Gas chromatographic carrier gas selection and carrier gas flow rate
Time:2019/01/24
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Typical carrier gases include helium, nitrogen, argon, hydrogen, and air 10ml Gc vials. In general, the choice of carrier gas depends on the type of detector. For example, a discharge ionization detector (DID) requires helium as a carrier gas. However, when analyzing a gas sample, the carrier gas is sometimes selected based on the parent of the sample. For example, when analyzing a mixture in argon, it is preferable to use argon as a carrier gas because this avoids chromatography. The peak of argon appears in the figure. Safety and availability also affect the choice of carrier gas, for example, hydrogen is flammable, while high purity helium is difficult to obtain in some areas. (See: Helium - Distribution and Production) Many times, the detector not only determines the type of carrier gas, but also determines the purity of the carrier gas (although the sensitivity requirements also greatly affect the purity of the carrier gas). ). Generally, the carrier gas used in gas chromatography should have a purity of 99.995% or more.
Typical trade names for identifying purity include "zero gas grade", "high purity (UHP) grade", "4.5 grade" and "5.0 grade". [4] The effect of carrier gas flow rate on the analysis is similar in mode to temperature (see below). The higher the carrier gas flow rate, the faster the analysis speed, but the worse the resolution. Therefore, the choice of the optimum carrier gas flow rate, as well as the choice of column temperature, requires a balance between analytical speed and resolution. The carrier gas flow rate of a gas chromatograph produced before the 1990s is often controlled by the pressure at the carrier gas inlet (column pressure), and the actual carrier gas flow rate is passed through the flowmeter or soap membrane at the outlet end of the column. The measurement was carried out. Such a process is often complex, time consuming, and often frustrating. During the entire operation, the pressure in front of the column cannot be changed and the air flow must be stable. The relationship between the gas flow rate and the pre-column pressure can be calculated from the Poiseuille equation of the compressible fluid. However, many modern gas chromatographs have been able to automatically determine the gas flow rate using a circuit and control the flow rate by automatically controlling the column front pressure. Therefore, the carrier pressure and flow rate can be adjusted during operation 10ml Gc vials. The pre-column pressure/flow control program (similar to the temperature control program) appears.
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