When performing pyrolysis of soil and pyrolysis of poly(ethylene terephtalate) via TGA-MS and becoming a signal of mass 57, may I attribute it to [CH3CH2CH2CH2]+ and/or [CH3CH2CO]+ as a products of cleavage of soil organic matter and PET (alkanes, esters), e.g. like in following link?
Dear Jan,
supposed you used EI+ ionization, both is true (but where is your link?). Did you do pyrolysis of soil and PET separately or as soil/PET mixture? m/z 57 is indicative for aliphatic petroleum hydrocarbons (then followed by a series of peaks with delta-m/z=14 (CH2): 57, 71, 85, 99...) or for fatty acids (if saturated with the same peak series but additional peaks appear). m/z 57 may also came from F.A.M.E. (biodiesel), but then with m/z 74, 87, 143. In natural, uncontaminated soils I wouldn't expect high amounts of all of these: Petroleum hydrocarbons typically are contaminations, and natural fats/fatty acids/F.A.M.E. are easily bioavailable and degrade quickly.
Indicative for phthalates is m/z 149.
So I would not stick to m/z 57 for speciation, because it is very unspecific, but would choose more typical masses for the given compounds.
I can recommend you Hübschmann, "Handbuch der GC/MS" (VCH) for reading.
Hope my answer was helpful. Best regards
Thomas
Dear Thomas,
thank you very much for your kind answer. Sorry, the link is here:
http://www.chemguide.co.uk/analysis/masspec/fragment.html .
I am doing pyrolysis of soil and PET mixtures, but the results coming from separate analyses of soil and PET are showing, that 57 signal is present in pyrolysis products of both of them.
Best regards,
Jan
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