poor reproducibility of test solvent TEA in DMA using HS-GC

[ntruong]

Hi All,
I am having a major issue with our friend Triethylamine when it comes to the execution of residual solvents method validation. All the test solvents meet the protocol criteria except TEA for linearity, accuracy and precision. The column I used is DB-1, 60m. The oven setting for HS oven is 145°C, well above the boiling point of TEA. The GC program is ramped until all test solvents peaks come out and held at 245°C for a few minutes to allow the burn off of DMA. The column used is fairly new (only about 100 injections were made into the column). Could someone help me to resolve the issue?
1. Could it be due to the retention of TEA in DB-1 column? Has anyone had any experience with this? If it were the case, would extending the hold time at 245°C help in pushing out the stubborn TEA? Re-developing the method is not the option in my case.
2. How can I re-generate the DB-1 column? Is there a program I could use to clean out the residual TEA in column after a number of injections?
3. What causes the retention? compatibility issue between TEA and column or this is the nature of TEA?
Thanks in advance for all the help.

[chromatographer1]

You have other solvents besides TEA in the DMAc mix?

Is there some water present? or other protonic solvents?

Any acids present like TFA or acetate? or ions like chloride?

If any of these questions are in the affirmative, then you are only seeing chemistry in action.

Your drug matrix will have great effect upon the recovery of TEA.

Any base can react with fused silica and with methyl silicone. What film thickness are you using for the DB-1 column?

I validated a TEA HS analysis with a Carbowax and OV-1301 column once to a limit of 50 ppm.

But I never used a 100% methyl silicone column. Nor would I try.

Try a base deactived Carbowax or a more polar column and see if you can get a linear response from your matrix dissolved in DMAc.

best wishes,

Rod

[ntruong]

Thanks Rod for your prompt attention

You have other solvents besides TEA in the DMAc mix?

ACN, Ch2Cl2, Tolune, pyridine, EtOAc.

Is there some water present? or other protonic solvents?

No

Any acids present like TFA or acetate? or ions like chloride?

The only acetate we have is ethyl acetate.

Any base can react with fused silica and with methyl silicone. What film thickness are you using for the DB-1 column?

3.0um
I solvent-rinsed the column with hexane and methanol, collected and injected the rinses and found no TEA. There goes my theory about TEA retention. The problem I have now is I cannot re-develop the method. I have to make do with what I have.
Any more insights ho to resolve this matter is greatly appreciated.
Regards,

[chromatographer1]

As far as you can determine, minimize the amount of water in your DMAc and other analytes and matrix.

You can try using another column (NEW is possible).

Is there anything you might have possibly changed with your equipment from the time the method was originally validated?

(vial size, sample size, lot of solvent?)

best wishes,

Rod