Method SIM- GC-MS

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

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Goodmorning everyone !

I'm approaching the Gc-Ms with a shimadzu QP2010u. I have already found a 54-minute scan method with collecting m / z 50 -500. I wanted to fine-tune the method with a SIM method. the analyzes we perform are on food matrices (fruit) using the EPA 8081 method. can you give me some suggestions for how to create a SIM method knowing the retention times of my compounds? how many ions do I put? how many acquisition effect (maximum 64 ions each acquisition)?
please !
thank you all for your attention
if they should serve other data I can attach a .pdf with my method and examples of molecules

thanks
Alberto,

You would set time ranges during which each compound should be monitored, the specific ions, and the dwell time. You should get at least 10 points across a peak. You can monitor only one ion pet compound but 3 are recommended: one for quantitation and two qualifiers for confirmation of compound id.

Best of Luck!
Arne
Hey Arne

I research about 60 pesticides. How can I organize each purchase window? I order the compounds in order of RT and I take for each compound three ions? in case of molecules that come out at very close times, how can I divide the buying window?


Thank you very much for your attention

There are an examples of my compound (end the run at 44 minutes ):
Principio Attivo T.R. sper. ione 1ione 2
Methomyl, 10,00 105 71
Hexaflumuron 10,43 141 113
Acephate 11,65 136 94
Cimoxanil 13,00 111 167
Triflumuron 13,70 139 155
Ortofenil fenolo 14,00 170 169
Ethoprophos 14,50 158 97
Lufenuron 14,65 176 178
Omethoate, 16,47 156 110
flonicamid 16,49 174 146
Imidacloprid, 16,85 141 157
Dicloran 17,04 176 178
Hexaflumuron 17,37 176 178
Lufenuron 18,89 350 352
Ethoxyquin 19,84 202 174
Fenpyroximate, 19,90 213 212
Dimethoate, 20,26 87 93
Benfluralin 20,58 292 264
Teflutrin 20,75 177 197
ect .......
Hey Alberto,

It would be easier if someone could show you these things hands-on.

Albertospd wrote:
I order the compounds in order of RT and I take for each compound three ions?


Yes. Within a window, the order of compounds does not matter. They are all measured across the window. I believe 2 ions for pesticides is generally accepted.

Albertospd wrote:
in case of molecules that come out at very close times, how can I divide the buying window?


You want to avoid putting a window end/start when a peak elutes. I think this also depends on software - i can image some software can deal with this, but it's not an ideal situation since there is likely a baseline and peak point difference hindering a good quantification. Look at full scan chromatogram and look for spots where no compounds are eluting, for example:

Window 1 start @ 9,00min
Methomyl, 10,00 105 71
Hexaflumuron 10,43 141 113
Acephate 11,65 136 94
Window 1 end @12,30min
Window 2 start @12,30min
Cimoxanil 13,00 111 167
Triflumuron 13,70 139 155
Ortofenil fenolo 14,00 170 169
Ethoprophos 14,50 158 97
Lufenuron 14,65 176 178
Window 2 end @ 15,50min
Window 3 start @ 15,50min
Omethoate, 16,47 156 110
........

Do you have knowledge about peak points/dwell times or is this concept new for you? For advice about these settings, we'll need to know how wide the peaks are (+-).
Dear Rndirk

I know these concepts and they are not new but I do not know how many points each peak collects. I replace a person who unfortunately is not there and therefore I am trying to understand also through your help something since I can not talk to him.


thanks for your availability
Method GC

Sliptless
injection 250 °C
oven 50 °C
50 °C - 1 min
25 °C --> 120 °C --- 2 min
5 °C ----> 300 °C --- 12 min
total time 54 min
MS method : SCAN

7.5 ----54 min (event time 0.25 sec)
scan speed 2500
start m/z 50 to 560
Dear Alberto,
I don't know if you still need this, but GCMS Solution has a very useful tool for making SIM methods. After you have a proper scan chromatogram, you click 'Method' at the top of the window and choose 'Creation of Automatic MRM or SIM table'. It sets retention time windows and monitored ions automatically, but you can make changes afterwards if you need it.
When I make SIM method I usually choose one main ion and two qualifiers.
Hope I helped you a bit.

Anna
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