J. Sep. Sci. 2002, 25, 539 542 Kusch, Knupp 539
Peter Kusch,
Analysis of residual styrene monomer and other
Gerd Knupp
volatile organic compounds in expanded
Fachhochschule Bonn-Rhein- polystyrene by headspace solid-phase
Sieg, University of Applied
microextraction followed by gas chromatography
Sciences, Fachbereich
Biologie, Chemie und
and gas chromatography/mass spectrometry
Werkstofftechnik, von-Liebig-
Str. 20, D-53359 Rheinbach,
A method for determination of residual styrene monomer and other volatile organic
Germany
compounds in expanded polystyrene (EPS) was developed using HS SPME and gas
chromatography with FID. The extraction products were identified by GC/MS. Good
reproducibility of the measurements with RSD values between 3.2  3.6% was achiev-
ed by extraction using a 75 lm Carboxen-polydimethylsiloxane fiber at 608C with
15 min sample sonication. The contents of residual styrene monomer in two samples
of EPS were 153.2 and 65.7 mg/kg, respectively. Other compounds identified in EPS
were pentane, benzene, toluene, ethylbenzene, isomers of xylene, n-propylbenzene,
1,2,4-trimethylbenzene, o-methylstyrene, benzaldehyde, benzyl alcohol, and aceto-
phenone.
Key Words: Styrene; Expanded polystyrene (EPS); Headspace SPME; Carboxen-
poly(dimethylsiloxane); GC/MS;
Received: October 4, 2001; revised: February 6, 2002; accepted: February 20, 2002
Several headspace-GC or -GC/MS methods have been
1 Introduction
used to determine the level of styrene residues emitted
EPS is an expanded polystyrene, produced by polymeriz- from polystyrene [3, 16]. However, no previous work on
the analysis of residual styrene monomer and other vola-
ing styrene monomer and adding pentane as a blowing
tile organic compounds in EPS by SPME-GC or SPME-
agent. It is used for food packaging and for protection of
GC/MS has been reported in the literature.
products against damage during transport and storage.
EPS is also used in the building industry for insulation of
exterior walls and foundations.
In this work, headspace SPME followed by GC and GC/
It has been known for a long time that EPS emits residual
MS has been applied to the analysis of residual styrene
styrene monomer and other volatile organic compounds
and other volatile organic compounds in EPS. The poly(di-
(VOCs) at ambient temperature. Styrene is harmful when
methylsiloxane) (PDMS) SPME coating is one of the most
inhaled, is irritating to eyes, nose, throat, skin, and acts as
widely used coatings for extracting volatile analytes from
a depressant on the central nervous system, causing neu- environmental samples via absorption [17]. In contrast,
rological impairment [1].
the sensitivity of adsorptive solid SPME coatings, such as
PDMS/divinylbenzene (PDMS/DVB) and Carboxen/
VOCs have to be determined in mixtures in many areas of
PDMS (CAR/PDMS), was reported to be much higher
analytical endeavor, such as environmental, food, foren-
compared to PDMS for extracting VOCs [18 19]. We
sic, fragrance, oil, pharmaceutical, and polymer/copoly-
have selected the CAR/PDMS fiber for our investigations.
mer analysis [2]. The method of choice for many of these
The fiber works very well in the headspace extraction
polymer/copolymer analyses is static headspace sam-
mode. Carboxen has a similar surface to DVB. The major
pling [3 4], dynamic headspace sampling [5 8], pyroly-
difference is the much higher content of micropores of the
sis [9, 10], and more recently solid-phase microextraction
Carboxen/PDMS fiber, making it the overwhelming choice
(SPME) [11 15] followed by GC and GC/MS determina-
as material for the extraction of volatile and low molecular
tion.
analytes at trace levels. Carboxens differ from other por-
ous carbons because the pores are not sealed but pass
Correspondence: Dr. Peter Kusch, Fachhochschule Bonn-
entirely through the particle and allow analytes to desorb
Rhein-Sieg, von-Liebig-Str. 20, D-53359 Rheinbach, Ger-
more efficiently than in the case of the sealed pores com-
many.
