The gas chromatograph consists of several main parts: a cabinet, which plays the role of supporting components, a column temperature box, which is used to heat the chromatographic column; 2. Gas path part, which provides the gas required by all components of the chromatograph; 3, sampling device, ready for sampling parts; 4. Detector, which plays the role of sample detection; 5 denotes a circuit part providing temperature control and detector signal amplification and output control.

Working principle of thermal conductivity detector: Thermal conductivity detector is a detection device composed of thermal resistance sensors, which is based on the principle of gas thermal conductivity and thermal resistance effect. The thermal resistance of the detector is a heat conducting element made of rhenium tungsten wire. It is installed in the gas chamber of metal (stainless steel or brass) thermal conductivity cell and connected to form a typical Whiston bridge circuit.

When the composition and flow rate of the carrier gas flowing in the gas chamber of the thermal conductivity cell are stable, the temperature of the thermal conductivity cell body is constant, and the current flowing through the tungsten-rhenium wire thermal resistor is constant, the thermal energy generated on the thermal resistor is balanced with the thermal energy lost by factors such as the carrier gas conducting heat to the cell body, and the bridge circuit composed of the tungsten-rhenium wire thermal resistor is in a balanced state. When the measured gas composition is brought into the gas chamber by carrier gas, a series of changes have taken place: the gas composition in the gas chamber has changed? Change of thermal conductivity of mixed gas? Temperature change of thermal resistance? Resistance change of thermal resistance? When the bridge balance is broken, the corresponding electrical signal is output, which has a certain linear function relationship with the measured gas concentration and is recorded by the secondary signal recorder. This is the working principle of thermal conductivity detection for gas analysis.

Working principle of electron capture detector: The radiation (β-ray) generated by the sealed radioactive source (63Ni) in ECD detector unit ionizes inert gas (nitrogen), and pulse voltage is applied to the electrode of the detector to capture electrons and generate current. Strong electronegative molecules with strong electron absorption ability enter it, absorb electrons and form negative ions. Because molecules with negative ions move slower than free electrons, the time to reach the positive electrode increases, and the probability of recombination with positive ions increases, which reduces the electron density in the detector and the number of electrons captured by one pulse. According to the decreasing degree of the number of electrons, multiple pulses are added to ensure that the total number of electrons per unit time, that is, the current, remains unchanged, and the change of the number of pulses is directly proportional to the density of strongly electronegative molecules.