Stir-Bar Sorptive Extraction
of Trace Organic Compounds
from Aqueous Matrices
Frank David,1 Bart Tienpont2 and Pat Sandra,1,2
1
Research Institute for Chromatography, Kortrijk, Belgium,
2
University of Ghent, Ghent, Belgium.
Stir-bar sorptive extraction is a new solventless sample preparation method for the extraction and
enrichment of organic compounds from aqueous matrices. The method is based on the same principles as
solid-phase microextraction (SPME). Compared with SPME, a relatively large amount of extracting phase
is coated on a stir bar. Solutes are extracted into the coating, based upon their octanol water
partitioning coefficient and upon the sample extraction medium phase ratio. The technique has been
applied successfully to trace analysis in environmental, biomedical and food applications. Users can
obtain extremely low detection limits.
To determine organic trace compounds in consumption in analytical laboratories has (220 �C 320 �C), and has interesting
aqueous matrices, an analytical method an important effect on analytical costs. In diffusion properties. Extraction with
normally requires an extraction and most instances, miniaturized sample polydimethylsiloxane can therefore be
enrichment step before analysts can perform preparation techniques can also be compared with a micro-liquid liquid
chromatographic separation and detection. automated and coupled on-line to the extraction. After extraction, the solutes can
During the extraction and enrichment step, analysis. On-line coupling of extraction and be introduced quantitatively into the
the trace solutes are isolated from the analysis, whereby the whole extract is analytical system by thermal desorption.
matrix, and the concentration of the solutes transferred to the analytical system, results This process provides high sensitivity because
is increased to enable their identification or in a higher sensitivity and lower potential the complete extract can be analysed.
quantification. In environmental, food analyte loss. Alternatively, analysts can use Baltussen and co-workers3 recently
safety, biomedical and other analyses, smaller sample volumes. reviewed the principles and applications of
analysts use a variety of extraction and In the past, analytical chemists paid a lot sorptive extraction. The main difference
enrichment techniques. These methods are of attention to solventless sample between SPME and stir-bar sorptive
based upon liquid liquid extraction, solid- preparation techniques based upon extraction is the much higher mass of
phase extraction (SPE), liquid gas extraction sorptive extraction. These techniques polydimethylsiloxane available in the latter,
methods such as purge-and-trap and include SPME1 and stir-bar sorptive which results in high recoveries and higher
liquid gas equilibrium techniques such as extraction.2 Sorptive extraction has proven sample capacity.
static headspace. to be an interesting and environmentally In this  Sample Prep Perspectives
Miniaturization has become a dominant friendly alternative to liquid extraction. In column, we will describe the principles of
trend in analytical chemistry. Typical examples sorptive extraction, the analytes are stir-bar sorptive extraction and present
of miniaturization in sample preparation extracted from the matrix (mostly aqueous) some typical applications in different
techniques are micro-liquid liquid into a non-miscible liquid phase. In contrast analytical areas.
extraction (or in-vial liquid liquid to extraction with adsorbents in which the
extraction), disc cartridge SPE, on-line SPE analytes are bound to active sites on a Stir-Bar Sorptive Extraction
and solid-phase microextraction (SPME). In surface, the total amount of extraction Principle
combination with state-of-the-art analytical phase is important in sorptive extraction, Different research groups in the mid
instrumentation, the overall method can not the surface only. The most widely used 1980s4 7 described the extraction of
result in faster analysis, higher sample sorptive extraction phase is organic compounds from an aqueous or
throughput, lower solvent consumption polydimethylsiloxane. This phase is well gas phase using open-tubular traps coated
and less manpower per sample while known as a stationary phase in gas with thick polydimethylsiloxane films.
maintaining or even improving sensitivity. chromatography (GC), is thermostable, can However, practical limitations  such as
In particular, the reduction of solvent be used in a broad temperature range low sample capacity and low breakthrough
2 LC" GC Europe July 2003
Sample Preparation Perspectives
volumes  limited the applicability of phase ratio and thus on the amount of it is also clear that the extraction efficiency
polydimethylsiloxane-coated open-tubular polydimethylsiloxane applied. This increases with increasing KPDMS/w. Because
traps. Some 10 years ago, Arthur and relationship is shown in Equation 1. KPDMS/w is similar to the octanol water
Pawliszyn1 developed a microextraction distribution coefficient (Ko/w), chemists can
CPDMS
KO/W H" KPDMS/w
method based upon polydimethylsiloxane predict extraction efficiencies. Besides the
Cw
sorption, namely SPME. By its simplicity KPDMS/w factor, the phase ratio (
and performance, SPME created a lot of volume sample/volume polydimethylsiloxane)
mPDMS Vw

interest in sorptive extraction techniques. also is important. The higher the
( )( )
mw VPDMS [1]
Advantages of sorptive extraction include polydimethylsiloxane amount, the lower
predictable enrichment, the absence of the and the higher the extraction
mPDMS

displacement effects, inertness and rapid efficiency.
