Thermal conductivity detector for

Semonian and Manes have devised an approach which provides continuous data from which the desorption isotherm can be constructed. Their method utilizes a calibrated thermal conductivity detector for sensing the effluent concentration from a cell filled with adsorbate and slowly purged with a carrier gas. The amount desorbed at any relative pressure is calculated by integrating the effluent flow rate and thermal conductivity signal. 

The most common detectors for GC are the non-selective flame ionisation detector and thermal conductivity detector. For element speciation, selectivity is definitely advantageous, allowing less sample preparation and less demanding separation. Of the conventional GC detectors, the electron capture detector is very sensitive for electrophilic compounds and therefore has some selectivity for polar compounds containing halogens and metal ions. It has been used widely... 

Abbreviations tfa trifluoracetylacetone hfa hexafluoroacetylacetone DMF dimethylform-amide DBSO di-n-butylsulfoxide - TCD thermal conductivity detector for other detector abbreviations see Table 1.2. 

Use of a Small Volume Thermal Conductivity Detector for Capillary Gas Chromatography... 

Detection in liquid chromatography has long been considered one of the weakest aspects of the technique. Low concentrations of a solute dissolved in a liquid modify the properties of the liquid to a much smaller extent than low concentrations of a solute in a gas. For this reason there is no sensitive universal, or quasi-universal, detector such as the flame ionization or thermal conductivity detectors for GC. A comprehensive review of detectors has been published by Fielden (38), as well as two recent books by Scott (39) and Patonay (40). The Fundamental Review issue of Analytical Chemistry, published in even-numbered years, contains a comprehensive review of developments in instrumentation for LC, including detection techniques. 

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 gaseous samples were analyzed using GC with MSS A, Pora PLOT Q (PPQ), and WAX columns and a thermal conductivity detector for the analysis of hydrogen, carbon monoxide, carbon dioxide, methane, and other gases [3]. The volume concentration of each gas of interest was calculated based on an external standard method. 

No detectors for LC are as universally applicable as the name ionization and thermal conductivity detectors for gas chromatography described in Section 27B-4. GC detectors were specifically developed to mca.surc small concentrations of analytes in flowing gas streams. On the other hand, L.C detectors have often been traditional analytical instrumenl.s adapted with flow cells to measure low concentrations of solutes in liquid streams. A major challenge in the development of LC has been in adapting and improving such devices." ... 

The flux measurement system consists of the gas flow system which delivers a gas mixture of known concentration to a membrane cell, a gas chromatograph with thermal conductivity detector for analysis of the feed and produot side gas streams, and a computer for data acquisition and reduction. The gas streams were saturated with water upstream of the membrane cell. A cold trap removed the water prior to chromatographic analysis. All measurements were made... 

The columns are 1/16 stainless steel tnbing packed with a media that selectively retards the flow of the gas components. The selectivity of the colnmn is dependent on the boiling point or partial pressme of the individual pure components of natural gas. The lighter components will travel through the column system faster than the heavier components. Each componnd travels at a slightly different rate through the column system and is eventually physically separated into a discrete band of the pure component. As the pure component bands elnte from the column system they enter the thermal conductivity detector for quantification. 

It is generally desirable to have a detector which detects all substances well. Such a device is impossible to achieve, since each detector is based on the measurement of a particular substance property and different substances have correspondingly differing substance properties. There are, however, detectors which are suitable for very broad substance ranges. Flame ionization detectors and thermal conductivity detectors, for example, are virtually universal. Even with these types, though, different properties... 

Reduction of the oxidic precursors resulting from the oxidation of the supported complex cyanides leads to metal or alloy particles. Figure 4 shows temperature-programmed reduction (IPR) profiles measured with the thermal conductivity detector for the oxidic precursors of iron, copper-iron and nickel-iron catalysts. With the pure iron catalyst profiles for the alumina and for the titania supported ones are presented. The reduction profiles of the iron-copper and... 

In the dynamic flow technique, a gas mixture of the desired concentration of adsorbate gas, such as nitrogen balanced with a non-adsorbing gas, usually helium, is flown across the sample. Nitrogen is adsorbed on the surface and the total amount is detected by a thermal conductivity detector. For each point of the isotherm, a different gas mixture and measurement cycle will be conducted. In this technique, a single-point measurement can be made to determine BET surface area, in a very short time, with certain assumptions (ASTM D4567, D5604). 

For thermal conductivity detectors. For flame Ionization detectors (FID), reproducibilities, R, are the same except in the 20 to 95 % recovered range where ... 

For measuring the inert species, some of which are present in the majority of gases, the thermal-conductivity detector (TCD) is often the detector of choice for gas analyses. Since the TCD is a concentration detector and its sensitivity is lower than that of mass-flow detectors such as the flame-ionization detector (FID), relatively high concentrations of compounds in the carrier gas are needed. This means that packed columns, with their high loadability, are still quite popular for such analyses. 

Thermal Conductivity Detector In the thermal conductivity detector (TCD), the temperature of a hot filament changes when the analyte dilutes the carrier gas. With a constant flow of helium carrier gas, the filament temperature will remain constant, but as compounds with different thermal conductivities elute, the different gas compositions cause heat to be conducted away from the filament at different rates, which in turn causes a change in the filament temperature and electrical resistance. The TCD is truly a universal detector and can detect water, air, hydrogen, carbon monoxide, nitrogen, sulfur dioxide, and many other compounds. For most organic molecules, the sensitivity of the TCD detector is low compared to that of the FID, but for the compounds for which the FID produces little or no signal, the TCD detector is a good alternative. 

The gas chromatograph (GC) is a Hewlett-Packard 5890 GC with a thermal conductivity detector. A 5A mole sieve column is used with argon carrier gas this gives peaks going in the same direction for both hydrogen and nitrogen. 

Catalytic activity for the selective oxidation of H2S was tested by a continuous flow reaction in a fixed-bed quartz tube reactor with 0.5 inch inside diameter. Gaseous H2S, O2, H2, CO, CO2 and N2 were used without further purification. Water vapor (H2O) was introduced by passing N2 through a saturator. Reaction test was conducted at a pressure of 101 kPa and in the temperature range of 150 to 300 °C on a 0.6 gram catalyst sample. Gas flow rates were controlled by a mass flow controller (Brooks, 5850 TR) and the gas compositions were analyzed by an on-line gas chromotograph equipped with a chromosil 310 coliunn and a thermal conductivity detector. 

The instrumentation for temperature-programmed investigations is relatively simple. The reactor, charged with catalyst, is controlled by a processor, which heats the reactor at a linear rate of typically 0.1 to 20 °C min . A thermal conductivity detector or, preferably, a mass spectrometer measures the composition of the outlet gas. 

The product gases were continuously analyzed for NO and NO2 using a chemiluminescent analyzer, and discontinuously for N2O, N2, CO, CO2 and O2 by GC equipped with a thermal conductivity detector and an electron capture detector, specifically for the N2O analysis, using a Poraplot Q column and a molsieve 5A column for separation. 

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). 

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