tuning the MS for low res VS high res

[PeterPopoff]

how is each one done properly and what is the point of doing it. If I'm going to be running MRM SIM events in low resolution mode, is it best to tune the spectrometer q1 vand q3 for low resolution rather than regular resolution as is done during auto tuning? I'm using a shimadzu instrument.

[lmh]

I can't comment on Shimadzu on this one, but I'd suggest being a bit cautious what you gain from changing resolution on a quad. Waters offer a whole array of different resolutions on their Xevo instruments, but almost every user only uses one setting! The thing is that "high" resolution on a quad is still unable to differentiate between near-isobaric compounds, so setting the resolution to, say, 0.4 instead of 0.7Da achieves virtually nothing when it comes to selectivity, but costs you sensitivity. Any half-way decent quadrupole can give good sensitivity at 0.7Da, so why set it worse? In effect, check what high- and low-resolution mean, and stick to about 0.7 for everything, and you won't go far wrong!
As I said, I can't comment on Shimadzu, but I do notice that manufacturers tend to copy each other's ideas in order to be competitive. If Waters sell tandem mass specs with completely pointless "high" resolution settings, then it's quite possible Shimadzu would feel obliged to follow suit, just to avoid the risk that some customer would make this the deciding factor in a competitive tender.

[bunnahabhain]

There really is a slight shift in found masses when changing the resolution settings on the Quattro Ultima Pt. So if you decide to use lower resolution to gain higher sensitivity, use a mass calibration with the same resolution settings.

[lmh]

oh yes, that's certainly true. You should choose a resolution and stick to it for method development and all subsequent samples.