If you have difficulty finding an air leak, the following procedure provides a way to determine whether the leak is in the GC or the MSD. This procedure is not recommended for normal troubleshooting because if it is not performed correctly it can result in a plugged or damaged capillary column.
Turn off the GC/MSD interface heater and injection port heaters. Reduce the GC oven to room temperature. Allow all heated zones to cool.
WARNING! Make sure the oven and injection port are cool before removing the column.
CAUTION! Heating a capillary column without carrier gas flow can damage the column.
Remove the GC column from the injection port.
Cap the end of the column with a septum.
Wait 15 – 20 minutes.
Steps 2 and 3 allow a small amount of air into the MSD. If you continue before the MSD has a chance to pump away this air, the results of this test will be invalid.
Run another air and water check.
Compare the results of the first check with the second check.
If the results are essentially the same, the leak is in the MSD or in the column nut on the end of the GC/MSD interface. If the results are significantly different, the leak is probably in the injection port of the GC.
Remove the septum.
Score and break off the first 30 mm of the capillary column.
CAUTION! If the column is not broken off correctly, it can be plugged by septum or column fragments.
Reinstall the column in the injection port.
Depending on the location of the leak, go to: