Method for the determination of the position of unsaturation in a compound
A mass spectrometric method for determining the position of unsaturation in a compound is disclosed.
1. A method for determining the position of unsaturation in a compound comprising one or more unsaturated chains, the method comprising:
(i) ionizing the compound to provide ions;
(ii) selecting ions of a given mass-to-charge ratio;
(iii) allowing the selected ions to react with ozone to give ozone induced fragment ions;
(iv) mass analysis and detection of the ozone induced fragment ions formed in step (iii); and
(v) determining the position of unsaturation in the compound based on the difference between the mass-to-charge ratio of the ions selected in step (ii), and the mass-to-charge ratio of one or more of the ozone induced fragment ions formed from the selected ions in step (iii).
2. The method of claim 1 , wherein the unsaturation is one or more carbon-carbon-double bonds.
3. The method of claim 1 , wherein the one or more unsaturated chains are alkenyl chains.
4. The method of claim 3 , wherein the alkenyl chains terminate with a methyl or methylene group.
5. The method of claim 1 , wherein the compound is selected from the group consisting of: polymers, lipids, metabolites, fatty acids, drugs, biological extracts and natural products.
6. The method of claim 1 , wherein the one or more ozone induced fragment ions in step (v) is an ozone induced fragment ion comprising an aldehyde functional group, or an ozone induced fragment ion which is a Criegee ion.
7. The method of claim 1 , which is used in conjunction with CID mass spectrometry.
8. The method of claim 3 , further comprising the step of determining the stereochemistry of one or more carbon-carbon double bonds located in the one or more alkenyl chains based on the relative abundance of the ozone induced fragment ions.
9. A method for determining the position(s) of one or more carbon-carbon double bond(s) in a compound comprising one or more unsubstituted alkenyl chains, the method comprising:
(i) ionizing the compound to provide ions;
(ii) selecting ions of a given mass-to-charge ratio;
(iii) allowing the selected ions to react with ozone to give ozone induced fragment ions;
(iv) mass analysis and detection of the ozone induced fragment ions formed in step (iii); and
(v) determining the position(s) of the double bond(s) in the compound according to any one of the following formulae (I) to (V):
n
=
m
/
z
(
M
)
-
m
/
z
(
Criegee
)
+
32
+
2
b
14
(
I
)
n
=
m
/
z
(
M
)
-
m
/
z
(
aldehyde
)
+
16
+
2
b
14
(
II
)
n
=
m
/
z
(
M
)
-
m
/
z
(
Criegee
-
H
2
O
)
+
14
+
2
b
14
(
III
)
n
=
m
/
z
(
M
)
-
m
/
z
(
Criegee
-
NMe
3
)
-
27
+
2
b
14
(
IV
)
n
=
m
/
z
(
M
)
-
m
/
z
(
aldehyde
-
NMe
3
)
-
43
+
2
b
14
(
V
)
wherein:
“n” is an integer representing the position of the carbon-carbon double bond as numbered from the carbon of the terminal methyl or methylene group of the alkenyl chain;
“M” refers to the ions selected in step (ii);
“aldehyde” refers to the ozone induced fragment ion comprising an aldehyde functional group as a result of ozone induced dissociation of M;
“Criegee” refers to the ozone induced fragment ion located 16 mass units above the mass of the aldehyde fragment ion as a result of ozone induced dissociation of M;
“Criegee-H 2 O” refers to the secondary fragment from the Criegee ion resulting from loss of water (−18 Da);
“Criegee-NMe 3 ” refers to the secondary fragment formed from the Criegee ion in phosphocholine-containing compounds resulting from loss of trimethylamine (−59 Da);
“aldehyde-NMe 3 ” refers to the secondary fragment formed from the aldehyde ion in phosphocholine-containing compounds resulting from loss of trimethylamine (−59 Da); and,
“b” is an integer representing the number of double bonds between the position of fragmentation and the carbon of the terminal methyl or methylene group of the alkenyl chain.
10. A method for determining the position of a double bond in a compound of the general formula M 1 -(CH═CH)-M 2 , wherein M 1 and M 2 independently represent any organic residue, the method comprising:
(i) ionizing the compound to provide ions;
(ii) selecting ions of a given mass-to-charge ratio;
(iii) allowing the selected ions to react with ozone to give ozone induced fragment ions;
(iv) mass analysis and detection of the ozone induced fragment ions formed in step (iii);
and
(v) determining the position of the double bond in the compound based on the relative masses of M 1 and M 2 . Step (v) may be carried out as follows:
(a) determining the mass of M 1 by subtracting 29 Da from the observed mass of the ozone induced fragment ion comprising an aldehyde functional group; or
(b) determining the mass of M 1 by subtracting 45 Da from the observed mass of the ozone induced fragment ion which is a Criegee ion;
(c) determining the mass of M 2 by solving the following formula for M 2 : M=M 1 +M 2 +C 2 H 2 , wherein M is the mass of the ions selected in step (ii), and
(d) assigning the position of the double bond based on the relative masses of M 1 and M 2 .
11. A system for determining the position(s) of unsaturation in a compound comprising one or more unsaturated chains, the system comprising:
(i) means for ionizing the compound to provide ions;
(ii) means for selecting ions of a given mass-to-charge ratio;
(iii) means for allowing the selected ions to react with ozone to give ozone induced fragment ions;
(iv) means for mass analysing and detecting the ozone induced fragment ions formed in step (iii); and
(v) means for determining the position of unsaturation in the compound based on the difference between the mass-to-charge ratio of the ions selected in step (ii), and the mass-to-charge ratio of one or more of the ozone induced fragment ions formed from the selected ions in step (iii).