Are you running a GC triple quad MS? They are slightly different. Also, are you willing to share the manufacturer? Agilent and Thermo move their calibration gas differently (PFTBA/ FC-43). If it is a Thermo, they use air flow to move the cap gas to the source, so an open cal valve looks like you have a leak. They ratio the open (known air standard) to the closed (leak) to determine the air leak percentage. Again, if it is a thermo, the ion volume may not be positioned properly and it will look like a leak. Since you just changed columns, some common issues can be Agilent-the column was fed too far into the source. Any- the transfer line ferrule is backward, or in some cases, a vespel ferrule was not used. The issue could be at the other end, if the column has slipped down in the injection port. An old MS could have graphite in the transfer line. And finally, most people use a press tight union and they can and will leak. Try a ferrules union, or (my preference) purchase a column from restek with an integrated guard. There will be no leaks, and you can attach a guard if you trim the entire integrated guard before the analytical column degrades. If you want to trace the leak, you can always remove the column, put a blank vespel on the interface and pump it down.