Chromatographic analyses of fatty acid methyl esters by HPLC-UV and GC-FID

Article abstract of DOI:10.1590/S0103-50532012000400023

An analytical method using high performance liquid chromatography with UV detection (HPLC-UV) (method A) was used for simultaneous determination of total amounts of triacylglycerides, diacylglycerides, monoacylglycerides and fatty acid methyl esters in alcoholysis of different oil (cotton, canola, sunflower, corn and soybean) samples. Analyses were carried out at 40 °C for 20 min using a gradient of methanol (MeOH) and 2-propanol-hexane 5:4(v/v) (PrHex):100percent of MeOH in 0 min, 50percent of MeOH and 50percent of PrHex in 10 min maintained with isocratic elution for 10 min. Another HPLC-UV method (method B) with acetonitrile isocratic elution for 34 min was used to determine the fatty acid composition of oils analyzing their methyl ester derivatives. Contents were determined with satisfactory repeatability (relative standard deviation, RSD < 3percent), linearity (r² > 0.99) and sensitivity (limit of quantification). Method B was compared with an official gas chromatographic method with flame ionization detection (GC-FID) from American Oil Chemists' Society (AOCS) in the determination of fatty acid methyl esters (FAME) in biodiesel real samples.

Full text of DOI:10.1590/S0103-50532012000400023

J. Braz. Chem. Soc., Vol. 23, No. 4, 763-769, 2012.
Printed in Brazil - ©2012 Sociedade Brasileira de Química
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Article
A
Chromatographic Analyses of Fatty Acid Methyl Esters by HPLC-UV and GC-FID
Myller S. Carvalho,a Márcio A. Mendonça,b David M. M. Pinho,a
Inês S. Resckc and Paulo A. Z. Suarez*,a
aLaboratório de Materiais e Combustíveis, Instituto de Química, bFaculdade de Agronomia e
Medicina Veterinaria and cLaboratório de Ressonância Magnética Nuclear, Instituto de Química,
Universidade de Brasília, 70910-900 Brasília-DF, Brazil
Um método analítico por cromatografia líquida de alto rendimento com detecção ultravioleta
(HPLC-UV) (método A) foi utilizado na determinação simultânea dos valores totais de
triacilglicerídeos, diacilglicerídeos, monoacilglicerídeos e ésteres metílicos de ácidos graxos na
alcólise de diferentes óleos (algodão, canola, girassol, milho e soja). As análises foram realizadas
a 40 °C por 20 min usando gradiente de metanol (MeOH) e 2-propanol-hexano 5:4 (v/v)
(PrHex): 100% de MeOH em 0 min, 50% de MeOH e 50% de PrHex em 10 min mantido com
eluição isocrática por 10 min. Outro método por HPLC-UV (método B) com eluição isocrática
de acetonitrila por 34 min foi utilizado na determinação da composição de ácidos graxos de óleos
analisando seus derivados de éster metílico. Os conteúdos foram analisados com satisfatória
repetibilidade (desvio padrão relativo, RSD < 3%), linearidade (r2 > 0,99) e sensibilidade (limite
de quantificação). O método B foi comparado com o método oficial cromatográfico gasoso com
detecção através de ionização por chama (GC-FID) da American Oil Chemists’ Society (AOCS)
na determinação de ésteres metílicos de ácidos graxos (FAME) em amostras reais de biodiesel.
An analytical method using high performance liquid chromatography with UV detection
(HPLC-UV)(methodA)wasusedforsimultaneousdeterminationoftotalamountsoftriacylglycerides,
diacylglycerides, monoacylglycerides and fatty acid methyl esters in alcoholysis of different oil
(cotton, canola, sunflower, corn and soybean) samples.Analyses were carried out at 40 °C for 20 min
using a gradient of methanol (MeOH) and 2-propanol-hexane 5:4 (v/v) (PrHex): 100% of MeOH
in 0 min, 50% of MeOH and 50% of PrHex in 10 min maintained with isocratic elution for 10 min.
