1. Chemsheets AS007 (Mass spectroscopy)
22/11/2018
ToF MASS SPECTROMETRY
© AS July-2016

2. © www.chemsheets.co.uk AS 1011 15-July-2016
Stage 1 – IONISATION
Elements and low Mr compounds
X(g)  X+(g) + e–
e.g. Mg(g)  Mg+(g) + e–
Loss of electron
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3. © www.chemsheets.co.uk AS 1011 15-July-2016
Stage 1 – IONISATION
High Mr compounds (e.g. proteins)
X(g) + H+  XH+(g)
gains a proton
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4. © www.chemsheets.co.uk AS 1011 15-July-2016
Stage 2 – ACCELERATION
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5. Stage 3 – FLIGHT TUBE Lighter particles move faster and
so have a shorter time of flight
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6. © www.chemsheets.co.uk AS 1011 15-July-2016
Stage 3 – FLIGHT TUBE
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7. © www.chemsheets.co.uk AS 1011 15-July-2016
Stage 4 – DETECTION
+ve ions hit –ve plate and produce electric current
size of current proportional to number of ions
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8. © www.chemsheets.co.uk AS 1011 15-July-2016
The Mass Spectrum
Copper
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9. © www.chemsheets.co.uk AS 1011 15-July-2016
Average mass
2 balls with mass 100 g
3 balls with mass 200 g
10 balls with mass 400 g
average mass = total mass of all balls
number of balls
= (2x100)+(3x200)+(10x400)
2+3+10
= = 320 g 15
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10. © www.chemsheets.co.uk AS 1011 15-July-2016
800 g loaf
average mass = total mass of all loaves
number of loaves
= (4x400)+(10x800)
4+10
= = 686 g 14
400 g loaf
I have these loaves – what is the average mass?
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11. © www.chemsheets.co.uk AS 1011 15-July-2016
Neon
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12. © www.chemsheets.co.uk AS 1011 15-July-2016
ISOTOPES
Ions with different isotopes produce different signals.
Most important for Br and Cl.
Br: 50% 79Br % 81Br
Cl: 75% 35Cl % 37Cl
If two or more Br/Cl atoms, then spectrum is more complicated.
Often small peaks at m/z + 1 due to 2H and 13C.
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13. © www.chemsheets.co.uk AS 1011 15-July-2016
butane
CH3CH2CH2CH3
[CH3CH2CH2CH3]+
Mr = 58
[CH3CH2CH2CH3]+ with 1 x 2H/13C
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14. © www.chemsheets.co.uk AS 1011 15-July-2016
butanone
CH3CH2COCH3
Mr = 72
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15. © www.chemsheets.co.uk AS 1011 15-July-2016
chlorine
Cl2
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16. © www.chemsheets.co.uk AS 1011 15-July-2016
bromomethane
CH3Br
[CH379Br]+
[CH381Br]+
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17. © www.chemsheets.co.uk AS 1011 15-July-2016
chloromethane
CH3Cl
[CH335Cl]+
[CH337Cl]+
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