Sensitivity issue with some pesticides
Posted: Tue Jul 26, 2022 12:54 pm
by stdev
Hello everyone,
in a LC-MS/MS method, I am facing serious sensitivity issues with some pesticides. About 90% of the measured pesticides appear great, but the following are barely visible in 1 ug/mL in the standard solution:
Clopyralid, MCPB, 1-naphthyl acetic acid, 2,4-DB, aminopyralid, mesotrione and others
Any suggestions?
Re: Sensitivity issue with some pesticides
Posted: Tue Jul 26, 2022 3:14 pm
by James_Ball
Not all pesticides work with LC and not all work with GC.
Compare this list that work well with LCMSMS
https://www.restek.com/en/products/refe ... ure/40244/
To this list that work well with GCMSMS
https://www.restek.com/en/products/refe ... ure/41952/
I notice that 2,4-D is not in either of those lists, but I have used LCMSMS to analyze for it before, but the sensitivity is less for it than most other analytes.
The ones you have trouble seeing my require different polarity of the source, or different temperature and flow rates versus the rest of your list. This can be a problem when trying to do a large list in one injection. You cannot optimize for all the analytes at the same time, so some will have good sensitivity and others not so good. May need APCI and not ESI. Not sure of your instrument setup to know what options you have.
Re: Sensitivity issue with some pesticides
Posted: Thu Jul 28, 2022 8:08 am
by H.Thomas
Most of the pesticides you mentioned are acids, and would be more sensitive using negative ionization and an eluent containing acetic acid rather than formic. What was your method (instrument, LC and MS parameters)?