How to use gas chromatograph

Method of using gas chromatograph 1. Requirements for chromatograph analysis room (1) There must be no strong magnetic field, flammable and strong corrosive gas around the analysis room. (2) The indoor ambient temperature should be in the range of 5 to 35 degrees, the humidity is less than or equal to 85% (relative humidity), and the indoor air circulation should be maintained. Conditional factories are best equipped with air conditioners.

How to use gas chromatograph

1. Requirements for chromatograph analysis room

(1) There must be no strong magnetic field, flammable and strong corrosive gas around the analysis room.

(2) The indoor ambient temperature should be in the range of 5 to 35 degrees, the humidity is less than or equal to 85% (relative humidity), and the indoor air circulation should be maintained. Conditional factories are best equipped with air conditioners.

(3) Prepare a working platform that can withstand the entire set of instruments, has a moderate width and height, and is easy to operate. Generally, a cement platform is preferred in the factory (0.6 to 0.8 meters high). The platform cannot be close to the wall, and should be 0.5 to 1.0 meters away from the wall, which is convenient for 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 a line with high-power power-consuming equipment or frequently-changed electrical equipment. The power supply must be well grounded. Generally, an iron rod (wire) with a length of about 0.5 to 1.0 meters is nailed to the wet ground (or salt solution infusion), and then the power supply ground point is connected to it. In short, the grounding resistance should be less than 1 ohm. (Note: It is recommended that both the power supply and the case are grounded, so that the effect is better).

2. Air source preparation and purification

(1) Gas source preparation Prepare high-pressure steel cylinders that require gas in advance (usually available in large and medium-sized cities). Zhuang's gas cylinders can only contain this gas, and the color of each cylinder represents a gas. Not interchangeable. Generally, three kinds of gases, nitrogen, hydrogen, and air are used. It is best to prepare two cylinders for each gas for future use. Some plants may use hydrogen generators and air compressors, but the air compressor must be oil-free. When the cylinder pressure drops to 1 ~ 2Mpa, the cylinder should be replaced. Generally, the manufacturer can use 99.99% of the above gas, and the electronic capture detector must use more than 99.999% of the high-purity gas source.

(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 gas is used, some chromatographs are equipped with purifiers and filled with 5A molecular sieves, activated carbon, silica gel, which can basically meet the requirements. If the general hydrogen generator is used, the purification of water must be strengthened, so the area of ​​the drying tube should be increased (the volume is more than 450 cubic centimeters, the filler is preferably 5A molecular sieve), and the volume is larger after the generator To reduce or overcome the impact of the gas source pressure fluctuation on the instrument baseline. If an air compressor is used as the air source, the air inlet of the air compressor should be strengthened for air filtration and the volume of the purification tube should be increased. The drying tube should be filled with half 5A molecular sieve and half activated carbon. General domestic oil-free gas compressors can meet the needs.

3. Complete set inspection and placement of chromatograph

After unpacking the instrument, according to the list of accessories in the data bag, carry out an item-by-item inventory and keep spare parts of vulnerable parts properly. Then place it on the working platform according to the requirements of the instrument's instruction manual, and connect the various parts of the instrument to the wiring diagram and the plugs and sockets, and finally connect the recorder and data processor. Be careful not to misconnect each connector.

4. Connection of external gas circuit

(1) Installation of pressure reducing valve

Some instruments are equipped with a pressure relief valve, if not, they must be purchased. Two oxygen valves and one hydrogen pressure reducing valve were used. Install 2 oxygen pressure reducing valves and 1 hydrogen pressure reducing valve to nitrogen, air and hydrogen cylinders respectively (note that the hydrogen pressure reducing valve thread is reversed, and add the attached O-shaped plastic gasket at the interface, In order to seal), after tightening the nut, close the regulating handle of the pressure reducing valve (that is, loosen), open the high pressure valve of the cylinder, at this time, the high pressure gauge of the pressure reducing valve should be instructed. After closing the high pressure valve, the indicated pressure should not drop. Otherwise, leakage should be eliminated in time (use a gasket or raw material to seal), sometimes the high pressure valve will also leak, pay attention. Then turn the adjustment handle to expel the residual air.

