Interesting question, following the answers

You can buy a GC-C-IRMS for the determination of isotopic ratios in certain organic substances and some pollutants.

But only with the GC (FID detector) you can have the concentration of these organic substances and see their importance in the environment.

13C and !5N NMR spectroscopy is a good option for your work.

:Please refer: Kogel-Knabner 1997.

It all depends on the mass analyzer.

GC-MS has a quadrupole analyzer and an electron ionisation source generally kept at 70eV to fragment organics into smaller ions having different m/z.

GC also can have a TOF (Time of Flight)

While IRMS is used with peripheral having combustion source. in case of organic carbon, carbon is transformed to carbon dioxide and magnetic sector mass analyzer seperates the 13CO2 and 12CO2.

If you wish to identify the organic contaminants and also want to analyse isotopic composition of the specific compound, you wont be able to perform it with a single instrument.

For identification, you need GC-MS and for isotopic composition you need an IRMS.

GC coupled to IRMS will only able to provide results based on the known external standards and that too is subjected to erroneous values as a single peak in GC might correspond to 2 compounds eluting at the same retention time (co-elution).

I would recommend a GC-MS as you are dealing with organic contaminants and not the isotopic composition.

The short answer is purchase a GC Isolink II from Thermo. Here is why.

As previous respondents have already pointed out, one cannot use a GC/MS to analyse (quantify) variations in stable isotopic composition at near natural abundance level. GC/MS is only useful for serious tracer work (enrichment levels >0.5 APE). Conversely, GC-IRMS are non-scanning instruments designed to measure isotopic composition at near natural abundance level. To this end, compounds are combusted to yield N2 and CO2 which compounds cannot be identified. However, if you have not made a purchasing decision yet, there is a solution. Based on my original design, with their GC Isolink II Thermo are now offering an instrument that gives yiu the best of both worlds. Here, a GC is coupled to both an MS and an IRMS in such way to yield MS identification of a given and compound 13C abundance value simultaneously.

Prof. Wolfram stated it correctly. The system provided by thermo is a GC-MS-IRMS and it will surely surely serve the purpose.

I appreciate for your kind replies. Wolfram Meier-Augenstein you've provided a great info that I can definitely consider for our purchase. I think this info will also help those who has either tight budget or not enough room for two instruments.

In case anybody is interested in the origin of the GC Isolink II‘s design/ set-up.

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