Flow of the carrier gas in open-tubular capillary columns in temperature-programmed gas chromatography

A second-order non-linear partial different equation was derived to describe the dependence of carrier gas pressure in the column on the column distance and the time under temperature programmed conditions. This equation was solved numerically by the modified finite difference method for various column parameters. Constant inlet and outlet pressures were used as boundary conditions. The retention times calculated on assumption of a constant pressure profile along the column. Significant differences between retention times of corresponding solutes calculated by the two methods were found, especially when relatively long columns(L>50m) with small internal diameter(d<0.3mm)and high temperature program rates (r>5°/min)are used.     

Radio gas chromatography on capillary columns using a multi-column system (column-switching)

Summary A gas chromatographic system with capillary columns (fused silica) for the analysis of radiolabelled compounds is described. The system presented is based on a dual column gas chromatograph equipped with column switching facllity and a variable splitter at the column outlet combined with a dead-volume free adapter for the radioactivity monitor for continous measurement of radioactivity in the column effluent. The first column works as a separation column and the second is roughly shortened and used as a feed to the mass detector. The adjustment of the split ratio is regulated by the inlet pressures for the carrier gas supplying both columns. For mass detection all conventional systems can be used. Detection of radioactivity by a gas proportional counter (system based on a combustion technique). Three flow modes can be adjusted: a) total column effluent to the mass detector or b) to the radioactivity monitor, and c) simultaneous flow (dependent on the chosen split ratio) to mass-and radioactivity detectors. The system was developed for use in clinical chemistry and tested with labelled and unlabelled steroids. The method for peak identification by means of relative retention times and methylene units was possible also for radioactive peaks when a heart cutting technique was used. The radio gas chromatographic system presented allows the development of radiochromatograms with the same peak characteristics as in conventional capillary gas chromatography.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Fast Temperature Programming in Gas Chromatography using Resistive Heating

The features of a resistive-heated capillary column for fast temperature-programmed gas chromatography (GC) have been evaluated. Experiments were carried out using a commercial available EZ Flash GC, an assembly which can be used to upgrade existing gas chromatographs. The capillary column is placed inside a metal tube which can be heated, and cooled, much more rapidly than any conventional GC oven. The EZ Flash assembly can generate temperature ramps up to 1200°/min and can be cooled down from 300 to 50°C in 30 s. Samples were injected via a conventional split/splitless injector and transferred to the GC column. The combination of a short column (5 m×0.25 mm i. d.), a high gas flow rate (up to 10 mL/min), and fast temperature programmes typically decreased analysis times from 30 min to about 2.5 min. Both the split and splitless injection mode could be used. With n-alkanes as test analytes, the standard deviations of the retention times with respect to the peak width were less than 15% (n = 7). First results on RSDs of peak areas of less than 3% for all but one n-alkane indicate that the technique can also be used for quantification. The combined use of a short GC column and fast temperature gradients does cause some loss of separation efficiency, but the approach is ideally suited for fast screening as illustrated for polycyclic aromatic hydrocarbons, organophosphorus pesticides, and triazine herbicides as test compounds. Total analysis times – which included injection, separation, and equilibration to initial conditions – were typically less than 3 min.     

Retention time locking procedure for comprehensive two-dimensional gas chromatography

In gas chromatography (GC) reproducible retention times are in many cases highly favorable or in some cases even required. In one-dimensional GC, retention time shifts can be eliminated or minimized using a procedure called retention time locking (RTL). This procedure is based on adjusting the (constant) column head pressure. Unfortunately, this RTL procedure cannot be used in comprehensive two-dimensional gas chromatography (GC × GC) given the fact that peaks will shift in both dimensions. Adjusting the column head pressure in GC × GC will only minimize or eliminate the primary retention time shifts. In this paper, a fast and easy to perform, two-step retention time locking procedure for two-dimensional gas chromatography (2D-RTL) is proposed and its feasibility is demonstrated. This 2D-RTL procedure involves adjustment of the column head pressure or constant column flow, followed by the adjustment of the so-called effective secondary column length. The secondary column length is increased or decreased, simply by moving it stepwise through the modulator. It is demonstrated that retention time shifts in both the primary- and secondary-dimension, which may occur after e.g. replacing the column set, can be minimized to less than half peak base width. The proposed 2D-RTL procedure is used successfully for approximately 1 year in our laboratory.     

