Fast comprehensive two-dimensional gas chromatography with cryogenic modulation

The fast separation of a mixture of 29 compounds by using comprehensive two-dimensional gas chromatography is reported. Capillary column sets with shorter lengths and smaller inner diameter in both the first and second dimensions have been tested, for both fast chiral and achiral separations. Fast chiral separations, which included enantiomer separations of limonene, linalool, citronellol, and alpha-isomethylionone, were achieved within 23 min, which corresponds to approximately 2-fold faster than analyses under conditions previously considered as normal. Fast achiral separations, which do not have the restriction of requiring a minimum quality of chiral resolution, were obtained within 5 min, which is markedly faster than separations on the normal column set under conditions more commonly employed. The achiral fast GC x GC method used a 5 m x 0.1 mm i.d. first dimension column, interfaced to a 0.3 m x 0.05 mm i.d. second column, with temperature program rate of 35 degrees C.min-1; a modulation period of 1 s was employed. Peak widths at baseline on the first column were a little over 1 s, while modulated peak widths at half-height recorded with a flame ionization detector operating at 200 Hz were approximately 30 ms. The benefits and limitations of GC x GC for fast chiral and achiral separations are reported and discussed.     

Thermal modulation for multidimensional liquid chromatography separations using low-thermal-mass liquid chromatography (LC)

We report on a proof-of-principle experiment with a novel thermal modulation device with potential use in two-dimensional liquid chromatography (LC × LC) systems. It is based on the thermal desorption concept used in two-dimensional gas chromatography (GC × GC) systems. Preconcentration of neutral analytes eluting from the first dimension column is performed in a capillary "trap" column packed with highly retentive porous graphitic carbon particles, placed in an aluminum low-thermal-mass LC heating sleeve. Remobilization of the trapped analytes is achieved by rapidly heating the trap column, by applying temperature ramps up to +1200 °C/min. Compared to the nonmodulated signal, the presented thermal modulator yielded narrow peaks, and a concentration enhancement factor up to 18 was achieved. With a thermally modulated LC separation of an epoxy resin, it is shown that when the thermal modulation is applied periodically, the trapped and concentrated molecules can be released periodically and that the modulating interface can both serve as a preconcentration device and as an injector for the second dimension column of an LC × LC setup. Because of the thermal modulation, a high-molecular-weight epoxy resin could be adequately separated and the different fractions were identified with a GPC analysis, as well as an offline second dimension LC analysis.     

Comprehensive two-dimensional gas chromatography via differential flow modulation

A novel comprehensive two-dimensional gas chromatograph has been developed that utilizes differential flow modulation. This technique uses a 6-port valve to collect effluent from a primary column and periodically inject the effluent into a secondary column. The flow in the secondary column is kept 20 times larger than the flow in the primary column so the contents of the sample loop can be flushed into the secondary column in 5% of the collection time. Peaks widths at half-maximum of approximately 0.06 s are generated for a 1.0 Hz secondary injection frequency. Sensitivity is not compromised, as 80% of the sample passes through both columns and reaches the detector. This simple yet effective technique has been used to analyze mixtures of alkanes, alkenes, aldehydes, alcohols, aromatics, esters, and ketones with high speed and high resolution.     

On-line coupling of supercritical fluid extraction with multidimensional microcolumn liquid chromatography/gas chromatography.

An on-line multidimensional supercritical fluid extraction/microcolumn liquid chromatography/capillary gas chromatography system (SFE/LC/GC) has been developed and applied to the quantitative determination of trace levels (parts per billion) of chlorpyrifos insecticide in grass field samples. This system provides all the advantages of an on-line multidimensional system, including increased resolving power, high sensitivity, quantitation, precision, and automation potential. Off-line analysis of the grass extracts by GC with an electron capture detector yielded a complex chromatogram from which it was difficult to quantitate the chlorpyrifos, but analysis of the extract by LC/GC yielded a simple chromatogram from which chlorpyrifos could be quantitated. On-line SFE/LC/GC resulted in reduced sample preparation with the grass extract being deposited directly on the LC microcolumn via an impactor interface, followed by the LC/GC separation. The reproducibility of the on-line SFE/LC/GC procedure was studied and found to yield a relative standard deviation of 10.8% for the determination of chlorpyrifos insecticide in grass field samples at a concentration of 160 ng/g. Using this method, the entire analysis including extraction, clean-up, and gas chromatography required less than 0.1 mL of organic solvent.     

