Journal of Chromatography A Method for determination of fatty acid ...

Journal of Chromatography A, 1216 (2009) 8545–8548
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Journal of Chromatography A
journal homepage: www.elsevier.com/locate/chroma
Method for determination of fatty acid amides in polyethylene packaging
materials—Gas chromatography/mass spectrometry
Gang Lv a,b,∗ , Libing Wang a , Jun Liu a , Shufen Li b
a Technical Center for Safety of Industrial Products, Tianjin Entry-Exit Inspection and Quarantine Bureau, No. 6 Pukou Road, Hexi District, Tianjin 300042, China
b Institute of Chemical and Engineering, Tianjin University, No. 92, Weijin Road, Nankai District, Tianjin 300072, China
article
info
abstract
Article history:
Received 7 January 2009
Received in revised form
10 September 2009
Accepted 2 October 2009
Available online 8 October 2009
Keywords:
Fatty acid amides
Gas chromatography/mass spectrometry
Pressurized solvent extraction
Derivation
A new method for determination of fatty acid amides in polyethylene packaging film was developed
using gas chromatography/mass spectrometry (GC/MS). Liquid extraction, Soxhlet extraction ultrasonicassisted
extraction and pressurized solvent extraction (PSE) methods were compared and the results
showed that pressurized solvent extraction was the best for extracting these compounds. After extraction,
solvent was blown by nitrogen and a trifluoroethyl derivation step was carried out. The derivative
compounds were identified and quantified by GC/MS using an HP-Innowax column. The retention times
were 6.20 min for derivative hexadecanoamide, 8.56 min for derivative octadecanamide, 8.84 min for
derivative oleamide and 13.68 min for derivative erucamide, respectively. The detection limits were
61.0 ng g −1 , 74.0 ng g −1 , 103.0 ng g −1 , and 105.0 ng g −1 , respectively, and the linearity were good. The proposed
method was applied satisfactorily to determine these chemicals in different types of polyethylene
samples.
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
Slip agents, such as fatty acid amides, were used in polyethylene
(PE) to bloom to the surface once the film has been produced
and reduce friction coefficients during extrusion, injection molding
and compression molding [1]. The level of fatty acid amides in
the polymers is rather low, normally; the concentration is between
1% and several percent depending on the type of polymers and the
processing conditions [2].
According to the EU Directive 2007/42/EC, the total migration
limits of fatty acid amides are 2 mg/dm 2 . The fatty acid amides
are oil insoluble, hydrophobic and nonvolatile compounds, the
characters of which show that they are difficult for the extraction
procedure and detection procedure.
Traditionally, the extraction of fatty acid amides from polymers
has been carried out by Soxhlet extraction, ultrasonic-assisted
extraction and supercritical fluid extraction [3–9]. Since fatty acid
amides are insoluble in most of the solvents, the selection of solvent
is a key step during the extraction.
Studies have shown that slip agents have potential toxicity to
cause skin irritant and erucamide is apparently hydrolysed to erucic
acid, which can produce heart damage. The analysis of fatty acid
∗ Corresponding author at: Technical Center for Safety of Industrial Products,
Tianjin Entry-Exit Inspection and Quarantine Bureau, No. 6 Pukou Road, Hexi District,
Tianjin 300042, China. Tel.: +86 22 83326947; fax: +86 22 23395372.
E-mail address: ganglvchen@sohu.com (G. Lv).
amides in polymers is of great significance due to wide application
of polyethylene film in food and medical packaging. In recent
years, there have been some studies focusing on the analysis of
fatty acid amides, for example, Mir Ali Farajzadeh used HPLC and
GC methods to determine the lubricants and evaluate analysis of
real samples of polyethylene [2], Alvaro Garrido-Lopez compared
three gas chromatography methods in determining the slip agents
in polyethylene (PE) film [10]. These articles revealed some appropriate
ways to determine slip agents in the PE materials, but some
deficiency remains, for example, the low detection limit is relatively
high. In this paper, trifluoroethyl acetylation was carried out before
the slip agents were injected into the GC/MS. The results showed
that the method proposed can be used to monitor slip agents in
food and medical packaging materials.