E-mail: [e-mail] monly found in charcoals and many carbon molecular
Fax: [phone]
sieves.
i WILEY-VCH Verlag GmbH, 69469 Weinheim 2002 1615-9306/2002/0806 0539$17.50+.50/0
Short Communication
540 Kusch, Knupp J. Sep. Sci. 2002, 25, 539 542
a carrier gas. The helium inlet pressure was 140 kPa and
2 Experimental
the split flow was 50 mL/min. A SPME glass liner for split/
2.1 Materials splitless injector was used (Supelco).
The oven temperature was programmed from 808C (1 min
The fused silica capillary columns tested in this investiga-
hold) at 58/min to 1008C and then 88/min to 2208C (10 min
tions were obtained as follows: 30 m60.32 mm ID, film
hold) or from 608C (1 min hold) at 28C to 1008C and then
thickness 4.0 lm, SPB-1 Sulfur from Supelco (Bellefonte,
88/min to 2008C (10 min hold). Chromatographic data were
PA, USA); 60 m60.25 mm ID, film thickness 0.25 lm,
processed with TurboChrom 4.0 software (Perkin-Elmer).
Optima d-3 from Macherey-Nagel (Düren, Germany);
60 m 6 0.25 mm ID, film thickness 0.25 lm, DB-5ms
GC/MS measurements were made using an Thermo-
from J&W Scientific (Folsom, CA, USA); 60 m60.25 mm
Quest Trace 200 gas chromatograph (ThermoQuest CE
ID, film thickness 0.25 lm, BPX-50 from SGE (Mel-
Instruments, Milan, Italy) interfaced to a ThermoQuest/
bourne, Australia); 60 m60.32 mm ID, film thickness
Finnigan Voyager quadrupole mass spectrometer (Ther-
0.50 lm, Rtx-225 from Restek (Bellefonte, PA, USA);
moQuest/Finnigan MassLab Group, Manchester, UK)
50 m60.32 mm ID, film thickness 1.0 lm, Permaphase
with an ThermoQuest Xcalibur data system, the NIST 98
CPMS/225 from Perkin-Elmer (Norwalk, CT, USA);
spectra library, and a CombiPAL autosampler (CTC Ana-
30 m60.25 mm ID, film thickness 0.25 lm, SolGel WAX
lytics AG, Zwingen, Switzerland).
from SGE and 60 m60.32 mm ID, film thickness
The oven was programmed from 608C (1 min hold) at 58/
0.20 lm, Rtx-2330 from Restek.
min to 1008C and then 108/min to 2208C (10 min hold).
The SPME fiber holder for manual use and the 75 lm Car-
Helium 6.0 grade (Westfalen) was used as a carrier gas.
boxen-Polydimethylsiloxane (CAR/PDMS) fibers were
A constant pressure of 70 kPa helium was used during the
obtained from Supelco (Bellefonte, PA, USA). The fiber
whole analysis. The temperature of the split/splitless
was conditioned at 2808C for 30 min prior to use.
injector was 2508C and the split flow was 10 mL/min. The
transfer line temperature was 2708C. The ion source tem-
20-mL headspace glass vials with an aluminum-coated
perature was kept at 2008C. Ionization was induced by
silicone rubber septum and pressure released aluminum
impacting electrons with a kinetic energy of 70 eV. The
seal, obtained from LABC Labortechnik (Hennef, Ger-
detector voltage was 350 V. Mass spectra and recon-
many), were used.
structed chromatograms (total ion current, TIC) were
A Sonorex Super RK 31H compact ultrasonic bath from
obtained by automatic scanning in the mass range m/z
Bandelin electronic (Berlin, Germany) was employed for
46 204. Compound identification was carried out by com-
sample agitation.
parison of retention times and mass spectra of standards,
study of the mass spectra, and comparison with data in
the NIST 98 spectra library.
