Mass Spectrometer

Uses mass spectrometer

Presence of isotopes and its abundance

Relative atomic mass of an element

Relative Molecular mass of a molecule

Structure of organic compound

Distinguish between structural isomers

CH3CH2CH2OH OH | CH3CHCH3

CH3 | CH3C-CH3

| CH3

CO2

structural

formula

Organic structure determination

Mass Spectrometer

Parts of Mass Spectrometer

Sample injection

Vaporization Chamber • Sample heat to vapour state

Ionization Chamber • Molecule bombard with electrons form positive ions

Accelerator Chamber • M+ ions accelerated by Electric field

Deflector • M+ ions deflected by magnetic field

Detector • Convert abundance of M+ ions to electrical current. • M+ ions neutralize by electrons (more e needed - higher current – higher intensity of peak) • Intensity of peak show -relative abundance of ions

Sample X bombarded by electron • Form positive M+ ion • Accelerated (Electric Field) • Deflected (Magnetic Field) and Detected X + e- → X+ + 2e-

Vaporization Ionization Accelerator Deflector Detector 3 2 1 5 4

2

1

3 4

Click here notes from chemguide Detail notes from chem msu

5

Mass Spectrometer

Parts of Mass Spectrometer

Vaporization Ionization Accelerator Deflector Detector 3 2 1 5 4

Click here for simulation

Vaporization Injection/ vaporization of sample liquid state gaseous

Ionization

• Form radical cations, M+

Acceleration

• M+ ions accelerated by electric field

Deflection

• M+ ion deflected by magnetic field

Deflection depend: •mass/charge (m/z) ratio: (m/z) ratio HIGH↑ - Deflection LOW↓

Deflection depend: • mass/charge (m/z) ratio: (m/z) ratio LOW↓- Deflection HIGH ↑

37CI+

35CI+

35CI2+

2

3 4

1 5 Detector

• Convert abundance of M+ ions to electrical current. • M+ ion neutralize by electrons (more e needed - higher current – higher intensity of peak) • Intensity of peak show -relative abundance of ions

Excellent Online Spectra Database. Click here to view

Mass Spectra Online Database

1 Search methane molecule, CH4

Video on mass spectrometer

Mass/charge m/z Relative

abundance

Isotopic peak M+ + 1 Molecular ion peak, M+

2 Fragmentation pattern CH4 3 Mass Spectrum CH4

Video Ionization/fragmentation Video how MS works Video Mass spectrometer Video how MS works

http://www.tutorvista.com/content/science/science-i/atoms-molecules/atom.php

Relative Atomic Mass Isotopes are present

Weighted average mass- due to presence of isotopes

Relative Isotopic Mass, (Ar) of an element: •Relative isotopic mass = Average mass of one atom of element 1/12 x mass of one carbon-12 • Relative isotopic mass, carbon = 12.01

Video on Isotopes

RAM = 12.01

Relative Abundance 98.9% 1.07%

13

Why RAM is not a whole number?

Relative Isotopic Mass: = (Mass 12C x % Abundance) + (Mass 13C x % Abundance) = (12 x 98.9/100) + (13 x 1.07/100) = 12.01

Video on weighted average Weighted average calculation

Video on Isotopes

RAM calculation

12

Mg - 3 Isotopes

24 Mg – (100/127.2) x 100% - 78.6% 25 Mg – (12.8/127.2) x 100% - 10.0% 26 Mg – (14.4/127.2) x 100% - 11.3%

Relative Isotopic Mass: = (Mass 24 Mg x % Ab) + (Mass 25 Mg x % Ab) + (Mass 26M g x % Ab) = (24 x 78.6/100) + (25 x 10.0/100) + (26 x 11.3/100) = 24.30

Relative Abundance % Abundance

Pb - 4 Isotopes

204Pb – (0.2/10) x 100% - 2% 206Pb – (2.4/10) x 100% - 24% 207Pb – (2.2/10) x 100% - 22% 208Pb – (5.2/10) x 100% - 52%

Relative Isotopic Mass = (Mass 204Pb x % Ab) + (Mass 206Pb x % Ab) + (Mass 207Pb x % Ab) + (Mass 208Pb x % Ab) = (204 x 2/100) + (206 x 24/100) + (207 x 22/100) + (208 x 52/100) = 207.20

Convert relative abundance to % abundance

Convert relative abundance to % abundance

Relative Abundance % Abundance

Relative Isotopic Mass

Mg - 3 Isotopes

26 Mg - 11.3% - m/z highest – deflect LEAST 25 Mg - 10.0% 24 Mg – 78.6% - m/z lowest – deflect MOST

Relative Isotopic Mass: = (24Mg x % Ab) + (25Mg x % Ab) + (26Mg x % Ab) = (24 x 78.6/100) + (25 x 10.0/100) + (26 x 11.3/100) = 24.30

Mass spectrometry to determine Relative Isotopic Mass

Deflect MOST Deflect LEAST

Pb - 4 Isotopes

208Pb – 52% - m/z highest – deflect LEAST 207Pb - 22% 206Pb - 24% 204Pb – 2% - m/z lowest – deflect MOST

Relative Isotopic Mass = (204Pb x % Ab) + (206Pb x % Ab) + (207Pb x % Ab) + (208Pb x % Ab) = (204 x 2/100) + (206 x 24/100) + (207 x 22/100) + (208 x 52/100) = 207.20

Deflect MOST Deflect LEAST

CI - 2 Isotopes

37 CI – 24.5% - m/z highest – deflect LEAST 35 CI – 75.5% - m/z lowest – deflect MOST

Relative Isotopic Mass: = (35CI x % Ab) + (37CI x % Ab) = (35 x 75.5/100) + (37 x 24.5/100) = 35.5

Mass spectrometry to determine Relative Isotopic Mass

Deflect MOST Deflect LEAST

Br - 2 Isotopes

81Br – 49.3% - m/z highest – deflect LEAST 79Br – 50.6% - m/z lowest – deflect MOST

Deflect MOST Deflect LEAST

35CI 37CI

35CI 37CI

Relative Isotopic Mass: = (79Br x % Ab) + (81Br x % Ab) = (79 x 50.6/100) + (81 x 49.3/100) = 79.9

79Br 81Br

79Br 81Br

H - 3 Isotopes

3H – trace amt 2H – 0.015% - m/z highest – deflect LEAST 1H – 99.9% - m/z lowest – deflect MOST

Relative Isotopic Mass: = (1H x % Ab) + (2H x % Ab) = (1 x 99.9/100) + (2 x 0.015/100) = 1.007

Mass spectrometry to determine Relative Isotopic Mass

Deflect MOST Deflect LEAST

C - 3 Isotopes

14C- trace amt

13C – 1.1% - m/z highest – deflect LEAST 12C – 98.9% - m/z lowest – deflect MOST

Deflect MOST Deflect LEAST

1H 2H

1H 2H

Relative Isotopic Mass: = (12C x % Ab) + (13C x % Ab) = (12 x 98.9/100) + (13 x 1.1/100) = 12.01

12C 13C

12C 13C

3H

14C

Ionization forming M+

CH3CH2CH2 : CH3 + e → CH3CH2CH2+.CH3 + 2e

• Fragmentation of M+ produce 43 CH3CH2CH2

+·CH3 → CH3CH2CH2+ + ·CH3

• Fragmentation of M+ produce 15 CH3CH2CH2

+·CH3 → CH3CH2CH2· + +CH3

Ionization and Fragmentation Process- CH3CH2CH2CH3

Ionization Process - CH3CH2CH2CH3

• Bombarded by electron form cation

• Molecular ion, M+ = 58 • (CH3CH2CH2CH3)+ = 58

Fragmentation Process CH3CH2CH2CH3 • Molecular ion, M+ undergo fragmentation • Cation and Radical form • Cation - Detected • Radical –Not detected (No charged)

