Chromatography thermal conductivity

MEVIS/IPM, membrane inlet mass spectrometry/isotope pairing method TCD, gas chromatography-thermal conductivity detector AIT, acetylene inhibition technique IPM, isotope pairing method with isotope ratio mass spectrometry MIMS, membrane inlet mass spectrometry Stoichiometery, benthic flux DICiDIN stoichiometry MIMS + N03, membrane inlet mass with N03 amendment 15N2 production, 15N03 or 15NH4 conversion to 15N2. 

Products were collected and weighed to determine a mass balance. Except for two experiments, in which the volume of gases exceeded the capacity of the gas collection system and the last portion was vented, the mass balance ranged from 95 to 98% ( 14). We measured C, H, N, and acid-evolved CO2 content for all retorted shales and for some burnt shales from the cracking experiments. Oils were analyzed for C, H, and N. Gases were analyzed by gas chromatography (thermal conductivity detector for h2> CO2 N2, and CH4 flame ionization detector for... 

The chromatogram can finally be used as the series of bands or zones of components or the components can be eluted successively and then detected by various means (e.g. thermal conductivity, flame ionization, electron capture detectors, or the bands can be examined chemically). If the detection is non-destructive, preparative scale chromatography can separate measurable and useful quantities of components. The final detection stage can be coupled to a mass spectrometer (GCMS) and to a computer for final identification. 

Alternatively, gas chromatography may be used Fig. XVII-5 shows a schematic readout of the thermal conductivity detector, the areas under the peaks giving the amount adsorbed or desorbed. 

Thermal Conductivity Detector One of the earliest gas chromatography detectors, which is still widely used, is based on the mobile phase s thermal conductivity (Figure 12.21). As the mobile phase exits the column, it passes over a tungsten-rhenium wire filament. The filament s electrical resistance depends on its temperature, which, in turn, depends on the thermal conductivity of the mobile phase. Because of its high thermal conductivity, helium is the mobile phase of choice when using a thermal conductivity detector (TCD). 

Gas Chromatography. Gas chromatography is a well recognised method for the analysis of H—D—T mixtures. The substrate is alumina, AI2O2, coated with ferric oxide, Fe202. Neon is used as the carrier gas. Detectors are usually both thermal conductivity (caratherometer) and ion chamber detectors when tritium is involved (see Chromatography). 

The detector. The function of the detector, which is situated at the exit of the separation column, is to sense and measure the small amounts of the separated components present in the carrier gas stream leaving the column. The output from the detector is fed to a recorder which produces a pen-trace called a chromatogram (Fig. 9.1fr). The choice of detector will depend on factors such as the concentration level to be measured and the nature of the separated components. The detectors most widely used in gas chromatography are the thermal conductivity, flame-ionisation and electron-capture detectors, and a brief description of these will be given. For more detailed descriptions of these and other detectors more specialised texts should be consulted.67 69... 

Thermal conductivity detector. The most important of the bulk physical property detectors is the thermal conductivity detector (TCD) which is a universal, non-destructive, concentration-sensitive detector. The TCD was one of the earliest routine detectors and thermal conductivity cells or katharometers are still widely used in gas chromatography. These detectors employ a heated metal filament or a thermistor (a semiconductor of fused metal oxides) to sense changes in the thermal conductivity of the carrier gas stream. Helium and hydrogen are the best carrier gases to use in conjunction with this type of detector since their thermal conductivities are much higher than any other gases on safety grounds helium is preferred because of its inertness. 

This technique detects substances qualitatively and quantitatively. The chromatogram retention time is compound-specific, and peak-height indicates the concentration of pollutant in the air. Detection systems include flame ionization, thermal conductivity and electron capture. Traditionally gas chromatography is a laboratory analysis but portable versions are now available for field work. Table 9.4 lists conditions for one such portable device. 

Carbon dioxide chemisorptions were carried out on a pulse-flow microreactor system with on-line gas chromatography using a thermal conductivity detector. The catalyst (0.4 g) was heated in flowing helium (40 cm3min ) to 723 K at 10 Kmin"1. The samples were held at this temperature for 2 hours before being cooled to room temperature and maintained in a helium flow. Pulses of gas (—1.53 x 10"5 moles) were introduced to the carrier gas from the sample loop. After passage through the catalyst bed the total contents of the pulse were analysed by GC and mass spectroscopy (ESS MS). 

