This section describes how to check the instrument for leaks. If an air leak is clearly present, locate the leak as described in "2. MS Vacuum Leak Check", and take corrective measures.
Operating an instrument with an air leak can cause a decrease in sensitivity, an increase in noise, filament burnout or other problems. Always check for leaks after performing maintenance.
GC leak will have different symptoms than an MS leak. Normally, carrier gas will leak from the system if there is a GC leak, while air will be drawn into the system when there is an MS leak. To check for GC leaks, refer to "1. GC Carrier Gas Leak Check". To check for MS leaks, refer to "2. MS Vacuum Leak Check" and "3. Vacuum Leak Check Using Peak Monitor".
To check for GC carrier gas leaks, a blank plug is installed in the injection port column connection, and the split and purge vents are sealed with a blank nut. This seals the carrier gas in the injection port flow line, the carrier gas flow line, and the split and purge gas flow lines. Leaks are detected by observing the change in pressure of the sealed carrier gas over time. Changes in carrier gas pressure are observed by monitoring the window displayed by selecting [HOME] - [Injection Port] on the GC-2030 Touch Panel.
1) Shut down the instrument. Turn the MS power source off, but leave the GC-2030 power source on.
2) Open the GC column oven door, and remove the column on the injection side.
3) Install the blank plug in place of the column in the injection port.
4) Install G-type blank nuts in the vents for the split and purge gas, respectively.
5) Ensure that the carrier gas supply pressure (cylinder pressure) exceeds 350 kPa.
6) Select [HOME] - [Injection Port], and set the items as follows.
• Injection Mode : Split
• Flow Control Mode : Press
• Inlet Press : 350 kPa
• Total Flow : 100 mL/min
7) Turn [On] the flow controller control, and turn [On] the AFC control.
8) Wait 5 minutes and verify that the injection pressure is between 300 and 400 kPa. If the pressure is above 400 kPa, loosen the column nut slightly and let the pressure decrease. If the pressure is below 300 kPa, increase the injection pressure slightly.
9) Verify that the total flow is below 2 mL/min. A total flow greater than 2 mL/min indicates a carrier gas leak.
10) Turn [Off] the flow controller control.
11) Allow pressure to stabilize after turning off the AFC Control.
12) Verify that the pressure does not decrease by more than 5 kPa per 10 minutes. A pressure decrease exceeding 5 kPa per 10 minutes indicates a leak.
13) While the carrier gas is sealed under pressure, possible leaks can be checked by using an electronic gas leak detector (available commercially) at the connections, such as the G-type nuts and injection port nuts.
14) When a leak is detected, tighten the part or remove it and inspect for problems. Replace the three aluminum spacers when a G-type nut is removed.
15) If a leak was detected because of a pressure decrease after step 14, replace the injection port septum, and verify that the O-ring is properly installed on the glass insert in the injection port.
Repeat the pressure leak test described in steps 8 - 12.
16) If a leak continues to be detected, the leak is probably located in the flow lines of the split vents. Tighten the G-type nut on the split line, or remove the nut and check for problems.
Replace the three aluminum spacers when a G-type nut is removed.
17) Repeat the pressure leak test described in steps 8 - 12.
NOTE: Precautions for sealing GC carrier gas under pressure:
a) Ensure that there are no leaks after disassembling and reconnecting a G-type nut.
b) Replace the three aluminum spacers when a G-type nut is removed.
c) Do not touch any GC parts other than the G-type nut on the split line. Contact
a Shimadzu sales or service representative.
d) Do not use soapy water on the GC injection port and AFC piping.
This section describes MS vacuum leak check procedures. Leaks can be large enough to take the rotary pump off-line, or small enough to allow the turbomolecular pump to function almost normally.
Ensure that the O-ring is properly installed on the MS door. The O-ring seals the connection between two surfaces, preventing vacuum leaks and maintaining the proper vacuum in the MS.
When the MS door is opened to perform maintenance, observe the following precautions to avoid leaks.
NOTE: Observe the following precautions to prevent vacuum leaks:
• Do not forget to install the O-ring.
• Install the O-ring properly.
• Remove any foreign material from the O-ring.
• Remove foreign material, including pieces of O-ring, from sealing surfaces.