(2) The external gas path connection method introduces the gas in the steel cylinder into the chromatograph, some use stainless steel tubes (φ2 × 0.5mm), and some use pressure-resistant plastic tubes (φ3 × 0.5mm). The use of plastic tubes is easy to operate, so plastic tubes are generally used. If plastic pipes are used, stainless steel liners (φ2 × 20mm) and some plastics for sealing are required at the joints. The length of the plastic tube from the cylinder to the instrument depends on the need, and it should not be too long. Then use the plastic tube to connect the gas source to the instrument (gas inlet).

(3) The leak detection of the external gas path closes the valve knobs of the carrier gas, hydrogen, and air on the host gas pavement plate, and then opens the high pressure valves of each cylinder, adjusts the output pressure of the low pressure gauge on the pressure reducing valve, so that the carrier gas and air pressure It is 0.35 ~ 0.6Mpa (about 3.5 ~ 6.0kg / cm3), and the hydrogen pressure is 0.2 ~ 0.35 Mpa. Then close the high-pressure valve. At this time, the indicated value of the low-pressure meter on the pressure-reducing valve should not decrease. If it decreases, it indicates that there is a leak in the connecting gas circuit and should be eliminated.

5. Check the air tightness of chromatograph

Air tightness inspection is a very important task. If there is a leak in the gas path, it will not only directly cause the instrument to work unstable or reduce sensitivity, but also have the risk of explosion. Therefore, this work must be carried out before operation (gas tightness) The inspection is generally to check the carrier gas flow path. If the hydrogen and air flow paths have not been dismantled, it is not necessary to check).

The method is to open the chromatographic column box cover, remove the column from the detector, block the column opening, and 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 host panel, this The pressure gauge should have instructions. Finally, turn off the carrier gas knob. The pressure indication value of the pre-column should not drop within half an hour. If there is a drop, there will be a leak, which should be excluded. If there is a leak in the air path of the main unit, remove the relevant side plate of the main unit, and use soapy water (preferably sodium dodecyl sulfonate solution) to check the leaks one by one (hydrogen, air can also be leaked), and finally Dry with water.

2. Commissioning of the instrument Connect the gas circuit and the instrument as described above. After installation, the following inspection and commissioning work can be carried out.

1. Check the components of the chromatograph circuit Before starting the instrument, the carrier gas flow path should be connected first, and the carrier gas knob (ie: carrier gas steady flow valve) on the host panel should be adjusted so that the carrier gas flow rate is 20 ~ 30ml / min.

(1) Start the host and turn on the main power switch of the host, the motor in the column box starts to work, and check if there is any abnormal sound. If there is, immediately cut off the power and further check and eliminate. Some chromatographs self-diagnose when they start up, and display the operation status of the instrument: normal or abnormal, which part of the abnormal display includes problems, wiring errors, etc.

(2) Check the temperature control of each channel according to the instructions, and check the column temperature (including program temperature increase), sampler temperature and detector temperature one by one, whether it can be kept constant at high, medium and low temperatures, especially if the column is required Temperature and temperature control accuracy reaches 0.01 degrees.

Precautions and methods for gas chromatography installation and commissioning

Release date:

1. Installation of chromatograph

1. Requirements for chromatograph analysis room

(1) There must be no strong magnetic field, flammable and strong corrosive gas around the analysis room.

(2) The indoor ambient temperature should be in the range of 5 to 35 degrees, the humidity is less than or equal to 85% (relative humidity), and the indoor air circulation should be maintained. Conditional factories are best equipped with air conditioners.

(3) Prepare a working platform that can withstand the entire set of instruments, has a moderate width and height, and is easy to operate. Generally, a cement platform is preferred in the factory (0.6 to 0.8 meters high). The platform cannot be close to the wall, and should be 0.5 to 1.0 meters away from the wall, which is convenient for 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 a line with high-power power-consuming equipment or frequently-changed electrical equipment. The power supply must be well grounded. Generally, an iron rod (wire) with a length of about 0.5 to 1.0 meters is nailed to the wet ground (or salt solution infusion), and then the power supply ground point is connected to it. In short, the grounding resistance should be less than 1 ohm. (Note: It is recommended that both the power supply and the case are grounded, so that the effect is better).

2. Air source preparation and purification

(1) Air source preparation

Prepare high-pressure steel cylinders that require gas in advance (commonly available in large and medium-sized cities). Zhuang's gas cylinders can only contain this kind of gas. The color of each cylinder represents a gas and cannot be interchanged. Generally, three kinds of gases, nitrogen, hydrogen, and air are used. It is best to prepare two cylinders for each gas for future use. Some plants may use hydrogen generators and air compressors, but the air compressor must be oil-free. When the cylinder pressure drops to 1 ~ 2Mpa, the cylinder should be replaced. Generally, the manufacturer can use 99.99% of the above gas, and the electronic capture detector must use more than 99.999% of the high-purity gas source.

