LC/MSMS Pesticide and polarity switching...

[cell]

Hi to all,
I work in a private lab and we analyze pesticide in food (fruit and vegetables for 80%).
At this moment with have 2 API 3200 and 1 API 4500Q.
I'm trying to improve run time and I want to try polarity switching.
I would merge 2 runs:
Positive 74 MRM transitions
Negative 55 MRM transitions

What do you think about that?

Thanks

[Gaetan Glauser]

The 4500 can switch polarity in 50 ms, so this may be feasible. However the 3200 needs 700 ms, which means at least 1.4 s to switch from one polarity to another and back. Probably too much if your chromatographic peaks are reasonably thin.

[mckrause]

You really have 55 pesticides that are that much better in negative ion? We only have a handful - maybe a dozen. I've always had issues with polarity switching and reproducibility on my Sciex, so my opinion would be to avoid it. If you have enough sample load that you need to double up runs then you most certainly can justify purchasing another system.