I am going to attempt to develop a method for analysis of polycyclic aromatics using lc/ms and I was wondering if anyone has a good method for that. Also, it would be good to know at what concentration I should prepare a standard. I will be monitoring for PAHs in soot extracts.

Thank you

There are standard protocols with standard columns around. Contact a column manufacturer!

The literature for methods in LC-MS is rapidly growing; for an example look at article in issue 3 of The Analyst, 2000 pag. 417
“Electrospray mass spectrometric determination of 1-nitropyrene and non-substituted polycyclic aromatic hydrocarbons using tropylium cation as a post-column HPLC reagent”.

You will probably not be able to see underivatized PAHs with LC/MS, even if you use APCI, unless they are heterocyclic. Chromatography should be simple, but a pre- or post-column derivitization will probably be needed.

Anon-
Why exactly will I not be able to see them if they are not derivitized? I'm sure you're right; many of the articles I found deal with partially oxidized pahs or something like that. I did do a couple of runs with some simple 2-8 ring structures (just the hydrocarbons with nothing else on them). Chromatography was fine, but the mass spec data did not really show anything.

If you have any insights, I would appreciate it.

Ross

Ross,
I haven't seen it explained in the literature, but here is what I think happens (I tried it then ended up using fluorescence detection). The MS has to see an ion. The ions formed in LCMS are even electron ions formed by the gain or loss of H+. You aren't actually changing the number of electrons when you form the ion. The aromatic electron distribution of PAHs can spread the charge out over the molecule so the detector doesn't see it. I think the charge has to be site-localized rather than evenly distributed. Someone else may have a more technical explaination, but that is what I think is happening.

That's kind of what I thought might be happening too. I'll see if I can find anything else in the literature about it or change to a different type of compound. Thanks.

I recall a poster that was presented at ASMS 2001 where they were doing PAH with a new source using photoionization, APPI. It looked promising. If you go on their WEB site www.asms.org and search on PAH, you should be able to find it. I believe it's manufactured by Agilent but I'm not 100% sure.

Good luck, let us know of your progress as it is still a hot topic.
Richard.

Does it has to be LC-MS?
I have seen excellent GC-MS separations up to 6 membered rings (coronene). Identification with MS is then trivial.