High boiling compounds by GC/MS

[bhuvfe]

cheers,

What I'm interested in is long chain alkane type molecules, oil fractions etc. Is a C80 chain out of the question?

It seems to be possible if you can afford a SBM-GC-MS (http://www.avivanalytical.com/Supersonic-GC-MS.aspx).

I've seen presentations\paper from the guy above of hydrocarbons close to your C80 (polywax 850). The molecular ions using this technique are favored (expecially for hydrocarbons) and so seeing a M+. between 60- 100 % intensity is quite common.

I found out that there's a picture on their website.

http://www.avivanalytical.com/Uploads/E ... %20fig.jpg

[AV]

In order to elute long chain alkanes such as above C40 one needs to use short columns with thin film and particularly with high column flow rates as is done in SIMDIS analysis by GC-FID. The main problem in GC-MS however is that above C30 they are no molecular ions and due to the similarity of fragmantation patterns the mass chromatograms are without additional information compared to GC-FID. This is particularly true for branched isomers and at high ion source temperatures that are required to eliminate ion source related peak tailing. For the analysis of long chain alkanes at 300C ion source temperature already for C20 no molecular ion will be exhibited.
If such analysis is essential go to www.avivanalytical.com and contact them for further information.

[ods-at-pacific]

There are three spectra in the NIST08 Mass Spectral Database that have >50 C atoms and only C and H. All three are from D. Henneberg and where probably obtained using a direct insertion probe. One is a straight-chain C60 and the other is a straight-chain C54. The molecular ion peaks have intensities of between 3.5% and 4.5% of the base peak. The third spectrum is of an aromatic cyclooctane with the eight hydrogen atoms replaced with phenyl groups. The base peak in this spectrum is the molecular ion peak. The estimated retention index on a non-polar column using an n-alkane scale is ~6,000 for all three compounds.