# How to quantify 100+ pesticides with GC/MS in SIM?

Hi everyone!

In my lab, we set a method for the analysis of 10 pesticides with an single quadrupole GC/MS in SIM mode. No problems. Now we want to add, analyse and quantify more than 100 compounds in SIM too but the MS methos alerts me that 420 ions are too much (130 compounds x 3 ions = 420 ions). So, my question is: How can I analyse and, most important thing, quantify all these new compounds?

Any suggestion?

Thank you so much!

Parents
• You need to create time segments with small groups of SIM ions.  Longer SIM ion dwell time improves sensitivity and noise rejection, so keep the individual ion dwell times as long as possible - 50ms or more each if you can - and keep the SIM group cycle time reasonable so that you get enough SIM data points across each peak for good shape and quantitation.

• thank you for you answer. i created 8 time segments and the biggest ones have 20 compounds (20 x 3 ions = 60 ions). maybe is it better if i create more time segments with less compounds?

• 60 ions in a time segment is still too many.  I like down around eight to ten SIM ions in each time segment maximum - (if you're choosing 3 ions per compound then nine to twelve max).  That way I can have longer dwell times on each ion and still have enough cycles to get good peak shape.

• Cool! So I just have to split my 31 minutes run into little tiny time segments with no more than 4 compounds per segment. correct?

• UPDATE

I split my run in 45 time segments with the maximum number of 12 ions for segment (not every segment has 12 ions.. 4 or 5) but the same message appears when I want to save the MSD method

• UPDATE

I split my run in 45 time segments with the maximum number of 12 ions for segment (not every segment has 12 ions.. 4 or 5) but the same message appears when I want to save the MSD method

Children
• Too many ions selected for plotting:

Uncheck most of them!

Also, your Cycle time is about 2 seconds -- which is too slow for most peaks, especially as you are doing SIM/Scan acquisition.  You need to reduce your dwell times to get a cycle time ----  so you get at least 10 SIM cycles across your chromatographic peaks for decent quantitation.   This is a dance with many partners and your parameters may need some tweaking.

• well..i cannot check that ions because that are my quant ions. The only thing I can do is reduce the dwell time. I can try to do it in SIM mode only.

• Those plots are for the online graph during the run.  You only need one checked per time segment so that you can see that data is being acquired. It has nothing to do with quantitation.

• so i can untick them if I understand correctly. and for the dwell time? i set the dwell time to 50 for the time segment with 3 compound (9 ions), 30 for the time segment with 4 compound (12 ions) and 70 for the time segments with 2 compounds (6 ions) as you can see in my screenshot