Minimum analysis time in capillary gas chromatography vacuum- versus atmospheric-outlet column operation

Previous studies on open tubular column operation at vacuum outlet vs. atmospheric outlet pressures focused on comparisons of given columns, or comparisons of columns with the same inner diameters. It was demonstrated that, for a given separation problem, vacuum outlet operation of columns with a constant i. d. always yields the shortest analysis times (under minimum plate height conditions). In this paper, the comparison of vacuum vs. atmospheric outlet operation is broadened to columns with different dimensions. A general equation for the gain in speed of analysis by vacuum outlet operation of any column, as compared to atmospheric outlet operation of all possible open tubular columns with the same maximum plate number is presented. The resulting equation is further evaluated for thin film columns of different dimensions. It appears that vacuum outlet operation is beneficial only, in terms of speed of analysis, if low maximum plate numbers are required. The gain in speed of analysis is more pronounced for wide-bore than for narrow-bore columns.     

聚硅氧烷离子液体用于快速气相色谱固定相的研究

合成了聚硅氧烷键合离子液体[PSOMIM][NTf2],并将其用作快速气相色谱柱的固定相.初步探索了采用短柱及小内径毛细管柱(3 m×75 μm i.d.)时的分离性能及固定相膜厚对分离性能的影响.与常规柱(8m×0.25 mmi.d.)相比,在不损失分离度的前提下,分离速度可提高1～6倍;当膜厚为0.056 μm时,可以将分离速度提高2～4倍.实验结果表明,聚硅氧烷键合离子液体固定相可以有效弥补由于缩短柱长所导致的分离度减小的问题,在快速气相色谱固定相方面具有较好的应用前景.     

在线分析脱丙烷塔顶中气体组分的气相色谱柱系统研究

 根据生产要求 ,对裂解装置中高压和低压脱丙烷塔顶中工艺气的气相色谱在线监控柱切换流程进行了研究。通过 3个进样器的二次异步进样 ,结合前吹、反吹等技术 ,应用 7根柱子 ,成功地在 6min内实现了对 C2 ' S、丙烷、丙烯、丙炔、丙二烯及 C4' S的在线分离分析。现场应用表明 ,研制的柱切换系统满足工艺监控要求。     

Temperature‐programmed multicapillary gas chromatograph microcolumn for the analysis of odorous sulfur pollutants

We report the fabrication and performance of a silicon‐on‐glass micro gas chromatography eight‐capillary column based on microelectromechanical systems technology that is 50 cm long, 30 μm wide, and 300 μm deep. According to the theory of a gas chromatography column, an even gas flow among different capillaries play a vital role in the peak broadening. Thus, a flow splitter structure is designed by the finite element method through the comparison of the velocity distributions of the eight‐capillary columns with and without splitter as well as an open tubular column. The simulation results reveal that eight‐capillary column with flow splitters can receive more uniform flow velocity in different capillaries, hence decreases the peak broadening and in turn increases the separation efficiency. The separation experiment results show that the separation efficiency of about 22 000 plates/m is achieved with the chip column temperature programmed for analysis of odorous sulfur pollutants. This figure is nearly two times higher than that of the commercial capillary column coated the similar stationary phase. And the separation time of all the components in the microcolumn is less than 3.8 min, which is faster than the commercial capillary column.     

A new type of capillary column for gas chromatography

A new type of capillary column for gas chromatography was proposed. A sorbent layer (for example, stationary liquid phase) is supported on the internal capillary surface, and the internal (interstitial) volume is packed with nonporous large particles of a sorbent (particle diameter is 0.1—0.6 of the capillary internal diameter). The external surface of the particles can also be coated with the sorbent layer (for example, stationary liquid phase). The specific separation efficiency (number of separation) on the new type column is by 1.6—2.3 times higher than that of the initial classical capillary column.     

OPTIMIZATION OF MULTI-STEP LINEAR PROGRAMME TEMPERATURE IN CAPILLARY GAS CHROMATOGRAPHY

An optimal method to select the optimal temperature of multi-step linear programme temperature in capillary gas chromatography, by simultaneously considering the effects of column temperature and differences of column distance to be moved on resolution and analytical times, has been developed. We called this optimal method a moving overlapping resolution mapping method because the immigrating position of solute in column is traced. The validity of this optimal method has been verified.     

Two-dimensional ion chromatography using tandem ion-exchange columns with gradient-pulse column switching

A two-dimensional ion chromatography (2D-IC) approach has been developed which provides greater resolution of complex samples than is possible currently using a single column. Two columns containing different stationary phases are connected via a tee-piece, which enables an additional eluent flow and independent control of eluent concentration on each column. The resultant mixed eluent flow at the tee-piece can be varied to produce a different eluent concentration on the second column. This allows analytes strongly retained on the first column to be separated rapidly on the second column, whilst maintaining a highly efficient, well resolved separation of analytes retained weakly on the first column. A group of 18 inorganic anions has been separated to demonstrate the utility of this approach and the proposed 2D-IC method provided separation of this mixture with resolution of all analytes greater than 1.3. Careful optimisation of the eluent profiles on both columns resulted in run times of less than 28 min, including re-equilibration. Separations were performed using isocratic or gradient elution on the first column, with an isocratic separation being used on the second column. Switching of the analytes onto the second column was performed using a gradient pulse of concentrated eluent to quickly elute strongly retained analytes from the first column onto the second column. The separations were highly repeatable (RSD of 0.01–0.12% for retention times and 0.08–2.9% for peak areas) and efficient (typically 8000–260,000 plates). Detection limits were 3–80 ppb.     