2.2 Chemicals
The chemicals used were BTEX standard solution N8 722
372 obtained from Macherey-Nagel (Düren, Germany),
2.5 Procedure
styrene (stabilized) for synthesis obtained from Merck-
A standard solution of MEK (internal standard) was pre-
Schuchardt (Hohenbrunn, Germany), ethyl methyl ketone
pared by making up 100 mg of the substance with DMF to
(MEK, internal standard), and N,N-dimethylformamide
(DMF), both of analytical grade, supplied by Merck (Darm- 100 mL. A 30 lL aliquot of this solution (containing 30 lg
of the internal standard) was added from a 100 lL syringe
stadt, Germany).
to 50 mg of the crumbled EPS sample sealed in a 20 mL
headspace glass vial with aluminum-coated silicone rub-
2.3 Samples
ber septum. The septum of the vial was pierced with the
needle of the SPME device and the fiber was exposed
Samples of commercially available expanded polystyrene
approximately 10 mm above the sample. Afterwards the
(Styropor) from Germany (sample A) and from Australia
glass vial with the SPME injector was placed in an ultraso-
(sample B) were used in our investigations.
nic bath and agitated by sonication for 1 to 30 min at ambi-
ent temperature, at 408C and at 608C. Furthermore, EPS
2.4 Instrumentation
samples were heated in the heating block of the Combi-
PAL autosampler equilibrated at 808C without agitation.
GC analyses were performed on a Perkin-Elmer (Nor-
walk, CT, USA) AutoSystem gas chromatograph After a sorption time of 1 to 30 min in the headspace
equipped with split/splitless injector at 2508C and a flame- above the sample, the fiber was retracted into the protec-
ionization detector (FID) operated at 2708C. Helium 5.0 tive sheath and removed from the vial. It was transferred
grade (Westfalen AG, Muenster, Germany) was used as without delay into the injection port of the gas chromato-
J. Sep. Sci. 2002, 25, 539 542 Analysis of styrene and other VOCs in EPS 541
graph or the GC/MS. The fiber was thermally desorbed in
the injector at 2508C for 3 min and the run was started.
The samples for GC/MS identification were analyzed with-
out using an internal standard solution.
For the determination of the HS SPME response factor
50 lL (0.0530 g) of styrene and 50 lL (0.0394 g) of MEK
were placed a 10 mL flask and the flask was filled up with
DMF. 1 mL of the solution obtained was then diluted 1:10
with DMF. 2 mL of the diluted solution was transferred to
the headspace vial for adsorption onto the CAR/PDMS
fiber and than analyzed by GC after thermal desorption of
the fiber in the injector. The HS SPME conditions and the
analytical conditions were the same as in the determina-
tion of EPS samples.
3 Results and discussion
The studies were conducted to establish the optimum
conditions for extraction, desorption, chromatographic
separation, and identification of the VOCs from the
expanded polystyrene using headspace SPME followed
by GC and GC/MS. Extraction temperature and time,
sample agitation technique, and desorption temperature
and time are very important parameters in the optimiza-
tion of the SPME. In general, the highest possible tem-
perature should be used. In headspace SPME, an
increase in extraction temperature leads to an increase of
Figure 1. SPME/GC/FID chromatograms of a headspace of
analyte concentration in the headspace, and helps to facil-
EPS at ambient temperature, agitated for 15 min by sonica-
itate faster extraction [17]. However, at high temperature,
tion. Top chromatogram: sample A, bottom chromatogram:
coating headspace partition decreases and the fiber coat-
sample B. Fused silica capillary column: Rtx-225,
ing begins to lose its ability to adsorb analytes. Thus the 60 m60.32 mm ID, film thickness 0.5 lm. Column tempera-
ture: programmed from 808C (1 min hold) at 58/min to 1008C
temperature effect between 25 808C was studied.
