Peak width and distance from a reference value answer different questions in mass-spectral evidence.
Identify width and location quantities
Mass-spectral resolution reporting requires the m/z at which it is evaluated and the definition of the difference or peak width used. A full-width-at-half-maximum convention is one specified basis. Mass accuracy instead concerns closeness of the measured coordinate to its reference or true value. Primary reference: Thermo Fisher Scientific: HRAM definitions.
A narrow peak need not be centered at the correct reference coordinate. These two quantities can influence interpretation together, but one label cannot replace the other. State the width criterion before computing a ratio or comparing an instrument specification.
Calculate independent fictional fields
Take an original peak centered at m/z 500.002 with FWHM 0.010. The explicitly width-based ratio is 500.002/0.010 = 50000.2. If its defined reference coordinate is 500.000, the signed relative error is (500.002 - 500.000)/500.000 times 10^6, or +4 ppm.
Moving the center to 500.000 while keeping width 0.010 changes the error to zero and the width-based ratio to 50000. Narrowing the first peak to width 0.005 changes its ratio to 100000.4 but leaves its +4 ppm error. These toy operations isolate location from width; they are not instrument observations.
Retain both results on the worksheet
Include measured center, reference coordinate and its ion basis, width, width definition, width-based ratio and signed error. Do not call a single assigned width proof that an arbitrary pair of nearby peaks is baseline separated. Shape and the applicable criterion still matter.
A meaningful review compares the requested evidence with its method-specific requirements rather than using one impressive number for every question. The example sets no acceptable ppm value or resolution target. It neither guarantees identity nor describes the performance of an HM analytical instrument.
Customer Questions
Does narrowing the toy peak remove its +4 ppm error?
Its center is unchanged.
Which width convention is used?
Full width at half maximum is explicit.
Is any ratio a universal separation guarantee?
Peak shape and the criterion still matter.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
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