CHARACTERIZATION OF FATTY ESTER ETHOXYLATES
BY COUPLED CHROMATOGRAPHIC TECHNIQUES.
BERND TRATHNIGG1, W.HRECZUCH2
Institute of Chemistry, Karl-Franzens University, Graz, Austria
2
„Blachownia“ Institute of Heavy Organic Synthesis, Kędzierzyn-Koźle, Poland
1
ABSTRACT
Fatty acid methyl ester ethoxylates (FAMEE), which can be prepared by direct ethoxylation of fatty acid
methyl esters (FAME), are a promising alternative to the well known fatty alcohol ethoxylates (FAE),
which are in widespread use as nonionic surfactants.
These products can be characterized by different modes of liquid chromatography:
Size exclusion chromatography (SEC, GPC) separates according to molecular size.
Liquid chromatography under critical conditions (LCCC) allows a separation according to functionality.
Liquid adsorption chromatography (LAC) separates according to chemical composition and to molar mass.
These techniques may be combined in different ways :
1. Independent analysis of the entire sample by complementary techniques yields different projections of the three-dimensional surface describing the sample.
2. Semipreparative separation in the first dimension and subsequent analysis of the fractions in the
second dimension is laborious, but reliable.
EXTRAIT
Des éthoxylates des ésters méthylique d’acides graisses (FAMEE), qui peuvent etre préparés par une
éthoxylation directe des ésters méthylique d’acides graisses (FAME), sont une altérnative promisantes
en contraire des éthoxylates des alcohols gras (FAE) connus, qu’on utilize très souvent comme tenside
non-ionique.
Ces produits peuvent etre characterisés par des différentes méthodes chromatographiques:
SEC, GPC ( Size exclusion chromatography ) sépare d’après la taille des molécules.
LCCC (Liquid chromatography under critical conditions) sépare d’après les groupes fonctionelles.
LAC ( Liquid adsorption chromatography) sépare d’après la composition chimique et la masse
moléculaire.
Ces téchniques peuvent etre combinées dans des modes différents:
1. L’analyse indépendante du sample complet via des téchniques complémentaires donne en trois
dimensions des projéctions différentes de la surface qui décrit la sample.
2. La séparation semi-quantitative dans la première dimension suivi par une analyse des fractions
dans la deuxième dimension. Ce mode comprend beaucoup de travail mais e plus reliable.
ZUSAMMENFASSUNG
Fettsäuremethylester (FAMEE), die durch direkte Ethoxylierung von Fettsäuremethylestern (FAME)
erhalten werden können, sind eine vielversprechende Alternative zu den bekannten FettalkoholEthoxylaten (FAE), die als nichtionische Tenside viel verwendet werden.
Diese Produkte können durch verschiedene chromatographische Methoden charakterisiert werden:
Ausschlußchromatographie (SEC, GPC) trennt nach der Größe der Moleküle.
Flüssigkeitschromatographie unter kritischen Bedingungen (LCCC) erlaubt eine Trennung nach
funktionellen Gruppen.
Adsorptionschromatographie (LAC) trennt nach chemischer Zusammensetzung und Molmasse.
Diese Techniken können auf verschiedene Art kombiniert werden:
1. Unabhängige Analyse der gesamten Probe mittels komplementärer Techniken liefert verschiedene
Projektionen der dreidimensionalen Fläche, die die Probe beschreibt.
2. Semipräparative Trennung in der ersten Dimension mit nachfolgender Analyse in der zweiten
Dimension ist arbeitsaufwendig, aber zuverlässig.
CHARACTERIZATION OF FATTY ESTER ETHOXYLATES
BY COUPLED CHROMATOGRAPHIC TECHNIQUES.
BERND TRATHNIGG1, W.HRECZUCH2
Institute of Chemistry, Karl-Franzens University, Graz, Austria
2
„Blachownia“ Institute of Heavy Organic Synthesis, Kędzierzyn-Koźle, Poland
1
ABSTRACT
Fatty acid methyl ester ethoxylates (FAMEE), which can be prepared by direct ethoxylation of fatty acid
methyl esters (FAME), are a promising alternative to the well known fatty alcohol ethoxylates (FAE),
which are in widespread use as nonionic surfactants.
