July 17, 2024, 05:42:05 AM
Forum Rules: Read This Before Posting


Topic: About GC-MS  (Read 2126 times)

0 Members and 1 Guest are viewing this topic.

Offline kamiyu

  • Full Member
  • ****
  • Posts: 181
  • Mole Snacks: +8/-7
  • Gender: Male
About GC-MS
« on: June 24, 2014, 03:43:35 PM »
Do you think the intensity of the GC chromatograph is a reliable indication of relative concentration?

Linear relationship? or something?

Offline kriggy

  • Chemist
  • Sr. Member
  • *
  • Posts: 1520
  • Mole Snacks: +136/-16
Re: About GC-MS
« Reply #1 on: June 25, 2014, 12:15:07 PM »
I would say yes but also suggest doing calibration curve

Offline Furanone

  • Chemist
  • Full Member
  • *
  • Posts: 211
  • Mole Snacks: +34/-2
  • Gender: Male
  • Actually more a Food Chemist
Re: About GC-MS
« Reply #2 on: July 18, 2014, 09:25:53 PM »
In a general sense, yes, but each chemical compound will have a unique response factor that you would multiply by the area (or height) of that chemical's peak to obtain the true concentration, and these can be significantly different for different compounds. MS peak quantification is based on how well each type of molecule fragment when an electron beam hits them coming out the end of GC column into ionization chamber (and usually this is only a small percent), so compounds where a higher % of molecules fragment from the electron beam and also more fragments are created since each created ion that passes through quadrapole will hit the electron multiplier detector is counted will give a higher response (TIC).

In flame ionization detection (FID), quantification response is based on the combustion of organic material so there will be a higher relative response for molecules with more -C-C- or -C-H bonds so running fatty acid methyl esters will have a quantification bias for the longer chain fatty acids and a compound such as carbon dioxide would give virtually no response.

In my experience both GC-MS and GC-FID analyses I run in a food lab look similar to each other and have fairly good relative quantity responses (ie. there are no examples seen where a tiny peak has a massive quantity while a large peak works out to be a trace quantity).

Hope this helps
"The true worth of an experimenter consists in pursuing not only what he seeks in his experiment, but also what he did not seek."

--Sir William Bragg (1862 - 1942)

Sponsored Links