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New TCD detector baseline dip
Posted: Mon Oct 03, 2022 4:56 pm
by LabProARW
My new TCD detector on 7890a is experiencing a uncharacteristic plunge at what would be the tail after my brominated compound peak but not after my phthalate peak. The plunge recovers pretty quickly. The plunge where the tail of the peak is almost looks like a smaller negative peak. The baseline recovers pretty soon. This only happened now after a new TCD was installed - this effect has seemed to mostly flatten out over the course of days and many injections of the material. It was messing up my quantitation due to the integration problem it causes trying to establish peak end of that brominated peak. I have never seen this before and need help figured this out!!
Re: New TCD detector baseline dip
Posted: Thu Nov 10, 2022 3:04 am
by AICMM
This one has my curiosity piqued.
You are running a bromo compound on a TCD ~ so relatively high levels since you can see it with a TCD.....
And you had it running successfully before? I would assume you are using helium carrier? And you are using a capillary column running up to how hot???
Best regards,
AICMM
Re: New TCD detector baseline dip
Posted: Fri Apr 07, 2023 9:26 am
by GasMan
Has this problem been resolved ? What column is being used?
Gasman
Re: New TCD detector baseline dip
Posted: Tue Apr 11, 2023 3:18 pm
by LabProARW
This one has my curiosity piqued.
You are running a bromo compound on a TCD ~ so relatively high levels since you can see it with a TCD.....
And you had it running successfully before? I would assume you are using helium carrier? And you are using a capillary column running up to how hot???
Best regards,
AICMM
Yes I have been running this method and conditions for years.
UPDATE:
The strange situation has resolved itself after working on the EPC controller connections. I think when replacing an EPC controller having it positioned exactly right is critical. It wasn't until I took the EPC out and reinstalled it that the problem resolved itself.
Re: New TCD detector baseline dip
Posted: Tue Apr 11, 2023 6:38 pm
by GasMan
The reason that I asked , is that some years ago we saw a similar problem with fatty acids, namely butyric acid. The Agilent TCD works on a switching principle where it switches at 5 Hz between the sample from the column and the carrier gas. The signal is the difference between the two gas streams. If sample "sticks" to the detector and is "slow" to leave the detector you will get a false signal. Agilent does supply a special modified detector to solve this problem.
Gasman