These products can be characterized by different modes of liquid chromatography:
Size exclusion chromatography (SEC, GPC) separates according to molecular size.
Liquid chromatography under critical conditions (LCCC) allows a separation according to functionality.
Liquid adsorption chromatography (LAC) separates according to chemical composition and to molar mass.
These techniques may be combined in different ways :
1. Independent analysis of the entire sample by complementary techniques yields different projections of the three-dimensional surface describing the sample.
2. Semipreparative separation in the first dimension and subsequent analysis of the fractions in the
second dimension is laborious, but reliable.
EXTRAIT
Des éthoxylates des ésters méthylique d’acides graisses (FAMEE), qui peuvent etre préparés par une
éthoxylation directe des ésters méthylique d’acides graisses (FAME), sont une altérnative promisantes
en contraire des éthoxylates des alcohols gras (FAE) connus, qu’on utilize très souvent comme tenside
non-ionique.
Ces produits peuvent etre characterisés par des différentes méthodes chromatographiques:
SEC, GPC ( Size exclusion chromatography ) sépare d’après la taille des molécules.
LCCC (Liquid chromatography under critical conditions) sépare d’après les groupes fonctionelles.
LAC ( Liquid adsorption chromatography) sépare d’après la composition chimique et la masse
moléculaire.
Ces téchniques peuvent etre combinées dans des modes différents:
1. L’analyse indépendante du sample complet via des téchniques complémentaires donne en trois
dimensions des projéctions différentes de la surface qui décrit la sample.
2. La séparation semi-quantitative dans la première dimension suivi par une analyse des fractions
dans la deuxième dimension. Ce mode comprend beaucoup de travail mais e plus confiable.
ZUSAMMENFASSUNG
Fettsäuremethylester (FAMEE), die durch direkte Ethoxylierung von Fettsäuremethylestern (FAME)
erhalten werden können, sind eine vielversprechende Alternative zu den bekannten FettalkoholEthoxylaten (FAE), die als nichtionische Tenside viel verwendet werden.
Diese Produkte können durch verschiedene chromatographische Methoden charakterisiert werden:
Ausschlußchromatographie (SEC, GPC) trennt nach der Größe der Moleküle.
Flüssigkeitschromatographie unter kritischen Bedingungen (LCCC) erlaubt eine Trennung nach
funktionellen Gruppen.
Adsorptionschromatographie (LAC) trennt nach chemischer Zusammensetzung und Molmasse.
Diese Techniken können auf verschiedene Art kombiniert werden:
1. Unabhängige Analyse der gesamten Probe mittels komplementärer Techniken liefert verschiedene
Projektionen der dreidimensionalen Fläche, die die Probe beschreibt.
1
2
Institute of Chemistry, Karl-Franzens University, Heinrichstr. 28, A-8010 Graz, Austria
„Blachownia“ Institute of Heavy Organic Synthesis, Kędzierzyn-Koźle, Poland
2. Semipräparative Trennung in der ersten Dimension mit nachfolgender Analyse in der zweiten
Dimension ist arbeitsaufwendig, aber zuverlässig.
Introduction
Fatty acid methyl ester ethoxylates (FAMEE) can be prepared by direct ethoxylation of fatty acid methyl
esters (FAME). These new products are a promising alternative to the well known fatty alcohol ethoxylates (FAE), which are in widespread use as nonionic surfactants.
Their characterization is, however, not an easy task, because FAMEE (just like FAE) typically consist
of different polymer homologous series (with different end goups).
Consequently, a full characterization requires a two-dimensional separation (according to functionality
and molar mass distribution).
