GC/MS Leak (Intuvo 9000+5977B SQMSD)

Which ion source is installed? What is the column configuration and the flows? Do you have a splitter installed?  How long since you replaced the GasClean carrier gas filter element or is it only the Big Universal Trap?  Did it start after changing the tank?  Have you used a gas leak detector on all fittings and valves prior to the GC?  Is this the only GCMS on the tank?  Have you done a leak-down test of the carrier gas supply?

The N2:O2 is about 4:1, so air is the best suspect, for sure. If you have the extractor ion source installed, try changing the flow down to 0.6 ml/min and see if the air goes up or down and raise the column flow to 1.5 ml/min and see as well.  This is not a super valid test as the change in column flow changes the sensitivity of the system and the way PFTBA enters the ion source, but it often tells something.  If you have the HES ion source installed this test is not valid as the changes in response with flow also change the spectral tilt so at higher column flows the air always looks higher.

Hi!

Sorry, that I didn't provide enough information.

• Ion source installed is "Stainless Steel (SST) EI 350";
• Quad Temp: 150°C;
• Source Temp: 230°C;
• MSD Transfer Temp: 250°C;

• Column installed is DB_WAX_UI (123-7033UI)  30m x 320μm x 0,5μm   -  flow rate: 4 ml/min  -   with oven program:
  • 120°C - hold 5 min;
  • 8°C/min up to 230°C;
  • Hold 8 min;
    • Total run time: 26,75 min.
• No splitter installed;
• Septum Purge: 3 ml/min;
• Split Ratio: 1:50
• Gas Saver: 15 ml/min - after 3 min.

As a filter for helium gas, only Big Universal Trap is used, without GasClean filter. And no, leak didn't start after changing the filter, it started prior to that (it was only changed as a precautionary). Nitrogen inside new filter was purged.

paulsalverda said:

Have you used a gas leak detector on all fittings and valves prior to the GC?  Is this the only GCMS on the tank?  Have you done a leak-down test of the carrier gas supply?

Yes, all fittings and valves were checked for leaks prior to the GC. No leaks have been found. Yes, it is the only GCMS on the helium tank. And yes, carrier gas supply is all good.

Even without extractor ion source, I did some AWL's with 0.6ml/min, 1.5ml/min and 4ml/min flow rates.

0.6ml/min  Flow Rate:

1.5ml/min  Flow Rate:

4ml/min  Flow Rate (method's flow rate):

What I don't clearly understand - shouldn't abundance of N2, O2 etc. ions be higher with 4ml/min flow rate - compared to 0.6ml/min and 1.5ml/min flow rates? As prior two have much higher abundances of these ions.

Problem solved, found that guard chip bolt (towards inlet top assembly) is bad and leaking because of unsecure connection - needs to be replaced.

Through mass profile it wasn't seen previously, because of much longer time for air duster masses to be detected (decently longer flow path). Where if other part in flow path is leaking - ability to see where is the leak almost instantly.

Thank you for the suggestions paulsalverda !

4 ml/min is the maximum flow into the 5977 turbo pump system. This high flow certainly reduces the sensitivity of the MS. If you have acceptable results that's nice but lowering the flow rate into the MS to the typical 0.8 to 1.4 ml/min will result in much higher sensitivity.

Glad you found the issue!

Only now I stumbled upon such tip. I will make corrections in the method and do comparative analysis.

Thank you once more!

I suggest you change to a narrower bore column, 121-7022-INT  J&W DB-WAX Intuvo GC column module, 20 m, 0.18 mm, 0.18 µm. (compatible only with the Intuvo 9000 GC System)  and run that at 1.0  ml/min.

One other important bit.  15 ml/min of GasSaver flow may be insufficient.  Yes it's an allowed setpoint, but I have seen air in the MS just from not enough total GC inlet flow, especially at higher oven temperatures.  Consider changing that to 30 ml/min.