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IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.
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IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.

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IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.

IB Chemistry on Mass Spectrometry and Isotopes for Option A HL.

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  • 1. Mass Spectrometer Uses mass spectrometer Relative atomic mass of an element Relative Molecular mass of a molecule Presence of isotopes and its abundance CO2 Organic structure determination Distinguish between structural isomers CH3CH2CH2OH Structure of organic compound OH | CH3CHCH3 CH3 | CH3C-CH3 | CH3 structural formula
  • 2. Mass Spectrometer Parts of Mass Spectrometer 1 Vaporization 2 3 Ionization Accelerator 4 5 Deflector Detector Sample injection 5 Detector 1 • 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 Vaporization Chamber • Sample heat to vapour state 2 Ionization Chamber • Molecule bombard with electrons form positive ions 3 Accelerator Chamber • M+ ions accelerated by Electric field 4 Deflector • M+ ions deflected by magnetic field Sample X bombarded by electron • Form positive M+ ion • Accelerated (Electric Field) • Deflected (Magnetic Field) and Detected X + e- → X+ + 2e- Click here notes from chemguide Detail notes from chem msu
  • 3. Mass Spectrometer Parts of Mass Spectrometer 1 1 Vaporization 2 Vaporization Injection/ vaporization of sample liquid state  gaseous 2 3 Ionization Accelerator Click here for simulation 4 5 Deflector 5 Detector 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 Ionization • Form radical cations, M+ Deflection depend: •mass/charge (m/z) ratio: (m/z) ratio HIGH↑ - Deflection LOW↓ 37 CI+ 35 CI+ 35 CI2+ 3 Acceleration • M+ ions accelerated by electric field 4 Deflection • M+ ion deflected by magnetic field Deflection depend: • mass/charge (m/z) ratio: (m/z) ratio LOW↓- Deflection HIGH ↑
  • 4. Mass Spectra Online Database Excellent Online Spectra Database. Click here to view 1 Search methane molecule, CH4 2 3 Fragmentation pattern CH4 Mass Spectrum CH4 Mass/charge m/z Relative abundance Molecular ion peak, M+ Isotopic peak M+ + 1 Video on mass spectrometer Video Ionization/fragmentation Video how MS works Video how MS works Video Mass spectrometer
  • 5. Relative Atomic Mass Isotopes are present Why RAM is not a whole number? 12 Relative Abundance 98.9% 13 1.07% RAM = 12.01 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 Relative Isotopic Mass: = (Mass C x % Abundance) + (Mass 13C x % Abundance) = (12 x 98.9/100) + (13 x 1.07/100) = 12.01 12 Video on Isotopes Video on weighted average Video on Isotopes http://www.tutorvista.com/content/science/science-i/atoms-molecules/atom.php RAM calculation Weighted average calculation