Basically, different modes of liquid chromatography can be applied in the analysis of polymers:
Size exclusion chromatography (SEC) separates according to molecular size (not actually molar
mass !)[1]. It is performed in isocratic mode, typically in pure solvents. A full separation of all oligomers
is generally not achieved because of the limited separation power of SEC. Hence response factors
may vary within a peak (due to variation of chemical composition or molar mass), which complicates
quantitation. In the analysis of oligomers, corrections of response factors for their molar mass dependence have to be made. Multiple detection allows not only an accurate quantitation, but yields also
information on chemical composition[2,3].
Liquid chromatography at the critical point of adsorption (often also called LC under critical conditions (LCCC) is run at a special temperature and mobile phase composition, at which all chains with
the same repeating unit elute at the same volume (regardless their length), which means, that the polymer chain becomes chromatographically invisible. In this case, a separation according to a structural
units other than the repeating unit (e.g. the end groups) can be achieved[4]. LCCC is also run under
isocratic conditions, but typically in mixed mobile phases. For molecules containing two hydrophobic
groups, separation may, however, follow a different mechanism, which causes a separation of the
lowest oligomers even at the critical point of adsorption for the repeating units.
In LCCC, quantitation is complicated by the fact, that each peak contains an entire polymer homologous series with unknown concentration and composition plus an unknown amount of one component
of the mobile phase (due to preferential solvation of the polymer coils). Hence direct quantitation by
dual detection is not possible. If LCCC is, however combined with dual detector SEC as the second
dimension, the composition can be obtained. With coupled density and RI detection in both dimensions, a quantitatively accurate mapping of FAE and FAMEE can be achieved[5,6].
Liquid adsorption chromatography (LAC) separates according to chemical composition and to molar mass[7-9]. Unlike SEC, the selectivity of LAC is typically very high, for samples with a higher
poldispersity often too high. Under isocratic conditions, only lower oligomers are separated, while
higher oligomers appear as very broad peaks, which can hardly be integrated, and some more are
obviously not even eluted. Using gradient elution, a full separation of individual oligomers can be
achieved.
Depending on the nature of the samples (and the chromatographic technique), different concentration
detectors can be used in HPLC of polymers: The most familiar detectors are the UV-detector, which
can, however, only be applied to samples absorbing light of a wavelength, for which the mobile phase
is sufficiently transparent, and the Refractive Index (RI) detector. The density detector (according to
the mechanical oscillator principle) is very useful in polymer analysis, especially in combination with
other detectors.
The UV detector detects UV-absorbing groups in the polymer, which may be the repeating unit, the end
groups, or both. As no group absorbing at a reasonable wavelength is present in FAMEE, UV detection cannot be applied. Derivatization with UV-absorbing reagents is not feasible, either.
Both the density and RI detector can only be applied in isocratic elution. Consequently, the analysis of
higher FAMEE by LAC with gradient elution faces a severe detection problem.
In the last years, the Evaporative Light Scattering Detector (ELSD) has become a promising tool for
such analytical tasks[10-12].
It is claimed to be a „mass detector“, because is should detect any non-volatile material in any mobile
phase composition. Unfortunately, the sensitivity of this instrument depends on various parameters,
which can not always be easily controlled, and its response to polymer homologous series is not as
well understood as that of RI and density detector. Moreover, the response of such an instrument is
generally not linear with concentration, the response factors of individual oligomers are different, and
they depend not only on the operating conditions, but also on the composition of the mobile phase, in
which they are eluted [13]!
The techniques mentioned above may be combined in different ways to achieve multidimensional separations:
1. Independent analysis of the entire sample by complementary techniques yields different projections of the three-dimensional surface describing a polymer, such as functionality type distribution
(FTD) by LCCC and molar mass distribution (MMD) by SEC or (gradient) LAC. This approach is
easy to use, but may lead to erroneous results, for example, if the individual homologous series
have different MMD.
2. Direct transfer from the first dimension[14] faces several problems: mobile phases must be compatible, which is not always the case; the flow rate of the first dimension must be low enough to
allow a complete separation in the second dimension to take place within the time required to fill
the sample transfer loop; especially the later fractions from the first dimension are highly diluted.
3. Semi(preparative) separation in the first dimension and subsequent injection of the fractions (after
evaporation of the solvent) into the second dimension (SEC or LAC) is laborious, but reliable: A
quantitation of both dimensions is possible[6,15], and there are no problems with incompatible (or
interfering) mobile phases.
Experimental
The following materials were used:
 Oxirane from the Mazovian Petrochemical Works, Płock, Poland
 Fatty esters and fatty alcohol ethoxylates, which were used as reference materials in the chromatographic analysis, were purchased from FLUKA (Buchs, Switzerland)
 Ethoxylated rape oil acid methyl esters were obtained in laboratory scale at the „Blachownia“ ICSO,
Kędzierzyn-Koźle, Poland.
Synthesis of ethoxylates.
Ethoxylation was performed in a 2-L stainless-steel autoclavee, equipped with a mechanical stirrer and
a cooling coil. The reactor was charged with the ester substrate and the proprietary calcium based
catalyst. Then the reactor was closed and an automative procedure of the synthesis was started. The
reactor system was equipped with a Programmable Logic Control System (PLC) allowing feeding the
desired amount of EO under the assumed parameters of pressure and temperature controlled by the
PLC microprocessor. After completion the reaction product was discharged and weighed.
Chromatography:
All HPLC measurements were performed using the density detection system DDS70 (CHROMTECH,
Graz, Austria), which has been developed at Graz K-F University. Each system was connected to a
MS-DOS computer via the serial port.
Data acquisition and processing was performed using the software package CHROMA, which has
been developed for the DDS 70. The columns and density cells were placed in a thermostatted box, in
which at temperature of 25.0°C was maintained for all measurements.
Size Exclusion Chromatography (SEC) measurements were performed in chloroform (HPLC grade,
Rathburn) at a constant flow rate of 1.0 ml/min, which was maintained by a Gynkotek 300C HPLC
pump. An ERC 7512 RI detector (ERMA) was combined with the density detection system DDS70.
Samples were injected using a VICI injection valve (from Valco Europe, Switzerland) equipped with a
100 µl loop, the concentration range was 4 - 8 g/l. Two different columns were used in SEC: Waters
Styragel HR 3 (300x7.8 mm) and PLgel 100  (600x7.8 mm, from Polymer Laboratories, UK).
The SEC calibrations were obtained using pure oligomers of EO (Fluka, Buchs, Switzerland)). Chemical composition along the MMD was determined from density and RI detection using the software
CHROMA (CHROMTECH, Graz, Austria).
Liquid Chromatography at the Critical Point of Adsorption (LCCC) measurements were performed in
methanol-water 97:3 (w/w) (both solvents from Merck, HPLC grade) on a column packed with
Spherisorb ODS2 (5 µm, 80 , 4.6x250 mm) from PhaseSep (Deeside, Clwyd, UK) at a flow rate of
0.5 ml/min, which was maintained by a two JASCO 880 PU pumps (from Japan Spectrosopic Company, Tokyo, Japan). The sample volume was 50 µl. A Bischoff 8110 RI detector was combined with
the DDS70. In semipreparative measurements, a 250x10mm column packed with the same stationary phase was run at 2.0 ml/min. The injected volume was 500 µl.
In normal phase Liquid Adsorption Chromatography (NP-LAC) measurements, the mobile phase was
ndelivered by an ISCO 2350 HPLC pump (from ISCO, Lincoln, NE, USA), Gradients were formed by
low pressure mixing using an ISCO 2361 gradient programmer. In gradient elution, mobile phase A
was pure acetone, mobile phase B was acetone-water 80:20 (w/w). The following gradient profile was
used: start 100 % A, then in 5 min to 10 % B, 20 min to 100% B, 10 min constant at 100 % B, then
within 1 min back to 100 % A. All separations were performed on a column packed with Spherisorb
S5W (5 µm, 80 , 4.6x250 mm).