Chromatography Interaction between phases Retention at given time or volume Thermal conductivity, flame-ionization, MS Chromatogram ... 

C30 oil, homopolymer of 1-decene, Ethyl Corp., Inc.) served as the start-up solvent for the experiments. The catalyst (ca. 5-8 g) was added to start-up solvent (ca. 300 g) in the CSTR. The reactor temperature was then raised to 270°C at a rate of l°C/min. The catalyst was activated using CO at a space velocity of 3.0 sl/h/g Fe at 270°C and 175 psig for 24 h. FTS was then started by adding synthesis gas mixture (H2 CO ratio of 0.7) to the reactor at a space velocity of either 3.1 or 5.0 sl/h/g Fe. The conversions of CO and H2 were obtained by gas chromatography (GC) analysis (HP Quad Series Micro-GC equipped with thermal conductivity detectors) of the product gas mixture. The reaction products were collected in three traps maintained at different temperatures—a hot trap (200°C), a warm trap (100°C), and a cold trap (0°C). The products were separated into different fractions (rewax, wax, oil, and aqueous) for quantification by GC analysis. However, the oil and the wax (liquid at room temperature) fractions were mixed prior to GC analysis. 

VDU screen via suitable electronic amplifying circuitry where the data are presented in the form of an elution profile. Although there are a dozen or more types of detector available for gas chromatography, only those based on thermal conductivity, flame ionization, electron-capture and perhaps flame emission and electrolytic conductivity are widely used. The interfacing of gas chromatographs with infrared and mass spectrometers, so-called hyphenated techniques, is described on p. 114 etseq. Some detector characteristics are summarized in Table 4.11. 

In addition to the analytical columns (columns used mainly for analytical work), so-called preparative columns may also be encountered. Preparative columns are used when the purpose of the experiment is to prepare a pure sample of a particular substance (from a mixture containing the substance) by GC for use in other laboratory work. The procedure for this involves the individual condensation of the mixture components of interest in a cold trap as they pass from the detector and as their peak is being traced on the recorder. While analytical columns can be suitable for this, the amount of pure substance generated is typically very small, since what is being collected is only a fraction of the extremely small volume injected. Thus, columns with very large diameters (on the order of inches) and capable of very large injection volumes (on the order of milliliters) are manufactured for the preparative work. Also, the detector used must not destroy the sample, like the flame ionization detector (Section 12.6) does, for example. Thus, the thermal conductivity detector (Section 12.6) is used most often with preparative gas chromatography. 

The prepared mixtures were placed in the extraction vessel, and stirred for 2 h and then left to settle for 4 h. Samples were taken by a syringe (Gaschromatographic s Hamilton 0.4 p,L) from both the upper (methylcyclohexane) phase and lower layers (aromatic phase). Both phases were analyzed using Konik gas chromatography (GC) equipped with a thermal conductivity detector (TCD) and Shimadzu C-R2AX integrator. A 2 m x 2 mm column was used to separate the components... 

Experimental Procedure. Figure 3 presents a schematic diagram of the apparatus. The chromatograph is a Varian Aerograph Series 1400 with a thermal conductivity detector and an associated Varian CDS 111 Chromatography Data System (integrator). We modified the chromatograph in two ways ... 

Gas-liquid chromatography. A process for determining the components of a gaseous stream. The gas is passed through a series of fine mesh screens. The finest are coated with a liquid. The setup causes the components to move through at different rates. At the tail end, they are detected, one after another, by thermal conductivity changes, density differences, or ionization detectors. 

In modern combustion analysers, a tiny sample (about 2 mg) is accurately weighed and oxidised at a high temperature in an oxygen atmosphere. The product mixture of CO, HjO, Nj and SO is separated by gas chromatography and the mass of each component is measured using a thermal conductivity detector. From these product masses, the mass of each of the elements C, H, N and S in the sample can... 

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