Chromatography Forum

Hi all

I have a group of closely eluting peaks from African wild dog preputial gland that elute slightly before benzoic acid on a Restek wax column, and whose mass spectra consist almost solely of an m/z 58 ion, with a few very small peaks for lighter ions. These search on the NIST library as various N,N-dimethyl..........amines, sometimes with other substituents. The 58 fragment is presumably (CH3)2NCH2 but the spectra are completely uninformative as to what the "tails" might be.

Does anyone have any suggestions as to how I might get at least a hint of the structures ? - GC-MS based techniques would be preferred since that is all I have on site. I had thought to reduce ionisation energy to try to get some molecular ion, or otherwise to increase it to try to fragment the "tail". CI is also a possibility. Failing an analytical approach, are there any educated guesses as to likely molecular weights given elution from a 30 m x 0.32 mm x 0.5 um PEG column running helium at 35 cm/s about 1 min before benzoic acid at around 180C ?

Thanks.

Peter

Hi Peter
It seems as you wrote to be a fragment of an amine with (CHH3)2NCH2.
To get a molecular ion CI would be your best choice for amines
If you wish you can write me and I will be happy to get your sample and analyze it with our 5975-SMB GC-MS with Cold EI with the added benefit that we could use our TAMI software to obtain elemental formula and avoid any ion source degradation if this is a labile and highly polar compound.
Amirav
amirav@tau.ac.il

Thank you Amirav, that is a very generous offer.

I will be in touch by e-mail.

Peter

I'm not familiar with that particular matrix, but I've seen two sets of peaks with MS like that. They elute later than benzoic acid though (at least they do on a non-polar column).

1 - In tertiary amines (seen from thermal decomposition of quaternary ammonium compounds such as benzalkonium chloride) the EI spectrum was mainly 58, along with a very small molecular ion. e.g dimethyl dodecyl amine (C14H31N) had a tiny 213. On a non-polar column (DB5) they elute right after the corresponding n-alkane. So dimethyl dodecyl amine with 14 carbons and 1 nitrogen eluted just a couple seconds after n-C15. And the related homologues (dimethyl C10 & C14 &C16 amines) behaved similarly, RT-wise and spectra-wise.

2 - When I ran a multi-residue extract of raw eggs years ago, there were 3 closely eluting small peaks where 58 was pretty much the only mass peak. There was no good library search match. These were relatively late eluters (between the C18 fatty acids and cholesterol). I speculated they might have derived from phospholipids. However, 10+ years later I haven't figured out what they were, and haven't seen any other food or other samples that gave peaks like that.

I didn't have CI or other 'soft ionization' capabilities to look for the molecular ion. I've tried switching the tuning to emphasize the heavier masses (in HP Agilent, the Standard Spectra tune does that better than Autotune) and cranking up the EM by 200 or so. On-column injection could avoid thermal degradation in the hot injection port, but I didn't have that either. If you can get your extract to Amirav, that would be excellent. It's amazing what he's done to expand the GC-MS range. DH

Hi all

I have a group of closely eluting peaks from African wild dog preputial gland that elute slightly before benzoic acid on a Restek wax column, and whose mass spectra consist almost solely of an m/z 58 ion, with a few very small peaks for lighter ions. These search on the NIST library as various N,N-dimethyl..........amines, sometimes with other substituents. The 58 fragment is presumably (CH3)2NCH2 but the spectra are completely uninformative as to what the "tails" might be.

Does anyone have any suggestions as to how I might get at least a hint of the structures ? - GC-MS based techniques would be preferred since that is all I have on site. I had thought to reduce ionisation energy to try to get some molecular ion, or otherwise to increase it to try to fragment the "tail". CI is also a possibility. Failing an analytical approach, are there any educated guesses as to likely molecular weights given elution from a 30 m x 0.32 mm x 0.5 um PEG column running helium at 35 cm/s about 1 min before benzoic acid at around 180C ?

Thanks.

Peter

I'm not familiar with that particular matrix, but I've seen two sets of peaks with MS like that. They elute later than benzoic acid though (at least they do on a non-polar column).

1 - In tertiary amines (seen from thermal decomposition of quaternary ammonium compounds such as benzalkonium chloride) the EI spectrum was mainly 58, along with a very small molecular ion. e.g dimethyl dodecyl amine (C14H31N) had a tiny 213. On a non-polar column (DB5) they elute right after the corresponding n-alkane. So dimethyl dodecyl amine with 14 carbons and 1 nitrogen eluted just a couple seconds after n-C15. And the related homologues (dimethyl C10 & C14 &C16 amines) behaved similarly, RT-wise and spectra-wise.

2 - When I ran a multi-residue extract of raw eggs years ago, there were 3 closely eluting small peaks where 58 was pretty much the only mass peak. There was no good library search match. These were relatively late eluters (between the C18 fatty acids and cholesterol). I speculated they might have derived from phospholipids. However, 10+ years later I haven't figured out what they were, and haven't seen any other food or other samples that gave peaks like that.

I didn't have CI or other 'soft ionization' capabilities to look for the molecular ion. I've tried switching the tuning to emphasize the heavier masses (in HP Agilent, the Standard Spectra tune does that better than Autotune) and cranking up the EM by 200 or so. On-column injection could avoid thermal degradation in the hot injection port, but I didn't have that either. If you can get your extract to Amirav, that would be excellent. It's amazing what he's done to expand the GC-MS range. DH

Hi all

I have a group of closely eluting peaks from African wild dog preputial gland that elute slightly before benzoic acid on a Restek wax column, and whose mass spectra consist almost solely of an m/z 58 ion, with a few very small peaks for lighter ions. These search on the NIST library as various N,N-dimethyl..........amines, sometimes with other substituents. The 58 fragment is presumably (CH3)2NCH2 but the spectra are completely uninformative as to what the "tails" might be.

Does anyone have any suggestions as to how I might get at least a hint of the structures ? - GC-MS based techniques would be preferred since that is all I have on site. I had thought to reduce ionisation energy to try to get some molecular ion, or otherwise to increase it to try to fragment the "tail". CI is also a possibility. Failing an analytical approach, are there any educated guesses as to likely molecular weights given elution from a 30 m x 0.32 mm x 0.5 um PEG column running helium at 35 cm/s about 1 min before benzoic acid at around 180C ?

Thanks.

Peter

Interesting, thanks. A possible origin from phospholipids is intriguing since the preputial gland has a sebaceous component. Benzoic acid's elution is retarded on a wax column, and so we might be looking at similar compounds. I have run some samples with PTV injection, which is gentler than flash vaporization, so I need to review that for any differences. I must also check back for what I have run on a non-polar column.

I certainly plan to take Amirav up on his offer, but getting biological samples across borders involves a lot of paperwork !.

Peter