> Dear Group,
>                 I have been investigating stable carbon isotope ratios of
> organic contaminants in the sub-surface of a disused manufactured gas
> plant. This involves injecting solvent extracts and getting the
> mass spectra and d13C ratio.  Whenever molecular sulphur is identified on
> the quadropole, the 46/44 ratio for the background subtraction on the IRMS
> (Isoprime, Micromass) goes off the scale, making automated or manual
> correction practically impossible. Has anyone any ideas what is causing
> the 46 ion? I can't figure it out. I hope the answer is not too obvious!
>                                 Thank you

Dear James,

I'm afraid it just might be. Obvious that is. The answer that is.

If you have a look at the EI mass spectrum of CS2 you will find
fragment ions at m/z44 and m/z46 in the predicted ratio for natural
abundant S isotopes. These fragments correspond to 12C32S and
12C34S, respectively.

You either have contamination of CS2 present or it is formed in-
situ. The EI mass spectrum of CS2 contains the following peaks in
decreasing order of intensity: m/z76, mol peak and base peak (and
its M+2), m/z32 (and 34) and m/z44 (and 46).

Hope this helps.


All the best,

                      Wolfram



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Dr. W. Meier-Augenstein, CChem MRSC
Senior Research Fellow

University of Dundee, Dept. of Anatomy & Physiology,
OMS, DUNDEE  DD1 4HN, United Kingdom

Tel. (B): +44-(0)1382-34/5124 or /4574
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