• Do not scratch sealing surfaces.
• Do not forget to install the Vespel ferrule where the column connects to the interface.
• Firmly tighten the column interface nut.
• Change the GC septum on a regular basis (around 80 to 100 injections).
If the rotary or turbomolecular pumps are not functioning properly:
1) The sound of air exhausting from the rotary pump does not diminish after a few minutes.
2) The turbomolecular pump operates, but the vacuum system power shuts down after about 5 minutes.
If the situation in step 2 occurs, a vacuum leak is indicated. Wait for the MS to vent, then check the front door and the connection between the column and interface according to the above precautions for preventing vacuum leaks. If a vacuum leak occurs in a location other than the front door or connection between the column and interface, contact
a Shimadzu sales or service representative.
Vacuum leaks too small to prevent proper operation of the instrument can still affect the instrument performance. This section describes the procedure for checking for those leaks. The operations described in this section can be used provided that the instrument and turbomolecular pump are functioning properly and the Turbo Pump light is green in the [Vacuum Control] dialog box.
This method monitors the water (m/z 18) and nitrogen (m/z 28) peaks from the [Peak Monitor] window. The height of these two peaks is compared to check for small vacuum leaks.
1) Click the GCMS Real Time Analysis Assistant Bar Tuning icon. The [Tuning] window opens.
2) Click the Assistant Bar [Peak Monitor View] icon. This opens the [Peak Monitor] window.
3) In the [Peak Monitor] window, set [Acquisition Mode] to [Q3 Scan] and set the m/z of ions to monitor to 18 (water) and 28 (nitrogen), or choose the [Water, Air] in [Monitor Group].
4) Set the detector voltage to about 0.60 - 1.50 kV so that the peaks for m/z 18 and m/z 28 are visible.
5) Turn on the filament.
6) Compare the peak heights for m/z 18 and m/z 28. If the height of m/z 28 is more than twice that of m/z 18, a vacuum leak is indicated.
NOTE: In some cases, the peak at m/z 19 can be bigger than that at m/z 18 immediately after pulling a vacuum.
NOTE: If it contains CID gas (argon), a peak will appear at m/z 20 for divalent argon ions (Ar2+).
7) When a vacuum leak is detected, shut down the instrument. Turn off the main instrument switch.
8) Follow the precautions for vacuum leak prevention described in "2. MS Vacuum Leak Check"
NOTE: If an optional accessory for sample introduction is connected, the vacuum leak check may not meet standards, even if there is not leakage in the GC/MS.
Insufficient purging may result in a high 28 m/z to 18 m/z ratio. When this occurs, increase the total flow of the GC to around 200 mL/min to purge.
This procedure is based on the suction produced when a vacuum leak occurs in the MS. If there is a leak, the petroleum ether applied to the contact surface between the column and the interface will be detected at that time in the "Peak Monitor" window, by the m/z 43 peak. The vacuum check is performed by monitoring the fluctuations of this m/z 43 peak.
NOTE: Precautions when Performing Vacuum Leak Check with Petroleum Ether
• Use only petroleum ether.
• Do not spill petroleum ether on any electronics.
• Do not allow petroleum ether to contact any site other than contact surface between the interface and column.
1) Click on the Tuning icon in the GCMS analysis assistant bar. The "Tuning" window opens.
2) Click on the Peak Monitor View icon in the Assistant bar to open the "Peak Monitor" window.
3) Set the m/z for the ion to be monitored in the "Peak Monitor" window to 43 (fragment ion of petroleum ether). Set the magnification factor to 50 - 100.
4) Select "Q3 Scan" at "Acquisition Mode".
5) Set the detector voltage to 0.60 - 1.00 kV.
6) Turn on the filament.
7) Fill a syringe with petroleum ether.
8) Apply petroleum ether to the contact surfaces of the front door and between the column and interface.
9) Observe the m/z 43 peak in the "Peak Monitor" window. If the m/z 43 peak fluctuates greatly (increases), there is vacuum leak at the petroleum ether application site.
10) Repeat the procedures described in steps 7 and 8. If there is no change in the m/z 43 peak, there is no leak.
11) If a vacuum leak has been detected, follow the precautions for vacuum leak prevention described in "2. MS Vacuum Leak Check".
