1) Thermal conductivity detector The thermal conductivity detector (TCD) of the gas chromatograph belongs to the concentration detector, that is, the response value of the detector is proportional to the concentration of components in the carrier gas. Its basic principle is that different substances have different thermal conductivity and respond to almost all substances, so it is the most widely used universal detector. Because the sample is not destroyed in the detection process, it can be used for preparation and other joint identification techniques. 2) Hydrogen flame ionization detector (FID) of gas chromatograph uses the chemical ionization of organic matter under the action of hydrogen flame to form ion flow, and detects it by measuring the intensity of ion flow. The detector has the advantages of high sensitivity, wide linear range, light working conditions, low noise and small dead volume, and is a common detector for detecting organic compounds. However, the samples are destroyed in the detection process, and generally only those organic compounds that burn in hydrogen flame and produce a large number of carbocation can be detected. 3) Electron Capture Detector The electron capture detector (ECD) of the gas chromatograph uses the ability of electronegative substances to capture electrons and detects them by measuring the electron flow. ECD has the characteristics of high sensitivity and good selectivity. It is the only detector and the most effective detector for analyzing trace electronegative organic compounds at present. The stronger the electronegativity of the element, the higher the sensitivity of the detector and the higher the response to compounds containing halogen, sulfur, oxygen, carbonyl and amino. Electron capture detector has been widely used in the analysis and determination of organochlorine and organophosphorus pesticide residues, metal complexes, metal-organic polyhalides or polysulfides. It can use nitrogen or argon as carrier gas, and the most commonly used is high purity nitrogen. 4) Flame photometric detector (FPD) has high sensitivity and selectivity for sulfur-containing and phosphorus-containing compounds. The detection principle is that when phosphorus-containing and sulfur-containing substances burn in hydrogen-rich flame, they emit characteristic spectra respectively, and the intensity of characteristic light is measured by photomultiplier tube through interference filter. 5) The mass spectrometer detector (MSD) of mass spectrometer gas chromatograph is a kind of mass and universal detector, and its principle is the same as that of mass spectrometry. It can not only give the chromatogram (total ion current chromatogram or reconstructed ion current chromatogram) that can be obtained by general GC detector, but also give the mass spectrum corresponding to each chromatographic peak. Computer automatic retrieval of standard library can provide analytical structure information of compounds, which is an effective tool for qualitative analysis of gas chromatography.