Another HPLC-UV method (method B) with acetonitrile isocratic elution for 34 min was used
to determine the fatty acid composition of oils analyzing their methyl ester derivatives. Contents
were determined with satisfactory repeatability (relative standard deviation, RSD < 3%), linearity
(r2 > 0.99) and sensitivity (limit of quantification). Method B was compared with an official gas
chromatographic method with flame ionization detection (GC-FID) from American Oil Chemists’
Society (AOCS) in the determination of fatty acid methyl esters (FAME) in biodiesel real samples.
Keywords: biodiesel, triacylglycerides, gas chromatography, liquid chromatography,
methyl ester
Introduction
microemulsions with short chain alcohols and pyrolysis or
transesterification of triacylglycerides. Transesterification
is a widespread process used for obtaining biodiesel and
involves the catalyzed reaction of triacylglycerides
(TAGs) and short-chain mono-alcohols (such as
methanol and ethanol) to produce fatty acid methyl or
ethyl esters (biodiesel).3,4 This process was the chosen
technology by several biofuel programs, such as the
National Program of Production and Use of Biodiesel
(PNPB) in Brazil.2 Biodiesel is considered the best fuel
substitute for diesel due to its physical properties, which
The direct use of fats and oils (mainly composed by
triacylglycerides) in diesel engines is problematic and
can lead to many problems, such as carbon deposit due
to its poor atomization, high viscosity and thickening of
lubricating oil as a consequence of its low volatility.1,2
There are many possible solutions to address the
viscosity problem, which are dilution with diesel fuel,
*e-mail: psuarez@unb.br

764
Chromatographic Analyses of Fatty Acid Methyl Esters by HPLC-UV and GC-FID
J. Braz. Chem. Soc.
are close to those of fossil diesel.1 Advantages of biodiesel
include biodegradability, higher flash point and reduction
of most regulated exhaust emissions (such as sulfur and
aromatic content).2,5
Scheme 1 shows the transesterification reaction of
these TAGs with alcohol to obtain the most common
fatty esters contained in biodiesel: palmitic (16:0), stearic
(18:0), oleic (18:1, cis-9), linoleic (18:2, cis-9,12) and
linolenic (18:3, cis-9,12,15).5 Moreover, the diversity of
carbon chains, degree of unsaturation, stereochemistry
(cis/trans) and position of double bonds in the carbon
chain make biodiesel as a complex mixture that contains
a broad spectrum of fatty acid types, complicating their
characterization.
The fatty acid profiles are of considerable importance
in the biodiesel analysis. Some chromatographic methods
have been created and improved to analyze the biodiesel6.
Among these, thin layer chromatography (TLC),7
gas chromatography (GC),8 high-performance liquid
chromatography (HPLC),9-11 gel permeation chromatography
(GPC),12 nuclear magnetic resonance (NMR)13 and near
infrared spectroscopy (NIR)14 are included.
The American Oil Chemists’ Society (AOCS)
recommends in its standard Cd 14c-94 and Ce 1c-89
methods the use of gas chromatography with flame
ionization detection (GC-FID).15,16 Although GC suffers
from many drawbacks, it has been the most used technique
for analyzing the complex mixture of compounds involved
in the transesterification, including triacylglycerides (TAG),
diacylglyceride (DAG), monoacylglyceride (MAG),
monoalkyl esters, alcohol and free glycerol.15,17 It is worth to
mention that these determinations cannot be carried out in
an unique analysis because different methods are required.
HPLC offers an useful alternative to GC and many
liquid chromatographic methods have been developed.9,18
Many workers, however, may find that HPLC offers some
advantage and indicate some critical points of GC: (i) the
presence of heat-labile compounds affects the quantification
of FAME (fatty acid methyl esters), (ii) the carbon chain
polyunsaturated of the fatty acids may undergo structural
changes, isomerization and decomposition under high
temperatures, (iii) it is not possible to collect fractions
of the separated fatty acid esters for further analysis,
(iv) baseline drift, and (v) GC analysis frequently
requires derivatization step by saponification furthered to
methylation, consuming reagents as hexane, BF3 and NaCl,
being time-consuming and labor-intensive.11,17
In this work, HPLC (called method B) and GC
techniques are compared with respect to the determination
of FAMEs in biodiesel. For this study, the main refined
vegetable oils used in European Union, United Stated and
Brazil were chosen: cotton, canola, sunflower, corn and
soybean oils. Although the present study is limited to
the investigation of these oils, it is possible to extend our
method to other fats and oils if they have their composition
based on similar fatty acids. For instance, despite olive and
palm-tree oil have not been investigated, their composition
usually contains up to 97% of the fatty acids here studied.
Scheme 1. Transesterification of triacylglycerol (any feedstock). R1, R2 and R3 are the carbon chains of aliphatic esters and R4 are of alcohols. It is illustred
the main fatty acid esters in oils used in this work: palmitic (16:0), estearic (18:0), oleic (18:1), linoleic (18:2) and linolenic (18:3).

Vol. 23, No. 4, 2012
Carvalho et al.
765
Moreover, the present investigation deals with the
application of an analytical method (called method A)
in HPLC in order to determine the total amounts of the
chemical substances involved in the reaction between
vegetable oils and methanol.
GC quantitative analysis
FAME was identified by direct comparison with the
standard mixture and the percentage of individual FAME
was made in relation to total area of the chromatogram.
As far as the different studied fatty acid methyl esters have
similar carbon chain length, it was assumed that they have
the same response factor and volatility, allowing to make
a direct comparison of the peak areas to determine the
sample composition.
Experimental
Materials
Cotton, canola, sunflower, corn and soybean oils were
purchased in local market. HPLC grade acetonitrile,
methanol, 2-propanol and hexane were obtained fromVetec
Química Fina Ltda (Brazil). Nitrogen (industrial grade)
was obtained from White Martins (Brasília-DF, Brazil) and
used without further purification. The standards of methyl
linolenate (18:3), methyl linoleate (18:2), methyl oleate
(18:1, cis), methyl elaidate (18:1, trans), methyl stearate
(18:0) and methyl palmitate (16:0) were purchased from
Aldrich (St. Louis, MO, USA). The reference standard
FAME mixture (C4-C24) for GC was obtained from Supelco
(Bellefonte, PA, USA).
HPLC chromatographic instruments and procedures
The analyses were carried out in CTO-20A (Shimadzu,
Tokyo, Japan) high-performance liquid chromatography
(HPLC) equipment with an ultraviolet detector (UV)
setted at 205 nm. All chromatograms were generated by
LabSolutions software (Shimadzu, Japan).
MethodA:9 it was used a single Shim-PackVP-ODS C18
reversed-phase column (250 mm × 4.6 mm, 5 µm) kept at
40 °C. The injection volume of 10 µL and the flow-rate of
1 mL min-1 with gradient elution of methanol (MeOH) and
2-propanol-hexane 5:4 (v/v) (PrHex) were used: 100%
of MeOH in 0 min, 50% of MeOH and 50% of PrHex in
10 min maintained with isocratic elution for 10 min. The
yield of the transesterification reaction was calculated by
comparing the sum of the peak areas of the chromatogram
components. Desired sample amount (ca. 25 mg) was
dissolved in 2 mL of 2-propanol-hexane 5:4 (v/v).
Method B:18 it was used two Shim-Pack VP-ODS C18
reversed-phase columns (250 mm × 4.6 mm, 5 µm) in
series kept at 40 °C. The injection volume of 10 µL and the
flow-rate of 1 mL min-1 with isocratic elution of acetonitrile
for 34 min were used. Desired sample amount (ca. 25 mg)
was dissolved in acetonitrile and injected without previous
treatment.
