LCMS purchase

[push]

I am going to buy a new LCMS.
I need 0.1 mass resolution and good quanitification possibilities.
Which LCMS to chose?

Ion Trap, Triple quad, Orbitrap, Linear Ion Trap?

[leadazide]

A Q Exactive (Orbitrap)will without a doubt be an instrument that will deliver what you demand.. But the price tag is also up there.. You might be able to make do with the Exactive Plus and relay on the HR/AM for your selectivity.. this is a cheaper option and you still get an Orbitrap based instrument.. and you have the posibility of upgrading to Q Exactive at a later time..

I think you will be hard pressed to run a triple quad down to 0.1 res and still have decent tranmission through the quad..

[lmh]

A lot depends on what is behind that requirement for 0.1unit mass resolution.

If what you mean is "I'd like an instrument that reads mass accurately to 0.1 units" then any modern quadrupole-based instrument will do the job. In my experience pure ion-traps are potentially a little less accurate, but in the same ball-park. Orbis and ToFs will, of course, do muuuuuuch better.

If you want to resolve peaks that are only 0.1 units apart, then a quadrupole won't do it, but an orbitrap is a bit of an overkill. Your application is uncomfortably between the two. There are traps with this sort of resolution (e.g. Bruker's trap, which claims a resolution of about 30,000 I think - completely stunning!), but this is resolution without accompanying mass-accuracy, and is really intended for people who want to resolve isotope peaks on proteins/peptides with very high charge-states. There are also ToFs that offer appropriate resolution, but they'll come with a price-ticket that's similar to an Orbitrap.

The next questions are (1) How sensitive do you want to go? and (2) Will you ever need full-scan qualitative work? If you need the ultimate in sensitivity, a triple quad has a lot to offer, but my limited experience is that super-sensitive triple quads are awful for general purpose full-scan work, where a trap will do much better. I haven't tried something like the Q-Exactive, so I have no idea where it would fit in.

Incidentally, the question on linear trap versus 3d trap is complicated. Thermo will tell you that linear is utterly the best (because it's what they do) and Bruker will tell you that 3d is best (because it's what they do). Both companies have tackled the problem of space-charging and capacity in the old-fashioned 3d traps, but in different ways, and the best thing is to get a good technical rep from each company to explain what they've done, and then test the rival instruments with some samples of your own. Good luck!

[jenche]

Bruker's trap (amaZon SL and amaZon speed) absolutely can't achieve 30.000 in resolution. Their specification sheet indicate a peak width of 0.5u : http://www.bruker.com/products/mass-spe ... tails.html

I don't know exactly the price tag of an Orbitrap, but you can also look at the entry range Q-TOF (Agilent 6520, Bruker Compact or Impact, ABSciex 4600...) which should not be that expensive (albeit probably still more expensive than an ion trap or a single quadrupole).

[CE Instruments]

Bruker do show data for resolution of 32000 but this is for deconvoluted multiply charged ions. The link you show quotes resolution at the fastest scan speed of 52000 u/s with better than 0.5 resolution. The maximum scan speed for full resolution is 32000 u/s. As it is a trap you can change the compromises to get better resolution. This feature was also in the old LCQ from Thermo although I can't remember the specs.

These posts are sooo ambiguous Budget and actual application make the major pointers, all this thread does currently is troll arguments about the merit of vastly different possible solutions

Editted to clarify

[lmh]

jenche, the quote of "up to 30,000" resolution comes from a Bruker AmaZon Speed document, and was taken at a (slow) scan speed of 5200 units per second. I have also seen data that appears to back up the claim, although I haven't actually measured the resolution myself formally. But it's the trade-off: you can get much better resolution out of a trap by scanning the trap very slowly, but that may not be compatible with scanning over a large mass range and doing rapid chromatography.

The Thermo traps do their higher-than-normal-resolution scans over limited mass-ranges, as "ZoomScan" etc., souped-up to ultra zoom scans and things in an LTQ, but I haven't explored how far this has gone (I have access only to a low-res DecaXP which only has the original zoomscan, and an Orbitrap, and who's going to bother doing ion-trap zoom-scans when you have an Orbi sitting at the back?!).

CEInstruments, I wasn't trying to troll, just say what you are saying: different instruments do different jobs, so the important thing is to look at the job-requirements first.

[jenche]

I've just found (and read) the Amazon Speed brochure with the high resolution results, and you're right

Anyway, to get back on the original topic, it might help to know for what kind of analysis the new system would be used.

[CE Instruments]

lmh, sorry your post was informative. the "troll" post is the original post by push, far too little info and asks to compare four vastly different technologies with nothing more than a resolution requirement to choose
I note they have not come back to comment yet either

[lmh]

yeah, sorry, I was feeling a bit grumpy too! My message-board advice is usually the same anyway: go and try lots of instruments from lots of manufacturers. Far better to test than to rely on hearsay from people you've never met, on a message board. Very few of those who post here (and certainly not me) have actually got all the relevant instruments sitting side by side for comparison, and none will know exactly the applications and situation of the original poster. It's just scary buying such expensive equipment.