  • 6. Relative Isotopic Mass Mg - 3 Isotopes Relative Abundance % Abundance Convert relative abundance to % abundance 24 Mg – (100/127.2) x 100% - 78.6% Mg – (12.8/127.2) x 100% - 10.0% 26 Mg – (14.4/127.2) x 100% - 11.3% 25 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 Pb - 4 Isotopes Relative Abundance % Abundance Convert relative abundance to % abundance 204Pb – (0.2/10) x 100% - 2% – (2.4/10) x 100% - 24% 207Pb – (2.2/10) x 100% - 22% 208Pb – (5.2/10) x 100% - 52% 206Pb 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
  • 7. Mass spectrometry to determine Relative Isotopic Mass Mg - 3 Isotopes 26 Mg - 11.3% - m/z highest – deflect LEAST Mg - 10.0% 24 Mg – 78.6% - m/z lowest – deflect MOST 25 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 Deflect MOST Deflect LEAST Pb - 4 Isotopes 208Pb – 52% - m/z highest – deflect LEAST - 22% 206Pb - 24% 204Pb – 2% - m/z lowest – deflect MOST 207Pb 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
  • 8. Mass spectrometry to determine Relative Isotopic Mass 35CI CI - 2 Isotopes 37 CI 35 CI Relative Isotopic Mass: = (35CI x % Ab) + (37CI x % Ab) = (35 x 75.5/100) + (37 x 24.5/100) = 35.5 35CI – 24.5% - m/z highest – deflect LEAST – 75.5% - m/z lowest – deflect MOST 37CI Deflect MOST Deflect LEAST 79Br Br - 2 Isotopes 81Br 79Br Relative Isotopic Mass: = (79Br x % Ab) + (81Br x % Ab) = (79 x 50.6/100) + (81 x 49.3/100) = 79.9 37CI 79Br Deflect MOST 81Br – 49.3% - m/z highest – deflect LEAST – 50.6% - m/z lowest – deflect MOST 81Br Deflect LEAST
  • 9. Mass spectrometry to determine Relative Isotopic Mass 1H H - 3 Isotopes 2H 3H 3H – trace amt – 0.015% - m/z highest – deflect LEAST 1H – 99.9% - m/z lowest – deflect MOST 2H Relative Isotopic Mass: = (1H x % Ab) + (2H x % Ab) = (1 x 99.9/100) + (2 x 0.015/100) = 1.007 1H Deflect MOST 2H Deflect LEAST 12C C - 3 Isotopes 14C- 13C 14C trace amt – 1.1% - m/z highest – deflect LEAST 12C – 98.9% - m/z lowest – deflect MOST 13C Relative Isotopic Mass: = (12C x % Ab) + (13C x % Ab) = (12 x 98.9/100) + (13 x 1.1/100) = 12.01 12C Deflect MOST 13C Deflect LEAST
  • 10. Ionization and Fragmentation Process- CH3CH2CH2CH3 Fragmentation Process CH3CH2CH2CH3 • Molecular ion, M+ undergo fragmentation • Cation and Radical form • Cation - Detected • Radical –Not detected (No charged) Ionization Process - CH3CH2CH2CH3 • Bombarded by electron form cation • Molecular ion, M+ = 58 • (CH3CH2CH2CH3)+ = 58 Ionization M+, m/z = 58 Ionization and Fragmentation of M+ • Form - m/z = 58, 43 and 15 Ionization and Fragmentation of M+ • Form- m/z = 58 and 29 CH3CH2CH2CH3 + e → CH3CH2CH2CH3+ + 2e H H | | CH3CH2CH2 C:H + e → CH3CH2CH2 C+.H + 2e | | m/z = 58 H H Ionization forming M+ CH3CH2CH2 : CH3 + e → CH3CH2CH2+.CH3 + 2e m/z = 58 • Fragmentation of M+ produce 43 CH3CH2CH2+·CH3 → CH3CH2CH2+ + ·CH3 m/z = 43 m/z = 15 Ionization and Fragmentation Will MOVE (ACCELERATED) Unpair electron NOT move m/z = 58 • Fragmentation of M producing 29 CH3CH2+·CH2CH3 → CH3CH2+ + .CH2CH3 + m/z = 29 • Fragmentation of M+ produce 15 CH3CH2CH2+·CH3 → CH3CH2CH2· + +CH3 Positively charged Ionization forming M+ CH3CH2:CH2CH3 + e → CH3CH2+·CH2CH3 + 2e
