author:seohtm Add the Time:2015-7-7 15:32:27 Click: 813

      GC detection system consists of a detector, an amplifier and a recorder and other components. GC detector performance requirements: versatility or private good; wide response range, can be used for constants and trace analysis; good stability, low noise; low dead volume, fast response; wide linear range, easy quantification; Operation simple and durable. GC detector detection feature classification can be divided according to their concentration detector and mass detector. GC detectors used are as follows:
     
     1. Thermal conductivity detector (thermal conductivity detector, TCD)
     Structure: load detecting pond thermal element body, made of thermal conductivity, thermal conductivity and then resistor Wheatstone bridge.
     Principle: The carrier gas hot hot heat conduction and forced convection thermistor power consumption arising from loss reached thermodynamic equilibrium, when there are components of the carrier gas into the thermal conductivity due to the thermal conductivity of different components of the carrier gas thermal equilibrium is broken, thermistor temperature changes, the resistance value will be changed, the output voltage of the Wheatstone bridge imbalance signal, the signal is recorded to obtain peaks.
     Applications: thermal conductivity detector is a versatile non-destructive concentration detector, in theory can be applied to the detection of any component, but because of low sensitivity, it is generally used for constant analysis.
     
     2. The flame ionization detector (flame ionization detector, FID)
     Structure: metal cylinder made shell, with internal combustion nozzle, the carrier gas and the components from the column effluent with hydrogen (if necessary as well as makeup) together to escape from the nozzle and combustion air around the nozzle. Near the nozzle fitted emitter and collector, forming an electric field between the poles.
     Principle: FID hydrogen combustion heat is generated in the air for energy, generated ions combustion component while forming ion flow in the electric field. Ionogenic mechanism components in the flame, so far is not very clear.
     Working conditions: temperature generally should prevent accumulation of water in more than 150 ℃; Hydrogen: Nitrogen: air = 1: 1: 10.
     Performance and application: FID is versatile destructive mass detector. High sensitivity, wide linear range, is widely used in the detection of constants and trace organics.
     
     3. NPD (nitrogen-phosphorus detector, NPD)
     Structure: Similar to a flame ionization detector, but between the flame nozzle and collector, equipped with the bead (silicate, rubidium, Rb2O · SiO2).
     Principle: Some researchers have proposed a number of different mechanisms, but they can not satisfactorily explain the experimental phenomena.
     Working conditions: two modes of operation, NP mode and P mode, the working conditions are not the same.
     Performance and application: NPD is a selective detector. When the NP mode of operation for the determination of organic compounds containing nitrogen and phosphorus; when P mode of operation for the determination of phosphorus-containing organic compounds. As selective detectors, the detection sensitivity of the compound is very high, less than other detector.
     
     The electron capture detector (electron capture detector, ECD)
     Structure: positive and negative electrodes and the detection chamber β- ray source, the best sources currently used are Ni63, no γ radiation decay, β-ray energy generated by a low, long half-life, it can be used to 400 ℃.
     Principle: The detection chamber β- ray particles emit radiation sources (primary electrons), and by detecting the carrier gas collision chamber secondary electrons and positive ions in the electric field, respectively, to the opposite polarity electrode movement themselves, forming detector room background current, when the component has a negatively charged (that is able to capture electronic components) into the testing room, testing indoor captured electrons becomes negatively charged ions, since the electrons are captured components, making detection Room reduce the background current generated inverted signal peaks.
     Working conditions: carrier gas is generally used in high-purity nitrogen, oxygen and trace gases can trace water pollution detection chamber must be purged to remove.
     Performance and application: ECD is a concentration-type selective detector for negatively charged components can give a very significant response signal.
     For analyzing a halogen compound, polynuclear aromatic hydrocarbons, some of the metal chelate and steroids.
     
     5. The flame photometric detector (flame-photometric detector, FPD)
     Structure: burning and is generally divided into two parts, a photoelectric; former flame combustion chamber, with similar FID, which by the filter and a photomultiplier tube and other components.
     Principle: The components in the hydrogen-rich (H2: O2> 3) components of the combustion flame to varying degrees, into fragments or atoms, each outer electron is excited due to the collision, when an electron from the excited state returns lower state or ground state, the emission wavelength of the spectral characteristics, the spectral characteristics of such selected by measuring interference filter (compounds containing phosphorus, sulfur, boron, nitrogen, halogens, etc. can produce this spectrum). Such as sulfur produced in the flame spectrum of 350-430nm, 480-600nm spectral phosphorus produced.
     Working conditions: the amount of hydrogen to be fed more than usual amount of hydrogen required for combustion, that is, in the case of the combustion of hydrogen-rich flame.
     Performance and application: FPD mass selective detector type, mainly used to determine the sulfur, phosphorus-containing compounds, the signal is almost a thousand times higher than the hydrocarbons. Widely used in analysis of trace sulfur compounds and organic phosphorus pesticide compounds in petroleum products.
     
     6. Other Detector: mass spectrometer, Fourier transform infrared spectroscopy, AED, SCD, ELCD, PID, HID and so on