Exercise 7 results (Accurate Mass)


General

The problem with this exercise was that if you committed an error on the way all consecutive steps were wrong. And there were some non-evident difficulties in the tasks. To alleviate the effect and to reward work done I granted five points for meaningful work, even if containing errors. The most frequent error was ignorance of ionisation or incorrect compensation, I was unable to figure it out in all cases. The easiest way is to enter the found mass value as it is and then enter either H- for negative or H+ for positive ion Electrospray (and just ‘+’ for GC/MS-Electron impact, in case..)

The performance looks as follows – I am fine with all the results I got –

Correct solutions

Step
Points
Total: 13
Task 1Task2Task 3
Consideration of mass spectrum

4Points
M=284/14 = max 20 carbons and M+1=18% -> ca. 18 carbons. Mass defect .08 = Cl, Br, F, many O’s. M+2= 35% -> exactly one Cl and maybe one Sulfur. M=329/14 = max. 23 carbons.
M+1=15% -> ca. 15 carbons. Mass defect 0.008 = Cl, Br, F, many O’s. M+2= 37% -> exactly one Cl and maybe 1 Sulfur – to detect this was the difficulty: 15 carbons give only 1.2% 13C contribution on M+2
M=409/14 = max. 29 carbons
M+1=27% -> ca. 27 carbons. Mass defect=0.27 = very few heteroatoms. M+2 is ca 5% -> only carbon related (27 carbons produce 4.22%, use the simulator program) – therefore the 5% can’t come from sulfur = no Cl, no Br, no S
mass
ionisation
Constraints (proposal)

1 Point
M = 285.07977
H+
C15-20 H5-40 N0-10 O0-10 Cl1 S0-1
M= 330.007420
H-
C12-23 H5-50 N0-10 O0-10 Cl1 S0-1
M= 408.287767
H-
C22-29 H20-70 N0-5 O0-5 Cl0 S0 Br0
mass tolerance calculation

1 point
0.6mDa/285Da= 2.1 ppm = 2.5 ppm0.6mDa/329Da= 1.8 ppm = 2ppm0.6mDa/407Da= 1.5 ppm = 2ppm
Formula

1 Point

Identity and Reflections

1 Point
Chlorine containing natural metabolites are rare. The compound has only been found in the patient group = could be a drug. Check top candidates for psychiatric drugs ->
C16H13ClN2O
Diazepam

Note: In this case with a halogenide and a small mass defect there is a large mass accuracy gap to the next hits, so the assignment is pretty safe
Chlorine containing natural metabolites are rare. The compound has only been found in the patient group = could be a drug. Check top candidates for possibility to be administered in cardiovascular indications ->
C12H11ClN2O5S
Furosemide

Note: In this case with a halogenide and a small mass defect there is a large mass accuracy gap to the next hits, so the assignment is pretty safe
Present in treatment and control = probably natural metabolite and/or dietetic (from food). Many carbons and few heteroatoms = lipid, steroid or sterol or ester thereof. Candidate list should contain
C24H40O5
Cholic acid. Very likely to occur after high fat breakfast..

Note: In this case without halides and a ‘normal’ mass defect the top hits are not much different, so the assignment is relatively unsafe and depends much on the accuracy of our calibration.

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