Special carrier gases

Special carrier gases. These include mixtures such as 8.5 percent hydrogen in helium. 

This type of analysis requires several chromatographic columns and detectors. Hydrocarbons are measured with the aid of a flame ionization detector FID, while the other gases are analyzed using a katharometer. A large number of combinations of columns is possible considering the commutations between columns and, potentially, backflushing of the carrier gas. As an example, the hydrocarbons can be separated by a column packed with silicone or alumina while O2, N2 and CO will require a molecular sieve column. H2S is a special case because this gas is fixed irreversibly on a number of chromatographic supports. Its separation can be achieved on certain kinds of supports such as Porapak which are styrene-divinylbenzene copolymers. This type of phase is also used to analyze CO2 and water. 

A sensitive determination of organotin compounds in sediments is based on separation of the chlorides R SnCl4- , n = 1-3, R = Me, n-Bu, Ph, by GC-FPD or GC-ECD using a DB-608 open tubular column with HC1 doping of the carrier gas LOD 30 ng Sn/g of sediment77. A modification of this method uses GC-FPD with DB-1 capillary column and a 611.5 nm filter. The column requires special pretreatment with an HBr/EtOAc solution78. 

In the Philips total oxygen demand meter the zirconium oxide is specially prepared and is in the form of two series connected tubes or cells through which a nitrogen carrier gas is allowed to flow. Each cell is provided with two pairs of annular (internal and external) electrodes and the whole assembly is maintained at about 600°C. 

Both the GC-MS and GC-IR instruments obviously require that the column effluent be fed into the spectrometer detection path. For the IR instrument, this means that the IR cell, often referred to as a light pipe, be situated just outside the interferometer (Chapter 8) in the path of the light, of course, but it must also have a connection to the GC column and an exit tube where the sample may possibly be collected. The infrared detector is nondestructive. With the mass spectrometer detector, we have the problem of the low pressure of the mass spectrometry unit coupled with the ambient pressure of the GC column outlet. A special method is used to eliminate carrier gas while retaining sufficient amounts of the mixture components so that they are measurable with the mass spectrometer. 

Between the early 1950s, when the dual viscous-flow mass spectrometer was introduced by Nier and the mid 1980s only minor modifications have been made on the hardware of commercial mass spectrometers. Special efforts have been undertaken in the past years to reduce the sample size for isotope measurements. This has led to a modification of the classic dual inlet technique to the continuous-flow isotope ratio monitoring mass spectrometer in which the gas to be analyzed is a trace gas in a stream of carrier gas, which achieves viscous-flow conditions. Today, the majority of gas mass spectrometers are sold with the continuous flow system, instead of the dual inlet system. 

We point out here that the colloid prepared by these methods is very clean, because the carrier gas used is usually high-purity grade at six-nine, the chamber is once evacuated to depress the extent of contaminating oxygen and moisture, and the liquids themselves are always purified by sublimation process except for the solution trap method. To transfer the colloidal suspension after preparation, a specially designed stock bottle with a Luer-lock syringe is normally used in order to enable the operations under Ar flow to avoid unexpected air contamination. Therefore, we can carry the suspension liquid away from the production chamber without exposure to air, which means that the surface of colloidal metal is very clean if it does not react with suspension liquids. 

After concentration of the extract by microdistillation [25] or by special procedures [26] to facilitate the identification of the odorants, an aliquot is separated by high-resolution GC and the effluent is split into a flame ionisation detector (FID) and a sniffing port [27]. The positions of the odorants in the gas chromatogram are assessed by sniffing the carrier gas as it flows from the port. This procedure is denoted GC-O. 

In some cases (see below) a KF drying oven is required to get the water from a sample into the titration vessel. For these special cases, a solid sample (usually) is placed into a specially designed KF oven where the sample is heated, and the water goes into the vapor phase. A stream of dry carrier gas (usually, N2 or air) sweeps the liberated moisture into the reaction vessel, where it is titrated by either the coulometric or the volumetric method. It is critical that the carrier gas is dry and that there are no leaks along the pathway to the reaction vessel. Passing the carrier gas over activated molecular sieve prior to the sample will ensure that the gas is dry. 

Special care has to be taken, however, that the quinoline titer truly represents the minimum amount of catalyst poison. In most cases this type of base is adsorbed by inactive as well as active sites. Demonstration of indiscriminate adsorption is furnished by the titration results of Roman-ovskii et al. (52). These authors (Fig. 13) showed that introduction of a given dose of quinoline at 430°C in a stream of carrier gas caused the activity of Y-zeolite catalyst (as measured by cumene conversion) to drop with time, reach a minimum value, then slowly rise as quinoline was desorbed. The decrease in catalytic activity with time is direct evidence for the redistribution of initially adsorbed quinoline from inactive to active centers. We have observed similar behavior in carrying out catalytic titrations of amorphous and crystalline aluminosilicates with pyridine, quinoline, and lutidine isomers. In most cases, we found that the poisoning effectiveness of a given amine can be increased either by lengthening the time interval between pulse additions or by raising the sample temperature for a few minutes after each pulse addition. 

For loop jet mills, air or carrier gas is also injected into a grinding loop or race track through specially designed nozzles. Solid particle are injected into this... 

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