How to analyze 20 % HNO3 solution...

[bunnahabhain]

... without destroying my LC-MS?

I have the following challenge: A customer has an application using a membrane. One batch of this membrane (PFSA) does not perform well. They have washed it with 20 % HNO3 and then it is fine. No metals are causing this effect (ICP measurements and comparison with good batches show no difference). Washing with alcohols and water does not help.
Now they asked me if I could measure LC/MS fingerprints of extracts prepared with 20 % HNO3 from a good and from the bad batch to find out the possible contamination.
Any ideas?
Thanks a lot,
Jörg

[osp001]

Offhand, I'd ask if they could try solvent washes and run those if the membranes work correctly after that. Ethanol and water washes may not work, but chloroform, dichloromethane, etc. may prove more useful.

If that's a no-go, split the sample, adjust the pH to something more palatable, and hope enough of your putative analyte stays in solution to tickle your detector.

[lmh]

are they sure the nitric acid washed something out, or is it possible that it modified the membrane chemically? If it did wash something out, it's quite possible the something will now be oxidised beyond all recognition anyway - that's a pretty ferocious cleaning agent.

[bunnahabhain]

Thanks lmh and osp001, I recommended the customer to extract the membrane with a stronger organic solvent and see if the process works then.