( )
mw
thermal desorption at mild temperatures. Figure 1 shows the influence of Ko/w and
In SPME, however, the amount of extraction The distribution coefficient between phase ratio on extraction efficiency. For
medium (e.g., the amount of polydimethylsiloxane and water (KPDMS/w) is SPME, the volume of polydimethylsiloxane
polydimethylsiloxane coated on the fibre) is defined as the ratio between the is approximately 0.5 �L. This results in poor
very limited. For a typical 100 �m concentration of a solute in the recoveries for solutes with low Ko/w values;
polydimethylsiloxane fibre, which is the polydimethylsiloxane phase (CPDMS) over for example, values less than 10 000. In
most widely used fibre, the volume of the concentration in the water (Cw) at stir-bar sorptive extraction, 25 125 �L
extraction phase is approximately 0.5 �L. equilibrium. This ratio is equal to the ratio polydimethylsiloxane coatings are used.
Consequently, the extraction efficiency for of the mass of the solute in the Consequently, the sensitivity is increased by
solutes that are partially water soluble can polydimethylsiloxane phase (mPDMS) over the a factor of 50 to 250. The theoretical
be quite low.8 For very apolar compounds, mass of the solute in the aqueous phase (mw) extraction efficiency reaches 100% for
however, competition can occur between times the phase ratio ( , with Vw/VPDMS). solutes with Ko/w values larger than 500
the aqueous phase, the SPME fibre, the The recovery, expressed as the ratio of (log P greater than 2.7). The theoretical
glass wall of the extraction vessel, and the the extracted amount of solute (mPDMS) recoveries can be calculated for a given
surface of the polytetrafluoroethylene stir bar over the original amount of solute in the sample volume, selected stir-bar
used to stir samples.9,10 water (m0 mw mPDMS), is thus dimensions, and a solute using the
Based upon these observations, a new dependent upon the distribution coefficient KowWIN software program (Syracuse
extraction method was developed. Stir bars KPDMS/w and on , as described in Equation 2. Research Corp., Syracuse, New York, USA),
were coated with a layer of which is based upon a log Ko/w calculator.
KPDMS/w
polydimethylsiloxane and then used to stir
( )

aqueous samples, thereby extracting and Practical Considerations
mPDMS
[2]
enriching solutes into the polydimethylsiloxane Stir bars: Twister polydimethylsiloxane-
m0
KPDMS/w
coating. The technique was named stir-bar coated stir bars are available from Gerstel
1
( )

sorptive extraction.2 This extraction phase GmbH (M�llheim a/d Ruhr, Germany).
is the same as that used on These stir bars have three essential parts.
polydimethylsiloxane-coated fibres in Using this equation, analysts can The first and innermost part is a magnetic
SPME, but the coating uses 50 to 250 calculate the theoretical recovery for a stirring rod, which is necessary for
times greater amounts of extraction phase. solute with a known partition coefficient transferring the rotating movement of a
After extraction, the solutes are thermally and a given phase ratio. From Equation 2, stirring plate to the sample liquid. The
desorbed and analysed by GC in a similar
manner to SPME. Alternatively, analysts can
Figure 1: Recovery for solutes in function of the octanol water partitioning
use liquid desorption. The basic principles
coefficient Ko/w for SPME (10 mL sample, 100 �m polydimethylsiloxane fibre)
of SPME and stir-bar sorptive extraction
and for stir-bar sorptive extraction (10 mL sample, 10 mm 0.5 mm
thus are identical.
polydimethylsiloxane-coated stir bar)
Sorptive extraction by nature is an
equilibrium technique, and for water
100
samples the extraction of solutes from the
Stir-bar sorptive
aqueous phase into the extraction medium
extraction
80
Solid-phase
is controlled by the partitioning coefficient
microextraction
of the solutes between the silicone phase
60
and the aqueous phase. Recent studies
have correlated this partitioning coefficient
with the octanol water distribution 40
coefficients (Ko/w). Although not fully correct,
the octanol water distribution coefficient
20
gives a good indication if and how well a
given solute can be extracted with SPME or
10
stir-bar sorptive extraction.