H H

| | CH3CH2CH2 C:H + e → CH3CH2CH2 C

+.H + 2e | | H H

Ionization forming M+

CH3CH2:CH2CH3 + e → CH3CH2+·CH2CH3 + 2e

• Fragmentation of M+ producing 29 CH3CH2

+·CH2CH3 → CH3CH2+ + .CH2CH3

Ionization M+, m/z = 58

CH3CH2CH2CH3 + e → CH3CH2CH2CH3+ + 2e

Ionization and Fragmentation of M+ • Form - m/z = 58, 43 and 15

m/z = 58

m/z = 43

m/z = 15

Ionization and Fragmentation of M+ • Form- m/z = 58 and 29

m/z = 58

m/z = 58

m/z = 29

Ionization and Fragmentation

Unpair electron Positively charged

Will MOVE (ACCELERATED) NOT move

CH3CH2CH2CH3

CH3CH2CH2CH3+- 58 - m/z highest –deflect LEAST

CH3CH2CH2+ – 43

CH3CH2+ – 29

CH3+ –15 - m/z lowest– deflect MOST

Ionization/ Fragmentation pattern for CH3CH2CH2CH3

Deflect MOST Deflect LEAST

CH3CH2CH2CH3+

CH3CH2CH2+

Ionization

CH3+

CH3+

Ionization and Fragmentation Process

Fragmentation

Ionization of CH3CH2CH2CH3

CH3CH2CH2CH3 + e → CH3CH2CH2CH3+ + 2e → 58

or CH3CH2:CH2CH3 + e → CH3CH2

+·CH2CH3 + 2e → 58

Mass spectrum CH3CH2CH2CH3 Ionization CH3CH2CH2CH3

CH3CH2+

CH3CH2CH2CH3+

Fragmentation of M+ CH3CH2CH2

+·CH3 → CH3CH2CH2+ - 43

CH3CH2

+·CH2CH3 → CH3CH2+ – 29

CH3CH2CH2

+·CH3 → +CH3 - 15

CH3CH2CH2CH3+ - 58 - m/z highest –deflect LEAST

CH3CH2CH2+ – 43

CH3CH2+ – 29

CH3+ –15 - m/z lowest– deflect MOST

CH3CH(CH3)CH2CH3+- 72 - m/z highest –deflect LEAST

CH3CH(CH3)CH2+ – 57

CH3CH(CH3)+ - 43 CH3CH2

+ – 29 CH3

+ –15 - m/z lowest– deflect MOST

Ionization/ Fragmentation pattern CH3CH(CH3)CH2CH3

Deflect MOST Deflect LEAST

CH3CH(CH3)CH2CH3+

Ionization

CH3+

CH3+

Ionization and Fragmentation Process

Fragmentation

Ionization of CH3CH(CH3)CH2CH3

CH3CH(CH3)CH2CH3 + e → CH3CH(CH3)CH2CH3 + + 2e → 72 or CH3CH(CH3)CH2CH3 + e → CH3CH(CH3)CH2