2. Experimental
2.1. Apparatus and software
All chromatographic measurements were performed with an
Agilent system comprised of a 6890N Gas Chromatograph fitted
with an Agilent 7683 auto-sampler, a split–splittless injector
for capillary columns and a 5973N mass spectrometer (Agilent
Technology, USA). Auto-tune was carried out with perfluorotributylamine
to enhance the sensitivity of GC/MS, and a
complete spectrum mode (SCAN) was applied to ascertain the peak
of the target components; selected ion monitoring (SIM) modes
0021-9673/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.chroma.2009.10.008

8546 G. Lv et al. / J. Chromatogr. A 1216 (2009) 8545–8548
Table 1
Optimized analytical conditions for derivative fatty acid amides by GC/MS.
GC
MS
Instrument Agilent 6890 Instrument Agilent 5973
Column HP-5MS 30 m × 0.25 mm × 0.25 m Ionization EI
Oven temperature Set at 200 ◦ C for 5 min, then increase to 250 ◦ C at rate of 15 ◦ C/min, and keep for 5 min Energy 70 eV
Flow rate 1 mL/min SCAN 50–400 amu
SIM
57 amu, 97 amu, and 124 amu
Injection volume 1 L Solvent delay 4.0 min
Carry gas He (99.999%)
were applied to determine the amount of fatty acid amides in packaging
materials. The optimized analytical conditions are given in
Table 1.
Chemstation software (Rev.D.00.01, Agilent Technology, USA)
designed for a 5973N mass selective detector was used for data
acquisition, and Minitab software (Rev15, TechMax Information
Technology Co., Ltd.) was used to perform regression analysis.
2.2. Materials and reagents
Hexadecanoamide, octadecanamide, oleamide (cis-9-
octadecenoamide) and erucamide (cis-13-docosenoamide) were
purchased from Tokyo Kasei Kogyo Co., Ltd., Tokyo, Japan. Trifluoroacetic
anhydride is purchased from Sigma–Aldrich. Methanol,
isopropanol, chloroform and hexane were of HPLC grade and
purchased from Merck Inc., Darmstadt, Germany. The water used
in the experiments was ultra pure and the polyethylene packaging
materials are bought in local shop.
2.3. Sample treatment and extraction procedure
Polyethylene (PE) packaging material samples were cut approximately
to 1 cm 2 by scissors, then the samples were extracted with
isopropanol and chloroform complex solvents (1:1, v:v) by techniques
of liquid extraction Soxhlet extraction, ultrasonic-assisted
extraction and pressurized solvent extraction, respectively. The
parameters of the three different methods were listed in Table 2.
After the extractions, the extracts were blown to dry by nitrogen
gas.
It was shown that the nonvolatility presented by fatty acid
amides make them unsuitable for directly detection by GC/MS. In
order to improve volatility, sensitivity and performance of the chromatographic
response, a previous derivation step was investigated.
Trifluoroethyl acetylation is a suitable procedure for alcohols,
organic acids and other amines [11], and trifluoroacetic anhydride
is often used as a derivative reagent.
Fig. 1 shows the total ion current chromatogram of fatty acid
amides (Fig. 1a) and their derivatives (Fig. 1b). The identification of
the peaks was carried out by comparing retention times and also
by the search engine of GC/MS library (NIST), and the mass spectra
obtained in scan mode are shown in Fig. 2. Octadecanamide,
and oleamide coeluted before derivative procedure was carried
out, as shown in Fig. 1(a). The chromatographic performance of the
fatty acid amides improved significantly after derivation, of which
peak 1, peak 2, peak 3 and peak 4 represent derivative hexadecanoamide,
derivative octadecanamide, derivative oleamide and
derivative erucamide, respectively.