Methyl ester preparation
Methyl esters were synthesized using potassium
hydroxide (KOH) as catalyst and methanol at room
temperature. After 1 h, the stirring was stopped and the
reaction product was separated into two phases by simple
decantation. FAME (upper phase) was further purified by
washing ten times with water. Then, FAME was dissolved
in dichloromethane, kept standing over magnesium sulfate,
filtered and the volatiles removed under reduced pressure.
The transesterification reaction utilized a total molar ratio
of methanol:oil:KOH of 7:1:0.01.11
GC chromatographic instruments and procedures
HPLC quantitative analysis
The analyses were conducted with a GC 3400cx
gas chromatograph (Varian Star) equipped with a
split/splitness injector and flame ionization detector
(FID). A capillary fused silica column SPTM 2380
(30 m × 0.25 mm × 0.2 mm film thickness) with matrix
active group stabilized poly(90% biscyanopropyl/10%
cyanopropylphenyl siloxane) phase was operated under
programmed temperature conditions: 140-240 ºC at
5 ºC min-1 in 30 min (detector and injector temperatures
of 260 °C), injection volume and mode of 0.4 µL and split
(100:1), and nitrogen gas as carrier gas (20 cm min-1). The
desired amount (ca. 20 mg) of samples was dissolved in
2 mL in hexane before injection.
The external calibration method was adopted for
standardization, as previously determined.18 The FAME
peak identification was determined by the comparison
of retention time of the reference standards in the same
condition. The HPLC method was validated by the
determination of the linearity, limits of detection and
quantification and repeatability.
The calibration curves were constructed in a FAME
desired concentration and the integrated peak areas versus
the amounts of methyl ester standard were plotted for each
FAME. It was used the software Origin 7.5 (OriginLab
Corporation) to make the calibration curves, applying the

766
Chromatographic Analyses of Fatty Acid Methyl Esters by HPLC-UV and GC-FID
J. Braz. Chem. Soc.
method of least-squares to calculate the parameters a, b,
r2 and sy (a is the angular coefficient or slope, b is the linear
coefficient or intercept, r2 is the correlation coefficient and
sy is the standard deviation of axes y). Standard solutions
of each FAME were prepared by the dilution of the desired
weight of standard FAME in acetonitrile and analyzed in the
concentration range. The solutions for 18:3 were 3.4, 13.4,
67.8, 202.9, 503.8 and 952.0 mg L-1. The solutions for 18:2
were 5.4, 1437.0, 3482.6, 20255.9 and 68411.1 mg L-1. The
solutions for 18:1, cis, were 161.2, 1556.1, 2789.3, 3985.4,
104736.1 and 131316.0 mg L-1. The solutions for 18:1, trans,
were 159.9, 676.7, 1005.7, 10829.4 and 24950.2 mg L-1.
The solutions for 16:0 were 156.3, 452.8, 4320.8, 20064.3,
35761.0 and 43808.5 mg L-1. The solutions for 18:0 were
133.6, 333.8, 666.9, 810.9, 9089.7 and 18138.3 mg L-1.
The limit of detection (LOD) and the limit of
quantification (LOQ) were determined by the successive
decrease of the concentration of the prepared standards
until the smallest detectable peak. This concentration was
multiplied by 3 and 10 to obtain the limits of detection and
quantification, respectively.
note that if there is water in the reaction media, the hydrolysis
of the different ester may take place affording free fatty acid
(FFA) and the respective alcohol.1 Thus, the analysis of the
reaction yield in these different products is a major challenge.
The HPLC analysis of the methanolysis of soybean,
cotton, canola, corn and sunflower oils in the final mixture
results in several peaks corresponding to FFA, MAG, DAG,
TAG and FAME, as shown in Figure 1 for methanolysis
soybean oil in low reaction yield. As can be depicted
in Figure 1, the only difficulty of this method was the
separation of FFA and MAG, and a good resolution for the
other components was achieved. Table 1 shows the results
of the HPLC method A from methanolysis of different
vegetable oils with high reaction yields in FAME. These
results exhibit an important advantage of HPLC when
compared with GC: the possibility of analyzing all fatty
acids and their derivatives in only one analysis.
