extraction of 20 g of muscle meat. The determination of cholesterol oxides under their trimethylsilyl derivatives was performed by using capillary gas chromatography. The use of a fused-silica open tubular capillary column 30 m×0.25 mm I.D. coated with 5% phenylmethylsilicone and with a film width of 0.25 μm permitted the separation of all the species. Two modes of injection (on-column and solvent venting) were evaluated and compared for the analysis of cholesterol oxides. On-column capillary gas chromatography (cGC) gave better absolute areas relative standard deviation (R.S.D.) values: 3% to 6% vs. 5% to 7% for solvent venting cGC. Regression analysis for each cholesterol oxide was performed for the two modes of injection. The possibility of large volume injection (10 μl) by using the solvent venting mode was also evaluated in order to increase the sensitivity of the detection of cholesterol oxides. R.S.D. values for absolute areas ranging from 6% to 14% were obtained. The validation of the method was carried out within the range of 0.1–1 ppm. Absolute and relative recovery values ranging from 80% to 100% were obtained. Statistical analysis revealed that the method was reproducible. cGC–mass spectrometry was also used to confirm the peaks detected by cGC: the total ion chromatogram mode was used for the analysis of samples containing concentrations down to 0.1 ppm of cholesterol oxides. The analysis of fresh and cooked chicken meat revealed the presence of cholesterol oxides proceeding from the autoxidation of the cholesterol B-ring. Finally, saponification was found to be not as accurate as the described procedure for cholesterol oxides analysis.

Sampling and analysis of 1,3-butadiene in air by gas chromatography on a porous-layer open-tubular fused-silica column

The preparation of standards for 1,3-butadiene analysis is complicated, because butadiene is a gas at room temperature. The method to prepare stock solutions developed in this study is reliably, as confirmed by a standard plot from these independent stock solutions. The qualitative and quantitative analysis was carried out using high-resolution gas chromatography with flame ionization detection (FID) and a fused-silica porous-layer open-tubular (PLOT) column. The use of acetonitrile as a desorption solvent gave a good recovery from charcoal and no interfering impurities were present. Active and passive sampling were tested in the laboratory and in petrochemical plants. These two methods had a very good correlation when tested in the field.

Fast Temperature Programming on Fused-Silica Open-Tubular Capillary Columns by Direct Resistive Heating

A method for extremely fast temperature-programmed gas chromatography is described. The column is heated by passing an electric current through a thin conductive film applied to the outer surface of a fused-silica open-tubular column. The low thermal mass of the column allows rapid heating and cooling. A computer generated voltage ramp may be empirically adjusted to produce a linear separation of the members of a homologous series. Sample introduction is by on-column thermal modulation. High-speed detection is by a micro thermal conductivity detector. Repetitive chromatograms can be generated as often as 1/s with peaks as sharp as 40 ms at the baseline

Cyclodextrin PLOT columns for the gas-solid chromatographic separation of light hydrocarbons and inorganic gases

Alpha and beta cyclodextrin (α- and β-CD) were chemically bonded to porous layer fused silica open tubular columns and used as gas-solid chromatographic (GSC) stationary phases for the separation of C1 to C6 hydrocarbons and a variety of inorganic gases. In general, these cyclodextrin PLOT columns were superior to the analogous packed columns. The capillary columns show similar selectivities with an increase in efficiency and number of theoretical plates over the packed columns. The cyclodextrin stationary phases show good selectivities toward the light hydrocarbons and inorganic gases on capillary columns as short as ten meters. Subambient temperatures allow the baseline resolution of oxygen from nitrogen. These columns have been effectively utilized at temperatures up to 260°C without loss of efficiency or degradation of selectivity.

Measurement of solute diffusion in polymers by inverse gas chromatography using fused-silica open tubular columns

Inverse gas chromatography (i.g.c.) using a fused-silica open tubular column has been developed and evaluated for measuring diffusion coefficients of small molecules in polymers; this diffusivity data can be used, for example, to model reactive extrusion processes. We have shown the applicability of this technique by measuring the diffusion and partition coefficients of various small molecules in polystyrene, poly(methyl methacrylate) (PMMA), and poly(methyl methacrylimide). The results for polystyrene and PMMA were in good agreement with existing data by gravimetric sorption/desorption, packed column and glass capillary column i.g.c. techniques. The diffusion data for the polyimide were generated for the first time.

Determination of clenbuterol and salbutamol in urine by capillary gas chromatography with capillary columns of 100 μm

A method to determine clenbuterol and salbutamol in calf urine is described. Two independent extraction procedures using Extrelut (clenbuterol) and octadecylsilica (salbutamol) were used; the extracts obtained were mixed and purified over a cyanopropyl minicolumn. Trimethylsilyl derivatives were prepared and analysed by GC—MS in selected-ion monitoring mode using a fused-silica open tubular capillary column, 10 m × 100 μm coated with 5% phenylmethylsilicone. Splitless injection was optimized to achieve low percentage residual standard deviation of absolute areas. The best conditions were: injection volume 0.5 μl, column head pressure 22 p.s.i. (1 p.s.i. = 6894.76 Pa), inlet temperature 250°C and glass liner volume 250 μl. The recoveries of the complete procedure were in the range 50–60% for both compounds.