Open-tubular gas chromatography using capillary coated with octadecylamine-capped gold nanoparticles

The octadecylamine-capped gold nanoparticles (ODA-Au-NPs) were prepared and directly used to coat the capillary wall. The hydrophobic coating acted as the stationary phase for open-tubular gas chromatography (OTGC). The ODA-Au-NPs can be adsorbed tightly onto the inner surface of fused silica capillary column via electrostatic interaction and enhanced interaction of van der Waals between gold nanoparticles and the capillary wall. Thus, the modification of the inner surface of capillary column by ODA-Au-NPs can be achieved simply by flushing the capillary with a solution of ODA-Au-NPs and the resulted ODA-Au-NPs coating is very stable. No perceptible degradation in the ODA-Au-NPs-based separation was observed after ∼1900 sample runs. This type of columns also provided excellent chromatographic performances: high number of theoretical plates, outstanding run-to-run and column-to-column reproducibility, and high selectivity for a wide range of test mixtures. An efficiency of 2474 theoretical plates per meter for chlorobenzene was obtained on an ODA-Au-NPs-modified 1.6 m × 100 μm i.d. fused silica capillary column.     

Development of a switchable multidimensional/comprehensive two-dimensional gas chromatographic analytical system

In this study, a new system for analysis using a dual comprehensive two-dimensional gas chromatography/targeted multidimensional gas chromatography (switchable GC × GC/targeted MDGC) analysis was developed. The configuration of this system not only permits the independent operation of GC, GC × GC and targeted MDGC analyses in separate analyses, but also allows the mode to be switched from GC × GC to targeted MDGC any number of times through a single analysis. By incorporating a Deans switch microfluidics transfer module prior to a cryotrapping device, the flow stream from the first dimension column can be directed to either one of two second dimension columns in a classical heart-cutting operation. Both second columns pass through the cryotrap to allow solute bands to be focused and then rapidly remobilized to the respective second columns. A short second column enables GC × GC operation, whilst a longer column is used for targeted MDGC. Validation of the system was performed using a standard mixture of compounds relevant to essential oil analysis, and then using compounds present at different abundances in lavender essential oil. Reproducibility of retention times and peak area responses demonstrated that there was negligible variation in the system over the course of multiple heart-cuts, and proved the reliable operation of the system. An application of the system to lavender oil, as a more complex sample, was carried out to affirm system feasibility, and demonstrate the ability of the system to target multiple components in the oil. The system was proposed to be useful for study of aroma-impact compounds where GC × GC can be incorporated with MDGC to permit precise identification of aroma-active compounds, where heart-cut multidimensional GC-olfactometry detection (MDGC-O) is a more appropriate technology for odour assessment.     

Low-pressure gas chromatography: Recent trends and developments

In the past few years, low-pressure gas chromatography (LP-GC) has been applied for the fast analysis of various pollutants in different environmental and food matrices. A typical LP-GC set-up involves the use of a short microbore column (typically 0.5–1 m × 0.10 mm internal diameter) at the injector side connected with a zero dead-volume connector to a short megabore column (typically 10 m × 0.53 mm) to be used with higher gas velocities. This set-up maintains atmospheric injection conditions, while the analytical column is operated under low-pressure conditions that are compatible with mass-spectrometer analyzers. Although the use of LP-GC results in a loss of separation efficiency, it offers a 3–5-fold reduction in analysis time for organic compounds and thus increased sample throughput and enhancement of the signal-to-noise ratio leading to improved detection limits. Considering the significance of, and the potential interest in, this topic, this review briefly describes the concept of LP-GC. Furthermore, we explore recent developments and applications of LP-GC, with a focus on the use of various column systems and analyzers. Finally, we critically evaluate the prospects for, and the limitations of, LP-GC.     

