Sunday, June 16, 2019
Reducing FT-ELIT size!?! Is this idea actually realistic?
So...the fourier transform electrostatic ion trap (FT-ELIT) has been an idea that has bounced around for a while -- but this recent-ish paper in JASMS makes it seem like it might actually be a competitive technology!
Here is the basic idea (from someone totally and completely unqualified to describe said idea) -- instead of ejecting ions from the ion trap in a linear manner by ramping up the RF (DC/RF ratio, depending on the trap architecture) so that they destabilize in the predicted order (cool review on this here) what if you did hard math instead? Could it possibly be that the ion trap is already physically capable of so much more, but we haven't utilized it properly? That's what the FT-ELIT looks like.
However, the earlier applications made it seem more like a novelty. "Cool! You can get like 10,000 resolution in that ion trap, but each scan takes like 6 hours? Riiiiight oooooonnnnn.....(backs away slowly....).
In this study we see competitive levels of performance from tweaking the trap and decreasing it's size (think about the boost in resolution/speed in the OrbitalTraps when you drop from a diameter of 30mm to 20mm). Huge boosts! They also get closer to measuring the initial injection of the ions off of the mirror that puts them in there.
What can they get with all this work?
22,000 resolution at an m/z of 1,150 in 300ms.
This is data from a high field (D20) Orbitrap using 60,000 resolution at m/z 200. At around 1,145 m/z it's getting superior resolution (26,000 or so), but similar ballpark.
What's a 60k scan in a high field? 96ms? I forget. Something in that range, definitely less than half the 300ms the FT-ELIT is using, so the D20 Orbitrap clearly wins. The D30 trap, I know for sure is 256ms for a 70,000 resolution scan when the D30 has eFT (similar to this improvement in this study, eFT is monitoring closer to the 0 time point when the ions are ejected directly into the Orbitrap.) Instruments without enabled eFT, such as the original Orbitrap? I think the FT-ELIT might actually win, by achieving comparable resolution in a shorter amount of time! At the very least, it is reaaaally close. I can't seem to find an Orbi Classic file on the shared drive and I got bored looking for one.
Okay -- I don't know if this is a reproducible thing or if it requires a football stadium of electronics to make it work, but it is certainly interesting to think about, right?
Since I'm too lazy to look on a network drive for an older Orbi file, I'm definitely not going to check the relative mass accuracy of the 2 devices (don't forget, Orbi resolution has only minor relatively minor changes on mass accuracy -- if you're doing over 15,000 resolution it doesn't improve mass accuracy to even do 500,000 (but revealing coeluting peaks you hadn't seen before may make it look like it does).
I should stop typing on the interwebs and go play outside.