+.CH3 + 2e → 72 or CH3CH(CH3)CH2CH3 + e → CH3CH(CH3)+.CH2CH3 + 2e → 72

Mass spectrum CH3CH(CH3)CH2CH3 Ionization CH3CH(CH3)CH2CH3

Fragmentation of M+ CH3CH(CH3)CH2

+ - 57 CH3CH(CH3)+ – 43

CH3CH2+ – 29

CH3+ - 15

CH3CH(CH3)+

15

CH3CH(CH3)CH2+

CH3CH(CH3)CH2CH3+

CH3CH2+

CH3CH(CH3)CH2CH3+

CH3CH(CH3)CH2CH3+- 72 - m/z highest –deflect LEAST

CH3CH(CH3)CH2+ – 57

CH3CH(CH3)+ - 43 CH3CH2

+ – 29 CH3

+ - 15 - m/z lowest– deflect MOST

CH3CH2CH2OH

CH3CH2CH2OH+- 60 - m/z highest –deflect LEAST CH2CH2OH+ – 45 CH2OH+ - 31 CH3CH2

+ – 29 CH3

+ –15 - m/z lowest– deflect MOST

Ionization/ Fragmentation pattern for CH3CH2CH2OH

Deflect MOST Deflect LEAST

CH3CH2CH2OH+

Ionization

CH3 +

CH3+

Ionization and Fragmentation Process

Fragmentation

Ionization of CH3CH2CH2OH

CH3CH2CH2OH + e → CH3CH2CH2OH+ + 2e → 60 or CH3CH2CH2OH + e → CH3CH2

+. CH2OH + 2e → 60

Mass spectrum CH3CH2CH2CH3 Ionization CH3CH2CH2OH

CH3CH2+

CH3CH2CH2OH+

Fragmentation of M+ CH3

+.CH2CH2OH→ +CH2CH2OH - 45

CH3CH2

+·CH2OH→ +CH2OH – 31

CH3CH2

+·CH2OH→ CH3CH2+ – 29

CH3

+.CH2CH2OH→ +CH3 - 15

CH2CH2OH+ CH2OH+

15 60

CH3CH2CH2OH+- 60 - m/z highest – deflect LEAST CH2CH2OH+ – 45 CH2OH+ - 31 CH3CH2

+ – 29 CH3

+ –15 - m/z lowest– deflect MOST

15 60

C(CH3)4+ - 72 - m/z highest –deflect LEAST

C(CH3)3+ – 57

C(CH3)2+ - 42

C(CH3)+ – 27 CH3

+ –15 - m/z lowest– deflect MOST

Ionization/ Fragmentation pattern C(CH3)4

Deflect MOST Deflect LEAST

C(CH3)4+

Ionization

CH3+

CH3+

Ionization and Fragmentation Process

Fragmentation

Ionization of C(CH3)4

C(CH3)4 + e → C(CH3)4

+ + 2e → 72

Mass spectrum C(CH3)4 Ionization C(CH3)4

C(CH3)3+

(C(CH3)4)

C(CH3)2+

C(CH3)+

C(CH3)4+ - 72 - m/z highest –deflect LEAST

C(CH3)3+ – 57

C(CH3)2+ - 42

C(CH3)+ – 27 CH3

+ –15 - m/z lowest– deflect MOST

Fragmentation of M+

C(CH3)3+ – 57

C(CH3)2+ - 42

C(CH3)+ – 27 CH3

+ –15

(C(CH3)4)+

Ionization/ Fragmentation pattern CH3(CH2)8CH3

Ionization

Ionization and Fragmentation Process

Fragmentation

Ionization of CH3(CH2)8CH3

CH3(CH2)8CH3 + e → CH3(CH2)8CH3+ + 2e → 142

Mass spectrum CH3(CH2)8CH3 Ionization

CH3(CH2)8CH3 CH3(CH2)8CH3

+

CH3(CH2)8CH3+ = 142 - m/z highest – deflect LEAST

CH3(CH2)7CH2+ = 127

CH3(CH2)6CH2+ = 113

CH3(CH2)5CH2+ = 99

CH3(CH2)4CH2+ = 85

CH3(CH2)3CH3+ = 71

CH3(CH2)2CH2+ = 57

CH3CH2CH2+ = 43

CH3CH2+ = 29

CH3+ = 15 – m/z lowest – deflect MOST

Loss of methylene gp, CH2 = 14

CH3(CH2)8CH3

CH3(CH2)7CH2+ = 127

CH3(CH2)6CH2+ = 113

CH3(CH2)5CH2+ = 99

CH3(CH2)4CH2+ = 85

CH3(CH2)3CH3+ = 71

CH3(CH2)2CH2+ = 57

CH3CH2CH2+ = 43

CH3CH2+ = 29

CH3+ = 15

Deflect LEAST

CH3+

Deflect MOST

CH3(CH2)8CH3+

Ionization/ Fragmentation pattern CH3(CH2)8CH3

Ionization

Ionization and Fragmentation Process

Fragmentation

Ionization of C6H5CH2OH

C6H5CH2OH + e → C6H5CH2OH+ + 2e → 108

Mass spectrum CH3(CH2)8CH3 Ionization

C6H5CH2OH+ = 108 - m/z highest – deflect LEAST C6H5CH2

+ = 91 C6H5

+ = 77 CH2OH+ = 31 OH+ = 17 – m/z lowest – deflect MOST

C6H5CH2OH C6H5CH2OH+

C6H5CH2OH

C6H5CH2OH+

C6H5CH2+ = 91

C6H5+ = 77

CH2OH+ = 31 OH+ = 17

C6H5CH2OH+ = 108 - m/z highest – deflect LEAST C6H5CH2

+ = 91 C6H5

+ = 77 CH2OH+ = 31 OH+ = 17 – m/z lowest – deflect MOST

OH+

Deflect MOST

Deflect LEAST

CI2 molecule

37CI-37CI - 74 - m/z highest – deflect LEAST 35CI-37CI –72 35CI-35CI –70 37CI –37 35CI –35 - m/z lowest– deflect MOST

Ionization/ Fragmentation pattern molecule CI2

Deflect MOST Deflect LEAST

35CI-35CI+

35CI+

35CI-37CI+

37CI-37CI+

Ionization

37CI+

35CI+

37CI-37CI+

Ionization and Fragmentation Process

Fragmentation

Fragmentation of CI2+ into CI+

CI+.CI → [ 35CI+ + 35CI·] + 2e –35 CI+.CI → [ 37CI+ + 37CI·] + 2e –37

Ionization of CI2 to CI2+

CI:CI + e- →[35CI+.35CI] + 2e – 70 CI:CI + e- →[35CI+.37CI] + 2e – 72 CI:CI + e- →[37CI+.37CI] + 2e – 74

m/z = 37

m/z = 35

Ratio (35CI : 37CI) - 3:1

Mass spectrum CI2 / CI atoms

Ratio (35CI35CI: 35CI37CI: 37CI37CI) - 9:6:1

Ionization CI2 molecule

37CI-37CI - 74 - m/z highest – deflect LEAST 35CI-37CI –72 35CI-35CI –70 37CI - 37 35CI –35 - m/z lowest– deflect MOST

Presence of Isotopes

Br2molecule

81Br-81Br - 162 - m/z highest – deflect LEAST 79Br-81Br –160 79Br-79Br –158 81Br –81 79Br –79 - m/z lowest– deflect MOST

Deflect MOST Deflect LEAST

79Br-79Br+

79Br+

79Br-81Br+

81Br-81Br+

Ionization

81Br+

79Br+

81Br-81Br+

Ionization and Fragmentation Process

Fragmentation

Fragmentation of Br2+ to Br+

Br+.Br → [ 81Br+ + 81Br·] – 81 Br+.Br →[ 79Br+ + 79Br·] – 79

Ionization of Br2 to Br2+

Br:Br + e- →[81Br+.81Br] + 2e – 162 Br:Br + e- →[79Br+.81Br] + 2e – 160 Br:Br + e- →[79Br+.79Br] + 2e– 158

m/z = 79

m/z = 81

Ratio (79Br : 81Br) - 1:1

Mass spectrum Br2 / Br atoms

Ratio (79Br79Br: 79Br81Br: 81Br81Br) – 1:2:1

Ionization Br2 molecule

81Br-81Br - 162 - m/z highest – deflect LEAST 79Br-81Br –160 79Br-79Br –158 81Br - 81 79Br – 79 - m/z lowest– deflect MOST

Ionization/ Fragmentation pattern molecule Br2 Presence of Isotopes

Ionization/ Fragmentation pattern CH3CH(CI)CH3

Ionization

Ionization and Fragmentation Process

Ionization

Ionization CH3CH(CI)CH3

CH3CH(CI)CH3+ e → CH3CH(CI)CH3+ + 2e → 78/80

Presence isotope 35CI and 37CI

CH3CH(37CI)CH3+ = 80 - m/z highest – deflect LEAST

CH3CH(35CI)CH3+ = 78

CH3CH(37CI)+ = 65 CH3CH(35CI)+ = 63 CH3CHCH3

+ = 43 CH3C

+ = 27 - m/z lowest – deflect MOST

CH3CH(37CI)+ = 65 CH3CH(35CI)+ = 63 CH3CHCH3

+ = 43 CH3C

+ = 27

CH3CH(CI)CH3 CH3CH(CI)CH3+

CH3CH(CI)CH3+

Isotopic peak (M+)= 78

Isotopic peak (M++2) = 80

CH3CH(35CI)CH3 CH3CH(37CI)CH3

Isotopic peak = 63

Isotopic peak = 65

CH3CH(35CI)+ CH3CH(37CI)+

CH3CH(CI)CH3 Fragmentation

CH3C+

Deflect MOST Deflect LEAST

Presence of M+ and (M++ 2) peak

Presence of Isotopes

Ionization/ Fragmentation pattern CH3CH2CH3Br

Ionization

Ionization and Fragmentation Process

Ionization

Ionization CH3CH2CH2Br

CH3CH2CH2Br + e → CH3CH2CH2Br+ + 2e → 122/124

Presence isotope 79Br and 81Br

CH3CH2CH281Br+ = 124 - m/z highest – deflect LEAST

CH3CH2CH279Br + = 122

CH2CH281Br+ = 109

CH2CH279Br+ = 107

CH281Br+ = 95

CH279Br+ = 93

CH3CH2CH2+ = 43

CH3C + = 27 - m/z lowest – deflect MOST

Isotopic peak (M+)= 122

Isotopic peak (M++2) = 124

Isotopic peak = 107

Isotopic peak = 109

Fragmentation

CH3C+

Deflect MOST Deflect LEAST

CH3CH2CH2Br CH3CH2CH2Br+

CH3CH2CH3Br

CH3CH2CH2Br+

CH2CH281Br+ = 109

CH2CH279Br+ = 107

CH281Br+ = 95

CH279Br+ = 93

CH3CH2CH2+ = 43

CH3C + = 27

CH3C+

Deflect MOST Deflect LEAST

CH3CH2CH2Br+

CH3CH2CH279Br CH3CH2CH2

81Br CH2CH279Br CH2CH2

81Br

Presence of M+ and (M++ 2) peak

Presence of Isotopes

Isomers, Propan-1-ol vs Propan-2-ol

Peak 45 is higher • Loss of methyl radical at both sides produce CH3CH(OH)+ • No m/z= 29 peak detected – No CH2CH3 found !

Fragmentation peaks (M - 15)+ = 45 -> (CH2CH2OH)+

(M - 29)+ =31 -> (CH2OH)+ (M - 31)+ = 29 -> (CH3CH2)+ (M - 45)+ =15 -> (CH3)+

Isomers of C3H8OH

Fragmentation peaks (M - 15)+ = 45 -> (CH3CH(OH))+ (M - 17)+ = 43 -> (CH3CHCH3)+ (M - 33)+ = 27 -> (CH3C)+

Vs

Loss of CH3

Loss of CH3CH2

Loss of CH2OH

Loss of CH2CH2OH

Loss of CH3

OH OH | | CH3 C

+·CH3 → CH3C+ + ·CH3

| | H H

m/z= 45

CH3CH2CH2OH

OH | CH3CHCH3

Loss of OH

Loss of OH, CH3, H

Peak 29 and 31 are found • Inductive effect of OH causes splitting of CH3CH2-|-CH2OH • m/z =29 peak detected – CH2CH3 present

CH3CH2 +· CH2OH → CH3CH2

+ + ·CH2OH

m/z= 29

CH3CH2 +· CH2OH → CH3CH2 ·

+ +CH2OH

m/z= 31

Propan-1-ol Propan-2-ol

15

Vs

Molecular Ion, M+ = 60 -> CH3CH2CH2OH+ Molecular Ion, M+ = 60 -> CH3CH(OH)CH3+

Isomers, 2 methylbutane vs 2, 2 dimethylpropane

CH3

| CH3CHCH2CH3

CH3 | CH3C-CH3

| CH3

Peak 29 absent • No CH3CH2 Peak 57 is higher • Loss of methyl radical produce tertiary carbocation • Tertiary carbocation – More stable

Fragmentation peaks (M - 15)+ = 57 -> CH3CH(CH3)CH2

+ (M - 29)+ =43 -> CH3CH(CH3)+ (M - 43)+ = 29 -> CH3CH2

+ (M - 57)+ = 15 -> CH3

+

Isomers of C5H12

Fragmentation peaks (M - 15)+ = 57 -> C(CH3)3

+ (M - 30)+ = 42 -> C(CH3)2

+ (M - 45)+ = 27 -> CH3C+ (M - 57)+ = 15 -> CH3

+

Vs

Loss of CH3

Loss of CH3CH2

Loss of CH3CH(CH3)

Loss of CH3CH(CH3)CH2

Loss of CH3

Loss of TWO CH3

Loss of THREE CH3

CH3 | CH3C+·CH3 | CH3

m/z= 57

CH3

| CH3 C

+ + ·CH3

| CH3

2 methylbutane

2, 2 dimethylpropane

Loss of C(CH3)3

Vs

Peak 29 absent • CH3CH2 present

Molecular Ion, M+ = 72 -> CH3CH(CH3)CH2CH3+ Molecular Ion, M+ = 72 -> C(CH3)4

+

Normal Mass Spectrometer Vs High Resolution Mass spectrometer

Normal Mass Spectrometer

• Molecular formula/weight

by adding all relative atomic mass • RMM for molecule = Sum of all RAM • RMM O2 = 16 + 16 = 32 • RMM N2H4 = (14 x 2) + (1 x 4) = 32 • RMM CH3OH = (12 + 3 + 16 + 1) = 32 • Molecular ion peak -O2, N2H4, CH3OH - SAME = 32

RAM, O = 16 RAM, N = 14 RAM, H = 1 RAM, C = 12

High Resolution Mass Spectrometer Measure to RMM to 4/5 decimal places

• Molecular formula/weight

by adding all relative atomic mass • RMM for molecule = Sum of all RAM • RMM O2 = 15.9949 + 15.9949 = 31.9898 • RMM N2H4 = (14.0031 x 2) + (1.0078 x 4) = 32.0375 • RMM CH3OH = (12.0000 )+ (3 x 1.0078) + 15.9949 = 32.0262 • Molecular ion peak- O2, N2H4, CH3OH is the NOT the same

RAM, O = 15.9949 RAM, N = 14.0031 RAM, H = 1.0078 RAM, C = 12.0000 Vs

Vs

O2, N2H4, CH3OH

same

O2 N2H4 CH3OH

different

http://www.absciex.com/

Video how MS works

High resolution Mass spectrum data

IB Questions on Mass Spectrometer

Mass spectrometer used to investigate isotopic composition of elements. Thallium has two isotopes shown below. 1) State symbol of two singly charged ions form. 2) State which ion will follow path marked X on diagram. Lighter -> DEFLECTED MORE 3) Doubly charged ions form. Suggest reason whether they would be deflected less than or more than ions at X and Y. DEFLECTED MORE. Cause deflection depends on m/z ratio. •Low Mass + High charge -> m/z ratio is low -> deflected more.

Naturally occuring boron has 2 isotopes, shown below. RAM of boron is 10.81.

