Mass Spectrometry using modern techniques

Mass spectrometry

1. Mass Spectrometry

2. Starter Activity.
List the 5 Main steps in
Mass spectrometry ?
What happens at each of
these steps ?

3. Mass Spectrometrystrong electromagnet
detector
electric field to
accelerate and focus
electron gun
sample
Vaporisation, Ionisation, Acceleration,
Deflection and detection

4. Mass Spectrometry
In module 1 –we used mass spectrometry
to determine
The relative abundances of different
isotopes of a sample of an element and
hence deduce the relative atomic masses
of the elements.
Identify the peak with the largest
mass/charge ratio and use this to
determine the identity of the molecule.

5. Mass Spectrometry
When an ethanol (molecule) sample is
introduced in to the mass spectrometer it
behaves in the same way as an element.
In that the sample is ionised –and
electrons are ‘fired’ at it to knock electrons
from the sample.
Ethanol has the formula C
2H
5OH
C
2H
5OH
(g)[C
2H
5OH]
+•
(g)+ e-

6. Mass Spectrometry
C
2H
5OH
(g)[C
2H
5OH]
+•
(g)+ e-
At the ionisation stage
An electron will be ‘knocked’ off the molecule -
forming the molecular ion.
When an electron is removed an single
unpaired electron remains...
The ion has a positive charge
This ion is known as the molecular radical ion
M
+•
molecular ion–accelerated in the mass
spectrometer, deflected and then detected.

8. Mass Spectrometry
[C
2H
5OH]
+•
(g)
Are the heaviest ions that can be produced
by a sample of ethanol and thus will
produce a peak on the mass spectrum -
known as the molecular ion peak.
The m/z value of the peak is the molecular
mass.
Thus the mass of ethanol is 46.

9. Why so many peaks.
Many of the ions then
break further –some of
the bonds are broken
upon ionisation and thus
we have smaller ions of
smaller molecular mass.
Only fragments with a
positive charge will be
detected.
IONISATION
FRAGMENTION
RE-ARRANGEMENT
MOLECULAR ION

10. Ethanol.
To analyse the Ethanol we need:
9 people to be Ethanol
1 person to ionise the Ethanol
1 person to be the detector

11. Fragmentation of Ethanol
Fragment Molecular
mass
CH
3
+
15
CH
3CH
2
+
29
CH
2
+
14
OH
+
17
CH
2OH
+
31

12. CH
3CH
2O
H
+
CH
2OH
+
This is the
most stable fragment
formed (base peak)
CH
3CH
2
+
CH
2
+
CH
3
+
OH
+

13. High Resolution mass spectrometer
A problem arises when using conventional mass
spectrometry.
The molecular mass of propane is 44
The molecular mass of Ethanal is also 44.
How are we able to distinguish between these
two molecules given that the molecular ion
formed in the conventional mass spectrometer
will form peaks at 44m/z.

14. High Resolution mass spectrometer
This can be resolved by using a high resolution mass spectrometer –
which works in the same way as a conventional mass spectrometer –
however it is more accurate.
Mr of Propane = 44 44.0624
Mr of Ethanal = 44 44.0261
Element Mass
1
H 1.0
14
N 14.0
16
O 16.0
12
C 12.0
Element Mass
1
H 1.0078
14
N 14.0031
16
O 15.9949
12
C 12.0000
Peaks
formed on
spectrum.

15. Into 3 groups please.

16. Give a fragmentation list for
the following :
Neon
Chlorine
Hexane
3-Phenyl-2-propenal (C
9H
8O)
2-Butenoic acid (C
4H
6O
2)

17. Homework.
To create a list of fragments
from the analysis of morphine.
Extension : How does it
differ to Codeine ?