Carrier gas selection

The detectors you will use will dictate your first choice of gases and later other factors defined in your analysis methods will finalize the carrier-gas selection process (1). Table 10.1 lists popular detectors for a gas chromatograph and the gases used with each detector. Table 10.2 provides guidelines for a chromatograph equipped with two flame ionization detectors that requires carrier gas, fuel, and an oxidant gas. Also provided are guidelines for makeup gas and other gas flows typical for these types of systems (2,3). Consult your instruction manual for specific gas requirements for your instruments. 

Safety and cost of carrier gases play a role in carrier-gas selection. Our concern for safety deals with the fact that colunms do break in ovens. Many analysts are concerned with using hydrogen as a mobile phase because of this fact. In the United States, hehum is inexpensive and readily available in high purity. For this reason, in the United States, the most conunon choice of carrier gas for capillary columns is helium. 

The extent and manner of NDE applied in different shipyards has been the subject of a recently completed exercise within LR. The exercise involved randomly selected shipyards building ship types which included oil tankers, bulk carriers, gas carriers, container ships, ro-ro and general cargo ships. The variation in extent of applied NDE that was observed is summarised in Table 1. 

Membrane separator. A separator that passes gas or vapor to the mass spectrometer through a semipermeable (e.g., silicon) membrane that selectively transmits organic compounds in preference to carrier gas. Membrane separator, membrane enricher, semipermeable membrane separator, and semipermeable membrane enricher are synonymous terms. 

The laser spray process uses a high power carbon dioxide laser focused onto the surface of the part to be metallized. A carrier gas such as belium blows metal particles into the path of the laser and onto the part. The laser melted particles may fuse to the surface, or may be incorporated into an aHoy in a molten surface up to 1-mm thick. The laser can be used for selective aHoying of the surface, for production of amorphous coatings, or for laser hardening. 

One of the methods of controlling air pollution mentioned in the previous chapter was pollution removal. For pollution removal to be accomplished, the polluted carrier gas must pass through a control device or system, which collects or destroys the pollutant and releases the cleaned carrier gas to the atmosphere. The control device or system selected must be specific for the pollutant of concern. If the pollutant is an aerosol, the device used will, in most cases, be different from the one used for a gaseous pollutant. If the aerosol is a dry solid, a different device must be used than for liquid droplets. 

Not only the pollutant itself but also the carrier gas, the emitting process, and the operational variables of the process affect the selection of the control system. Table 29-1 illustrates the large number of variables which must be considered in controlling pollution from a source (1-4). 

Conditions apparatus, Hewlett-Packard HP5890 equipped with an HP5972 mass-selective ion detector (quadruple) column, PTE-5 (30 m x 0.25-mm i.d.) with 0.25- am film thickness column temperature, 50 °C (1 min), increased at 20 °C min to 150 °C(5 min) and then at 4 °Cmin to 280 °C (30 min) inlet and detector (GC/MS transfer line) temperature, 250 and 280 °C, respectively gas flow rate, He carrier gas ImLmin" injection method, splitless mode solvent delay, 3 min electron ionization voltage, 70eV scan rate, 1.5 scanss scanned-mass range, m/z 50-550. The retention times of benfluralin, pendimethalin and trifluralin are 15.2, 25.1 and... 

Mass-selective detector, MSD5971A Temperature 280 °C Target ion m z 173 Reference ion m z 323 Helium carrier gas, O.bmLmin ... 

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