GC/MS 5977 Air Leak

Hello 

Recently we face problems with Air in our GC/MS. When i perform the Air&Water Check if only the MSD is connected with the splitter and two plugs the Nitrogen and Oxygen counts are around 3 times higher. Does anyone has an idea where possible air leaks can occur in the MSD?

One year ago we had to change the transfer line because it was damaged and caused an high air leak. I already checked the side plate O-ring and the Vent- Valve-ring without any signs of damage.

Current Params used: etune.u

Relative abundances:

18/69 = 1.83 Water% (counts=35504)

28/69 = 83.18 Nitrogen% (counts=1614848)

32/69 = 24.67 Oxygen% (counts=478912)

44/69 = 0.48 Carbon Dioxide% (counts=9312)

28/18 = 4548.36 Nitrogen/Water%

  • What is the physical column configuration? -- it sounds like you have a two way splitter - is it a purged splitter or a non-purged splitter? Is it a Purged Ultimate Union for backflush?  What piece of fused silica is between the splitter and the MS?  Do you have the proper graphite/vespel ferrule on the MS transferline?  Which nut are you using - the brass one or the Finger Tight column nut? The brass one uses a longer ferrule than the one used with the Fingertight nut.

    Do not overtighten the transferline. The most pressure that it needs to seal against is 14.7 psi -atmospheric.  If you think the nut needs to be tighter, vent and replace the ferrule.

    The Nitrogen to Oxygen ratio is about 4:1 - so that is air and not something like nitrogen in the carrier gas.

  • Isolate MS Leak by using Blocknut on TransferLine First. If all leaks are OK with Blocknut, replace the Ferrules in Splitter. I also faced the same issue of High N2 in 5977with Splitter. 

    It was resolved with change of Metal Ferrules in Splitter

  • The current configuration is a three-way non-purged splitter with one blind, one column and a capillary to the MS. And i used the finger tighten column nut but for some reason it didn´t worked well so i changed it back to the brass column nut with the long vespel ferrule. 

    How do i know that the ferrule is overtighten? 

  • I isolated the MS from the system and it was completly fine, so i guess it must be between the MS column nut and splitter.

    I changed the metal ferrule but the problem is still there. 

  • What does "one blind" mean?   What column and what restrictor(s) dimensions are installed?

    The finger tight column nut and short graphite/vespel ferrule work great when used properly. Install the column into the MS flush to the ceramic tipseal and then tighten the fingertight nut until the ferrule grabs the column so that the column can't be moved and for 0.25mm id columns tighten it only about 45° further.

    Fingertight column nut swaging guidelines

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