Hardware and method for Sulfur analysis

[MSCHemist]

I do sulfur compounds all the time as I work for a meat flavors company and sulfur are important meat flavors. There are a number of different detectors on the market FPD (old and nonlinear responses), PFPD, and Sulfur Chemiluminescence Detector. I use a MSD.

I have an old FPD on my 6890 that was purchased with the instrument 6 years ago. I wasn't here at the time as noone has ever really used it. I see no real benefit to it over the MSD most of what I do with sulfur is qualitative reports. I use HS SPME and give TIC's and % library reports for flavor duplications to the flavorists. I have found the sulfur compounds are actually pretty well behaving. They give good peak shape on the db-5, 1701, and wax column. I can see all sorts of sulfur compounds just fine from methyl mercptan, dimethyl sulufide allyl disulfide, thiophenes, furfuryl thioacetate....

The only issue I have is I somewhat frequently see Sulfur compounds not in any of my EI libraries I have Flavors, Wiley, and NIST 04 or so plus whatever custom entries I input from raw materials checks.

[Peter Apps]

The only issue I have is I somewhat frequently see Sulfur compounds not in any of my EI libraries I have Flavors, Wiley, and NIST 04 or so plus whatever custom entries I input from raw materials checks.

If you do not have a sulphur specific detector, how do you know that the compounds have sulphur in them ?. I have two puzzling unknowns with very strong molecular ions that search out as impossible sulphur or nitrogen compounds and come up with a 98% probability of containing sulphur in a spectrum processing software whose name eludes me at present, but which are completely invisible on a PFPD in sulphur or nitrogen mode. So, although the MS is convinced that there is sulphur there, in fact there isn't.

Peter

[AaronAIT]

The only issue I have is I somewhat frequently see Sulfur compounds not in any of my EI libraries I have Flavors, Wiley, and NIST 04 or so plus whatever custom entries I input from raw materials checks.

If you do not have a sulphur specific detector, how do you know that the compounds have sulphur in them ?. I have two puzzling unknowns with very strong molecular ions that search out as impossible sulphur or nitrogen compounds and come up with a 98% probability of containing sulphur in a spectrum processing software whose name eludes me at present, but which are completely invisible on a PFPD in sulphur or nitrogen mode. So, although the MS is convinced that there is sulphur there, in fact there isn't.

Peter

How does the M+2 peak look on these compounds?

[Peter Apps]

The only issue I have is I somewhat frequently see Sulfur compounds not in any of my EI libraries I have Flavors, Wiley, and NIST 04 or so plus whatever custom entries I input from raw materials checks.

If you do not have a sulphur specific detector, how do you know that the compounds have sulphur in them ?. I have two puzzling unknowns with very strong molecular ions that search out as impossible sulphur or nitrogen compounds and come up with a 98% probability of containing sulphur in a spectrum processing software whose name eludes me at present, but which are completely invisible on a PFPD in sulphur or nitrogen mode. So, although the MS is convinced that there is sulphur there, in fact there isn't.

Peter

How does the M+2 peak look on these compounds?

Are those big peaks really the molecular ions ? is the question before that one ! I suspect that the "sulphur compounds" just happen to fragment to give very low intensity M+, and a pattern of fragments that is plausible for a sulphur compound of much lower MW. CI is the next step to get a decent sized "molecular" ion for the MW, and then high res MS.

Peter

[MSCHemist]

I known they are sulfur compounds because a lot of my samples are loaded with a diverse amount of mercaptans, sulfides, disulfides, trisulfides. I saw one compound that the closest match was methyl thiirane and shared many ions but it also had larger fragments larger than the molecular mass of Methyl thirrane.

You can also smell them on our ODP.

[Peter Apps]

Hi MSchemist

Maybe the problem peaks are co-elutions - you have methyl thiirane in the peak, but something else as well that provides the heavier fragments. When I was doing GC-MS-GCO for flavours the large majority of the unknowns turned out to be multiple compounds in one peak when I used heart-cutting 2D GC to pull things apart some more.

In GCO you will still smell the sulphur compound even if it is co-eluting, and a sulphur-specific detector will show the peak as being a sulphur compound, but there is something else there as well (which might, of course be another sulphur compound).

Have you tried running on a different stationary phase ?

Peter

[MSCHemist]

I doubt it I have run it on multiple columns db-5 and Wax and I now use a 1701 as my work horse. Usually when things coelute there is at least some sign or it like a small dip in the line or slightly different spectra when looking at either side of the peak.