% abundance x% (100 – x)% Determine percentage abundance of these isotopes. Answer: Let % abundance be x. 19% 81%

1

203 205

81 81

TI TI 203 205

81 81

X =

203

81

B 10 B 11

Relative Isotopic Mass: = (Mass 10B x % Ab) + (Mass 11B x % Ab) = (10 x x/100) + (11 x (100 – x)/100) = 10.81 X = 19%

B

B B 11 10

IB Questions on Mass Spectrometer

A sample of germanium is analysed in mass spec. The first and last processes are vaporization and detection. 1) State the names of other three processes in order in which they occur Answer: Ionization -> Acceleration -> Deflection 2) For each of the processes named in a (i), outline how the process occur Ionization -> Sample bombarded with high energy/high speed electrons Acceleration -> Cations (+ve charged ions) accelerated by an electric field Deflection -> Cations deflected by a magnetic field 3) Sample of germanium found to have following composition i)Define relative atomic mass. Average / weighted masses of all isotopes of an element. ii) Calculate RAM of sample, giving answer to two decimal places. 19%

2

Relative Isotopic Mass = (Mass 70Ge x % Ab) + (Mass 72Ge x % Ab) + (Mass 74Ge x % Ab) + (Mass 76Ge x % Ab) = (70 x 22.60/100) + (72 x 25.45/100) + (74 x 36.73/100) + (76 x 15.22/100) = 72.89

IB Questions on Mass Spectrometer

The following shows a mass spectrometer. 1)Identify the parts labelled A, B and C.

2)State and explain which one of the following will undergo greatest deflection. Answer : Greatest deflection -> lowest mass + highest charged -> m/z -> lowest 3) Mass spectrum for an element shown below: i) Explain why there is more than one peak. Existence of isotopes ii) Calculate the relative atomic mass of the element.

3

Relative Isotopic Mass

= (Mass 24 Y x % Ab) + (Mass 25 Y x % Ab) + (Mass 26 Y x % Ab) = (24 x 79/100) + (25 x 10/100) + (26 x 11/100) = 24.32

• electron gun • ionisation chamber • ionizer

• Electric field • Charged plates • Potential difference

• Magnetic field • Magnet • Electromagnet

greatest deflection – low mass, high charged

smallest deflection – high mass, low charged

Li2+ 6

Li+ 7

A

C

B

IB Questions on Mass Spectrometer

Vaporized magnesium is introduced into mass spec. One of the ions that reaches detector shown below. 1)Identify the number of protons, neutron and electrons Answer : 12 protons, 13 neutrons, 11 electrons

2) State how this ion is accelerated in mass spectrometer. Using a strong electric field/strong opposite charged plate/potential difference 3) The ion is also detected by changing the magnetic field. Deduce and explain by reference to m/z values of these two ions of magnesium, which of the ions and is detected using a stronger magnetic field. Answer: - due to lower charge -> m/z is higher -> deflected less -> needs a stronger magnetic field to deflect.

4

Cations (+ve) accelerated by (-ve) plates

Mg+ 25

12

Mg2+ Mg+ 25 25

Mg2+ 25

Mg+ 25

Smallest deflection – high mass, low charged Mg+ 25

Strong magnet/magnetic field to deflect it to bottom

IB Questions on Mass Spectrometer

Rubidium contains two stable isotopes shown below. RAM for rubidium is 85.47 1) Calculate % of each isotope in rubidium. Answer : Let % abundance be x %.

% Abundance x% (100 – x)%

1) 76.5% 23.5%

2) Vaporized sample is ionized and accelerated in a mass spec. How the use of magnetic field and detector enables the percentage of two isotopes to be determined.

5

Rb 85

Rb 87

Rb Rb 85 87

Relative Isotopic Mass: = (Mass 85Rb x % Ab) + (Mass 87Rb x % Ab) = (85 x x/100) + (87 x (100 – x)/100) = 85.47 X = 76.5%

Rb

Rb Rb 85 87

Detector • Convert abundance M+ ions to electrical current. • M+ ions neutralize by electrons (more e needed - higher current – higher intensity of peak) •Ratio of intensity peaks show ratio of ions in sample •Ratio of height of peaks due to 85Rb : 87Rb –> 76.5 : 23.5

Magnetic field/Deflector • M+ ions deflected by magnetic field

- lighter -> deflected more

- heavier -> deflected less

Rb 85

Rb 87