Chem, about mass resolution

In summary, the resolution required for a mass spectrometer is defined as M/(delta M), meaning that for larger molecules with bigger M.W., the resolution needed would also be larger even if the delta M value is the same. This is because larger molecules have more combinations and permutations that can give similar M.W., making it more difficult to distinguish between them. Additionally, in real life, there is often error and deviations in the data, requiring a higher resolution to accurately distinguish between peaks. This is particularly important in mass spec of polymers and proteins.
  • #1
In mass spectrometer, the resolution required was defined as
M/(delta M), So, it means for two larger M.W. molecules, the resolution required was larger than small M.W. molecules even the delta M was was the same...

But why ??!
why the instrument should have better resolution to distinguish different larger molecules ??!

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  • #2
Don't know much about mass spectroscopy.

But if I had to guess...

For small molecules, the empirical formula can be calculated from the MW. There's only one formula possible for the MW 130.1418, for example. Even mass spectrometers with low resolution can figure it out for small molecules. WIth large, particularly biological molecules there are more combinations and permutations that can give very similar MW's. So having a high resolution probably helps here. But I'm not sure. I don't handle many compounds more then several hundred daltons.
  • #3
Chemicalsuperfreak, thanks for your reply

I agree with your point.
However, I still don't understand in some sense.

For example, if 2 molecules, the first has atomic mass 22.01 and the second one has 22.00, the mass resolution required to distinguish THE TWO molecule was 22/0.01. Another 2 molecule have atomic mass 122.01 and 122.00, the resolution required for distinguish this TWO VALUE (PEAK) was 122/0.01.

As the delta M was 0.01, in common sense, what the instrument required was it can distinguish 0.01 mass difference. The mass of the peak were not related, if just consider two peak. In fact, mass resolution was defined as "the maximum resolution required to distinguish of two peak"

:smile: [?]
  • #4
Remember, in real life, you have crud in your data. You have error, you have deviations. It will require a higher level of resolution to distinguish between two peaks as their standard deviations may increase.

Now you may feel pity for all those people doing mass spec of polymers and proteins.

1. What is mass resolution in chemistry?

Mass resolution in chemistry refers to the ability of a mass spectrometer to distinguish between ions with slightly different mass-to-charge ratios. It is a measure of the instrument's ability to accurately measure small differences in mass.

2. How is mass resolution calculated?

Mass resolution is typically calculated by dividing the mass of the peak at its base by the peak's width at half of its maximum height. This value is then multiplied by the nominal mass of the ion being measured.

3. What factors affect mass resolution?

The two main factors that affect mass resolution are the strength of the magnetic field in the mass spectrometer and the design of the instrument's ion optics. Other factors that may impact mass resolution include the type of ionization source and the type of mass analyzer being used.

4. Why is mass resolution important in mass spectrometry?

High mass resolution is important in mass spectrometry because it allows for more accurate identification and quantification of compounds. It also helps to reduce interference and background noise, resulting in a more precise and reliable analysis.

5. How can mass resolution be improved?

There are several ways to improve mass resolution in mass spectrometry. These include increasing the strength of the magnetic field, optimizing the ion optics design, and using more advanced mass analyzers such as time-of-flight or Fourier transform ion cyclotron resonance (FT-ICR). Additionally, careful sample preparation and selection of appropriate ionization methods can also help to improve mass resolution.

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