Separation performance of graphene oxide as stationary phase for capillary gas chromatography

Graphene oxide(GO) has attracted extensive attention due to its unique properties and potential applications.Here,we report the investigation of GO nanosheets as a stationary phase for capillary gas chromatographic(GC) separations.The GO column,fabricated by a new one-step coating approach,showed average McReynolds constants of 308,suggesting the medium polar nature of the GC stationary phase.The GO stationary phase achieves good separation for analytes of different types with good peak shapes,especially for H-bonding analytes,such as alcohols and amines.The different retention behaviors of GO stationary phase from the conventional stationary phase may originate from its multiple interactions with analytes,involving H-bonding,dipole-dipole,π-π stacking and dispersive interactions.Moreover,GO column showed good separation reproducibility with relative standard deviation(RSD%) less than 0.24%(n = 5) on retention times of analytes.     

Effect of column combinations on two-dimensional separation in comprehensive two-dimensional gas chromatography: Estimation of orthogonality and exploring of mechanism

With the analysis of Chinese liquor Moutai as an example, the effect of different column combinations was studied on two-dimensional separation in comprehensive two-dimensional gas chromatography (GC × GC). A method to optimize column combinations was developed for achieving maximum orthogonality. Using a geometric approach to factor analysis, the degree of separation orthogonality was quantitatively estimated. The parameters evaluated include peak spreading angle, retention correlation, and practical peak capacity. When using the “reversed-type” column combinations (a polar column as the first dimension and a non- or less polar one as the second dimension), correlation coefficient was lower than or equal to 0.221, the spreading angle was higher than or equal to 77°, and more than 92% of the theoretical peak capacity was reasonably used. For Moutai liquor mainly consisting of some polar compounds, the HP-Innowax + DB1701 column combination was optimal. In addition, through the test of Grob mixture and McReynolds constant, the mechanism of solute-stationary phase interactions was disclosed in details, which validated the estimation of GC × GC orthogonality in a molecular level.     

Methods to determine the kinetic performance limit of contemporary chromatographic techniques

By combining separation efficiency data as a function of flow rate with the column permeability, the kinetic plot method allows to determine the limits of separation power (time vs. efficiency) of different chromatographic techniques and methods. The technique can be applied for all different types of chromatography (liquid, gas, or supercritical fluid), for different types of column morphologies (packed beds, monoliths, open tubular, micromachined columns), for pressure and electro‐driven separations and in both isocratic and gradient elution mode. The present contribution gives an overview of the methods and calculations required to correctly determine these kinetic performance limits and their underlying limitations.     

Temperature programmed retention indices: Calculation from isothermal data. Part 1: Theory

Direct conversion of isothermal to temperature programmed indices is not possible. In this work it is shown that linear temperature programmed retention indices can only be calculated from isothermal retention data if the temperature dependence of both the distribution coefficients and the column dead time are taken into account. Procedures are described which allow calculation of retention temperatures and from these, accurate programmed retention indices. Within certain limits the initial oven temperature and programming rate can be chosen freely. The prerequisite for this calculation is the availability of reliable isothermal retention data (retention times, retention factors, relative retention times, or retention indices) at two different temperatures for one column. The use of compiled isothermal retention indices at two different temperatures for the calculation of retention temperatures and thus temperature programmed indices is demonstrated. For the column for which programmed retention indices have to be determined, the isothermal retention times of the n-alkanes and the column dead time as a function of temperature have to be known in addition to the compiled data for a given stationary phase. Once the programmed retention indices have been calculated for a given column the concept allows the calculation of temperature programmed indices for columns with different specifications. The characteristics which can be varied are: column length, column inner diameter, phase-ratio, initial oven temperature, and programming rate.     

Comparative Study of Packed and Capillary Column Chromatography for the Characterization of Vacuum Gas Oils

Gas chromatographic methods are of widespread use in the petroleum industry for assessing petroleum and derivatives quality. The feedstocks for catcracking processes are very sensitive to the n-paraffin contents, which can be accurately determined using capillary column chromatography. Nevertheless, packed column chromatography does have potential advantages, viz. sometimes shorter analysis times, lower costs, higher column capacity, for vacuum gas oil analysis. This paper presents a method for such a determination using a Dexsil-300 packed column. The results obtained (n-alkane contents, carbon number distribution) agree fairly well with those obtained on a 30 m × 0.25 mm DB-1 fused silica capillary column.     

端羟基β-氰乙基甲基聚硅氧烷气相色谱毛细管柱的研制

Sol-gel capillary column for gas chromatography was prepared with Hydroxyl-Terminated β-cyan-ethyl methyl-Polysiloxane as stationary phase.On this column alkanes,aromatic compounds,amines,alcohols etc.were separated successfully,although the length of this column was only 2.5m.Experiments showed that the column-inertness was good and the unsymmetrical factor was 1.At high temperatures the stationary phase of the column showed excellent stability.Results showed that the relative standard deviation of the ret...