High-efficiency solvating gas chromatography using packed capillaries

In this study, column efficiency in packed capillary column solvating gas chromatography (SGC) was investigated. Long (>3 m) fused silica capillaries with an inner diameter of 250 μm were packed with 10 and 15 μm spherical porous (300 ?) octadecyl bonded silica particles using a CO(2) slurry packing method. A 336 cm × 250 μm i.d. fused silica capillary containing 10 μm particles provided a total column efficiency of 264?000 plates (k = 0.41), corresponding to a reduced plate height of 1.27, using CO(2) as the mobile phase at a column inlet pressure of 260 atm. A minimum plate height of 12.7 μm and a maximum plate number per unit time of 813 plates/s were obtained using packed capillary SGC. Retention factors were dependent on the column inlet pressure but independent of the pressure gradient along the column. Gasoline and diesel samples were separated under SGC conditions, and the results were comparable to those obtained using typical open tubular column gas chromatography.     

High-speed gas chromatography using synchronized dual-valve injection

A novel injection technique for high-speed gas chromatography is demonstrated. Synchronized dual-valve injection is shown to provide peak widths as low as 1.5 ms (width at half-height) for an unretained analyte. This was achieved using a 0.5-m DB-5 column with an internal diameter of 100 microm and a film thickness of 0.4 microm operated at a temperature of 150 degrees C with a column absolute head pressure of 85 psi, resulting in a dead time of only t(o) = 26 ms ( approximately 1900 cm/s, 26 mL/min). Using the DB-5 column in a 1-m length under the same instrumental parameters, with a resulting linear flow velocity of 935 cm/s (12.7 mL/min, t(o) = 117 ms), a minimum peak width of 3.3 ms was obtained. During an isothermal separation, 10 analytes were separated in a time window of 400 ms. A rigorous comparison of experimental and theoretical band-broadening data based on the Golay equation showed that band broadening is limited almost entirely by the chromatographic band broadening terms expressed by the Golay equation and not by extra column band broadening due to the injection process. Synchronized dual-valve injection offers a rugged and inexpensive design, providing extremely reproducible injections with peak height precision of 2.4% (RSD) and low run-to-run variation in retention times, with an average standard deviation less than 0.1 ms. Herein, synchronized dual-valve injection is demonstrated as a proof of principle using high-speed diaphragm valves. It is foreseen that the injection technique could be readily implemented using a combination of thermal modulation and high-speed valve hardware, thus optimizing the mass transfer and not significantly sacrificing the limit of detection performance for high-speed GC. Further implications are that, if properly implemented, high-speed temperature programming coupled with this new technology should lead to very large peak capacities for approximately 1-s separations.     

Partial modulation method via pulsed flow modulator for comprehensive two-dimensional gas chromatography

A partial modulation method by using a pulsed-flow modulator for comprehensive two-dimensional gas chromatography is proposed. The method is based on the fact that when a pulsed flow of inert gas is introduced into the conjunction between a primary and a secondary column, the concentration of analyte is disturbed, and a plug of higher or lower concentration is created. The plug, which forms a spike signal coupled to the primary GC signal, is then separated in a secondary column, creating a new dimension of GC information. The modulation is partial because only a fraction of the primary signal is modulated and converted into the secondary signal; the remaining primary signal stays unchanged. Therefore, this method yields a comprehensive two-dimensional chromatogram and a primary one-dimensional chromatogram in a single GC run. In this study, the modulation mode, modulation index, and modulation percentage are discussed and the reproducibility of peak areas and retention time are investigated. With a 5.8% modulation percentage and a primary peak half-width 1.7 times wider than the modulation time, the standard deviation for the peak areas are 0.15% for the primary and 0.78% for the secondary chromatograms. Chromatograms of laboratory-mixed hydrocarbons and of high-temperature fuel oil no. 6 standard are demonstrated.     

Longitudinally modulated cryogenic system. A generally applicable approach to solute trapping and mobilization in gas chromatography

This paper describes a novel approach to solute trapping and remobilization. It involves the use of a subambient trap, with a narrow capillary column passing through the cooled region. A mechanism allows for longitudinal movement of the trap relative to the chromatographic column or narrow transfer line through which analytes travel. Either the trap or the column can be moved, and the frequency or manner of relative movement determines the type of result obtained. A series of preliminary studies are described that define the general approach to using this device and demonstrate the unique benefits that may arise from the modulation movement. Significant improvement (reduction) in peak width occurs if the device is placed immediately prior to the detection system, and consequently a great increase in detection limits results. With a 25 cm length of capillary column between the trap and detector, it is calculated that the plate height of dodecane is 0.082 mm, equivalent to 12?100 plates/m. This was found to be much greater than that for dodecane analyzed on a 25 m column. By slow displacement of the column through the trap, it is demonstrated that the solute is trapped in the first 1 cm (or less) of the column located in the cold trap.     