100 101 102 103 104 105
However, it is very important in this
Ko/w
respect to realize that the sorptive
equilibrium is also dependent upon the
3 LC" GC Europe July 2003
Recovery (%)
Sample Preparation Perspectives
second part of the stir bar is a thin glass the thermal-desorption step. Rinsing does 150 �C are used along with liquid
jacket that covers the magnetic stirring rod. not cause solute loss, because the sorbed nitrogen cooling. Both systems allow fully
The third and outermost part is the layer of solutes are present in the automated control of all desorption,
polydimethylsiloxane sorbent into which polydimethylsiloxane phase. Finally, the trapping and injection conditions, including
the analytes are extracted. The glass layer is solutes are thermally desorbed. Desorption temperatures, flows and split or splitless
essential in the construction of a high- temperatures are application dependent, modes.
quality stir bar. It effectively prevents primarily determined by the volatility of the Table 1 provides an overview of stir-bar
decomposition of the polydimethylsiloxane solutes, and typically between 150 �C and sorptive extraction applications.2,11 36 We
layer, catalysed by the metal of the 300 �C. Desorption can be accomplished in will describe some typical applications
magnetic rod. 5 15 min under a 10 50 mL/min helium below.
Extraction procedure: Stir-bar sorptive flow. As an alternative to thermal
extraction of a liquid sample is performed desorption, analysts also can use liquid Applications of Stir-Bar Sorptive
by placing a suitable amount of sample in a desorption. Sampling also can be Extraction
headspace vial or other container. A performed in the headspace of a liquid or a Environmental analysis: Stir-bar sorptive
polydimethylsiloxane-coated stir bar is solid sample.11 extraction has been applied successfully in
added and the sample is stirred for Instrumentation: In contrast to SPME, in environmental analysis. The main
30 240 min. The extraction time is which desorption is performed in the inlet advantage of the technique is that it can
controlled kinetically; determined by of a gas chromatograph, stir-bar sorptive be applied to volatile organic compounds
sample volume, stirring speed and stir bar extraction is used in combination with a (VOCs) and semivolatile compounds. In
dimensions; and must be optimized for a thermal-desorption system. Because more combination with liquid desorption and
given application. Optimization is normally extraction phase is used, the desorption HPLC, the technique even can be used for
accomplished by measuring the analyte process is slower than that for a SPME non-volatile compounds. Depending upon
recovery as a function of the extraction fibre, and thus desorption combined with their octanol water partitioning, the
time. Optimum conditions are obtained cold trapping and reconcentration is compounds are extracted and enriched.
when no additional recovery is observed required. The whole process has been Successful applications include volatile
when the extraction time is increased automated. Two systems are available aromatic,2,11 halogenated solvent,2,11
further. commercially: the TDS-A classic thermal- polyaromatic hydrocarbon,12,13
After extraction, the stir bar is removed, desorption system and a specially designed polychlorinated biphenyl (PCB), pesticide,
dipped on a clean paper tissue to remove Twister desorption unit (both from Gerstel). odor compound,14,15 organotin
water droplets and introduced to an empty The systems can be mounted on gas compound16 and phenol17 analysis.
glass thermal-desorption tube. In some chromatographs equipped with a CIS-4 Because users can obtain a high
cases, we recommend rinsing the stir bar programmed-temperature vaporizing inlet enrichment factor, the sensitivity of stir-bar
slightly with distilled water to remove (Gerstel). The programmed-temperature sorptive extraction in combination with
adsorbed sugars, proteins or other sample vaporizing injector is operated as a cryotrap thermal desorption and GC mass
components. This step will avoid the for cryogenic refocusing of the thermally spectrometry (MS) is very high. Typically
formation of non-volatile material during desorbed analytes. Temperatures as low as detection limits of approximately 0.1 ppb
can be obtained for compounds with log
Ko/w larger than 2.5 and using the MS in
Figure 2: Extracted ion chromatogram at m/z 91 from the analysis of VOCs in
scanning mode. This capability makes the
drinking water spiked at 5 ng/L. Stir-bar sorptive extraction was performed on a 50
technique especially suitable for sample
mL sample using a 20 mm 0.5 mm Twister stir bar. The analysis was performed by
screening and multicompound analysis.
GC MS in selected-ion monitoring mode.
For target compound analysis, using
optimized extraction conditions and
6
GC MS in selected-ion monitoring mode,
2.5
researchers have reported sensitivities of
3
less than 1 part per trillion (ppt) (1 ng/L).14 16
2.0
Figure 2 shows a typical example. We
2 spiked a 50 mL drinking water sample at
4
1 8
1.5
10
the 5 ppt level with VOCs. The 60 min
extraction was performed using a 2 cm
5
1.0 0.5 mm film stir bar. After extraction, we
performed thermal desorption at 250 �C.
9
The GC MS analysis was performed in
0.5
7
selected-ion monitoring mode. The
different compounds can be detected
0.0
easily at this trace level.