  • 11. Ionization/ Fragmentation pattern for CH3CH2CH2CH3 CH3CH2CH2CH3 Ionization CH3CH2CH2CH3+ CH3CH2CH2+ CH3+ CH3CH2+ CH3CH2CH2CH3+- 58 - m/z highest –deflect LEAST CH3CH2CH2+ – 43 CH3CH2+ – 29 CH3+ –15 - m/z lowest– deflect MOST CH3+ Deflect MOST Ionization and Fragmentation Process CH3CH2CH2CH3 Ionization Ionization of CH3CH2CH2CH3 CH3CH2CH2CH3+ CH3CH2CH2CH3 + e → + 2e → 58 or CH3CH2:CH2CH3 + e → CH3CH2+·CH2CH3 + 2e → 58 Fragmentation CH3CH2CH2CH3+ Deflect LEAST Mass spectrum 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
  • 12. Ionization/ Fragmentation pattern CH3CH(CH3)CH2CH3 CH3CH(CH3)CH2CH3+ Ionization CH3CH(CH3)CH2CH3+ CH3CH(CH3)CH2+ CH3CH2+ CH3CH(CH3)+ CH3+ 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 15 CH3+ Ionization and Fragmentation Process CH3CH(CH3)CH2CH3 Ionization 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 Deflect MOST Fragmentation Fragmentation of M+ CH3CH(CH3)CH2+ - 57 CH3CH(CH3)+ – 43 CH3CH2+ – 29 CH3+ - 15 CH3CH(CH3)CH2CH3+ Deflect LEAST Mass spectrum 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
  • 13. Ionization/ Fragmentation pattern for CH3CH2CH2OH CH3CH2CH2OH Ionization CH3CH2CH2OH+ CH2CH2OH+ CH3CH2+ CH2OH+ CH3 + CH3CH2CH2OH+- 60 - m/z highest –deflect LEAST CH2CH2OH+ – 45 CH2OH+ - 31 CH3CH2+ – 29 CH3+ –15 - m/z lowest– deflect MOST 15 CH3+ Deflect MOST Ionization and Fragmentation Process CH3CH2CH2OH Ionization Ionization of CH3CH2CH2OH CH3CH2CH2OH + e → CH3CH2CH2OH+ + 2e → 60 or CH3CH2CH2OH + e → CH3CH2+. CH2OH + 2e → 60 Fragmentation Fragmentation of M+ CH3+.CH2CH2OH→ +CH2CH2OH - 45 CH3CH2+·CH2OH→ +CH2OH – 31 CH3CH2+·CH2OH→ CH3CH2+ CH3CH2CH2OH+ Deflect LEAST Mass spectrum CH3CH2CH2CH3 CH3CH2CH2OH+- 60 - m/z highest – deflect LEAST CH2CH2OH+ – 45 CH2OH+ - 31 CH3CH2+ – 29 CH3+ –15 - m/z lowest– deflect MOST – 29 CH3+.CH2CH2OH→ +CH3 60 - 15 15 60
  • 14. Ionization/ Fragmentation pattern C(CH3)4 (C(CH3)4) C(CH3)4+ Ionization C(CH3)3+ C(CH3)2+ C(CH3)+ 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 (C(CH3)4)+ CH3+ Ionization and Fragmentation Process C(CH3)4 Ionization Ionization of C(CH3)4 C(CH3)4 + e → C(CH3)4+ + 2e → 72 Deflect MOST Fragmentation Fragmentation of M+ C(CH3)3+ C(CH3)2+ C(CH3)+ CH3+ – 57 - 42 – 27 –15 Deflect LEAST Mass spectrum C(CH3)4 C(CH3)4+ C(CH3)3+ C(CH3)2+ C(CH3)+ CH3+ - 72 - m/z highest –deflect LEAST – 57 - 42 – 27 –15 - m/z lowest– deflect MOST
  • 15. Ionization/ Fragmentation pattern CH3(CH2)8CH3 CH3(CH2)8CH3 Ionization 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 CH3+ CH3(CH2)8CH3+ Deflect MOST Deflect LEAST Ionization and Fragmentation Process CH3(CH2)8CH3 Ionization Ionization of CH3(CH2)8CH3 CH3(CH2)8CH3 + e → CH3(CH2)8CH3+ + 2e → 142 Fragmentation 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 Mass spectrum CH3(CH2)8CH3 Loss of methylene gp, CH2 = 14
