Injecting acidic solvent to GC/FID

[Bethred]

What is the effect or is it OK to inject an acidic solution of methanol into a split inlet. Detector is an FID.

[chromatographer1]

It depends upon the acid used to make the methanol acidic.

Methanol contains water so aqueous acid never treats columns well.

Your question, while a good one, doesn't have enough information to give you a complete answer.

I would not do so unless the acid was an organic acid like acetic or formic.

best wishes,

Rod

[Rocknroll99]

Also you should also watch you syringe. I was injecting an acidic solution and the syringe plunger ceased causing big problems with the injector.

Increase washes rectified the problem (after I paid $$ for a new motor)

[Bethred]

Thank you all for your replies. The solution is 4 ml c. H2SO4 in 110 ml of Methanol. It is a methylation mixture used for methylating 2,4-D to it's methyl ester. We are following an old (but validated) C-PAC method to do an assay for 2,4-D. I will dilute the final solution some with methanol, but acid will still be present.

[chromatographer1]

Be sure to have a new capillary column available for use for other assays.

You might wish to remove 25cm of column from the inlet end after your analysis is completed in order to reuse the column.

Don't expect a fragile capillary column to deal with the acid as well as a rugged packed column. And don't forget, that a validated method using a packed column doesn't mean it is validated for a capillary column.

Some foolishly make assumptions like these but I am sure you won't.

best wishes,

Rod

[Bethred]

Rod,

thanks for your input. I especially like the comment regarding validation. Just try explaining that to my manager who gave me the method!

[Steve Reimer]

From experience (spelled with $$$), acidic methanol injected into a GC is a bad idea. There are several EPA drinking water methods that use that methylation technique but there is always a solvent exchange to a non-water miscible solvent before injection.
When I have done these procedures I learned the hard way to check the final product with pH paper before injection. If it turns red, it needs more neutralization or back extraction.
Failure to follow these precautions can be very expensive. If you are lucky the syringe will jam before the column is destroyed!