A SEDEX 45 ELSD (Sedere, France) was connected to the DDS 70. Nitrogen was used as carrier gas,
and the pressure at the nebulizer was set to 2.0 bar, the temperature of the evaporator to 30°C .
Samples were injected manually using a Rheodyne 7125 injection valve (from Rheodyne, Cotati, CA,
USA) equipped with an 50 µl loop.
Results and Discussion:
In this study, various fatty acid methyl esters (FAME) were ethoxylated, the composition of which varied in a wide range, as can be seen from Figure 1:
100.0
90.0
80.0
70.0
60.0
w t-%
50.0
40.0
30.0
20.0
Figure 1:
ME TI
ME PK 12-18 F
ME PK 8-18F
ME C 12 - 70
24
22
20
num ber of carbon atom s in fatty acid
18
16
14
12
10
8
6
-
ME SU
10.0
Fatty acid composition of fatty acid methyl esters (FAME) used for direct ethoxylation
Basically, the ethoxylates obtained from such esters consist of several polymer homologous series
(containing a variable number of ethylene oxide units) with different end groups (containing a variable
number of carbon atoms).
Consequently, different information will be obtained from different chromatographic techniques:
Size exclusion chromatography (SEC) yields the overall length of the molecules (fatty acid plus
oxyethylene chain). Moreover, chemical composition (weight fractions of fatty acid ester and polyoxyethylene chain, respectively) can be obtained from dual detection, provided that the corresponding
response factors of both detectors are known.
The principle of dual detection can be easily understood [2,3,6]: When a mass m i of a copolymer,
which contains the weight fractions wA and wB (= 1 - wA) of the monomers A and B, is eluted in the slice
i (with the volume V) of the peak, the areas xi,j of the slice obtained from both detectors depend on
the mass mi (or the concentration ci =mi/V) of polymer, its composition (wA), and the corresponding
response factors fj,A and f j,B , wherein j denotes the individual detectors.

x i, j  m i w A f j,A  w B f j,B

equation 1
The weight fractions wA and wB of the monomers can be calculated using equation 2:
x i,1
* f 2,A  f1,A )
x i,2
1
 1
x i,1
wA
(
* f 2,B  f1,B )
x i,2
(
equation 2
and therefrom the mass of polymer in the corresponding interval
mi 
x i,1
equation 3
w A * ( f1,A  f1,B )  f1,B
As can be seen from Table 1, the overall composition, which is found in this way for the ethoxylates as
well as also for the components FAME and PEG (which were used as reference materials) agrees very
well with the theoretical one. A simple calibration with a (sufficiently high molecular) poly(ethylene glycol) (such as PEG 4000) and the starting FAME is sufficient to yield the overall composition of ethoxylates with good accuracy.
Table 1:
Chemical composition of FAMEE based on the FAME from Fig.1, as determined by SEC
with coupled density and RI detection.
% EO (theor.)
60.0
70.0
80.0
FAME
PEG 4000
% EO (found)
ME C 12 – 70
ME PK 8-18F ME PK 12-18 F
60.5
58.8
59.1
70.2
70.0
69.4
81.3
79.3
79.2
0.0
100.3
ME TI
57.5
68.9
81.2
ME SU
60.3
71.9
78.3
The molar mass distribution (MMD) can be obtained using a calibration obtained with PEG standards.
In Figure 2, the MMD of such an ethoxylate is plotted together with the chemical composition as a function molar mass.
It can clearly be seen, the weight fraction of EO increases with molar mass (as expected), but there
is a shoulder at the high molecular end of the MMD, which has a somewhat different composition,
which can be due to a different functionality (nature or number of end groups).
This requires a different separation mechanism:
Liquid chromatography at the critical point of adsorption (LCCC) can be applied to separate the
individual polymer homologous series. On a reversed phase column, the polyether chain can be made
“chromatographically invisible”, and the separation occurs according to the length of the hydrophobic
group, as is hown in Figure 3. While the first (double) contains PEG or PEG monomethyl ether, the
main peaks represent the series with 12, 14, 16 and 18 carbon atoms in the fatty acid.