  • 16. Ionization/ Fragmentation pattern CH3(CH2)8CH3 C6H5CH2OH Ionization C6H5CH2OH+ C6H5CH2OH+ C6H5CH2+ C6H5+ CH2OH+ OH+ = 108 - m/z highest – deflect LEAST = 91 = 77 = 31 = 17 – m/z lowest – deflect MOST C6H5CH2OH+ Deflect LEAST OH+ Deflect MOST Ionization and Fragmentation Process C6H5CH2OH Ionization Ionization of C6H5CH2OH C6H5CH2OH + e → C6H5CH2OH+ + 2e → 108 Fragmentation C6H5CH2+ C6H5+ CH2OH+ OH+ = 91 = 77 = 31 = 17 Mass spectrum CH3(CH2)8CH3 C6H5CH2OH+ C6H5CH2+ C6H5+ CH2OH+ OH+ = 108 - m/z highest – deflect LEAST = 91 = 77 = 31 = 17 – m/z lowest – deflect MOST
  • 17. Presence of Isotopes Ionization/ Fragmentation pattern molecule CI2 CI2 molecule Ionization 35CI-35CI+ 35CI+ 35CI-37CI+ 37CI-37CI+ 37CI+ 37CI-37CI - 74 - m/z highest – deflect LEAST –72 35CI-35CI –70 37CI –37 35CI –35 - m/z lowest– deflect MOST 35CI-37CI 35CI+ Deflect MOST 37CI-37CI+ Deflect LEAST Ionization and Fragmentation Process CI2 molecule Ionization 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 Ratio (35CI35CI: CI37CI: 35 37 CI37CI) - 9:6:1 Fragmentation Fragmentation of CI2+ into CI+ CI+.CI → [ 35CI+ + 35CI·] + 2e –35 m/z = 35 + CI .CI → [ 37 + CI + m/z = 37 Mass spectrum CI2 / CI atoms 37CI-37CI - 74 - m/z highest – deflect LEAST 35CI-37CI –72 35CI-35CI –70 37 CI·] + 2e –37 Ratio (35CI : 37CI) - 3:1 37CI 35CI - 37 –35 - m/z lowest– deflect MOST
  • 18. Presence of Isotopes Ionization/ Fragmentation pattern molecule Br2 Br2molecule 79Br-79Br+ 79Br-81Br+ 81Br-81Br+ Ionization 79Br+ 81Br+ 81Br-81Br - 162 - m/z highest – deflect LEAST 79Br-81Br –160 79Br-79Br –158 81Br –81 –79 - m/z lowest– deflect MOST 79Br 79Br+ Deflect MOST Ionization and Fragmentation Process Br2 molecule Ionization 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 81Br-81Br+ Deflect LEAST Mass spectrum Br2 / Br atoms Fragmentation Fragmentation of Br2+ to Br+ Br+.Br → [ 81Br+ + 81Br·] – 81 m/z = 81 Br+.Br →[ 79 Br+ + 79 Br·] – 79 m/z = 79 Ratio (79Br79Br: Br81Br: 79 Br81Br) – 1:2:1 81 Ratio (79Br : 81Br) - 1:1 81Br-81Br - 162 - m/z highest – deflect LEAST –160 79Br-79Br –158 81Br - 81 79Br – 79 - m/z lowest– deflect MOST 79Br-81Br
  • 19. Presence of Isotopes Ionization/ Fragmentation pattern CH3CH(CI)CH3 CH3CH(CI)CH3 CH3CH(CI)CH3+ Ionization CH3CH(37CI)CH3+ CH3CH(35CI)CH3+ CH3CH(37CI)+ CH3CH(35CI)+ CH3CHCH3+ CH3C + CH3C+ = 80 - m/z highest – deflect LEAST = 78 = 65 = 63 = 43 = 27 - m/z lowest – deflect MOST CH3CH(CI)CH3+ Deflect MOST Deflect LEAST Ionization and Fragmentation Process CH3CH(CI)CH3 Ionization Ionization CH3CH(CI)CH3 CH3CH(CI)CH3+ e → CH3CH(CI)CH3+ + 2e → 78/80 Fragmentation CH3CH(37CI)+ = 65 CH3CH(35CI)+ = 63 CH3CHCH3+ = 43 CH3C + = 27 Presence of M+ and (M++ 2) peak Isotopic peak = 63 CH3CH(35CI)+ Isotopic peak = 65 CH3CH(37CI)+ Isotopic peak (M+)= 78 CH3CH(35CI)CH3 Presence isotope 35CI and 37CI Isotopic peak (M++2) = 80 CH3CH(37CI)CH3
