GC/GCMSGas Chromatography and Mass Spectrometry
1、 Shutdown steps
1. Turn off detector related parameters on the GC panel or workstation software:
-FID detector flame;
-FPD detector flame and high voltage (photomultiplier tube switch);
-ECD detector current/pulse switch;
-TCD detector bridge current (bridge current), bridge temperature or filament switch;
-NPD detector rubidium beads (rubidium bead current, voltage, etc.);
Note:
① The flame shutdown of the detector is the first step to prevent the condensation of water vapor generated by flame combustion during the cooling process of the detector;
② Mechanical valve type GC cannot use instrument panel or workstation software to turn off the flame. Simply close the hydrogen and air regulating valve or close the hydrogen and air gas pipeline switch valve to turn off the flame, or close the gas purifier switch valve to turn off the flame;
③ EPC (Electronic Flow Control) type GC, generally the detector will automatically turn off hydrogen and air after the flame is turned off, otherwise manually set to turn off;
④ When turning off key parameters of the detector, if using a capillary column, do not turn off tail blowing (filling column analysis without tail blowing option);
2. Set the temperature of each heating module to 40 ℃:
-Temperature of GC injection port, detector, converter, column box, etc;
-The temperature of external devices, such as pre-treatment instruments such as thermal desorption, headspace sampler, and blowdown trap;
Note: Instruments that can be controlled through GC workstations can save such steps as "Instrument Shutdown Method" and directly call and issue them.
3. Turn off the GC power switch
Wait until the temperature of each heating module drops below 80 ℃, then turn off the instrument power, and then turn off the GC workstation and computer;
4. Turn off the main and branch switches of each gas circuit:
-Carrier gas;
-FID, FPD, and NPD detectors for gas (hydrogen) and auxiliary gas (air);
-Power air (such as air) for pneumatic valves;
5. Cleaning:
-For samples with high viscosity and concentration, it is necessary to clean the residue inside the injection needle with solvent;
-Replace the injection pad and liner for start-up in the future;
-Dispose of waste liquid and discarded samples as required;
2、 Precautions
1. After shutting down, all gas source valves should be closed; If steel cylinders are used in the laboratory, the cylinder valve should be closed first. After the remaining gas in the gas circuit is discharged and the pressure gauge drops to zero, the pressure reducing valve should be closed;
2. After shutting down, turn off the laboratory exhaust equipment, main power switch, etc. according to regulations, and unplug sockets, etc;
3. Close the doors and windows, and cover the instrument cover of the GC that has not been used for a long time.
LC-MSLiquid chromatography-mass spectrometry
The mass spectrometer should be shut down and stopped. It is recommended to follow three steps:
1. Rinse the chromatography column, tubing, and spray needle, stop the liquid chromatography-mass spectrometry operation in Operator mode, remove the chromatography column, and replace it with a two-way valve. Replace the liquid mobile phase with methanol/water: 50/50, rinse the pipeline and nozzle with 0.8mL/min for about 30 minutes to remove salt residue. Then rinse with 100% methanol for another 10 minutes.
2. Turn off high pressure, release vacuum, and stop mass spectrometry
-Firstly, ensure that the liquid phase flow rate stops, then set the solvent removal gas temperature to the lowest value, and stop nitrogen gas after the temperature drops to 40 ℃
-Standby mass spectrometry, wait for 30 minutes, wait for the instrument to cool down
-Vent instrument, release vacuum, confirm that the molecular pump speed drops below 3%
-Turn off the mass spectrometer, liquid phase power switch, and isolation valve of the mass spectrometer
3. Turn off the air circuit and power supply
Close the nitrogen main valve of the liquid nitrogen tank or the power supply of the nitrogen generator, and turn off the UPS. Carefully check if the water, electricity, and gas in the laboratory have been turned off and the waste liquid has been emptied. Also, check if the position of the exhaust pipe is normal and complete the shutdown.