© 2012 AOAC INTERNATIONAL
confirmatory tool to verify the presence of TFA isomers. Most of
the time, a maximum number of four isomers is encountered.
Case 1
.—
Absence of C18:3 TFA isomers
.—No peak (if only one
peak is detected;
see
the comment above regarding the presence
of another C20:1 isomer in milk). The presence of only one C18:3
TFA isomer is not possible.
Case 2.—Presence of C18:3 TFA isomers (a minimum of two
isomers, C18:3 c,c,t and C18:3 t,c,c.)
.—The C18:3 t,c,c peak area
is approximately 80% of the C18:3 c,c,t peak area (ratio 5:4). This
ratio is always constant when other C18:3 TFA isomers are present.
Case 3.—Presence of C18:3 TFA isomers (three isomers, C18:3
c,c,t; C18:3 c,t,c; and C18:3 t,c,c).—
The same as described above
for Case 2, but with the C18:3 c,t,c. The peak area of this isomer is
always small and is sometime lower than the LOQ. In case of co-
elution with C20:1 n-9 (or another C20:1 isomer), its contribution
on total C18:3 TFA is negligible.
Case 4.—Presence of C18:3 TFA isomers (four isomers, C18:3
t,c,t; C18:3 c,c,t; C18:3 c,t,c; and C18:3 t,c,c)
.—The same as
described above (Cases 2 and 3), but with the C18:3 t,c,t. This
isomer is formed by the degradation of C18:3 c,c,t and C18:3
Table 2012.13A. Stoichiometric factors (Si FA) for converting the fatty acid methyl esters (FAME) to fatty acids (FA)
Chain length
Configuration and group
Abbreviation FAME m.w.
FA m.w.
TAG m.w.
Si (FA)
C4:0
SFA
102.1
88.1
302.4
0.863
C6:0
SFA
130.2
116.2
386.5
0.892
C8:0
SFA
158.3
144.2
470.7
0.911
C10:0
SFA
186.3
172.3
554.9
0.925
C12:0
SFA
214.4
200.3
639.0
0.935
C14:0
SFA
242.4
228.4
723.2
0.942
C14:1
ω-5 (or n-5)
cis
MUFA
240.4
226.4
717.1
0.942
C15:0
SFA
256.4
242.4
765.3
0.945
C15:1
ω-5 (or n-5)
cis
MUFA
254.4
240.4
759.2
0.945
C16:0
SFA
270.5
256.4
807.3
0.948
C16:1
ω-7 (or n-7)
cis
MUFA
268.5
254.4
801.3
0.948
C17:0
SFA
284.5
270.5
849.4
0.951
C17:1
ω-7 (or n-7)
cis
MUFA
282.5
268.4
843.4
0.950
C18:0
SFA
298.5
284.5
891.5
0.953
C18:1 TFA
trans
a
296.5
282.5
885.5
0.953
C18:1
ω-9 (or n-9)
cis
MUFA
296.5
282.5
885.5
0.953
C18.2 TFA
trans
a
294.5
280.5
879.4
0.952
C18:2
ω-6 (or n-6)
cis
PUFA
LA
294.5
280.5
879.4
0.952
C18:2 CLA
ω-6 (or n-6)
cis
/
trans
PUFA
CLA
294.5
280.5
879.4
0.952
C18:3
ω-6 (or n-6)
cis
PUFA
292.5
278.4
873.4
0.952
C18:3 TFA
trans
a
292.5
278.4
873.4
0.952
C18:3
ω-3 (or n-3)
cis
PUFA
ALA
292.5
278.4
873.4
0.952
C20:0
SFA
326.6
312.5
975.7
0.957
C20:1
ω-9 (or n-9)
cis
MUFA
324.6
310.5
969.6
0.957
C20:2
ω-6 (or n-6)
cis
PUFA
322.5
308.5
963.6
0.957
C20:3
ω-6 (or n-6)
cis
PUFA
320.5
306.5
957.5
0.956
C20:3
ω-3 (or n-3)
cis
PUFA
320.5
306.5
957.5
0.956
C20:4
ω-6 (or n-6)
cis
PUFA
ARA
318.5
304.5
951.5
0.956
C20:5
ω-3 (or n-3)
cis
PUFA
EPA
316.5
302.5
945.4
0.956
C21:0
SFA
340.6
326.6
1017.8
0.959
C22:0
SFA
354.6
340.6
1059.9
0.960
C22:1
ω-9 (or n-9)
cis
MUFA
352.6
338.6
1053.8
0.960
C22:2
ω-6 (or n-6)
cis
PUFA
350.6
336.6
1047.8
0.960
C22:6
ω-3 (or n-3)
cis
PUFA
DHA
342.5
328.5
1023.6
0.959
C24:0
SFA
382.7
368.7
1144.0
0.963
C24:1
ω-9 (or n-9)
cis
MUFA
380.7
366.6
1137.9
0.963
a
Does not include trans fatty acids into MUFA and PUFA sums.
