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The Basic Principles and Characteristics of Several Types of Gas Analyzers (1)

The Basic Principles and Characteristics of Several Types of Gas Analyzers (1)


1. Basic principles of mass spectrometer

The mass spectrometer is an instrument that separates and detects different isotopes. It is based on the principle that charged particles can be deflected in an electromagnetic field, and is a type of instrument that separates and detects material composition according to the difference in mass of material atoms, molecules or molecular fragments.

The specific working process is: the mass spectrometer takes the ion source, mass analyzer and ion detector as the core. The ion source is a device that ionizes sample molecules under high vacuum conditions. The ionized molecules will be further fragmented into smaller masses of fragment ions and neutral particles due to excessive energy. They get the average kinetic energy with the same energy under the action of the accelerating electric field and enter the mass analyzer.

The mass analyzer is a device that separates the ions of different masses entering it at the same time according to the charge-to-mass ratio q/m (q is charge, m is mass). The principle formula:
q/m=2U/B²r²
(U is the voltage, B is the magnetic induction intensity, and r is the radius). The separated ions sequentially enter the ion detector, collect and amplified ion signals, and are processed by a computer to draw a mass spectrum.

Advantages: The gas analyzer equipment can measure multiple gases, with fast test speed, high sensitivity, accurate results, high stability and repeatability.

2. Basic principles of gas chromatograph

The detection mixture consists of a carrier gas (the carrier gas is an inert gas and should not react with samples and solvents. Generally available and commonly used carrier gases are hydrogen, nitrogen, and helium. Helium has the best separation column effect, and helium is used For thermal conductivity measurement components, hydrogen is used when helium cannot be used, and the other is a mixture of helium and hydrogen for faster response), and the detection mixture passes through the chromatographic column (usually packed column and capillary column) interacts with the stationary phase in the chromatographic column (the filler that does not move in the chromatographic column, and the separation is called the stationary phase). The difference in the size of this interaction makes the components of each mixture flow out in order and are introduced in sequence Detector to obtain the detection signal of each component.

According to the order of introduction into the detector, after comparison, it is possible to distinguish which component is, and the content of each component can be calculated according to the peak height or peak area.

Gas chromatographs have different advantages because of different detectors.

(1) Hydrogen flame detector gas chromatograph.

The flame ionization detector (FID, flame ionization detector) is a detector that uses a hydrogen flame as an ionization source to ionize the measured substance and generate a micro current.

Advantage:
Responds to almost all organic substances, especially high sensitivity to meridian compounds, and the response value is proportional to the number of carbon atoms; insensitive to inorganic substances such as H:0, CO2 and CSz; insensitive to gas flow rate, pressure and temperature changes. It has a wide linear range, simple structure, convenient operation, and almost zero dead volume. Therefore, as a laboratory instrument, FID is widely used and is the most commonly used gas chromatography detector.

(2) Thermal conductivity detector gas chromatograph.

The thermal conductivity detector (TCD, thermal conductivity detector) is a concentration-type detector that uses the difference in thermal conductivity of the measured component and the carrier gas to respond (within a certain concentration range (linear range), the response value R (detection signal) is proportional to the concentration of the measured component in the mobile phase (R∝C)). It is an overall performance detector and a physical constant detection method.

Advantage:
It responds to all substances, simple structure, reliable performance, accurate quantification, low price, durable, and it is also a non-destructive detector.


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