Chromatography Forum

Hi,

First of all, I wonder if you know of any good reference to the different kind of additives that are used in plastic, or peaks that can migrate from plastic (with MS data preferably).

I have some peaks in my sample that has been shown to come from a PVC tube used in the production. If anyone happen to recognise any of these masses, suggestions on molecules are welcome. (Run of Waters QTOF with lockmass enabled, positive mode):

149.014
190.041
223.087
245.070

149,02332 [f+H]+ C8H4O3 Pthalic Anhydride fragment ion originating from phthalate esters

190,04987 [M+H]+ C10H7NO3 4-HCCA matrix compound

Source: supplemental data to
Keller, B.O.; Sui, J.; Young, A.B.; Whittal, R.M.: Interferences and contaminants encountered in modern mass spectrometry.
Analytica Chimica Acta (Review/tutorial, Special Issue on Mass Spectrometry), 2008.

Mattias,

You can find some info about additives directly from suppliers like CIBA or Great Lakes or you can buy one of these CDs http://www.chemtec.org/products.php?cat=9

Are the posted masses present as different chromatographic peaks?
Is it by ESI+?

Maybe diethylphthalate (M+H, M+Na) plus some fragments (149 phthalic anhydride)?

Regards,
bhuvfe

Thank you both, you have put me on the right track!

I have two well separated peaks with identical MS-spektra (ESI+). Sorry for the confusion, the masses are from within these peaks.

Phthalates sounds like a good idea, they seem all to have the fragment 149. I found about 80 MS-spektra of phthalates in www.massbank.jp, but no one fitted perfectly (although all phthalates with butyl in had the 223 fragment).

Just one theoretical question: It seems not possible to put any protons on these molecules, still I can see them in ESI+? Or can you add protons to the aromatic ring?

Protonating an aromatic ring by ESI is unlikely. But you have 4 O in phthalate esters and those give a + H ion (or other adducts).

Do you see a phthlate with mw 390 (neutral)? That should be quite a common one for PVC (dioctyl-phthlate).

If you decrease the cone voltage do you have an increase of the molecular ion?

I thought it was only possible to form positive ions in ESÃ

By ESI you can generally detect compounds with N, O, S, P (if they are polar enough).

149 is coming from in-source fragmentation (i.e. before the quadrupole of your Q-TOF). Decreasing the cone voltage might help to increase the molecular ion.

Switching polarity to negative mode might shed some light (if for instance what you are seeing is a mono-phthalate ester).

First of all, I have now confirmed that the peaks were indeed dibutylphtalates (two isomers) by comparison of retention times and UV-spectra.

But now I have got a new sample with another peak, most probably extracted from the new plastic tube (due to the phtalates issue, the quality was changed).

This new peak ionizes in negative mode (not tested positive). UV max at 256 nm, mass 151.0395 [M-H]. Suggested molecular formula: C8H7O3 [M-H]. MS/MS fragmentation gives only one peak, mass 92.0261 [M-H], suggested formula C6H4O [M-H].

I have searched in massbank.jp for these masses, but nothing was found. Seems to be a simple molecule? Do any of you have a feeling for what this can be? I assume that it must contain a carboxylic acid since it has good resonse in negative mode?

Maybe p-hydroxy-phenyl acetic acid ??

Do you see this compound at a concentration similar to your previous phthlates?

Do you see anything else getting out of the column?

Hi bhuvfe,

This peak is actually larger (as area%), but the response is probably very high since it is most likely an aromatic molecule. No other unexpected peaks were found except this large and very nice chromatographic peak. It elutes in a gradient at about 10% acetonitrile, so it cannot be too hydrophobic.

When searching directly for hydroxyphenylacetic acid, I found an MS/MS spektrum at massbank.jp: http://www.massbank.jp/jsp/Dispatcher.j ... 310&site=0. The m/z 92 fragment is there, but it is very small.

BTW, I have just learned that the new tubing is made of silicone and not PVC.

Any clues from the isotopic pattern of 151?

No Si or S?

Probably the preservative below or one of its salts(Na)?

http://en.wikipedia.org/wiki/Methylparaben

You may get some more info when running the sample in positive mode.

Thanks! It must be methyl paraben, it is used in the same factory. I have ordered a methyl paraben sample, and hope to run it on Monday.