Use of Sulfuric Acid as Volatile Mobile Phase Additive

[adam]

Hello

I wanted to ask people's opinion about the use of sulfuric acid in mobile phases when using detection modes like ELSD, CAD, or MS (where volatile mobile phases are needed).

We have had some discussion internally, and with vendors, and it's interesting how there seems to be a lot of difference of opinion on this issue.

Some people have noted that dilute solutions of sulfuric acid have boiling points around 100C, and claim they use it often with these types of detectors. Whereas others say that it will form SO42-, which is not volatile, and therefore sulfuric acid should not be used with these types of detectors.

So I am interested to poll the forum regarding people's opinions and experience with sulfuric acid in cases where volatile mobile phases are required.

Much Thanks

[Camisotro]

Hello

I wanted to ask people's opinion about the use of sulfuric acid in mobile phases when using detection modes like ELSD, CAD, or MS (where volatile mobile phases are needed).

We have had some discussion internally, and with vendors, and it's interesting how there seems to be a lot of difference of opinion on this issue.

Some people have noted that dilute solutions of sulfuric acid have boiling points around 100C, and claim they use it often with these types of detectors. Whereas others say that it will form SO42-, which is not volatile, and therefore sulfuric acid should not be used with these types of detectors.

So I am interested to poll the forum regarding people's opinions and experience with sulfuric acid in cases where volatile mobile phases are required.

Much Thanks

Concentrated sulfuric acid is an oxidizing acid. I would be afraid of it corroding metal parts if the water blows off leaving something concentrated behind.

Why are you thinking of using sulfuric acid? Is there no other alternative?

[tom jupille]

I'm not sure about the MS, but the ELSD and CAD actually detect aerosols. Sulfuric acid *will* form an aerosol, so I would think you would get a *very* high baseline.

In any case, I would *not* want to put concentrated sulfuric acid droplets in *any* detector.

[adam]

Yeah I see your points.

What I found attractive about it is that it allows for both low UV work and for volatile work, whereas nothing else that I know of allows for both. And I have recently spoken to one person who says they do use it routinely for situations where volatile mobile phases are needed.

But I think you may be right that the headaches associated with its use outweigh the benefits.

[Vlad Orlovsky]

we use TFA for UV (200 nm and up) and for ELSD. If you want to use sulfuric acid you will need to raise temperature to 80-100*C in ELSD and increase flow of nitrogen. I would also suggest to incorporate wash without any sulfuric acid after 10-50 runs.