A364 Mass Spectrometry Question by Jasmine Hou https://padlet.com/jasmine_hou1/9p5onnjo69vpdhwv Group discussion and submission en-us 2021-04-15 03:07:43 UTC 2026-01-22 21:00:09 UTC hello@padlet.com a) 3-Pentanone (CH3CH2COCH2CH3) in Figure below is analysed using electron impact mass spectrometry (EI-MS). Write down the fragmentation equations to show the formation of molecular and fragment ions of 3-Pentanone. jasmine_hou1 https://padlet.com/jasmine_hou1/9p5onnjo69vpdhwv/wish/1419340336 2021-04-15 03:10:04 UTC https://padlet.com/jasmine_hou1/9p5onnjo69vpdhwv/wish/1419340336 b) Figure below shows simplified MS spectrum of 3-Pentanone. jasmine_hou1 https://padlet.com/jasmine_hou1/9p5onnjo69vpdhwv/wish/1419344736 With reference to your answer in a), explain if the mass spectrometry is in good operating condition.  
(Relative atomic mass of C=12, O=16, N=14, H=1)
]]> 2021-04-15 03:12:01 UTC https://padlet.com/jasmine_hou1/9p5onnjo69vpdhwv/wish/1419344736 Team 1 jasmine_hou1 https://padlet.com/jasmine_hou1/9p5onnjo69vpdhwv/wish/1529787193 a) [CH3CH2COCH2CH3]^+ + 2e
(m/z value= 86)
[CH3CH2CO]^+ + [--CH2CH3]
(m/z value = 57)
[CH3CH2]^+ + [-COCH2CH3]
(m/z value = 29)
b) Major peaks are 86 m/z, 57 m/z, 29m/z
Bad condition,
There are peaks at 28 and 32, which shows that nitrogen and oxygen are present in the analysis. This is a gas interference with the sample. The MS is in a bad condition because the vacuum failed to remove external gas from the analysis.]]> 2021-05-17 04:07:43 UTC https://padlet.com/jasmine_hou1/9p5onnjo69vpdhwv/wish/1529787193 Team 2 jasmine_hou1 https://padlet.com/jasmine_hou1/9p5onnjo69vpdhwv/wish/1529787484 b) the MS is not in good operating condition. there are additional peaks that indicates leaks.]]> 2021-05-17 04:07:51 UTC https://padlet.com/jasmine_hou1/9p5onnjo69vpdhwv/wish/1529787484 Team 4 https://padlet.com/jasmine_hou1/9p5onnjo69vpdhwv/wish/1529787507 a) 
i) CH3CH2COCH2CH3 + e--> CH3CH2COCH2CH3+ + 2e
ii) CH3CH2COCH2CH3+ --> CH3CH2COCH2+ + CH3*
iii) CH3CH2COCH2CH3+ --> CH3CH2CO+ + CH2CH3*

B)
m/z = 86
m/z = 71
m/z = 57
System is in bad condition as there is a peak at 28, which indicates presence of N2, Nitrogen, meaning that there is air in the vacuum system, and it is in bad condition because the vacuum system failed to remove external gases from the analysis.

There are 3 major peaks at 86, 57 and 29. However, there are also peaks at 28 and 32. Hence, it is in bad condition]]> 2021-05-17 04:07:52 UTC https://padlet.com/jasmine_hou1/9p5onnjo69vpdhwv/wish/1529787507 Team 3 https://padlet.com/jasmine_hou1/9p5onnjo69vpdhwv/wish/1529787825 a) CH3CH2COCH2CH3 + e- {Mr (m value) = 86}
--> (CH2CH2COCH2CH3)^+ + 2e- {m/z =86}

CH3CH2COCH2CH3 + e- {Mr (m value) = 86} --> (CH2CH2COCH2)^+ + .CH3 {m/z = 71}

CH3CH2COCH2CH3 + e- {Mr (m value) = 86} --> (CH2CH2CO)^+ + .CH2CH3 {m/z = 57}

CH3CH2COCH2CH3 + e- {Mr (m value) = 86} --> (CH2CH2)^+ + .COCH2CH3 {m/z = 43}

b) No (bad). There is a peak at 28 indicating presence of Nitrogen (N2, Mr = 14 x 2), and since the 3-Pentanone sample has no Nitrogen atoms present or no m/z values of 28 in the fragmentation equation (28 is not an m/z value of major peaks), hence bad condition]]> 2021-05-17 04:08:04 UTC https://padlet.com/jasmine_hou1/9p5onnjo69vpdhwv/wish/1529787825 Team 5 https://padlet.com/jasmine_hou1/9p5onnjo69vpdhwv/wish/1529788288 a)
(CH3CH2COCH2CH3)+ e- =
(CH3CH2COCH2CH3)+ + 2e
-CH3CH2COCH2CH3 = (CH3CH2CO)+ + CH2CH3
-CH3CH2COCH2CH3 =
(CH3CH2)+ + COCH2CH3
-CH3CH2COCH2CH3 = (CH3)+ + CH2COCH2CH3


b)  The mass spectrometry is not in good operating condition.
m/z values of fragmented molecules:

(CH3CH2COCH2CH3)+ = 86
(CH3CH2CO)+ = 57
(CH3CH2)+ = 29
(CH3)+ = 15

All but one value, which is 15, corresponded to the peaks created by the detection of the fragmented molecules. There was a peak at 18, instead of at 15, which indicates H2O may be present in the mass spectrometry. At 28, 32 and 44, there were 3 peaks recorded, indicating that N2, O2 and CO2 were present as well. Thus, with air present in the mass spectrometry, the spectrometry is in a bad working condition as the vacuum pump is highly likely to be not working properly.







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