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"Robert E. Fields"  wrote:
}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
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.

In article <574ekf$nse@acmey.gatech.edu>, Huang@wuchem.wustl.edu says:
}
}Hello.  I have a question here if someone can help me.  Besides PEG, what 
}other scources can give a polymer-like patten with mass diffrence of 44 
}amu.   Thank you.
}
}
Alkyphenol ethoxylate type surfactants i.e. octyl and nonyl phenol
ethoxylates give mass spectra very similar to PEG since the repeating unit
is also an ethoxylate group in these cases. 

The next San Francisco bay area mass spectrometry (BAMS) meeting 
will be held on Tuesday, December 10, 1996, at the Holiday Inn 
Hotel, Foster City, CA.
            NEW MASS SPECTROMETRIC APPROACHES
             FOR SOLVING BIOLOGICAL PROBLEMS
                     Brian T. Chait
   The Rockefeller University, 1230 York Ave., NY 10021
We have recently developed a new matrix-assisted laser 
desorption (MALDI) ion trap mass spectrometer [1-3], which we 
have found to be an extraordinarily powerful tool for the 
analysis of biopolymers.  The capacity of the ion trap for 
high-sensitivity multi-stage mass spectrometry is of 
particular appeal for biological applications that require 
the determination of the primary structures of proteins - 
e.g., the identification of proteins, the elucidation of 
posttranslational modifications, and the determination of 
sites of interaction.  An attractive strategy for solving 
problems of this type involves enzymatic digestion of the 
protein, followed by mass spectrometric analysis of 
individual components of the resulting complex mixture of 
peptide ions.  This strategy, which does not require prior 
chromatographic separation of the peptides, is fast and 
sensitive.
In my talk I will discuss the development of the MALDI ion 
trap together with a range of applications of the approach 
described above, including protein identification of proteins 
components of complex biological machines, rapid mapping of 
disulfide bonds in proteins, definition of complex 
phosphorylation/dephosphorylation events in proteins, 
determination of protein glycosylation, and definition of 
functional sites of interaction between biopolymers.
If I have time, I will discuss the use of mass spectrometry 
in the determination of high resolution structures of 
proteins.
[1]  J. Qin, R. J. J. M. Steenvoorden & B.T. Chait "A 
practical ion trap mass spectrometer for the analysis of 
peptides by matrix-assisted laser desorption/ionization" 
Anal. Chem. 68 (1996) 1784 - 1791.
[2]  J. Qin & B.T. Chait "Matrix-assisted laser desorption 
ion trap mass spectrometry: efficient trapping and ejection 
of ions" Anal. Chem. 68 (1996) 2102 - 2107.
[3]  J. Qin & B.T. Chait "Matrix-assisted laser desorption 
ion trap mass spectrometry: Efficient isolation and effective 
fragmentation of peptide ions"  Anal. Chem. 68 (1996) 2108 - 
2112.
This meeting will follow the traditional BAMS format:
6:00 pm Social hour (no-host cocktails)
7:00 pm Dinner ($25, reservations required - see below)
8:15 pm Lecture (lecture is free, reservations not required)
Dinner reservations are required, and the deadline is Friday 
December 6 at noon.  Dinner choices are Champagne Chicken,
Coho Salmon Almondine, or Vermicelli with Sundried Tomatoes and
Portabello Mushrooms.  RSVP to Paul Schnier at (510) 642-6240 
or pds@uclink4.berkeley.edu.
For more information, please contact either Paul (phone/e-mail 
given above) or Hugh Gregg (phone, e-mail below).
--
Hugh Gregg
Lawrence Livermore Nat. Lab.
(510) 423-7501
hugh-gregg@llnl.gov