A caffeine sample was analyzed by MS and the spectrum shown below was generated

Question

A caffeine sample was analyzed by MS and the spectrum shown below was generated with peaks labeled A, B, and C. The following questions refer to this spectrum. (2 points) Which letters represent the Mt, (M+1, and (M+2)+ peaks in the spectrum? Which letter represents the base peak in the spectrum? Does the instrument have adequate resolving power to see caffeine's isotopes? How do you know? If the peak at 194.0802 m/z has a width of 0.15 m/z at half-height, what is the resolution of the spectrum 10000 7500Caffeine Formula:CoHON,O 50.00 CO 2500 91.0 192.0 193.0 1940 1950 196.0 1970 Mass

Explanation / Answer

A = M+, B = (M+1)+, C = (M+2)+ (info: which are generated because of isotropic contribution) A is the base peak (info: base peak is the most abundant peak in a mass spectra) Yes, the instrument can resolve isotopes, as you can see (M+1)+ and (M+2)+ peaks which are produced due to isotopes of the C, H atoms in caffeine. The resolution is expressed as (m/z)/?(m/z), where ?(m/z) is the width of the peak at a height, i.e. resolution = 194.08/0.15 = 1293.

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