GC-MS

320d

Can a GC-MS analysis clearly distinguish between a Benzene peak and a Benzoic acid peak?

Cheers,

craggles

Yeah, they're different masses so they'll be different on the mass spec and benzoic acid is more polar so that'll give different GC peaks.

320d

craggles wrote: »

Yeah, they're different masses so they'll be different on the mass spec and benzoic acid is more polar so that'll give different GC peaks.

Thanks for that - I had read in some papers that the could show similar peaks but suspected that it was not correct.

Jokesetal

Craggles was right and this link will give you the MS spectra (Fig 6a) for reference (http://www.rsc.org/education/teachers/learnnet/pdf/LearnNet/rsc/MS_txt.pdf)

Saying that the GC with an FID will also do this on a moderately polar column, with the benzoic acid being retained longer.

ianobrien

320d wrote: »

Thanks for that - I had read in some papers that the could show similar peaks but suspected that it was not correct.

The papers are probably correct. I'm assuming that it was a GC-MS with an EI source. This is a hard ionisation source, and will result in fragmentation of the molecules.

As benzene and benzoic acid share some structural similarities, I expect them to share fragments.

320d

Can a GC-MS be run with a different source to validate if it is benzene or benzoic acid?

ianobrien

There is no need. The fragmentation pattern will tell you. The loss of 18 & 45 should be enough.

Swap sources if you want, but there is no need.