Precautions and methods for gas chromatography installation and commissioning

1. Installation of chromatograph

1. Requirements for gas 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 80% (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. In general, the cement platform is preferred (0.6-0.8 meters high). The platform cannot be close to the wall, and should be 0.8-1.0 meters away from the wall, which is convenient for wiring and maintenance. (4) The power line capacity for the instrument should be above 3KVA, and the power source 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, a copper 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 grounding 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. Gas 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 certain gas cylinders can only contain this 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) 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. After unpacking the completeness check of the gas chromatograph and placing the instrument, carry out an item-by-item inventory according to the list of accessories in the data bag, and keep the spare parts of the 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 chromatography workstation or data processor. Be careful not to misconnect each connector.

4. External gas connection (1) The instrument installed with the pressure reducing valve is equipped with a pressure reducing valve, if not, you must purchase it. 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 0.3 ~ 0.4Mpa, and the hydrogen pressure is 0.2 ~ 0.25Mpa. 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. Chromatographic air tightness inspection of chromatograph is a very important work. If there is a leak in the air circuit, it will not only directly lead to unstable operation or reduced sensitivity of the instrument, but also have the risk of explosion, so before operation and use This work must be carried out (airtightness inspection is generally to check the carrier gas flow path, if the hydrogen and air flow paths have not been disassembled, you can not 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 0.3 ~ 0.4Mpa, 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 panel of the main unit, use soapy water (preferably sodium dodecyl sulfonate solution) to check the leaks one by one (hydrogen, air can also be tested for leaks), and finally the soap 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 panel of the host should be adjusted. (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, check the column temperature (including program temperature increase), the temperature of the sampler (vaporization chamber), and the temperature of the detector at a constant temperature, whether it can be kept constant at high, medium, and low temperatures. In particular, the precision of the column temperature control is required to reach 0.01 degrees.

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