3.2. Extraction procedure
3.2.1. The selection of extraction solvents
The lack of solubility of fatty acid amides in most of the
solvents was the main drawback to overcome for extraction procedure
and analytical method developments. In order to select
the best extraction solvents, the efficiency of different reagents
2.4. Derivative method
To the vials containing the dried residues, a volume of 100 L
of trifluoroacetic anhydride was added and 1.0 mL of CHCl 3 was
added into the vials. Then the vials were closed and mixed thoroughly
for 1 min using a vortex system. The derivative reaction was
performed at 40 ◦ C in a water bath for 30 min. Then, the derivatives
were allowed to cool to room temperature and diluted to proper
concentrations with CHCl 3 , the solutions were subjected to GC/MS
analysis. The compounds were demonstrated to be stable within 2
days.
2.5. GC/MS analysis
The instrumental parameters are listed in Table 1, and the samples
were introduced into the GC/MS system by an auto-sampler.
3. Results and discussion
3.1. Derivation and GC/MS analysis of fatty acid amides
Fig. 1. Total ion current chromatogram of standard compounds and derivatives
(a) 1: hexadecanoamide, 2: octadecanamide, 3: oleamide, and 4: erucamide
(100.0 mg L −1 ); (b) 1: derivative hexadecanoamide, 2: derivative octadecanamide,
3: derivative oleamide, and 4: derivative erucamide (1.0 mg L −1 ).

G. Lv et al. / J. Chromatogr. A 1216 (2009) 8545–8548 8547
Table 2
The parameters of different extractions using isopropanol and chloroform complex solvents (1:1, v:v).
Extraction method Sample weight (g) Time (h) Temperature ( ◦ C) Pressure (bar)
Liquid extraction 1.0 5.0 50 0
Soxhlet extraction 1.0 5.0 60 0
Ultrasonic-assisted extraction 1.0 0.5 50 0
Pressurized solvent extraction a 1.0 0.5 90 100
a Cell volume, 33 mL; static mode, 2 cycles; flush volume, 100% and purge time, 120 s.
Fig. 2. Mass spectra obtained in scan mode for derivative fatty acid amides: (a) hexadecanoamide, (b) octadecanamide, (c) oleamide and (d) erucamide.
was studied using pressurized solvent extraction, as shown in
Fig. 3.
Slip agents were extracted from the polymer with different solvents.
After filtration and derivation, the extracts were injected
in duplicate into the GC/MS system, and the results showed that
the presence of 1:1 of isopropanol in chloroform led to the best
extraction efficiency.
3.2.2. Extraction efficiency
To compare the extraction efficiency, liquid extraction, Soxhlet
extraction, ultrasonic-assisted extraction and pressurized solvent
extraction (PSE) were used to determine the known amount of
fatty acid amides in PE packaging film (0.5% of hexadecanoamide,
Fig. 3. Extraction of slip agents in various solvents.
octadecanamide, oleamide and erucamide in PE, respectively), of
which the thickness was 20 m. The recoveries of the fatty acid
amides were assessed by adding known amounts of standards to
the packaging materials, of which the initial concentrations of the
analytes already present in the samples. The fatty acid amides were
added during the mixing and extrusion stage of the PE packaging
film, and after 2 days the fatty acid amides would migrate through
the polymer bulk to the surface.
The recoveries were calculated based on the detected amount
divided by the known amount and multiplied by 100 (to calculate
the percentage), as shown in Table 3. In general, the recovery should
range from 90% to 110% for a quantitative method. The recoveries
of fatty acid amides ranged from 102% to 147% for pressurized solvent
extraction. This is due to some of the fatty acid amides migrate
from the polytetrafluroethylene (PTFE) pipe line into the solvents,
and cause the test results a little high. In the mean time, the pressurized
solvent extraction (PSE) is time-saving and solvent-saving.
When the pipe line free of fatty acid amine was used, the recoveries
improved significantly, and ranged from 94% to 105%.
The slip agents have a designed incompatibility with the bulk
polymer so that they are not bonded into the bulk but are free to
migrate. Since the packaging film was only 20 m thin, the recoveries
ranged from 94% to 105% for the four fatty acid amides. The
recoveries decreased as the carbon chain extended, because the slip
agents can be tuned by increasing the molecule chain length by
adding or subtracting carbon atoms. Adding more atoms increases
the chain length and slows down the speed of migration [12]. For
example, erucamides are longer chain, more heat stable and more
oxidation than oleamides and with a lower vapor pressure create
fewer volatiles during high temperature processing. The oleamides
migrate through to the surface more quickly.