HPLC separation and quantitave analysis: method B
Soybean biodiesel analyzed by method B is illustrated in
Figure 2. The relative standard deviations (RSD) obtained
The repeatability (n = 6) of the HPLC method B for
the retention time and integration area was tested for the
determination of a standard mixture solution of all FAMEs
used in this work: 202 mg mL-1 for 18:3, 3482 mg mL-1 for
18:2, 2790 mg mL-1 for 18:1, cis, 20000 mg mL-1 for 16:0,
676 mg mL-1 for 18:1, trans, and 810 mg mL-1 for 18:0. This
mixture was six times injected in the same day.
NMR spectroscopy
1H and 13C NMR data were recorded in a Varian
spectrometer (Mercury plus model, 7.04 T) operating at
300 and 75 MHz, respectively, using CDCl3 as solvent and
the chemical shifts are expressed in parts per million
(ppm). The absence of unsaturations in carbon chain was
determined by quantitative 1H NMR and 13C NMR analyses
at 25 °C and compared to the literature data.19
Figure 1. HPLC analysis of low yield of methanolysis of soybean oil in
the final mixture.
Table 1. Composition of the final mixture obtained after methanolysis
of different vegetable oils
Results and Discussion
Initial considerations: method A
Composition / %
Feedstock
FFA + MAGa
FAME
94
DAG
TAG
The transesterification of triacylglycerides with
methanol involves three consecutive reversible
reactions: triacylglycerides to diacylglycerides and to
monoacylglycerides and, finally, to glycerol and FAME, as
depicted in Scheme 1. Note that because of its reversibility,
it is not possible to complete the transesterification reaction
resulting in a mixture of TAG, DAG, MAG, FAME (for
methanol) and glycerol is obtained. It is also important to
Cotton
2
1
2
1
2
2
1
3
2
1
2
1
1
0
2
Canola
Sunflower
Corn
97
94
97
Soybean
95
aIn this method, it was not possible to separate free fatty acid and
monoacylglycerol; FFA: free fatty acid; MAG: monoacylglyceride;
FAME: fatty acid methyl esters; DAG: diacylglyceride; TAG:
triacylglycerides.

Vol. 23, No. 4, 2012
Carvalho et al.
767
for testing the repeatability (n = 6) for the retention time
were less than 1% and for the area less than 3%. As can
be depicted in Figure 2, a good separation can be achieved
within 34 min with the conditions used in this method.
Note that the separation obtained in this method was only
possible using two C18 columns in series. The retention
time increases with the increase of the chain length and the
decrease of the double bond number: 18:3 < 18:2 < 18:1,
cis ca. 16:0 < 18:1, trans < 18:0, being in accordance with
previous works reported in the literature.20 Unfortunately,
it was not possible to separate all the methyl ester, and it
was observed the pair 18:1, cis and 16:0 coelutes, which is
probably a result of this opposing tendencies cited above.17
for separation of lipids.22 In this work, it was possible
to separate and quantify the trans isomer forms of 18:3,
18:2 and 18:1 designate 18:3’, 18:2’ and 18:1, trans,
respectively. These trans isomers are eluted soon after the
correponding cis isomers due to a preferential π-π interaction
between acetonitrile and trans-olefins. This π-π interaction is
smaller for trans configuration than cis configuration due to a
major steric hindrance. These trans isomers of 18:3 and 18:2
may be formed in their refinement during the oil separation
process involving heating or isomerization in the course of
the hydrogenation reactions.23
The calibration curve for each fatty acid ester is
described in Table 2 and Figure 3. Table 2 reports the
parameters a, b, r2 and sy of the calibration curves, range
of concentration and retention time. Table 2 also shows
the LOQ values of the individual compound, which were
estimated by the successive decrease of the concentration
of the prepared standards until the smallest detectable
peak (relation signal:noise = 3). This concentration was
multiplied by 10 to obtain the limits of quantification.24
Figure 3 shows the calibration curves of FAME as a
function of integrated peak area versus concentration
Figure 2. HPLC chromatogram of soybean biodiesel using method B (as
described in the Experimental section: UV detection at 205 nm, flow-
rate of 1 mL min-1, column temperature at 40 °C and injection volume
of 10 µL).
