Chromatography Forum

I have this compound that keeps popping up in my samples and is apparently an important sulfur compound in our flavors. The best hit on the library is methyl thirrane which is only a 72% hit and I doubt that it is that as there is and 83 peak. I ran it with the ODP the other day and definately smells like a sulfur compound. I have NIST 04, Wiley, Flavors, and custom and it isn't a good match for anything in any of them. I am really desperate to identify it.

What is it's kovat's retention index?

Best regards,

AICMM

This sounds very familiar - I had two peaks that gave really good fits to a selection of three sulphur compounds, but none of them were the right retention index, and when I ran the sample on a pulsed photometric detector there was no sign of sulphur at all !! So much for library searches !

Do you have access to a high res MS ? - that will give you the empirical formulae of the fragments, and the molecular ion if there is one.

You might also try to find someone who is an expert at MS interpretation and get them to have a look at the spectrum.

Good luck, let us know how you get on.

Peter

MSChemist
Another way to help in the identification is to use the TAMI (Tal-Aviv Molecule Identifier) software of Aviv Analytical that is based on isotope abundance analysis. http://www.avivanalytical.com/Isotope-Abundance.aspx
You can send me the file if it is of Agilent Chemstation or MassHunter or Thermo XCalibur and I will send you the results of the likely elemental formula
You can also write here in this forum the abundance of M, M+1, M+2, M+3 and M+4 and the molecular ion mass with one decimal place after the rounded mass but a real file is better as the TAMI software will confirm or reject the NIST identification with a real file.
Amirav
amirav@tau.ac.il

Not sure the retention index. We haven't done that in quite some time because if it isn't in the flavors or other databases and we haven't run it as a raw material check it probably isn't listed in Kovats either.

Quite perplexing it is consitant with methy thirrane but it can't be because it has a 118 m/z peak which is larger than the compound. Methyl Thirrane would make sense if it is forming from allyl mercaptan.

major peak in order from most to least abundance are 41 74 84 and 118

Have you ruled out a co-elution of two compounds ? Can you run it on another stationary phase ?

Peter

I'm pretty sure I've seen it on both the wax and db-5 column. I like to run most scan samples on the wax column especially butter flavors or anything with lots of esters, acids, and acetoin. I use the db-5 when there are a lot of hydrocarbons or terpenoids.

It can be very difficult to resolve issues like this until you have an ABSOLUTELY unequivocal MW determination.

Re-analyze the sample, either

1) under CI conditions to give [M+H], [M+C2H5], [M+C3H5] with methane,

or if this is not possible,

2) under reduced EI voltage, to lower the degree of fragmentation

in case the m/z 118 ion is not the molecular ion.

Suppose the MW = 150.1; this may fit one of your library matches.
If not, run a search on Chemspider.com for compounds with MW 150.1 +/- 0.1; flag the S-containing compounds for further consideration.

Take note of what Amirav offers above - or at least of the portion of the spectrum he is directing you to! For a given molecular formula, for a compund made of terestrial chemical sources, the m, m+1, m+2 etc. relative abundances are set by the natural abundance of isotopes of the elements. This can be made difficult by molecules which like to fragment by loss of hydrogen. But, they tend to give themselves away. The ratio of m+2 to m can tell you how many sulfur atoms are present in the formula.

If you have an unknown that you need to identify and the library does not nail it, break out your copy of McLafferty and Tureek, Watson and Sparkman, or your other favorite intro. to mass spec and go through the steps for spectral interpretation.

Thanks very much to Dr. Amirav we are able to determine that there are two realted isomers after running it again on the wax column.

The formula is C6H14S

The spectra is not a match for dipropyl sulfide, ethyl n-butyl sulfide, nor methyl amyl sulfide. I'm afraid so far it remains a mystery. Perhaps a seven member ring compound with 1 sulfur 6 carbons.

Search of the formula by chemspider generated 28 possible structures.

http://www.chemspider.com/Search.aspx?q=C6H14S

It looks like the next step is to look at fragments and see what makes sense. Looking at the list of possible compounds, some of the substrutures in compounds in the list should be revealed in the mass spectrum - if they are present.

R + DB for C6H14S = 0; NOT a cyclic compound.

Loss of 34 Da (m/z 118 -----> 84) is consistent with H2S; loss of 33 Da (m/z 74 ----> 41) is consistent with HS radical cation loss.

This data suggests an alkyl thiol, rather than a sulfide.