ESI ionization: How to avoid in-source fragmentation

[bunnahabhain]

Hi everybody.
I am about to develop a method for the determination of a pesticide. I don't manage to get the M+H ion, but the first fragment ion is very abundant. I tried to play with capillary voltage, cone voltage, temperature, but nothing helped.
The instrument is a Quattro Ultima Pt. Eluent of choice is H2O/ACN + 0.1 % HCOOH. I changed to MeOH but this did not improve the situation. Any further ideas?

Thakns very much
Jörg

PS.: How do you folks think about it: Will it be acceptable for authorities if quantificationis based on a fragment instead of the parent molecule?

[Klaus I.]

It is difficult to say what are the proper parameters for you substance. A pronounced in-source fragmentation is also often caused by a dirty ion-source. Have you a possibility to compare the observed fragmentation with other instruments or measurements in the history?

Nevertheless, since this type of ion source is known to be quite thin-skinned when you are analyzing unstable molecules. It would be a good starting to have a closer look on the source. All parts of the source (and the probe) should be perfectly clean and should be as good as new.

[nbik]

Hi everybody.
I am about to develop a method for the determination of a pesticide. I don't manage to get the M+H ion, but the first fragment ion is very abundant. I tried to play with capillary voltage, cone voltage, temperature, but nothing helped.
The instrument is a Quattro Ultima Pt. Eluent of choice is H2O/ACN + 0.1 % HCOOH. I changed to MeOH but this did not improve the situation. Any further ideas?

Thakns very much
Jörg

PS.: How do you folks think about it: Will it be acceptable for authorities if quantificationis based on a fragment instead of the parent molecule?

Dear Jorg,
first of all can you tell us one thing - what operating mode you are working?
Quattro Ultima can make MS\MS mode so may be you just need to switch it off?

Also in-source fragmentation can be not only in source, it can be somewhere in the ion optic. For example Agilent's qtof can have fragmentation after glass capillary and it's also big problem sometimes. So may be you have the same problem.

I can't tell anything about quantification because i'm not expert but i think you can make MRM and quantify it.

[Gaetan Glauser]

As long as it matches the conditions required for reliable quantification, I do not see any issue with selecting a fragment. I think there have been many examples of MRM transitions in the literature which did not used the pseudo-molecular ion but fragments as precursor ion.

[bunnahabhain]

Thanks for the input, everyone. I played around with different solvents, and had much more luck using methanol/water with 5 mM NH4Fm instead of ACN/H2O with 0.1 % formic acid. The fragment is completely gone with methanol. Funny, because the literature method I wanted to use was based on ACN/H2O + FA.