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Excessive Column Bleed

Question asked by tom.hodsden on Aug 12, 2019
Latest reply on Aug 13, 2019 by noreuter

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GC (7890A) - MS (5975C)

I am observing high column bleed and cannot locate the source of the problem (see photo attached).

I have checked for an air leak (see tune reports attached, before and after the problem arose) and no leak appears to be present.

I have then cleaned the inlet port, tried a column bakeout, run over 10 blank samples and cut ~10 cm off the front of the column but the problem still persists.

This column is only 3 months old.

Can anyone suggest any other things I can do to locate the source of the problem before I requets an enigneer to come and take a look?

Thanks,

Tom

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james_jenkins

Aug 12, 2019 6:29 AM

Hi Tom,

I have updated the tags on your post for better visibility. Its hard to tell from the screen captures, if this is column related, the best way to isolate right now would be to try another column. This appears to me to be something more like possible contamination. Always hard to tell from screen captures.

Regards

James

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noreuter

Aug 13, 2019 12:15 AM

Hi Tom,

it would also help to have the type of column used and see the method parameters (especially the temp ramping).

Which m/z is your 100% abundance - 207, 283, 355 or another one?

Norbert

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tom.hodsden @ noreuter on Aug 13, 2019 12:54 AM

Hi Norbert,

I've attached a photo of the column and the method parameter file.

As for the m/z with 100 % abundance, I don't actually know. How do I find out? The tune report (attached in original report) seems to suggest that m/z 69 is the 100 % abundance though I may be wrong.

Thanks,

Tom

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acqmeth.txt.zip1.7 KB
Column208.8 KB

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noreuter

@ tom.hodsden on Aug 13, 2019 1:19 AM

Hi Tom,

click somewhere in the high baseline area to see a complete mass spectrum. In that spectrum check the m/z 207 and 284 and 355, they all come from polysiloxane degradation or contamination. Typically if it comes from the phase of a column 207 is the highest peak, if it comes from the septum then it is often 284 as largest peak, due to the higher crosslinking of the polysiloxane in the septum material.

I also agree with James that the use of a different column could help identify the source better, the best would be a Wax column as those do not generate siloxane bleeding patterns.

Norbert

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james_jenkins Aug 12, 2019 6:29 AM
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Hi Tom,
I have updated the tags on your post for better visibility. Its hard to tell from the screen captures, if this is column related, the best way to isolate right now would be to try another column. This appears to me to be something more like possible contamination. Always hard to tell from screen captures.
Regards
James
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noreuter Aug 13, 2019 12:15 AM
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Hi Tom,

it would also help to have the type of column used and see the method parameters (especially the temp ramping).
Which m/z is your 100% abundance - 207, 283, 355 or another one?

BR

Norbert
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- tom.hodsden @ noreuter on Aug 13, 2019 12:54 AM
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  Hi Norbert,
  
  I've attached a photo of the column and the method parameter file.
  As for the m/z with 100 % abundance, I don't actually know. How do I find out? The tune report (attached in original report) seems to suggest that m/z 69 is the 100 % abundance though I may be wrong.
  
  Thanks,
  
  Tom
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  - acqmeth.txt.zip1.7 KB
  - Column208.8 KB
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  - noreuter @ tom.hodsden on Aug 13, 2019 1:19 AM
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    Hi Tom,
    
    click somewhere in the high baseline area to see a complete mass spectrum. In that spectrum check the m/z 207 and 284 and 355, they all come from polysiloxane degradation or contamination. Typically if it comes from the phase of a column 207 is the highest peak, if it comes from the septum then it is often 284 as largest peak, due to the higher crosslinking of the polysiloxane in the septum material.
    
    I also agree with James that the use of a different column could help identify the source better, the best would be a Wax column as those do not generate siloxane bleeding patterns.
    
    Norbert
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Excessive Column Bleed

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