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From: "Robert E. Fields" <refields@worldnet.att.net>
Date: 24 Nov 1996 03:09:06 GMT
Subject: Resolution and Resolving Power
Organization: Frequent Flyers

I have a question about resolution and resolving power. Maybe I'm missing
something because it seems like such a simple question, but I've been
sifting through the literature and having trouble coming up with an answer.

I've found resolution defined as (delta)m/m and also as m/(delta)m - even
in different chapters of the same book though by different authors. When it
is quoted as "parts" the implication is (delta)m/m - i.e. 1 part in 1500.

Resolving power seems to always be defined as m/(delta)m.

I believe the correct answer is that resolution is (delta)m/m and resolving
power the inverse, but have seen so many quote mass spectrometer resolution
as m/(delta)m that I have to ask.

Is there an accepted/correct convention or are these essentially used
interchangably with the meaning clear from the use?

Thanks in advance,
Robert Fields


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From: dwheeler@nu-ins.u-net.com (Dave Wheeler)
Date: Tue, 26 Nov 1996 16:42:34 GMT
Subject: Re: Resolution and Resolving Power
Organization: U-NET limited

We believe that resolution is m/delta m.  For example for inorganic
sector mass spec resolutions of 4000 to 10000 are typical.  This would
give a 10% valley peak width of 0.025 amu at mass 100.

Regards, Phil Freedman. Nu Instruments.


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From: sumner@chemvx.tamu.edu (Lloyd W. Sumner)
Date: Mon, 2 Dec 1996 11:32:51 -0500
Subject: Resolution Definitions
Organization: *

Robert,

The American Society for Mass Spectrometry has published an article
entitled "Standard Definitions of Terms Relating to Mass Spectrometry:  A
Report from the Committee on Measurements and Standards of the American
Society for Mass Spectrometry" (P. Phrice, J. Am. Soc. Mass Spectrom.,
1991, 2, 336-348) that provides a guideline for the MS community with
regards to the definitions of resolution and resolving power.  My
preference is resolution defined at FWHM because it allows for evaluation
of instrumental performance while observing only a single peak as opposed
to the mixture necessary for the 10% valley definition. I hope you find
this info helpful. 

The replicated ASMS definitions are as follows:

Resolution:  10% valley definition, M/deltaM.  Let two peaks of equal
height in a mass spectrum at masses M and M-deltaM be separated by a
valley that at its lowest point is just 10% of the height of either peak. 
For similar peaks at a mass exceeding M, let the height of the valley at
its lowest point be more (by any amount) than 10% of either peak height. 
Then the resolution (10% valley definition) is M/deltaM.  It is usually a
function of M, therefore M/deltaM should be given for a number of values
of M. 

Resolution: peak width definition, M/deltaM.  For a single peak made up of
singly charged ions at mass M in a mass spectrum, the resolution may be
expressed as M/deltaM, where deltaM is the width of the peak at a height
that is a specified fraction of the maximum peak height.  It is recommeded
that one of three values 50%, 5%, or 0.5% be used.  For an isolated
symmetrical peak, recorded with a system that is linear in the range
between 5% and 10% levels of the peak, the 5% peak width definition is
technically equivalent to the 10% valley definition.  A common standard is
the definition of resolution based upon deltaM being full width of the
peak at half its maximum height, sometimes abbreviated "FWHM". 

Resolving Power (mass).  The abilitity to distinguish between ions
differing slightly in mass-to-charge ratio.  It may be characterized by
giving the peak width, measured in mass units, expressed as a function of
mass, for at least two points on the peak, specifically for 50% and for 5%
of the maximum peak height. 

Lloyd W. Sumner, Ph.D.
Associate Director, 
The Laboratory for Biological Mass Spectrometry

Voice #(409)845-8404             Fax#(409)845-4719
Email  Sumner@chemvx.tamu.edu


Lottery: A tax on people who are bad at math.




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From: sharma@physics.umanitoba.ca (Kumar S. Sharma)
Date: Thu, 12 Dec 96 12:41:05 PST
Subject: Re: Resolution and Resolving Power
Organization: University of manitoba

Resolution should be defined as delta(m) over m. Resolving power is the 
reciprocal of this (see the classic "Mass Spectroscopy" by H.E. Duckworth 
et al). This is similar to the definitions in other spectroscopic and 
spectrometric fields (in physics).

Kumar S. Sharma
Atomic Mass Determinations 
University of Manitoba