GC/MS EI fragmentation

[jiangds06]

one compound has too much fragmentation, so sensitivity is very low. How can I decrease the fragmentation and increase the sensitivity.

[Consumer Products Guy]

one compound has too much fragmentation, so sensitivity is very low. How can I decrease the fragmentation and increase the sensitivity.

Extract an ion of interest and use that, or use SIM (selected ion monitoring).

[jiangds06]

already used SIM.

one compound has too much fragmentation, so sensitivity is very low. How can I decrease the fragmentation and increase the sensitivity.

Extract an ion of interest and use that, or use SIM (selected ion monitoring).

[rb6banjo]

To my knowledge, you (thankfully) have no control over how the mass spectrometer fragments the molecules coming out of the GC. If you had control over the amount/degree of fragmentation, the libraries we have for identification would be useless. It pretty much is what it is.

Going to something like CI might be an option for you?

What is the analyte?

[James_Ball]

One option on an Agilent 5973 or 5975 would be to lower the Emission setting which decreases the current (but not the Electron Volts) at the filament. You will sacrifice a little overall sensitivity but it will bias the fragmentation towards higher masses because of less total fragmentation. The ion fragments should be the same, just biased more to the heavier masses.

If it is a compound with multiple chlorine molecules, well there isn't much you can do in that case, all the permutations of having multiple chlorine molecules with 35 and 37 masses causes a lot of fragments and lowers the intensity of each.

[jiangds06]

Thanks so much!

One option on an Agilent 5973 or 5975 would be to lower the Emission setting which decreases the current (but not the Electron Volts) at the filament. You will sacrifice a little overall sensitivity but it will bias the fragmentation towards higher masses because of less total fragmentation. The ion fragments should be the same, just biased more to the heavier masses.

If it is a compound with multiple chlorine molecules, well there isn't much you can do in that case, all the permutations of having multiple chlorine molecules with 35 and 37 masses causes a lot of fragments and lowers the intensity of each.

[Yama001]

Some models of Agilent will allow to to lower the electron energy, even in EI mode (70eV), though this produces non standard EI spectra. A lower source temp may also reduce fragmentation a bit.