(2) Air 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 gas is used, some chromatographs are equipped with purifiers and filled with 5A molecular sieves, activated carbon, silica gel, which can basically meet the requirements. If the general hydrogen generator is used, the purification of water must be strengthened, so the area of ​​the drying tube should be increased (the volume is more than 450 cubic centimeters, the filler is preferably 5A molecular sieve), and the volume is larger after the generator To reduce or overcome the impact of the gas source pressure fluctuation on the instrument baseline. If an air compressor is used as the air source, the air inlet of the air compressor should be strengthened for air filtration and the volume of the purification tube should be increased. The drying tube should be filled with half 5A molecular sieve and half activated carbon. General domestic oil-free gas compressor (made in Tianjin) can meet the needs.

3. Complete set inspection and placement of chromatograph

After unpacking the instrument, according to the list of accessories in the data bag, carry out an item-by-item inventory and keep spare parts of vulnerable parts properly. Then place it on the working platform according to the requirements of the instrument's instruction manual, and connect the various parts of the instrument to the wiring diagram and the plugs and sockets, and finally connect the recorder and data processor. Be careful not to misconnect each connector.

4. Connection of external gas circuit

(1) Installation of pressure reducing valve

Some instruments are equipped with a pressure relief valve, if not, they must be purchased. Two oxygen valves and one hydrogen pressure reducing valve were used. Install 2 oxygen pressure reducing valves and 1 hydrogen pressure reducing valve to nitrogen, air and hydrogen cylinders respectively (note that the hydrogen pressure reducing valve thread is reversed, and add the attached O-shaped plastic gasket at the interface, In order to seal), after tightening the nut, close the regulating handle of the pressure reducing valve (that is, loosen), open the high pressure valve of the cylinder, at this time, the high pressure gauge of the pressure reducing valve should be instructed. After closing the high pressure valve, the indicated pressure should not drop. Otherwise, leakage should be eliminated in time (use a gasket or raw material to seal), sometimes the high pressure valve will also leak, pay attention. Then turn the adjustment handle to expel the residual air.

(2) External gas connection method

Introduce the gas in the cylinder into the chromatograph, some use stainless steel tube (φ2 × 0.5mm), some use pressure-resistant plastic tube (φ3 × 0.5mm) The use of plastic tubes is easy to operate, so plastic tubes are generally used. If plastic pipes are used, stainless steel liners (φ2 × 20mm) and some plastics for sealing are required at the joints. The length of the plastic tube from the cylinder to the instrument depends on the need, and it should not be too long. Then use the plastic tube to connect the gas source to the instrument (gas inlet).

(3) Leakage detection of external gas circuit

Turn off the valve knobs of the carrier gas, hydrogen, and air on the host gas pavement plate, then open the high-pressure valves of each cylinder, adjust the output pressure of the low-pressure meter on the pressure-reducing valve, so that the carrier gas and air pressure are 0.35 ~ 0.6Mpa (about 3.5 ~) 6.0kg / cm3), the hydrogen pressure is 0.2 ~ 0.35 Mpa. Then close the high-pressure valve. At this time, the indicated value of the low-pressure meter on the pressure-reducing valve should not decrease. If it decreases, it indicates that there is a leak in the connecting gas circuit and should be eliminated.

5. Check the air tightness of chromatograph

Air tightness inspection is a very important task. If there is a leak in the gas path, it will not only directly cause the instrument to work unstable or reduce sensitivity, but also have the risk of explosion. Therefore, this work must be carried out before operation (gas tightness) The inspection is generally to check the carrier gas flow path. If the hydrogen and air flow paths have not been dismantled, it is not necessary to check).

The method is to open the chromatographic column box cover, remove the column from the detector, block the column opening, and 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 host panel, this The pressure gauge should have instructions. Finally, turn off the carrier gas knob. The pressure indication value of the pre-column should not drop within half an hour. If there is a drop, there will be a leak, which should be excluded. If there is a leak in the air path of the main unit, remove the relevant side plate of the main unit, and use soapy water (preferably sodium dodecyl sulfonate solution) to check the leaks one by one (hydrogen, air can also be leaked), and finally Dry with water.