3 You Are Given An Esi Ms M Z Spectrum In Positive Ionisation Mode Of A Pentapeptide I Ii The Molecular Formula Of 1 (99.1 KiB) Viewed 55 times
3 You Are Given An Esi Ms M Z Spectrum In Positive Ionisation Mode Of A Pentapeptide I Ii The Molecular Formula Of 2 (45.16 KiB) Viewed 55 times
3. You are given an ESI-MS m/z spectrum in positive ionisation mode of a pentapeptide, (i) (ii) The molecular formula of the pentapeptide is C28H37N:07. Taking the atomic weight of C = 12.0000 H= 1.0078 "'N = 14.0031 160 = 15.9949 a.m.u. determine the monoisotopic molecular weight for this peptide. Assign the base peak in the spectrum. Give the mass difference between it and the monoisotopic molecular weight of the peptide. Assign what is causing this mass difference. Assign the peak which comes at m/z=557.2. (iii) Taking the natural abundance of C as 99% and the natural abundance of C as 1%. (iv) Work out the probability of having the pentapeptide contain only "C. (v) Work out the probability of having the pentapeptide witli 27 !?C atoms and one 13 atom. (vi) The y-axis in the mass spectrum is % relative intensity and is related to the probability of that peptide ion being present in the sample of the peptide. Taking that the all 28 ?C atom peptide ions give a peak which is 100% calculate what will be the size in % of the peak for the pentapeptide with 27 12C atoms and one " atom. Compare this to the value you read from the graph. (vii) The small peak at m/z - 578,1 occurs because some of the peptide molecules are ionised by a common cation instead of H'. Suggest what this cation may be
Question 3; ESI MS m/z spectrum in positive ionisation mode of the pentapeptide 100 556.2 I 25 3572 578.1 100 200 300 400 500 600 m/z
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