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Fast,SelectiveTriglycerideAnalysis
Table I
Fatty acidand triglyceride nomenclature (afterGeeraert andSandra)
Triglyceridesarenaturallyoccurringesters of fatty acids and
glycerols. They arewidely analyzed in the food industry for
natural oil and fat characterization aswell as fat adulteration.The
triglyceridesusuallyareconverted to theirmethyl esters (FAMEs)
todetermine the fatty acid composition andpercent saturatedvs.
unsaturated fat.Triglycerideanalyses have become very important
in recent years since health conscious consumers are concerned
withminimizing their dietary intake of saturated fats to reduce the
risk of heart disease.
Fattyacidgroups in the triglyceridemolecule canbe classified as
saturated [myristicacid (C14:0),palmitic acid (C16:0), or stearic
acid (C18:0)],monounsaturated [oleic acid (C18:1)], or
polyunsaturated [linoleic acid (C18:2) or linolenic acid
(C18:3)]. Typically, triglycerides are characterizedby degree of
unsaturation. For example, a triglyceridemolecule containing
the groups stearic acid, oleicacid, and linoleicacid (denotedSOL)
would have a greater degree of unsaturation than that of
tripalmitin (denotedPPP). Table I shows the nomenclature of
fatty acids and triglycerides.
1
CapillaryGC columns are thepreferred analytical tool for
triglyceride analysis because they yield shorter analysis times,
higher efficiency, andbetter quantitation than packed
columnGC, HPLC, or SFC. TheRtx
®
-65TG column is truly an
improvement over classical packed columns because triglycerides
with the same carbonnumber but different degrees of unsaturation
canbewell separated.Also,minimal samplepreparation is
required for capillaryGC analysis. The sample is liquefiedby
warming and diluting to 50pg/µLwithdichloromethane or
diisopropyl ether
2,3
.Additional sample clean up is required if
significant amounts of monoglycerides, diglycerides, and fatty
acids areknown tobepresent in the sample
2
.
ColumnSelection forTriglycerideAnalysis
The highmolecular weights of triglycerides require capillary
columnswithhigh thermal stability.Low bleed columns also are
extremely important for accurate triglyceride quantitation.
Triglyceridepolarity increaseswith the degree of unsaturation in
the fatty acid (i.e., the number of double bonds present). The
triglyceridewith themostdoublebondshas thehighest polarity and
the longest retention time. Therefore, a high temperature is
required to elute the higher polarity triglycerides and
maintain a short analysis time. Lower response of highmolecu-
larweight triglycerides has been observed and originallywas
attributed to thermal decomposition of triglycerides in the
injection port. However, thedecreased response also can be
caused by both highmolecularweight discrimination in the
FattyAcids
Abbreviation
CommonName
IUPACName
ShortForm
La
lauric acid
dodecanoic acid
C12:0
M
myristicacid
tetradecanoic acid
C14:0
P
palmiticacid
hexadecanoic acid
C16:0
S
stearicacid
octadecanoic acid
C18:0
A
arachidic acid
eicosanoic acid
C20:0
Be
behenic acid
dodosanoic acid
C22:0
Lg
lignoceric acid
tetracosanoic acid
C24:0
O
oleic acid
cis
-9-octadecenoic acid
C18:1
L
linoleic acid
cis, cis
-9,12-octadecadienoic acid
C18:2
Ln
linolenic acid
cis, cis, cis
-9,12,15-octadecatrienoic acid
C18:3
Ga
gadoleic acid
cis
-11-eicosenoic acid
C20:1
Glycerides
Abbreviation
CommonName
CarbonNumber
#ofUnsaturatedFattyAcids
PPP
tripalmitin
48
0
PLO
palmito-linoleo-olein
52
2