低温精馏与低温气相色谱复合法分离氢同位素

采用低温精馏与低温气相色谱相结合的方法分离、浓缩氢同位素,探讨了分离过程操作参数间的内在联系.实验结果表明:氘浓度为10-3的100 m3原料气经过120 h的连续运行后,可以将氘浓度浓缩至91.5%;低温精馏柱随着回流比的增大,再沸器和冷凝器中氘浓度均减小;顶端采出量增大,再沸器中氘浓度明显增大;随再沸器加热功率的增加,液氢液位下降,床层压降增加,精馏柱操作压力从100 kPa上升到190 kPa,冷凝器和冷头为提供更多冷量温度降低;低温色谱的分离、浓缩效果十分显著,3次运行后将氘浓度从1.25×10-2提高到91.5%.     

Method for small-molecule discovery based on microscale-preparative multidimensional gas chromatography isolation with nuclear magnetic resonance spectroscopy

Absolute chemical identification requires obtaining a pure compound followed by structure elucidation using spectroscopic techniques, principally NMR spectroscopy and mass spectrometry. Classical isolation techniques suffer from insufficient resolution for complex samples, requiring time-consuming fractionation in multiple steps. Here, a novel preparative technique based upon capillary column multidimensional gas chromatography (MDGC) with 2D NMR to resolve, isolate, and identify pure volatile components from a complex sample is described. As a model application, geraniol was isolated from an essential oil matrix using MDGC and quantitatively resolved from 15 partially coeluting compounds from the first column. Geraniol was recovered from 10 (8.6 microg) and 100 injections (77.6 microg; purity >99%) for subsequent NMR analysis at 500 and 800 MHz (with cryoprobe). Proton and gCOSY NMR experiments were successfully performed at 12.3 microg/mL (10 injections), while gHSQC and gHMBC NMR experiments were obtained at 110.8 microg/mL (100 injections). This approach is applicable to the biodiscovery of volatile molecular species or, indeed, any volatile compound in a complex matrix that requires confirmation of component identity.     

Use of multidimensional lectin affinity chromatography in differential glycoproteomics

This paper reports studies comparing the relative degree of sialylation among human serum glycoproteins carrying complex biantennary N-linked, hybrid, and high-mannose oligosaccharides. Comparisons were made by coupling lectin affinity selection with stable isotope coding of peptides from tryptic digests of serum. After proteolysis, samples were split and differentially acetylated with stable isotope coding agents according to either origin or the separation method by which they would be fractionated. A lectin column prepared from Sambucus nigra agglutinin (SNA) was used to select and compare the concentration of sialic acid containing glycopeptides. The relative standard deviation in quantification using this method was 4%. Using this method the concentration of sialic acid containing glycoproteins from a normal individual were compared to those in a pooled serum sample from a large number of normal individuals. It was found that sialylation varied less than 2-fold in all but four or five glycoproteins. Further studies were done on the degree of sialylation within glycoproteins. Samples labeled with the light isoform of the coding agent were applied to a set of serial lectin columns consisting of a concanavalin A (Con A) column coupled to an SNA column for selecting sialic acid appended to glycopeptides with complex biantennary N-linked, hybrid, and high-mannose glycans. In contrast, samples labeled with the heavy isoform of the coding agent were applied to a Con A lectin column alone to select glycopeptides containing complex biantennary N-linked, hybrid, and high-mannose glycans, without regard to sialylation. Glycopeptides thus selected were mixed, deglycosylated by PNGase F, and fractionated by reversed-phase chromatography (RPC). The RPC fractions were then analyzed by ESI-MS. The relative standard deviation of the method was 4%. All glycopeptides identified contained sialic acid except one. Peptides in which the relative abundance of isotopic isoforms was equal were considered to indicate that the protein parent was fully sialylated at that specific glycosylation site.     

低温透平膨胀机用全动压气体轴承的设计与试验研究

介绍 15 0m3 /h制氧机用中压低温透平膨胀机 (PLK - 8 33× 2 / 2 0 - 5 )在转子转速12 16× 10 4r/min (比额定超速 14 % )工况下 ,获得了全动压气体轴承稳定运转的良好效果。还对螺旋槽止推轴承的性能进行了研究。试验结果表明 ,在国产高速低温透平膨胀机中改用全动压气体轴承是完全可行的。     

低温透平膨胀机用全动压气体轴承的设计与试验研究

介绍150m3/h制氧机用中压低温透平膨胀机(PLK-8.33×2/20-5)在转子转速12.16×104r/min(比额定超速14%)工况下,获得了全动压气体轴承稳定运转的良好效果.还对螺旋槽止推轴承的性能进行了研究.试验结果表明,在国产高速低温透平膨胀机中改用全动压气体轴承是完全可行的.     

