Gas chromatographs are widely used in biochemistry, petrochemical, medical and environmental protection, etc. It can not only be applied to quantitative and qualitative analysis, but also can determine the physical and chemical constants such as distribution coefficient, activity coefficient, molecular weight and specific surface area of the sample on the stationary phase.
The performance of different portable gas chromatographs determines the Detectors with different detection principles. This paper mainly analyzes the main characteristics and performance of several common portable gas chromatographs according to the detection principles of different Detectors.
1. Hydrogen flame Detector gas chromatograph
Hydrogen Flame Detector FID (Flame Ionization Detector)
It uses a hydrogen flame as an ionization source to ionize the measured substance and generate micro-electricity
flow Detector. It is a typical mass type Detector. The outstanding advantage is that it responds to almost all organic substances, especially the high sensitivity to hydrocarbon compounds, and the response value is proportional to the number of carbon atoms; it is not sensitive to inorganic substances such as H2O, CO2 and CS2; it is sensitive to gas flow rate, pressure and Insensitive to temperature changes. It has a wide linear range, simple structure, convenient operation, and almost zero dead volume. Therefore, as a laboratory instrument, FID has been widely used and is a commonly used gas chromatographic Detector.
The main disadvantage of FID is that it needs three kinds of gas source steel cylinders of combustible gas (hydrogen), combustion-supporting gas and carrier gas and its flow rate control system. Therefore, it is very difficult to make an integrated portable instrument, especially for the analysis and detection of sudden environmental pollution incidents, and there are potential dangers of ignition and explosion. The GC-190 miniature portable gas chromatograph launched by Shanghai Precision Scientific Instrument Co., Ltd. is mainly characterized by on-column heating with a temperature range of 25 to 250 °C, a miniature FID Detector with a sensitivity of 5 × 10 - 11 g/s; a linear range of 105, hydrogen as carrier gas. The main disadvantage of using hydrogen as a carrier gas is that it is difficult to control the hydrogen flame stability when adjusting the flow rate of the carrier gas.
2. Thermal conductivity Detector gas chromatograph
Thermal Conductivity Detector TCD (Thermal Conductivity Detector) is a concentration-type Detector that responds to the difference in thermal conductivity between the measured component and the carrier gas. It is an overall performance Detector and belongs to the detection method of physical constants. The basic theory, operating principle and response characteristics of thermal conductivity Detectors have been matured since the 1960s. Because it responds to all substances, has simple structure, reliable performance, accurate quantification, low price, durability, and is a non-destructive Detector, TCD is always full of vigorous vitality. In the past ten years, the output configured in commercial gas chromatograph is second only to FID, and its application range is wider.
Compared with other Detectors, the sensitivity of TCD is low, which is the main factor affecting its application in environmental analysis and detection. When helium is used as carrier gas and the gas flow is 2 m L, the detection limit can reach the order of 10 - 6 . Therefore, the portable gas chromatograph using this Detector is not suitable for the analysis and detection of general environmental pollutants indoors and outdoors, and is mostly used for the analysis and detection of pollution sources and sudden environmental pollution accidents.
3. GDD (Gas Density Detector)
Not only can many complex
It can perform qualitative and quantitative analysis of complex organic and inorganic mixtures, and can measure the molecular weight of substances. Therefore, it can be used to set the analysis correction factors of many substances, which is also an outstanding advantage of this Detector.
4. Electron capture Detector gas chromatograph
Electron capture Detector ECD (Electron Capture Detect-tor) is suitable for detecting compounds with high electron affinity such as halogenated hydrocarbons, and has high sensitivity. However, because it uses the radioactive isotope 63Ni, according to relevant Chinese laws, it is not suitable to be made into a portable gas chromatograph that can be moved at will.
This position mainly excerpts Guo Bing's "Gas Chromatograph and Its Application"