  • 20. Presence of Isotopes Ionization/ Fragmentation pattern CH3CH2CH3Br CH3CH2CH2Br CH3CH2CH2Br+ Ionization 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 CH3CH2CH2Br+ CH3C+ CH3C+ Deflect MOST CH3CH2 Deflect LEASTCH2Br+ Deflect MOST Deflect LEAST Ionization and Fragmentation Process CH3CH2CH3Br Ionization Ionization CH3CH2CH2Br CH3CH2CH2Br + e → CH3CH2CH2Br+ + 2e → 122/124 Fragmentation CH2CH281Br+ = 109 CH2CH279Br+ = 107 CH281Br+ = 95 CH279Br+ = 93 CH3CH2CH2+ = 43 CH3C + = 27 Presence of M+ and (M++ 2) peak Isotopic peak = 107 CH2CH279Br Isotopic peak = 109 Isotopic peak (M+)= 122 CH2CH281Br CH3CH2CH279Br Presence isotope 79Br and 81Br Isotopic peak (M++2) = 124 CH3CH2CH281Br
  • 21. Isomers, Propan-1-ol vs Propan-2-ol Isomers of C3H8OH Propan-2-ol Propan-1-ol CH3CH2CH2OH OH | CH3CHCH3 Vs Molecular Ion, M+ = 60 -> CH3CH2CH2OH+ Molecular Ion, M+ = 60 -> CH3CH(OH)CH3+ Fragmentation peaks Fragmentation peaks Loss of CH3 (M - 15)+ = 45 -> (CH2CH2OH)+ Loss of CH3 (M - 15)+ = 45 -> (CH3CH(OH))+ Loss of CH3CH2 (M - 29)+ =31 -> (CH2OH)+ Loss of OH (M - 17)+ = 43 -> (CH3CHCH3)+ Loss of CH2OH (M - 31)+ = 29 -> (CH3CH2)+ Loss of OH, CH3, H (M - 33)+ = 27 -> (CH3C)+ Loss of CH2CH2OH (M - 45)+ =15 -> (CH3)+ Vs 15 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 Peak 45 is higher • Loss of methyl radical at both sides produce CH3CH(OH)+ • No m/z= 29 peak detected – No CH2CH3 found ! OH OH | | CH3 C+·CH3 → CH3C+ + ·CH3 | | H H m/z= 45
  • 22. Isomers, 2 methylbutane vs 2, 2 dimethylpropane Isomers of C5H12 CH3 | CH3C-CH3 | CH3 2 methylbutane CH3 | CH3CHCH2CH3 2, 2 dimethylpropane Vs Molecular Ion, M+ = 72 -> CH3CH(CH3)CH2CH3+ Molecular Ion, M+ = 72 -> C(CH3)4+ Loss of CH3 Fragmentation peaks (M - 15)+ = 57 -> CH3CH(CH3)CH2+ Loss of CH3 Fragmentation peaks (M - 15)+ = 57 -> C(CH3)3+ Loss of CH3CH2 (M - 29)+ =43 -> CH3CH(CH3)+ Loss of TWO CH3 (M - 30)+ = 42 -> C(CH3)2+ Loss of CH3CH(CH3) (M - 43)+ = 29 -> CH3CH2+ Loss of THREE CH3 (M - 45)+ = 27 -> CH3C+ Loss of CH3CH(CH3)CH2 (M - 57)+ = 15 -> CH3+ Loss of C(CH3)3 (M - 57)+ = 15 -> CH3+ Vs Peak 29 absent • CH3CH2 present Peak 29 absent • No CH3CH2 Peak 57 is higher • Loss of methyl radical produce tertiary carbocation • Tertiary carbocation – More stable CH3 | CH3C+·CH3 | CH3 CH3 | CH3 C+ + ·CH3 | CH3 m/z= 57
  • 23. Normal Mass Spectrometer Vs High Resolution Mass spectrometer High Resolution Mass Spectrometer Normal Mass Spectrometer • Molecular formula/weight by adding all relative atomic mass RAM, O = 16 • RMM for molecule = Sum of all RAM RAM, N = 14 • RMM O2 = 16 + 16 = 32 RAM, H = 1 RAM, C = 12 • RMM N2H4 = (14 x 2) + (1 x 4) = 32 • RMM CH3OH = (12 + 3 + 16 + 1) = 32 • Molecular ion peak -O2, N2H4, CH3OH - SAME = 32 Vs Measure to RMM to 4/5 decimal places RAM, O = 15.9949 • Molecular formula/weight RAM, N = 14.0031 by adding all relative atomic mass RAM, H = 1.0078 • RMM for molecule = Sum of all RAM RAM, C = 12.0000 • 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 O2, N2H4, CH3OH O2 Vs same different High resolution Mass spectrum data Video how MS works http://www.absciex.com/ N2H4 CH3OH