Differential metabolomics using stable isotope labeling and two-dimensional gas chromatography with time-of-flight mass spectrometry

This work describes an approach to differential metabolomics that involves stable isotope labeling for relative quantification as part of sample analysis by two-dimensional gas chromatography/mass spectrometry (GCxGC/MS). The polar metabolome in control and experimental samples was extracted and differentially derivatized using isotopically light and heavy (D6) forms of the silylation reagent N-methyl-N-tert-butyldimethylsilyl)trifluoroacetamide (MTBSTFA). MTBSTFA derivatives are of much greater hydrolytic stability than the more common trimethylsilyl derivatives, thus diminishing the possibility of isotopomer scrambling during GC analysis. Subsequent to derivatization with MTBSTFA, differentially labeled samples were mixed and analyzed by GCxGC/MS. Metabolites were identified, and the isotope ratio of isotopomers was quantified. The method was tested using three classes of metabolites; amino acids, fatty acids, and organic acids. The relative concentration of isotopically labeled metabolites was determined by isotope ratio analysis. The accuracy and precision, respectively, in quantification of standard mixtures was 9.5 and 4.77% for the 16 amino acids, 9.7 and 2.83% for the mixture of 19 fatty acids, and 14 and 4.53% for the 20 organic acids. Suitability of the method for the examination of complex samples was demonstrated in analyses of the spiked blood serum samples. This differential isotope coding method proved to be an effective means to compare the concentration of metabolites between two samples simultaneously.     

Investigation on performances of non-loss storage for cryogenic liquefied gas

In this paper, effects of liquid volume fraction, temperature and work pressure in cryogenic vessels on the pressure rise rates in cryogenic vessels are analyzed. Graphs of the relation between storage-pressure and heat flow received by the container per unit of volume for various volume fractions are proposed, and also graphs of the relation between time and pressure of non-loss storage for various volume fractions are presented. The best volume fraction is defined. Also, the graphs of the relation between environmental temperature and the performance of non-loss storage are proposed. In addition, the phenomenon of liquid-temperature layering is analyzed and methods to reduce this layering are suggested. These results have significance in the design, usage and selection of cryogenic vessels.     

Theory to boil-off gas cooled shields for cryogenic storage vessels

An intermediate refrigeration with boil-off gas cooled shields using the boil-off gas stream is an alternative method to the conventional intermediate refrigeration with a cryogenic liquid.By using an analytical calculation method relations are derived, which enable complete predictions about the effectiveness of an intermediate refrigeration with boil-off gas cooled shields as a function of the number of shields for the different stored cryogenic liquids. For this theoretical derivation however, the restrictive assumption must be made that the thermal conductivity of the used insulation material has a constant value between the considered temperature boundaries.For purposes of a more exact calculation a numerical method is therefore suggested, which takes into consideration that the thermal conductivity is temperature-dependent. For a liquid hydrogen storage vessel with a perlite-vacuum insulation e.g., the effectiveness of one shield and its equilibrium temperature are given as a function of the position of the shield in the insulation space.     

The desorption of condensed noble gases and gas mixtures from cryogenic surfaces

In accelerators, operating at liquid-helium temperature, cold surfaces are exposed to intense synchrotron radiation and bombardment by energetic electrons and ions. Molecular desorption yield and secondary electron yield can strongly influence the performance of the accelerator. In order to predict the gas density during the operation, the knowledge of electron-induced desorption yields of condensed gases and of its variation with the gas coverage is necessary. Desorption yields under electron impact of various noble gases and gas mixtures condensed on a copper surface cooled at 4.2 K have been measured.     

低温色谱法制备贫氘氢样品的研究

采用无载带气的单维低温色谱分离技术,从制备流程设计出发,对分离方法、吸附材料、柱径柱长和操作参数进行了选择,并以氘丰度约为1.4×10-4的天然高纯氢为原料,在1 h之内成功制备出满足使用要求的贫氘氢样品.     

A multidimensional differential proteomic platform using dual-phase ion-exchange chromatography-polyacrylamide gel electrophoresis/reversed-phase liquid chromatography tandem mass spectrometry

Differential proteomic analysis has arisen as a large-scale means to discern proteome-wide changes upon treatment, injury, or disease. Tandem protein separation methods are required for large-scale differential proteomic analysis. Here, a novel multidimensional platform for resolving and differentially analyzing complex biological samples is presented. The platform, collectively termed CAX-PAGE/RPLC-MSMS, combines biphasic ion-exchange chromatography with polyacrylamide gel electrophoresis for protein separation, quantification, and differential band targeting, followed by capillary reversed-phase liquid chromatography and data-dependent tandem mass spectrometry for quantitative and qualitative peptide analysis. CAX-PAGE provides high protein resolving power with a theoretical peak capacity of 3570, extendable to 7600, a wide protein mass range verified from 16 to 273 kDa, and reproducible differential sample comparison without the added expense of fluorescent dyes and imaging equipment. Demonstrated using a neuroproteomic model, CAX-PAGE revealed an increased number of differential proteins, 137, compared with 82 found by 2D difference gel electrophoresis. When combined with RPLC-MSMS for protein identification, an additional quantification step is performed for internal validation, confirming a 2-fold or greater change in 89% of identified differential targets.