Transcript Slide 1

FOS 6355
Summer 2005
Russell Rouseff
Isotope Abundances
•
•
•
•
•
•
•
16O
(~99.76%)
17O (0.04%)
18O (0.20%)
12C (~98.9%)
12.0107 Amu
13C (~1.1%)
35Cl (75.77%) and 37Cl (24.23%) 35.4527
79Br (50.50%) and 81Br (49.50%) 79.904
High Resolution MS
Molecular ion M+ = 84.0937
C6H12
Possible compounds ??
element
number
mass
total
C
6
12
72
H
12
1
12
84
C5H8O
element
number
mass
total
C
5
12
60
H
8
1
8
O
1
16
16
Formula C6H12
Mass
C5H8O
84.0939 84.0575
Establishes molecular formula of unknown
IR-MS
• Mass spectrometry is also used to determine the
isotopic composition of elements within a
sample. Differences in mass among isotopes of
an element are very small, and the less
abundant isotopes of an element are typically
very rare, so a very sensitive instrument is
required. These instruments are called isotope
ratio mass spectrometers (IR-MS) and use a
single magnet to bend a beam of ionized
particles towards a series of cups which convert
particle impacts to electric current.
Menthol
Peppermint Oil
Time of Flight MS
Time of Flight MS
Ion Trap MS
Ion Trap Limitations
Requires careful quantitation
Limited dynamic range
Subject to space charge effects and ion
molecule reactions
No sensitivity gain using SIM
Vanillin - quadrupole
152
100
OH
O
O
50
106
109
81
122
53
27
29
76
39
65
78
92
136
95
15
0
10
20
30
40
50
(mainlib) Benzaldehyde, 2-hydroxy-3-methoxy-
60
70
80
90
100
110
120
130
140
150
160
Vanillin – Ion Trap
151
100
O
O
HO
50
123
81
109
65
53
51
41
63
55
77
67
93
137
0
40
50
(rouseff) Vanillin
60
70
80
90
100
110
120
130
140
150
160
170
151
Adam’s Library Spectrum
81
109
123
(a)
Vanillin Standard
(b)
Sample
(c)
40
60
80
100
mass (m/z)
120
140
160
Unpasteurized NFC GFJ
Intensity
TIC
20.5
20.6
20.7
20.8
20.9
21
21.1
21.2
Retention Time (min)
21.3
21.4
21.5
Unpasteurized NFC GFJ
TIC
Isopropyl Hexanoate
Intensity
o
Allo-Ocimene
o
20.5
20.6
20.7
20.8
20.9
21
21.1
21.2
Retention Time (min)
21.3
21.4
21.5
MS/MS
Vanillin – Ion Trap MS/MS
Purity: 765
Fit:
867
R-Fit: 780
Sample
300
Standard
200
40
60
80
100
120
140
mass (m/z)
100
0
7.5
8
8.5
Retention Time (min)
9
9.5
80000
m/z 151
60000
40000
TIC
20000
0
35.5
Arbitrary Y / Arbitrary X
File # 2 : SUR151
36
36.5
37
37.5
38
38.5
39
39.5
Stacked Y-Zoom CURSOR
Res=None
Common Neutral Fragments
mass loss
composition
1 amu
H
15
CH3
17
OH
18
H2O
19
F
20
HF
27
C2H3, HCN
28
C2H4, CO
30
CH2O
31
CH3O
32
CH4O, S
33
CH3 + H2O, HS
33
H2S
35(37)
Cl
Common Fragments
Linear Alkanes
Loss CH3 first - 15
Then ethene groups – C2H4 (28) or
methlene CH2 (14)
branched alkanes from more stable
carbocations
Decane
Esters, Acids and Amides
Loss of group attached to carbonyl, X group
forms substituted oxonium ion
From carboxylic acids
From unsubstituted amides
Alcohols
Lose hydrogen and hydroxyl radical
Also lose a-alkyl (or H) groups, forms
oxonium
ions
R1 and R2 in a position
56
31
100
41
43
27
OH
50
42
29
55
39
28
26
15
14
33
45
38
19
57
37
32
73
0
10
14
(mainlib) 1-Butanol
18
22
26
30
34
38
42
46
50
54
58
62
66
70
74
78
Aromatic Hydrocarbons
forms “aromatic cluster”, m+, m-1, m/e = 65
benzyl carbocation forms tropylium ion,
then loss of acetylene = m/e 65
benzyl carbocation
Aldehydes and Ketones
Major cleavage – loss of one side chain
(ketones)
generates substituted oxonium ion
McLafferty rearrangement
loss of neutral ethene – C2H4
71
100
43
O
O
29
88
27
50
41
42
39
60
45
73
70
28
101
15
14
55
31
69
57
47
116
90
0
10
20
30
(mainlib) Butanoic acid, ethyl ester
40
50
60
70
80
90
100
110
120
130
Ethers
Lose methyl group – CH3
M-15
forms substituted oxonium ion
Halides
Simple loss of halogen
molecular ions of Cl and Br show “halide
pair”
35Cl/37Cl
ratio is roughly 3.08:1
79Br/81Br
ratio is 1.02:1
Unknown Halide Spectrum
64
100
28
29
27
50
66
26
49
51
0
20
24
Ethyl Chloride
30 32
28
32
35 37
39 41
36
40
44
44
48 50
52
48
52
59
56
61
60
63 65
64
67
68
Unknown
Formula = C5H12O
Examples
Vanilla comparison
Identification of rose oil volatiles