How to use gas chromatograph

I. Installation of chromatograph 
1. Requirements for chromatograph analysis room 
(1) There should be no strong magnetic field, flammable and highly corrosive gases around the analysis room.
(2) The indoor ambient temperature should be within the range of 5~35 degrees, the humidity should be less than or equal to 85% (relative humidity), and the room should maintain air circulation. If conditions permit, it is best to install air conditioning. 
(3) Prepare a work platform that can withstand the entire set of instruments, with moderate width and height and convenient for operation. Generally, cement platforms (0.6~0.8 meters high) are preferred in factories. The platform should not be close to the wall, but should be 0.5~1.0 meters away from the wall for easy wiring and maintenance.
(4) The power line capacity for the instrument should be around 10KVA, and the power supply used by the instrument should not share the same line with high-power consumption equipment or power consumption equipment that often changes greatly. The power supply must be well grounded. Generally, an iron rod (wire) about 0.5~1.0 meters long is nailed into the wet ground (or salt solution is poured), and then the power supply ground point is connected to it. In short, the grounding resistance is required to be less than 1 ohm. (Note: It is recommended that both the power supply and the shell be grounded for better results). 

2. Gas source preparation and purification 
(1) Gas source preparation Prepare high-pressure cylinders of the required gas in advance (generally available in large and medium-sized cities). The cylinder of a certain gas can only hold this gas. The color of each cylinder represents a gas and cannot be interchanged. Generally, nitrogen, hydrogen, and air are used. It is best to prepare two cylinders for each gas as a backup. Some factories can also use hydrogen generators and air compressors, but the air compressor must be oil-free. Whenever the cylinder pressure drops to 1~2Mpa, the cylinder should be replaced. Generally, manufacturers use 99.99% of the above gases. The electron capture detector must use a high-purity gas source of more than 99.999%. 
(2) Gas source purification In order to remove the moisture, ash and organic gas components that may be contained in various gases, the gas should be strictly purified before entering the instrument. If all cylinder gases are used, some chromatographs are equipped with purifiers, and are filled with 5A molecular sieves, activated carbon, and silica gel, which can basically meet the requirements. If a general hydrogen generator is used, the water purification process must be strengthened. Therefore, the drying tube area should be increased (preferably with a volume of more than 450 cubic centimeters and preferably with 5A molecular sieve as the filler), and a larger storage barrel should be connected after the generator to reduce or overcome the impact of gas source pressure fluctuations on the instrument baseline. If an air compressor is used as the air source, the air filter at the air compressor inlet should be strengthened, the purification tube volume should be increased, and the drying tube should be filled with half 5A molecular sieve and half activated carbon. Generally, domestic oil-free gas compressors (produced in Tianjin) can meet the needs. 

3. Chromatograph completeness inspection and placement 
After unpacking the instrument, check each item according to the list of accessories in the information bag, and properly store the spare parts of the vulnerable parts. Then, according to the requirements of the instrument's instruction manual, place it on the work platform, and connect the various parts of the instrument according to the wiring diagram and the plugs and sockets, and finally connect the recorder and data processor. Be careful not to connect the connectors incorrectly. 

4. Connection of external gas line 
(1) Installation of pressure reducing valve 
Some instruments are equipped with a pressure reducing valve. If not, you need to purchase one. Two oxygen and one hydrogen pressure reducing valves are used. Install the two oxygen pressure reducing valves and one hydrogen pressure reducing valve on the nitrogen, air and hydrogen cylinders respectively (note that the threads of the hydrogen pressure reducing valve are reversed, and add the attached O-shaped plastic gasket at the interface for sealing). After tightening the nut, close the pressure reducing valve adjustment handle (i.e. loosen it), open the cylinder high pressure valve, and the pressure reducing valve high pressure gauge should indicate at this time. After closing the high pressure valve, the indicated pressure should not drop, otherwise there is a leak, which should be promptly eliminated (sealed with a gasket or raw tape). Sometimes the high pressure valve will leak, so pay attention. Then rotate the adjustment handle to exhaust the remaining gas. 
(2) External gas line connection method: Introduce the gas in the cylinder into the chromatograph. Some use stainless steel pipes (φ2×0.5mm), and some use pressure-resistant plastic pipes (φ3×0.5mm). Plastic pipes are easy to operate, so they are generally used. If plastic pipes are used, stainless steel liner pipes (φ2×20mm) and some sealing plastic materials are required at the joints. The length of the plastic tube from the cylinder to the instrument depends on the need and should not be too long. Then use the plastic tube to connect the gas source and the instrument (gas inlet). 
(3) Leakage detection of the external gas line Close the valve knobs of the carrier gas, hydrogen, and air on the main engine gas line panel, then open the high-pressure valves of each cylinder, and adjust the output pressure of the low-pressure gauge on the pressure reducing valve to make the carrier gas and air pressure 0.35~0.6Mpa (about 3.5~6.0kg/cm3), and the hydrogen pressure 0.2~0.35 Mpa. Then close the high-pressure valve. At this time, the indication value of the low-pressure gauge on the pressure reducing valve should not drop. If it drops, it means that there is a leak in the connected gas line, which should be eliminated. 