  • 24. IB Questions on Mass Spectrometer 1 Mass spectrometer used to investigate isotopic composition of elements. Thallium has two isotopes shown below. 203 81 205 TI TI 81 1) State symbol of two singly charged ions form. 203 205 81 81 2) State which ion will follow path marked X on diagram. X= 203 81 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. 10 B 11 B B % abundance x% (100 – x)% Determine percentage abundance of these isotopes. Answer: Let % abundance be x. Relative Isotopic Mass: = (Mass 10B x % Ab) + (Mass 11B x % Ab) = (10 x x/100) + (11 x (100 – x)/100) = 10.81 X = 19% 10 B 19% 11 B 81%
  • 25. IB Questions on Mass Spectrometer 2 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. Relative Isotopic Mass = (Mass x % Ab) + (Mass 72Ge x % Ab) + (Mass 74Ge x % Ab) + (Mass 76Ge x % Ab) 19% = (70 x 22.60/100) + (72 x 25.45/100) + (74 x 36.73/100) + (76 x 15.22/100) = 72.89 70Ge
  • 26. IB Questions on Mass Spectrometer 3 The following shows a mass spectrometer. 1)Identify the parts labelled A, B and C. • • • electron gun ionisation chamber ionizer C • • • Electric field Charged plates Potential difference B • • • Magnetic field Magnet Electromagnet A 2)State and explain which one of the following will undergo greatest deflection. Answer : Greatest deflection -> lowest mass + highest charged -> m/z -> lowest 7 Li+ 6 Li2+ smallest deflection – high mass, low charged greatest deflection – low mass, high charged 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. 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
  • 27. IB Questions on Mass Spectrometer 4 Vaporized magnesium is introduced into mass spec. One of the ions that reaches detector shown below. 25 Mg+ 12 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 Cations (+ve) accelerated by (-ve) plates 3) The ion 25 Mg2+ 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 magnetic field. Answer: 25 Mg+ 25 Mg2+ and 25 Mg+ is detected using a stronger - due to lower charge -> m/z is higher -> deflected less -> needs a stronger magnetic field to deflect. 25 Mg+ Smallest deflection – high mass, low charged Strong magnet/magnetic field to deflect it to bottom
  • 28. IB Questions on Mass Spectrometer 5 Rubidium contains two stable isotopes shown below. RAM for rubidium is 85.47 85 87 Rb Rb 1) Calculate % of each isotope in rubidium. Answer : Let % abundance be x %. 85 % Abundance Rb x% 87 Rb Rb (100 – x)% Relative Isotopic Mass: = (Mass 85Rb x % Ab) + (Mass 87Rb x % Ab) = (85 x x/100) + (87 x (100 – x)/100) = 85.47 1) = 76.5% X 85 87 76.5% 23.5% Rb Rb 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. Detector Magnetic field/Deflector • M+ ions deflected by magnetic field 85 - lighter -> deflected more 87 - heavier -> deflected less Rb Rb • 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

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