1. Chemical Ideas 6.5
Mass spectrometry

2. What’s inside? In the nucleus? Protons And around the nucleus?
Neutrons
Electrons

3. Location
How are they different?
Mass
Charge

4. Mass on Ar scale
Charge p 1 +1 n e- -1

5. Na Nuclear symbols p + n p ( = e-) 11 p? 12 e-? n? 23 11
Mass number =? Na 23 11
p ( = e-) 11 12
Atomic number =? p?
e-? n?

6. Cl Cl What are isotopes? p? p? e-? e-? n? n? 17 17 17 17 18 2035 37
e-?
e-? 17 17 18 20 n? n?
Atoms of the same element with:
The same atomic number but different mass numbers
Same number of protons but different numbers of neutrons

7. Why is 35Cl O.K.? Cl Cl Cl-37 Cl-35 Relative isotopic mass
Chlorine always
has an atomic
number of 17!
Relative isotopic mass Cl Cl 37 35 17 17
Cl-37
Cl-35

8. So what is relative atomic mass?
Cl-35
75%
25%
Cl-37

9. Relative atomic mass is the average of the relative isotopic masses
Cl-35
75%
Cl-37
25%
How do we get a relative atomic mass of 35.5?

10. Relative isotopic masses. The relative abundances.
What 2 things did we need to know?
Relative isotopic masses.
The relative abundances.

11. Use a mass spectrometer
How do we find them out?
Use a mass spectrometer

12. Mass spectrometry

13. sample inlet
vacuum chamber

14. Mg+ Mg e- e-

15. electric field
sample inlet
vacuum chamber

16. electric field flight path sample inlet Ion detector vacuum chamber
intensity
vacuum chamber
time measurement
m/z

17. KE = ½ mv2 Ion 1 Ion 2 KE = 16 KE = 16 m = 2 m = 8 v = 4 v = 2
Greater the mass, the less the velocity
Greater the mass, greater the time of flight
From time of flight, mass is calculated

18. electric field flight path sample inlet Ion detector vacuum chamber
intensity
vacuum chamber
time measurement
m/z

19. A mass spectrum …
100 80 60 % 40 20
m/z 35 36 37

20. Relative atomic mass is the average of the relative isotopic masses
Cl-35
75%
Cl-37
25%
How do we get a relative atomic mass of 35.5?

21. CH3CO+
CH3COCH3+
CH3COCH3
CH3 e- e- e-

22. Other fragments from propanone - CH3COCH3?
Which is the molecular ion?
CH3CO+
CH3
CH3+
CH3CO O O+
CH3C
CH3C+
Which give a peak on a mass spectrum?

23. Name it.
CH3
CH2 CH O
CH2
CH3
CH3
2-ethoxybutane

24. +
Base peak? 2?
Molecular ion ? 3? 1?