Thermal conductivity detectors, lead

In a typical pulse experiment, a pulse of known size, shape and composition is introduced to a reactor, preferably one with a simple flow pattern, either plug flow or well mixed. The response to the perturbation is then measured behind the reactor. A thermal conductivity detector can be used to compare the shape of the peaks before and after the reactor. This is usually done in the case of non-reacting systems, and moment analysis of the response curve can give information on diffusivities, mass transfer coefficients and adsorption constants. The typical pulse experiment in a reacting system traditionally uses GC analysis by leading the effluent from the reactor directly into a gas chromatographic column. This method yields conversions and selectivities for the total pulse, the time coordinate is lost. 

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... 

A parallel detection to MS with a thermal conductivity detector is not found often in practice as the mass spectrometric analysis of gases is mostly carried out with specially configured MS systems (RGA, residual gas analyser, mass range <100 Da). Also, the parallel coupling of an FID does not lead to results which are complementary to those of MS, as both detection processes give practically identical total ion chromatograms. The response factors for most of the organic substances are comparable. A parallel MS detection to the FID can be used for a routine FID method development (see applications section). 

Thermal isolation. If the detector is used in a hot environment or is cooled, then it must have some thermal isolation from the environment. The required thermal impedance depends on the temperature difference between the cold-sink and the environment and, if cooled, the available cooling power. To achieve that isolation may require the use of special high-thermal-impedance materials (see Chapter 12, Cryogenics) in some cases, the package may have to be evacuated or backfilled with a low-thermal-conductivity gas. Both of these impose special cleaning ( outgassing ) requirements, and necessitate an evacuation ( pump-out ) port, and hermetic seals for any windows and electrical leads. These vacuum issues are described in Chapter 13 (Vacuum). 

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