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Resolution vs m/z range dependency on Orbitrap

Posted: Tue Jun 27, 2017 8:33 am
by Suola
Hi all mass spec enthusiasts,

In NMR, the detection scheme is in principle very similar to that of Orbitrap, i.e., Fourier transform of image current on the detection circuitry (in time domain) to human readable spectrum (in ppm or m/z domain).

Further, in NMR, the digital resolution of the spectrum depends on the desired spectral width: the narrower the spectrum, the more closely the collected datapoints are in the spectrum, and thus higher the digital resolution.

Using this analogy, and not understanding all the intricacies of Orbitrap detection, I was wondering whether similar advantage can be obtained in Orbitrap by collecting narrower spectra, say m/z range 300-1300, instead of 300-2000, in order to get higher m/z resolution in the 300-1300 range?

Best,
Sami

Re: Resolution vs m/z range dependency on Orbitrap

Posted: Tue Mar 20, 2018 12:40 pm
by John F
Hi Sami,

In this case, the resolution is entirely dependent on the amount of time spent "listening" to the ions. The m/z range measured doesn't affect resolution, only the time spent "listening" to them.

You do, however, get a different advantage from a narrower scan range - improved signal. This is because the efficiency of the ion optics increases as the scan range narrows, and also because the IT settings (say 1e6 ions) is based on all the ions that are present for a scan. So, for MS1, if you have a wide range of ions and they sum to 1e6, then an ion of interest at 1000 m/z will be some percentage of the total intensity, and the absolute amount of these ions will be higher with narrower scan ranges. Practically speaking, this effect is heavily dependent upon sample complexity.

Re: Resolution vs m/z range dependency on Orbitrap

Posted: Wed Jun 06, 2018 10:20 am
by Suola
John F,

Thanks for the answer!

Cheers,
Sami