Chromatographic carrier gas

Because of the limited mass range, the gas chromatograph carrier gas, which is typically either high-purity hydrogen or helium (both with amu of 2), does not interfere with the mass spectral analysis. The capillary column can be... 

Observed by release of ASH3, from a liquid nitrogen-cooled trap, not by gas chromatograph. Carrier gas velocity, 600cmVmin. 

Further support that reduction may be important for 2,3,7,8-TCDD is provided by the observation that it undergoes reduction to the lower chlorinated isomers in electron Impact mass spectrometry when hydrogen is used as the gas chromatographic carrier gas (28). 

Figure 1.8 shows the basic parts of a simple gas chromatograph—carrier gas, flow controller, injector, column, detector, and data system. More detail is given in the next chapter. 

Helium Chromatographic Carrier Gas and Different Reagent Gases... 

Methane gas served as both the gas chromatographic carrier gas and the reagent gas in the chemical ionization source (at 1000 y pressure). The mass spectrometer was operated in the selected ion recording mode, and the quasimolecular ions of PF and Ara-Virazole were monitored at m/e 692 and m/e 517, respectively two fragment ions (loss of methyl group) were also monitored. A calibration curve was established using known amounts of PF added to pooled human serum. The observed areas of PF and the internal standard were used to calculate area ratios which, in turn, were used to determine the amount of PF in serum. Using this method minimum detectable quantity is 10 ng/ml serum lowest level at which quantification is still reliable is 100 ng/ml serum. 

Place the cylinder in a vertical position and repressure to 1723 kPa gage (250 psig) with the chromatographic carrier gas through the valve at the top of the cylinder, ensuring that no air enters during the operation. 

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. 

The technique just described requires the porous medium to be sealed in a cell, so It cannot be used with pellets of irregular shape or granular material. For such materials an alternative technique Introduced by Eberly [64] is attractive. In Eberly s method the porous pellets or granules are packed into a tube through which the carrier gas flows steadily. A sharp pulse of tracer gas is then injected at the entry to the tube, and Its transit time through the tube and spreading at the exit are observed. A "chromatographic" system of this sort is very attractive to the experimenter,... 

In gas chromatography (GC) the sample, which may be a gas or liquid, is injected into a stream of an inert gaseous mobile phase (often called the carrier gas). The sample is carried through a packed or capillary column where the sample s components separate based on their ability to distribute themselves between the mobile and stationary phases. A schematic diagram of a typical gas chromatograph is shown in Figure 12.16. 

A variable-size simplex optimization of a gas chromatographic separation using oven temperature and carrier gas flow rate as factors is described in this experiment. 

Dynamic headspace GC/MS. The distillation of volatile and semivolatile compounds into a continuously flowing stream of carrier gas and into a device for trapping sample components. Contents of the trap are then introduced onto a gas chromatographic column. This is followed by mass spectrometric analysis of compounds eluting from the gas chromatograph. 

Separator GC/MS interface. An interface in which the effluent from the gas chromatograph is enriched in the ratio of sample to carrier gas. Separator, molecular separator, and enricher are synonymous terms. A separator should generally be defined as an effusion separator, a jet separator, or a membrane separator. 

Avoid chromatographs requiring mixed carrier gas. Mixed carrier gas can introduce as many inherent accuracy problems as calibration gas, maybe more. There is almost always a way to avoid using mixed carrier gas. Find a way even if it is more expensive. 

Carrier gas An inert gas that moves the sample through the column of a gas chromatograph. 

Typically the effluent from a gas chromatograph is passed through a detector, which feeds a signal to a recorder whenever a substance different from pure carrier gas leaves the column. Thus, one... 

---