5. Gas tightness check of the chromatograph gas line 
Gas tightness check is a very important task. If there is a leak in the gas line, it will not only directly lead to unstable operation or reduced sensitivity of the instrument, but also cause the risk of explosion. Therefore, this work must be carried out before operation (gas tightness check generally checks the carrier gas line. If the hydrogen and air flow lines have not been disassembled, they can be checked). 
The method is to open the chromatographic column box cover, remove the column from the detector, block the column port, then open the carrier gas flow path, adjust the low pressure output pressure to 0.35~0.6Mpa, open the carrier gas knob on the main panel, and the pressure gauge should indicate. Finally, close the carrier gas knob. The pressure indication value before the column should not drop within half an hour. If it drops, there is a leak and it should be eliminated. If there is a leak in the main engine, remove the relevant side panels of the main engine, use soapy water (preferably sodium dodecyl sulfate solution) to check for leaks one by one (hydrogen and air can also be used for leak detection), and finally wipe the soapy water dry. 

2. Instrument debugging After connecting the gas path, instruments, etc. as described above and placing them well, the following inspection and debugging work can be carried out. 
1. Inspection of various components of the chromatograph circuit Before starting the instrument, the carrier gas flow path should be connected first, and the carrier gas knob (i.e., carrier gas steady flow valve) on the main panel should be adjusted to make the carrier gas flow rate 20~30ml/min. 
(1) Start the main engine. Turn on the main power switch. The motor in the chromatographic column box starts working. Check if there is any abnormal sound. If there is, immediately cut off the power supply and further check and eliminate it. Some chromatographs self-diagnose when they start up and display the operation status of the instrument: normal or abnormal. Abnormal display includes which part has a problem, wiring error, etc. 
(2) Check each temperature control. According to the instructions, check the column temperature (including program temperature rise), injector temperature, and detector temperature one by one to see if they can be kept constant at high, medium, and low temperatures. In particular, the column temperature control accuracy is required to reach 0.01 degrees.

