MSD lowest parameters for leak searching

Hi all,

 

I need to switch column every 2 weeks on a GC (7890B) / MS (5977A).

The first time I did it, I had a leak in the system and I had to vent it again to fix it (o-ring of the vent valve).

This took time because the heating zones are at 280, 280, 150ºC for transfer line, Source and Quad respectively.

I don't have Ar or polyfluoroethane spray for leak detection.

 

Today, following an Agilent document, I have created a Maintenance.M method with a cool.U tune file where heated zones will be at 100ºC or below. This method is loaded before venting the system.

So, after pump down, the heated zones will stay at those temperatures.

 

My question is: can I use the MSD to check for water/air leaks with those temperature parameters?

 

Thanks

  • I am, honestly, not sure.

    I suppose zones are heated to prevent condensation of compounds.

    At 100ºC and at low pressure, water should be in the gas fase like O2/N2.

     

    Anyway, I had to try it. I had a leak, of course, and waiting for hot zones to cool down was not an option.

    With the MSD's hot zones always at 100ºC, I vented the system until the pump was at <40%, did what I had to do and pumped it down again. After waiting like 10 minutes, I manually scanned 10 - 50 m/z to see ions abundance go down or stay the same. The process was repeated until I found the leak. Which was at the union of the column and the TD transfer line.

  • Yes.  Cold.M using Cold.U -- a method and tune file with the heaters all set to off or something like 40 C, are very useful.

     

    Remember that as little as a few ppm of oxygen can damage a column or kill the inertness of the liner if those parts are hot - even 100C is a bit too hot for the liner and column, in my experience.

     

    40% turbo pump speed is higher than recommended to remove the column from the MS.  It's not horrible if the column is still installed in the MS and you were only working at the Thermal Desorber/inlet/column connection, because the total flow to the MS would be restricted by the column.

     

    Switching the column every two weeks must be tedious, but honestly a full vent, removal, change, pumpdown, check is the best way.  There is hardware to make it easier if you need to change it more often, but those come with compromises.  Make sure and use the Finger Tight column nut and short ferrule on the MSD transferline connection.

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