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GC-FID - spikes in baseline

BChristle78

We have a GC-MA7890B with an FID detector and I are observing spikes in the baseline after we made a couple of changes.

We installed guard columns with unions on inlet and detector side, added a 2nd gas cylinder and required tubing, cleaned the FID detector and added a UPS to the computer next to the instrument.

When we saw the spikes we:

  • Checked all connections for leaks (snoop and leak check was fine)
  • We reinstalled new ferrules on both sides since the trim was found to not be good
  • We removed the 2nd cylinder and associated tubing (particles in tubing or gas supply?)
  • Removed guard columns and installed analytical column directly 

Thrse measures did not help.

We are planning to:

  • Install a deactivated fused silica column to see if the analytical column may be the issue (flaking of material)
  • Remove the UPS (electrical disturbance)
  • Checking FID detector again (loose electrical connection after putting it back together? Or introduction of debris when cleaning it?

Is there anything else you can think of that could cause these issues.

This is with guards

This is without guard columns, analytical column directly installed

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  • 0 in reply to BChristle78

    Thanks for asking!

    I screen grabbed and zoomed to make them the same retention timing. These red lines are the same size. It's interesting that these anomalies are nearly the same time apart or about double from one another. That may be a clue.

    The heights are all about the same, too.

    Do they get closer/farther if you change the column flow?

    Do they get closer/farther if you change the FID hydrogen or air flows?  Normal is 30 ml/min hydrogen and 400 ml/min air.  Try a test at 40 ml/min hydrogen and try a test at 300 ml/min air.

    I try to do the easiest things first, though. Cool off the FID.  Remove the column. Remove the column adapter if there is one on the bottom of the FID. Remove the collector castle and jet.  Use solvent dipped cotton swabs to thoroughly wipe out inside the detector.  Squirt solvent through the jet and wipe the jet thoroughly.  Rinse the collector, scrubbing if needed.  Reassemble.  After you install the jet, not too tight and not too loose, the last thing before putting the collector assembly back on spray it out with air duster.  Use a new 1/4" graphtie/vespel ferrule on the column adapter.  Don't overtighten and crack it, but make it quite tight. Reinstall the insulator cup and insulation. 

    Cap the detector in the oven.   I use an opened-up paper clip with a 1mm id graphite ferrule and install it like a column with the paper clip just barely sticking out of the ferrule.  You can also just install a few inches of column and plug the end in the oven by pressing it into the edge of a septum.   Then run the tests.  Spikes or no spikes?

    After maintenance there may be a few spikes but they should go away in less than 1/2 hour or so.

    Let us know the outcome.

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