Precautions and methods for installation and commissioning of gas chromatography 
Release date: 
I. Installation of chromatograph 
1. Requirements for chromatograph analysis room 
(1) There should be no strong magnetic field, flammable and highly corrosive gases around the analysis room. 
(2) The indoor ambient temperature should be within the range of 5~35 degrees, the humidity should be less than or equal to 85% (relative humidity), and the room should maintain air circulation. If conditions permit, it is best to install air conditioning. (3 
) Prepare a work platform that can withstand the entire set of instruments, with moderate width and height and easy operation. In general, cement platforms (0.6-0.8 meters high) are preferred in factories. The platform should not be close to the wall, but should be 0.5-1.0 meters away from the wall to facilitate wiring and maintenance. 
(4) The power line capacity for the instrument should be around 10KVA, and the power supply for the instrument should not share the same line with high-power consumption equipment or power consumption equipment that often changes drastically. The power supply must be well grounded. Generally, an iron rod (wire) about 0.5-1.0 meters long is nailed into the wet ground (or salt solution is poured), and then the power supply grounding point is connected to it. In short, the grounding resistance is required to be less than 1 ohm. (Note: It is recommended that both the power supply and the casing are grounded for better results). 
2. Preparation and purification of air source 
(1) Gas source preparation 
: Prepare high-pressure cylinders of the required gas in advance (generally available in large and medium-sized cities). The cylinders of a certain gas can only hold this gas. The color of each cylinder represents a gas and cannot be interchanged. Generally, nitrogen, hydrogen, and air are used. It is best to prepare two cylinders for each gas as a backup. Some factories can also use hydrogen generators and air compressors, but the air compressor must be oil-free. Whenever the cylinder pressure drops to 1~2Mpa, the cylinder should be replaced. Generally, manufacturers use 99.99% of the above gases, and the electron capture detector must use a high-purity gas source of more than 99.999%. 
(2) Gas source purification: 
In order to remove the moisture, ash and organic gas components that may be contained in various gases, the gas should be strictly purified before entering the instrument. If all cylinder gases are used, some chromatographs are equipped with purifiers, and are filled with 5A molecular sieves, activated carbon, and silica gel, which can basically meet the requirements. If a general hydrogen generator is used, the water purification process must be strengthened. Therefore, the drying tube area should be increased (preferably with a volume of more than 450 cubic centimeters and preferably with 5A molecular sieve as the filler), and a larger storage barrel should be connected after the generator to reduce or overcome the impact of gas source pressure fluctuations on the instrument baseline. If an air compressor is used as the air source, the air filter at the air compressor inlet should be strengthened, the purification tube volume should be increased, and the drying tube should be filled with half 5A molecular sieve and half activated carbon. Generally, domestic oil-free gas compressors (produced in Tianjin) can meet the needs. 
3. Chromatograph completeness inspection and placement 
After unpacking the instrument, check each item according to the list of accessories in the information bag, and properly store the spare parts of the vulnerable parts. Then, according to the requirements of the instrument's instruction manual, place it on the work platform, and connect the various parts of the instrument according to the wiring diagram and the plugs and sockets, and finally connect the recorder and data processor. Be careful not to connect the connectors incorrectly. 
4. Connection of external gas line 
(1) Installation of pressure reducing valve 
Some instruments are equipped with a pressure reducing valve. If not, you need to purchase one. Two oxygen and one hydrogen pressure reducing valves are used. Install the two oxygen pressure reducing valves and one hydrogen pressure reducing valve on the nitrogen, air and hydrogen cylinders respectively (note that the threads of the hydrogen pressure reducing valve are reversed, and add the attached O-shaped plastic gasket at the interface for sealing). After tightening the nut, close the pressure reducing valve adjustment handle (i.e. loosen it), open the cylinder high pressure valve, and the pressure reducing valve high pressure gauge should indicate at this time. After closing the high pressure valve, the indicated pressure should not drop, otherwise there is a leak, which should be promptly eliminated (sealed with a gasket or raw tape). Sometimes the high pressure valve will leak, so pay attention. Then rotate the adjustment handle to exhaust the remaining gas. 
(2) External gas line connection method: 
Introduce the gas in the cylinder into the chromatograph. Some use stainless steel pipes (φ2×0.5mm), and some use pressure-resistant plastic pipes (φ3×0.5mm). Plastic pipes are easy to operate, so they are generally used. If plastic pipes are used, stainless steel liner pipes (φ2×20mm) and some sealing plastic materials are required at the joints. The length of the plastic tube from the cylinder to the instrument depends on the need and should not be too long. Then use the plastic tube to connect the gas source and the instrument (gas inlet). 
(3) Leakage detection of the external gas line 
Close the valve knobs of the carrier gas, hydrogen, and air on the main engine gas line panel, then open the high-pressure valves of each cylinder, and adjust the output pressure of the low-pressure gauge on the pressure reducing valve to make the carrier gas and air pressure 0.35~0.6Mpa (about 3.5~6.0kg/cm3), and the hydrogen pressure 0.2~0.35 Mpa. Then close the high-pressure valve. At this time, the indication value of the low-pressure gauge on the pressure reducing valve should not drop. If it drops, it means that there is a leak in the connected gas line, which should be eliminated. 

5. Gas tightness check of the chromatograph gas line 
Gas tightness check is a very important task. If there is a leak in the gas line, it will not only directly lead to unstable operation or reduced sensitivity of the instrument, but also cause the risk of explosion. Therefore, this work must be carried out before operation (gas tightness check generally checks the carrier gas line. If the hydrogen and air flow lines have not been disassembled, they can be checked). 
The method is to open the chromatographic column box cover, remove the column from the detector, block the column port, then open the carrier gas flow path, adjust the low pressure output pressure to 0.35~0.6Mpa, turn on the carrier gas knob on the host panel, and the pressure gauge should indicate. Finally, turn off the carrier gas knob, and the pressure indication value before the column should not drop within half an hour. If it drops, there is a leak and it should be eliminated. If there is a leak in the air path of the host, remove the relevant side panels of the host, use soapy water (preferably sodium dodecyl sulfate solution) to check for leaks at each joint (hydrogen and air can also be checked in this way), and finally wipe the soapy water dry.