1. Principle of gas chromatography
Chromatography, also called layer analysis, is a physical separation technology.
The principle of Ader separation is to distribute the components in the mixture between two phases. One phase is stationary and is called the stationary phase. The other phase is the fluid that pushes the mixture through the stationary phase and is called the mobile phase.
As the mixture contained in the mobile phase passes through the stationary phase, it interacts with the stationary phase. Due to the differences in properties and structures of each component, the magnitude of the interaction also varies.
Therefore, under the same driving force, the residence time of different components in the stationary phase may be longer or shorter, and then flow out of the stationary phase in sequence. This method uses the two-phase distribution principle to separate the components in the mixture. The technology is called chromatographic separation technology or chromatography. When gas is used as the mobile phase, it is called gas chromatography.
Chromatography has the following characteristics: high separation efficiency and fast analysis speed. High sample consumption and high sensitivity. It has the unparalleled advantages of many chemical analysis methods such as wide application range.
2. Working principle of gas chromatograph
Taking advantage of the different distribution coefficients of each component in the sample between the gas phase and the stationary liquid phase, when the vaporized sample is brought into the chromatographic column by the carrier gas for operation, the components are repeatedly distributed between the two phases. .
Due to the different adsorption or solubility capabilities of each component of the fixed phase, each component runs at different speeds in the chromatographic column. After a certain column length, they separate from each other, leave the chromatographic column and enter the detector in sequence, and the ions generated The flow signal is amplified and the chromatographic peaks of each component are plotted on the recorder.
3. Components of Gas Chromatograph
1）. Carrier gas system: including gas source, gas purification, gas flow rate control and measurement;
2）. Sampling system: including sample injector and vaporization chamber (instantly vaporizes liquid samples into steam);
3）. Chromatographic column and column temperature: including constant temperature control device (separating multi-component samples into single components);
4）. Detection system: including detector and temperature control device;
5）. Recording system: including amplifiers, recorders, or data processing devices, and workstations.
4. What is retention time?
The time required from the beginning of injection to the maximum value of the elution curve of each component can be used as a mark of the position of the chromatographic peak. This time is called retention time, represented by t.
5. What is a chromatogram?
When the chromatographic column effluent passes through the detector system after injection, the curve of the response signal time or carrier gas effluent volume is called a chromatogram.
6. What are chromatographic peaks? Peak area?
1）. The differential curve of the response signal generated when the components flowing out of the chromatographic column pass through the detector system is called the chromatographic peak.
2）. The area surrounded by the peak from the peak to the baseline is called the peak area.
7. How to measure the carrier gas flow rate?
High-end chromatographs are equipped with automatic testing devices. If there is no automatic testing device, a soap film flow meter can be used for measurement. Connect the soap film flow meter to the test outlet (you can also disconnect the chromatographic column from the detector and connect the soap film flow meter to the test outlet). one end of the column) and test the flow rate per minute.
After the measurement, the chromatographic temperature rises and the pressure gauge indication will increase. This is because the resistance of the chromatographic column to gas increases as the temperature increases. Do not lower the pressure. The steady flow indication will not change when the chromatographic temperature increases. Test carrier gas flow rate at room temperature.
8. How to control the carrier gas flow rate?
The flow rate of the carrier gas is mainly controlled by the pressure reducing valve on the high-pressure cylinder on the gas line. The pressure is then stabilized by the pressure stabilizing valve of the instrument, and then passed through the flow stabilizing valve to control the flow of the carrier gas stably. The pressure given by the pressure reducing valve must be Higher than the regulated pressure. Non-programmed temperature chromatography generally does not have a flow stabilizing valve and only relies on a pressure stabilizing valve to control the flow rate.
Post time: Jul-24-2024