193/2/97
10fl THF ad 10 ml
Date: 980422
Chrom.Nr.:
6
method: FMEE1
weight-%
100
50
2
3
log M
PEG
mass distribution
Figure 2:
4
0
ME C12-70
MMD and chemical composition of an ethoxylate based on ME C 12-70, as obtained
from SEC with coupled density and RI detection.
193/2/97 35Grad
Offset RI-Fr. 20 sec
Date: 980616
Chrom.Nr.: 9
method: MEO95
2709.3
2273.6
response
9
8
7
6
5
4
3
2
1
1 2
1 2
3
3
4
4
5
5
6
6
-116.5
0.2
elution volume
density
Figure 3:
RI
65.1
-209.2
LCCC of an ethoxylate based on ME C 12-70, as obtained on a semi-preparative ODS2
column in methanol-water 95: 5 (detection: density and RI )
When the individual fractions are collected and injected in the SEC column, MMDs similar to the one
shown in Figure 4 are obtained: Obviously, the higher molecular shoulder has been removed. It is
found in peak 6, which should contain two hydrophobic groups. Surprisingly, this fraction has a trimodal
distribution, with a maximum at a considerably higher molar mass.
193/2/97 C12-Fraktio
Date: 980617
980616.09/3 ad 500fl
Chrom.Nr.: 5
method: FMEE1
weight-%
100
50
0
2
mass distribution
Figure 4:
3
log M
PEG
4
FAME C12-70
MMD and chemical composition of the C12 fraction (peak 3) from Figure 3, as obtained
from SEC with coupled density and RI detection.
193/2/97 Fr. 6
Date: 980618
980616.09/6 ad 300fl
Chrom.Nr.:
3
method: FMEE1
weight-%
100
50
2
mass distribution
Figure 5:
3
log M
PEG
4
0
FAME C12-70
MMD and chemical composition of peak 6 from Figure 3, as obtained from SEC with
coupled density and RI detection.
The third mechanism, which can be utilized, is Liquid adsorption chromatography (LAC): on a normal phase column, the retention is mainly determined by the number of EO units, while the hydrophobic group plays a minor role. In this case, the retention of the higher oligomers is too strong to allow an
isocratic analysis. Hence gradient elution has to be applied, which requires the use of an evaporative
light scattering detector, with all its problems in quantitation.
193/2/97 raw
Date: 980618
A: acetone, B: H2O
Chrom.Nr.: 2
method: S5WA1
response
2932.0
4
12 3
5 6 7 8 9 1011 1213
0.1
Sedex 45
Figure 6:
21.9
-140.7
elution volume
Separation of an ethoxylate based on ME C 12-70, as obtained on a normal phase column with gradient elution. Detection: ELSD.
Obviously, the lower oligomers are strongly underestimated, which is especially dramatic for the lower
(C12–C14) series. Fortunately, the most important FAMEE are based on rapeseed methyl ester, which
contains higher fatty acids (C16-C22). The separation of such a product is shown in Figure 7:
R 10 S
old solution
Date: 990511
Chrom.Nr.: 3
method: SW5A2
response
8319.0
1 2 3
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Sedex 45
Figure 7:
17.8
0.0
-396.1
elution volume
Separation of an ethoxylate based on rapeseed methyl ester, as obtained on a normal
phase column with gradient elution. Detection: ELSD.
Conclusions:
FAMEE can be analyzed by different chromatographic techniques: Gradient LAC on normal phases
shows very nice chromatograms with an excellent resolution, quantitation cna, however, be problematic due to the unclear response of the ELSD. On the other hand, SEC with coupled density and RI detection provides very reliable information on molar mass and chemical composition. LCCC can be applied to separate the individual homologous series, and the fractions thus obtained can be analyzed by
SEC or LAC in the second dimension.
References:
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
(13)
(14)
(15)
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