Difference between revisions of "Resolution (mass spectrometry)"

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==1997 ASMS Poster==
 
==1997 ASMS Poster==
 
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{{asms|
 
From the [[ASMS Terms and Definitions Poster]]:
 
From the [[ASMS Terms and Definitions Poster]]:
  
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'''Usage note''': Theoretical mass resolving power is useful for determining the relative difficulty in separating two peaks in a mass spectrum.  The "masses" are actually m/z values, and the subscript "d" indicates that the criterion used to determine Dm is simply the difference in mass between the two peaks.  One should be careful to notice the subtle distinction between Dmd, a quantity that is independent of instrumental performance, and Dmx, a quantity that is determined by instrumental performance.  It is important to realize that the theoretical mass resolving power makes no peak shape assumptions.  Therefore, the choice of overlap criterion, i.e., 10% valley, full width half height, etc. is the link between the theoretical mass resolving power and the experimentally measured "mass resolving power."  For an instrument to be capable of separating two particular ions, the instrument must possess a mass resolving power (over the range m + Dm) that is greater than the theoretical mass resolving power calculated for the ions in question.  For example, if it is desired to determine whether or not a particular mass spectrometer is capable of resolving 41K+ from 40Ar1H+, determine the theoretical mass resolving power:
 
'''Usage note''': Theoretical mass resolving power is useful for determining the relative difficulty in separating two peaks in a mass spectrum.  The "masses" are actually m/z values, and the subscript "d" indicates that the criterion used to determine Dm is simply the difference in mass between the two peaks.  One should be careful to notice the subtle distinction between Dmd, a quantity that is independent of instrumental performance, and Dmx, a quantity that is determined by instrumental performance.  It is important to realize that the theoretical mass resolving power makes no peak shape assumptions.  Therefore, the choice of overlap criterion, i.e., 10% valley, full width half height, etc. is the link between the theoretical mass resolving power and the experimentally measured "mass resolving power."  For an instrument to be capable of separating two particular ions, the instrument must possess a mass resolving power (over the range m + Dm) that is greater than the theoretical mass resolving power calculated for the ions in question.  For example, if it is desired to determine whether or not a particular mass spectrometer is capable of resolving 41K+ from 40Ar1H+, determine the theoretical mass resolving power:
 
   
 
   
Next, the instrumental mass resolving power of the instrument at m/z = 41 is compared with the theoretical mass resolving power.  For a quadrupole based instrument, a 10% valley overlap would correspond to a Dm of approximately 1 Da, assuming typical scan rates are used.  For a peak at m/z = 41, this corresponds to a "mass resolving power" = 41.  Therefore, this particular instrument does not possess mass resolving power capable of separating these two species.  >From the preceding discussion, it is apparent that even greater mass resolving power would be required for a separation if two adjacent peaks if the peaks are not of equal size and shape.  The lesser peak could be lost in the "wings" of the larger peak.  
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Next, the instrumental mass resolving power of the instrument at m/z &61; 41 is compared with the theoretical mass resolving power.  For a quadrupole based instrument, a 10% valley overlap would correspond to a Dm of approximately 1 Da, assuming typical scan rates are used.  For a peak at m/z &61; 41, this corresponds to a "mass resolving power" &61; 41.  Therefore, this particular instrument does not possess mass resolving power capable of separating these two species.  >From the preceding discussion, it is apparent that even greater mass resolving power would be required for a separation if two adjacent peaks if the peaks are not of equal size and shape.  The lesser peak could be lost in the "wings" of the larger peak.  
 
   
 
   
 
'''Another comment''':  Note that resolving power is dimensionless, but when defined as peakwidth, it usually has units of "parts-per-million" (of mass).  Thus, a resolution of 10,000 corresponds to 100 ppm.
 
'''Another comment''':  Note that resolving power is dimensionless, but when defined as peakwidth, it usually has units of "parts-per-million" (of mass).  Thus, a resolution of 10,000 corresponds to 100 ppm.
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==Sparkman==
 
==Sparkman==

Revision as of 17:02, 18 July 2009