and then 88/min to 2208C (10 min hold). Split/splitless injec-
The most efficient agitation method evaluated to date for
tor: 2508C, split flow 50 mL/min, FID: 2708C. Peak identifica-
tion: 1 = pentane (3.95 min); 2 = non-aromatics (5.88
SPME applications is direct sample sonication, which can
6.32 min); 3 = benzene (6.63 min); 4 = toluene (7.05 min);
provide very short extraction times [17]. In this work we
5 = ethylbenzene (7.60 min); 6 = m/p-xylene (7.81 min);
have used sonication as sample agitation method.
7 = o-xylene (8.48 min); 8 = styrene (9.10 min); 9 = n-propyl-
benzene (9.29 min); 10 = 1,2,4-trimethylbenzene (9.51 min);
The choice of the desorption temperature of the GC injec-
11 = o-methylstyrene (12.19 min); 12 = benzaldehyde
tor is also a critical point. The results obtained show that
(13.66 min); 13 = acetophenone (16.15 min); 14 = benzyl
after 3 min at 2508C a complete desorption of all com-
alcohol (16.80 min).
pounds was achieved.
For the chromatographic separation of residual VOCs In order to optimize the extraction temperature, the con-
from samples of the expanded polystyrene, several fused tent of styrene monomer in EPS was determined at four
silica capillary columns with stationary phases of different different temperatures. The internal standard method was
polarity were examined. The best results were achieved used for the quantitative determination according to
using the Rtx-225 (60 m, 0.32 mm, 0.5 lm) or Perma- Eq. (1):
phase-CPMS/225 (50 m, 0.32 mm, 1.0 lm) columns with
ci = A N fi N Wst N 106/Ast N Wp (1)
i
the (50%-cyanopropenyl)-dimethylpolysiloxane station-
ary phase. Figure 1 shows the GC/FID chromatograms of where A refers to the peak area of styrene, and A refers
i st
both the investigated EPS samples handled by SPME to the peak area of the internal standard (MEK), Wst is the
with the 75 lm CAR/PDMS fiber in the headspace mode mass of MEK, Wp is the mass of the sample (EPS), and fi
at ambient temperature and agitated by sonication for is the HS SPME response correction factor of styrene
15 min. The peaks were identified by GC/MS and by using (see Section 2.5). The HS SPME response correction fac-
the mixture of BTEX standards. tor of styrene was calculated according to Eq. (2):
542 Kusch, Knupp J. Sep. Sci. 2002, 25, 539 542
608C with sonication were studied. Figure 2 shows the
Table 1. Results of the GC/FID determination of residual
styrene in expanded polystyrene (EPS) after headspace
effect of the extraction time at 608C on the peak area of
SPME for 15 min at different temperatures. Samples at tem-
styrene determined in EPS, sample A. The extraction time
peratures 25, 40, and 608C were agitated by sonication.
of 15 min was chosen for subsequent analyses.
Styrene, mg/kg
EPS (A) EPS (B)
i 258C 408C 608C 808C 258C 608C
4 Conclusions
1 125 137 154 210 43 69
The proposed HS-SPME-GC procedure is appropriate for
2 111 128 157 194 41 66
determination of residual styrene monomer and other
3 127 143 161 192 34 67
4 141 112 145 221 38 66
VOCs in expanded polystyrene. The rapid, simple, and
5 131 134 147 199 47 63
cost-effective method with good repeatability can be
6 139 117 155 198 48 63
applied to the process control of EPS production and to
n 6 6 6 6 6 6
Mean 129.0 128.5 153.2 203.3 41.8 65.75
measure and screen styrene and VOCs in the environ-
RSD,% 7.7 8.5 3.6 5.0 11.7 3.2
ment.
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i
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time, different extraction times between 1 and 30 min at [JSS 1116]