8548 G. Lv et al. / J. Chromatogr. A 1216 (2009) 8545–8548
Table 3
The recoveries of target compounds obtained by different extraction.
Extraction mode Hexadecanoamide (%) Octadecanamide (%) Oleamide (%) Erucamide (%)
Liquid extraction 72 ± 9 101 ± 3 91 ± 7 91 ± 6
Soxhlet extraction 87 ± 6 132 ± 11 111 ± 2 131 ± 8
Ultrasonic-assisted extraction 79 ± 5 105 ± 7 104 ± 4 91 ± 9
Pressurized solvent extraction 102 ± 2 147 ± 8 134 ± 9 114 ± 3
Pressurized solvent a extraction 105 ± 3 101 ± 4 96 ± 3 94 ± 3
a The PSE pipe line free of target components was used.
Table 4
Analytical parameters of the GC/MS method for derivative fatty acid amides.
Parameters Derivative hexadecanoamide Derivative octadecanamide Derivative oleamide Derivative erucamide
Linearity range (gg −1 ) 0.2–100.0 0.6–100.0 0.4–100.0 0.4–100.0
Correlation coefficient (r 2 ) 0.9968 0.9988 0.9991 0.9983
Detection limit a (ng g −1 ) 61.0 74.0 103.0 105.0
RSD (%, n = 5) 1.88 2.34 1.96 2.53
a The detection limits were calculated by using signal/noise = 3.
Table 5
The results of fatty acid amides in polyethylene packaging materials.
Samples Hexadecanoamide Octadecanamide Oleamide Erucamide
Cont. (gg −1 ) RSD (%, n = 3) Cont. (gg −1 ) RSD (%, n = 3) Cont. (gg −1 ) RSD (%, n = 3) Cont. (gg −1 ) RSD (%, n =3)
1 97.0 3.0 203 6.1 389 5.0 201 8.1
2 ND 7.1 ND 3.3 243 5.1 213 5.7
3 ND 8.3 109 3.9 414 11.3 208 8.7
4 116 5.9 327 11.0 969 3.9 222 3.0
5 108 10.2 219 4.2 416 8.8 337 6.9
3.2.3. Analytical performance
In order to study the relative standard deviation associated to
the extraction and the detection of fatty acid amides in PE film by
PSE and GC/MS, five aliquots of the same sample were extracted
under the PSE procedure and the GC/MS conditions mentioned
above. Quantitative parameters, such as the linear range, correlation
coefficient and detection limit were also investigated. The
results are given in Table 4. The extracted standard curves obtained
in the linear ranges showed excellent linearities with coefficients
of correlation that were in variably greater than 0.99. Besides, the
relative standard deviation of the chromatographic determination
was less than 3.0%, which demonstrate good method precision.
3.3. Determination of fatty acid amides in packaging materials
To check the suitability of the method for the analysis of slip
agents, the method was applied to determine these analytes in five
PE film samples. The concentrations and RSD (%, n = 3) obtained
for the target compounds were listed in Table 5. The obtained
result showed that the selected samples contained high amounts of
amides. Hexadecanoamide and octadecanamide were not detected
in sample 2 and hexadecanoamide was not detected in sample 3.
The RSD was less than 10% in all cases.
4. Conclusions
A PSE-GC/MS method to determine fatty acid amides in
polyethylene film has been established. The main advantage of
the proposed method is the ability to determine mixtures of the
four fatty acid amide, and the low detection limits are relatively
lower than the method reported [2,3]. The PSE method also reduces
extraction time and solvent compared with traditional extraction
methods, such as liquid extraction, Soxhlet extraction and ultrasonic
extraction. PSE method is based on the use of solvent heated
above its boiling point in pressurized system in order to accelerate
the extraction process and enhance the solubility of the target
components. The speed of migration is also affected by the bulk
polymer structure. The slip agents are solubilized into the polymer
when it is molten but as the polymer cools it is precipitated out of
the polymer that crystallizes and acts as a lubricant. So, recovery of
PSE method applied to thin packaging film may be better than that
of thick film.
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