Different approaches have been described in the
literature1,19,22 aiming to separate and quantify cis/trans
fatty acids, but few ones have been completely satisfactory.
For instance, the standard American Oil Chemists’ Society
method uses infrared.21 However, long packed columns
with GC seem to be more targeted in the literature.3 Cation-
exchange column using silver ions has been often used
Figure 3. Calibration curves of pure fatty acid methyl ester (FAME)
standards: () 18:3, () 18:2, () 18:1, cis, () 16:0, () 18:1, trans and
() 18:0 (HPLC conditions of method B as described in the Experimental
section: UV detection at 205 nm, flow-rate of 1 mL min-1, column
temperature at 40 °C and injection volume of 10 µL).
Table 2. Parameters slope, intercept, correlation coefficient (r2) and standard deviation (sy) of calibration plot, time retention (tr) and limit of quantification
(LOQ) for each studied fatty acid methyl esters (FAME)
FAME
18:3
Slope / (area mg-1 L) Intercept / a.u.
r2
sy
Range of concentration / (mg L-1)
3.4 - 952.0
tr / min
13.26
16.33
21.06
21.00
22.42
30.46
LOQ / (mg L-1)
2.9
37816.0
9761.4
4507.4
6146.9
236.0
0
0
0
0
0
0
0.991
0.990
0.995
0.999
0.996
0.996
2.3
5.2
1.1
0.9
0.9
1.2
18:2
5.4 - 6.8 × 104
12.7
18:1 cis
18:1 trans
16:0
161.2 - 13.1 × 104
159.9 - 2.4 × 104
156.3 - 4.3 × 104
133.6 - 1.8 × 104
92.1
90.6
216.5
198.1
18:0
273.2

768
Chromatographic Analyses of Fatty Acid Methyl Esters by HPLC-UV and GC-FID
J. Braz. Chem. Soc.
Table 3. Chemical composition of biodiesel from selected oils in % obtained by gas (GC) and high-performance liquid chromatographies (HPLC)
Cotton
HPLC
Canola
HPLC
Sunflower
Corn
Soybean
HPLC
PHSa
FAME
GC
0.2
-
55.6
-
15.4
22.2
-
GC
5.7
-
22.4
-
60.9
4.9
-
GC
HPLC
0.5
GC
1.3
-
48.6
-
33.4
12.6
-
HPLC
1.5
GC
6.3
-
GC
0
HPLC
0
18:3
18:3’a
0.2
0
6.0
1.0
22.0
0.9
62.8
4.2
0
0.5
-
6.2
1.3
50.6
1.9
21.2
11.4
0
0.1
0.2
-
5.8
-
65.6
11.1
-
0
18:2
55.9
0.1
16.3
19.6
0
61.9
-
59.2
0.7
51.4
1.9
53.6
-
23.5
10.7
-
4.4
18:2’b
18:1 cis
16:0
6.7
24.6
6.2
-
21.1
5.3
30.7
12.7
0
38.3
11.6
32.4
5.7
18:1 trans
18:0
0
2.6
2.3
2.0
2.2
4.1
4.2
2.3
2.1
3.3
3.2
6.4
aPHS: partially hydrogenated soybean oil
of standard (mg L-1). Note that these results show good
linearity (r2 > 0.99) for all the compounds in the range of
concentration tested.