The optimization of capacity and efficiency when coupling fused silica open tubular columns in gas chromatography

There are a number of parameters which have to be chosen depending on the analysis being done in gas chromatography. While the choice of stationary phase material is based on the solutes to be separated, the thickness is dependent on the concentration and the volatility of the components to be analyzed. This study undertakes a coupled column phase ratio optimization by connecting a short piece of a particular column prior to a normal length of an analytical column. Various columns of different dimensions (phase ratio), but of the same stationary phase material (methyl silicone), are coupled together by a deactivated glass press-fit connector, and the efficiency and capacity are measured. The coupling of fused silica open tubular columns is optimized in efficiency by matching or decreasing the phase ratio of successive columns. Capacity optimization is accomplished by increasing the phase ratio of consecutive columns. Capacity and efficiency optimization are opposing each other; therefore, if some efficiency can be sacrificed a substantial increase in capacity is possible.

Computer-assisted optimization of the gas chromatographic separation of equine estrogens

The pharmaceutically important conjugated estrogens of the type excreted by pregnant mares were baseline-resolved by gas chromatography (GC) on a SE-30 fused-silica open tubular column after acid hydrolysis and conversion to their tert.-butyldimethylsilyl derivatives. The temperature-programmed conditions were optimized with the aid of DryLab GC software with excellent agreement between the predicted and experimental results. The composition of conjugated estrogens in Premarin tablets is described as an application of the method.

Critical comparison of gas-hexadecane partition coefficients as measured with packed and open tubular capillary columns

The use of gas chromatography to study the thermodynamics of solute-solvent interactions is very well established. Many successful measurements using non-polar solutes have been reported. However, the investigation of the properties of even moderately polar solutes, such as acetone, on porous particles in packed beds is fraught with potential chemical problems including interfacial adsorption at the solid-gas and liquid-solid interfaces. In order to minimize, but likely not eliminate such effects, we have employed fused-silica open tubular capillary columns. This approach affords, relative to other supports, a very inert solid surface with low net area for both the solid-gas and liquid-solid interfaces. Due to the very small amount of stationary phase liquid, it is not possible to measure the absolute value of the partition coefficient. However, it is possible to obtain precise measurements of relative partition coefficients. Using the absolute value of the partition coefficient for some reference solute, obtained by alternative methods, absolute values can be computed. In this work, we show that solute retention on n-hexadecane is independent of solute concentration over a usefully wide range in the amount of solute injected. Where the capacity factors do vary with the amount injected, they do so in a direction consistent with a partition dominated process. Values for the partition coefficients for 105 non-polar and polar solutes in n-hexadecane are reported and critically compared to literature values.

Evaluation of gas chromatographic columns for the determination of methylmercury in aqueous head space extracts from biological samples

Several gas chromatographic columns were evaluated for the determination of methylmercury in aqueous solution. The goal of the study was to further decrease the detection limit of the recently developed method of head space gas chromatography with microwave-induced plasma detection (HS-GC-MIP) for the determination of methylmercury in biological samples. The columns were first evaluated using gas chromatography with electron-capture detection (ECD). At the same time, the column efficiencies for the determination of ethyl- and phenylmercury were also studied. Of the packed columns the stationary phase used previously in HS-GC-MIP, AT-1000, yielded the best results. Better results were obtained with two wide-bore thick-film fused-silica open tubular (FSOT) columns, one of which was suitable for aqueous injections (Superox-FA) and the other for benzene or toluene (RSL-300). With these FSOT columns, absolute detection limits at the sub-picogram level were reached. A new HS-GC-MIP system was then constructed, which was adapted for the use of FSOT columns. As more sensitive measurements were obtained with a Superox-FA FSOT column than with an AT-1000 packed column using the GC-ECD system in the first part of this study, the FSOT column was evaluated in this HS-GC-MIP system for the determination of methylmercury in real tissue samples. It was demonstrated that the use of an FSOT column gives only a small decrease in the detection limit compared with a packed column; reconditioning of the FSOT column is, however, a disadvantage in routine measurements.

Narrow (5‐50‐μm i.d.) open tubular columns in liquid chromatography using immobilized polymethyloctadecylsiloxane as stationary phase

AbstractThis paper presents in detail the preparation of highly efficient, stable open tubular (OT) columns for reversed‐phase liquid chromatography. Chromatographic properties of 5‐50‐μm i.d. fused silica columns (1.5‐5 m in length) are described, and details of the coating procedure are discussed. On‐column fluorescence detection was used for the model substituted‐anthracene test solutes. Gas chromatography was used as a complementary technique for column characterization.The stationary phase studied, immobilized polymethyloctadecylsiloxane, PMSC18, was chosen because of its more lipophilic character compared to other siloxanes. As expected, a higher retention power was found compared to polydimethylsiloxane coatings.The polymeric stationary phase showed good properties. More than 900,000 plates were achieved in 25 min (k = 0.1) in a 5‐μm i.d. fused silica OT column. The stationary phase contribution to band broadening was less than 10% in an 11‐μm i.d. column at a flow rate thirty times uopt (k = 1.3).