Scavenger gases

Another interesting aspect of perfluorinated liquids is their high gas solubility. They can provide highly effective gas transport in chemical reactions and physical processes. In addition, PFCs can be used to absorb or scavenge gases. Table 6.8 shows the solubility of various gases in a perfluorohexane. 

Thiophene absorbs very strongly below 2400 A, and the transition is probably of the n, n ) type. The photochemistry of thiophene is very complex but thorough investigation of the effects of wavelength of irradiation (2139 and 2288 A), temperature (25-305 °C), pressure, light intensities and inert and scavenger gases such as O2 has shown that at least three intermediates lead to the observed products , viz. 

Atomic emission detector (AED) 1 X 10 g to 2 X 10" g of each element 1 X 10 to 1 X 10 10 to 10, element to element Requires the use of ultra high purity carrier and plasma gases Plasma produced in a microwave cavity operated at 2450 MHz Scavenger gases (H2, O ) are used as dopants Photodiode array is used to detect emitted radiation... 

Almost all of the excess kinetic recoil energy of the atoms is lost in various collision processes before the kinetic energy is low enough to permit the formation of a stable bond with any substrate molecule. The substrate alkene or alkyne is normally present as a minor component mixed with the source gas other scavenger gases, such as HI, are often present as well. 

The specified problems have served as the reason of that many industrial gas emissions at all are not exposed to clearing. As an example, it is possible to result smoke gases of the factories of metallurgy, power engineering, chemical, petrochemical and other industries, tank and scavenging gases of the various factories, emissions of a dust and steams of organic dissolvents in the production areas of the factories[21-24]. 

Fig. 15.6 Chromatogram of a standard mixture containing 11 organohalides. Stationary phase, SE-52 33mx0.3mm id, inj. temp. 200°C, column temp. 50°C, interface 250°C, detector temp. 250°C. Helium carrier gas flow rate 36ml s-1, scavenger gas flow 30mL...

Under our optimized sampling conditions, no blocking of the trap (visually verified at the manometer of the scavenging gas circuit) and no losses of volatiles during the adsorption phase (sensorially verified at the odor port) were observed. 

Chromatographic System Use a suitable gas chromatograph that is equipped with independent dual flame-ionization detectors and contains a 0.6-m x 6.35-mm (od) stainless-steel U-tube packed with Porapak P or equivalent. Use helium as the carrier gas at a flow rate of 60 mL/min, hydrogen as the fuel gas at a flow rate of 52 mL/min for each flame, and air as the scavenger gas for both flames at a flow rate of 500 mL/min. To ensure that the relative standard deviation does not exceed 2.0%, chromatograph a sufficient number of replicates of each Standard Preparation, and record the areas as directed under Procedure (see Chromatography, Appendix IIA). 

One of the auxiliary Tenax tubes (1) was placed inside the desorption oven (2), located upstream of the fixed Tenax trap (3) (0,2 g Tenax GC, 60-80 mesh, packed into a 7 cm by 2 mm i.d. stainless steel tube). At controlled temperature (lOO C) and low pressure (1,5 psl) the oven was flushed by a 25 mL/min flow of Helium for 10 min. Desorbed and diluted in scavenging gas (a), the volatiles were then concentrated and trapped in the Tenax trap, cooled to -30°C by circulation of liquid nitrogen. By switching a rotary valve (4), carrier gas (b) flowed through the trap... 

Figure 2. Schematic diagreun of the D.C.I. system a) scavenger gas b) carrier gas...

Addition of a scavenger gas such as SF6 or a chlorinated solvent to the source region will prevent corona discharge [48,49], but is generally less practical than simply lowering the capillary voltage. 

CoupUng capillary columns to the electron capture detector is not without problems. Unlike the flame detectors, relatively large detector cells are common due to certain constructional features of the ionization detectors housing a radioactive source. The use of a scavenger gas or a detector miniaturization are the currently used remedies to this problem. The miniaturization approach is obviously more attractive due to the concentration-sensitive nature of the detector, as already discussed above. 

Let us use the falling drop approach. The rate of increase of the concentration Caq of an irreversibly scavenged gas in a droplet can be estimated by a mass balance between the rate of increase of the mass of species in the droplet and the rate of transport of species to the drop... 

The response factor of an ELSD largely depends on the size of analyte particles entering the detection chamber. After exiting from the HPLC column, the eluent stream is nebulized, and a scavenger gas stream carries the effluent cloud through a hot drift tube where the solvent vaporizes. The droplet shrinks to the volume of the non-volatile material contained in the eluent. The average particle size in the cloud at a given time and the particle size distribution can be derived from the elution profile of the analyte and... 

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