As shown in Table 2 and Figure 2, the detection of the
various FAMEs are more sensitive when double bonds are
present in FAME. Thus, the response factor (or angular
coefficient) and limit of quantification of standard FAME
follow the order: 18:3 > 18:2 > 18:1, cis > 18:1, trans >
18:0 > 16:0.
compared to GC analysis and the results are presented in
Table 3. As expected, five fatty acid chains were found in
esters, totalizing more that 95% of total composition.
The comparison of the HPLC and GC methods for
the methyl ester determination using the same samples of
biodiesel shows that both methods give similar results. RSD
values ranged from 0 to 10%. Therefore, the proposed method
in HPLC is comparable to the GC standard method and can
be used in the analysis of fatty acid methyl esters.
As can be depicted in Figure 2, unlike provided by other
authors,9 saturated fatty acids have significant absorbance
at 205 nm and can be measured by the present method.
Indeed, 18:0 and 16:0 FAMEs exhibit a similar behavior
in the UV detector at 205 nm, as a consequence of their
structural similarity, practically resulting in coincident
calibration curves. It is also worth to mention, that trans
18:1 isomer has a higher slope than the cis form due to its
higher absorption of energy for π-π* transitions.9
Despite a hard work performed in order to find a
chromatographic resolution for 18:1 cis and 16:0, it was
impossible to avoid the co-elution of these compounds. It was
only possible to quantify 18:1 cis and 16:0 after hydrogenation
of biodiesel using Pd/C as catalysts (conditions: temperature
of 80 °C and hydrogen pressure of 100 atm).25 This procedure
leads to a total hydrogenation of biodiesel, resulting in only
18:0 and 16:0 chains, confirmed by 1H NMR and 13C NMR.
The total elimination of unsaturations was confirmed by the
absence of the olefinic (-CH=CH-) signal at 5.35 ppm for
1H NMR and at 134.12 ppm for 13C NMR. Thus, analyzing
once again the mixture, it was observed an increase of the
peak of 18:0 and a drastic decrease of the peak area at 21 min,
which is reduced to only 16:0 chains.
On the other hand, it becomes clear from Table 3 that
GC was not efficient to separate trans and cis isomers in
the partial hydrogenated soybean oil. In contrast, HPLC
using method B shows a good resolution for trans/cis
isomers and it was possible to quantify them. Note that
the peak corresponding to 18:1 cis in the GC analysis was
approximately the sum of the 18:1, cis and 18:1, trans
obtained by HPLC (65.6 ca. 38.7 + 32.4).
Conclusions
In summary, we have developed two HPLC-UV
analytical methods using UV detection at 205 nm suitable
for simultaneous determination of total amounts of
triacylglycerides, diacylglycerides, monoacylglycerides and
fatty acid methyl esters in alcoholysis of different oil samples
(method A) and to determine the fatty acid composition of
oils analyzing their methyl ester derivatives (method B).
These methods presented satisfactory repeatability
(RSD < 3%), linearity (r2 > 0.99) and sensitivity (limit of
quantification). Method B was compared with an official
AOCS method by GC-FID for FAME determination in
biodiesel real samples.
Determination of fatty acid compositions of real samples
Acknowledgements
In order to validate the method here presented, HPLC
method B was tested in real samples of methyl fatty acid
ester of cotton, canola, sunflower, corn and soybean oils and
WewouldliketothankCoordenaçãodeAperfeiçoamento
de Pessoal de Nível Superior (CAPES), Conselho Nacional
de Desenvolvimento Científico e Tecnológico (CNPq),

Vol. 23, No. 4, 2012
Carvalho et al.
769
Fundação de Apoio à Pesquisa do Distrito Federal
(FAPDF) and Fundação Banco do Brasil for partial financial
support. P. A. Z. Suarez, D. M. Pinho and M. S. Carvalho
are in debt with CNPq for their research fellowships.
13. Nebel, B.; Mittelbach, M.; Uray, G.; Anal. Chem. 2008, 80,
8712.
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15. American Oil Chemists’ Society, AOCS Official Method
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