0 10 15 20
Recently, researchers have paid attention
Time (min)
to the presence of odorous compounds in
drinking water. Compounds such as
Peaks: 1 toluene, 2 ethylbenzene, 3 m-xylene and p-xylene, 4 o-xylene,
2-methylisoborneol, geosmin and
5 2-chlorotoluene, 6 propylbenzene, 7 mesitylene, 8 tert-butylbenzene,
chlorinated and brominated anisoles have
9 sec-butylbenzene, 10 n-butylbenzene.
odour thresholds of less than 10 ng/L. Using
www.lcgceurope.com 4
6
Abundance ( 10
)
Sample Preparation Perspectives
stir-bar sorptive extraction these sample throughput with better sensitivity, 0.25 mm, 0.25 �m df HP-5MS column
compounds can be extracted with high reproducibility and accuracy.14,15 (Agilent Technologies, Inc., Wilmington,
recovery from drinking water samples. In Figure 3 shows the analysis of a water Delaware, USA). Detection was performed
comparison to labour-intensive techniques sample spiked with 2 ppt of 2-methyl- by MS in selected-ion monitoring mode.
such as isoborneol, geosmin and 2,4,6-trichloro- The compounds were detected at the 2-
closed-loop stripping, the stir-bar sorptive anisol. We analysed a 20 mL sample. The ppt level. For some solutes, extremely low
extraction method provides a much higher analysis was performed on a 30 m traces (picograms per litre or the parts-per-
quadrillion level) could be detected using
GC MS in negative-ion chemical ionization
Figure 3: Extracted ion chromatograms for 2-methylisoborneol (ion m/z 108), 2,4,6-
mode.15
trichloroanisole (ion m/z 197), and geosmin (ion m/z 112) from an analysis of odorous
Stir-bar sorptive extraction also can be
compounds spiked in drinking water at 2 ng/L. Stir-bar sorptive extraction was per-
combined with in situ derivatization. For
formed on a 20 mL sample using a 10 mm 0.5 mm Twister stir bar. The analysis was
phenols, Tienpont and co-workers17
performed by GC MS in selected-ion monitoring mode.
obtained excellent sensitivities by in situ
derivatization with acetic anhydride
5.6
(acylation). Derivatization and extraction
were performed simultaneously. The phenyl
4.8
acetates were extracted more efficiently
4.0 because the log Ko/w is higher than the
value for the corresponding phenols.
3.2
Biological fluids: Stir-bar sorptive
extraction also can be applied to the
2.4
1 determination of organic compounds in
3
2
biological fluids. Different classes of solutes
1.6
have been extracted from serum, plasma or
m/z 108
0.8 urine. These classes of solutes include
m/z 197
phenols, steroids, fatty acids, drugs of
m/z 112
0
abuse,18 barbiturates and
9 10 11 12 13 14 15
benzodiazepines,19 phthalates and
Time (min)
metabolites,21 and VOCs such as aldehydes
and sulphur compounds.22 Special
applications include the determination of
polynuclear aromatic hydrocarbon (PAH)
Figure 4: Extracted ion chromatograms at (a) ions m/z 72 and 276, (b) ion m/z 182,
metabolites, such as hydroxy PAHs, in
and (c) ions m/z 231 and 330 showing the presence of drugs in urine of a
urine23 and the determination of PCBs in
drug-addicted patient. Stir-bar sorptive extraction was performed on a 20 mL sample
sperm.24
using a 10 mm 0.5 mm Twister. The analysis was performed by GC MS in scanning
Urine samples can be extracted directly
mode.
or after enzymatic hydrolysis. In situ
derivatization also can be used. Blood
1
(a)
samples, including serum and plasma, bile
4.0
fluids and sperm, must be diluted with
3.0 water or a buffer solution before
extraction.
2.0 Figure 4 is a typical example that shows
the determination of drugs of abuse in the
2
1.0 urine of a drug-addicted patient. We
extracted a 5 mL urine sample directly
0 (without dilution) using a 10 mm
(b) 3 0.5 mm stir bar. Methadone (peak 1) and
0.5
its metabolite I (peak 2) can be detected in
the extracted-ion chromatogram [Figure
0.0
4(a)]. We also detected traces of
4
(c)
metabolites of d-9-tetrahydrocannabinol
0.5
(probably from cannabis use) (Figure 4b).
5
6
Cocaine also was detected in Figure 4b.
0.0
Although the log Ko/w of cocaine was
8 12 16 20 24 26 28
rather low
(log Ko/w 2.17), the compound could still
Time (min)
be detected by stir-bar sorptive
Peaks: 1 methadone, 2 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine
extraction thermal desorption GC MS at
(methadone metabolite), 3 cocaine, 4 cannabidiol, 5 cannabichromene,
trace levels.
6 cannabielsoin.
In combination with derivatization, polar
5 LC" GC Europe July 2003
3
Abundance ( 10
)
6
Abundance ( 10
)
Sample Preparation Perspectives
solutes also can be analysed, as demonstrated co-workers32 were able to determine Agilent 5973 mass-selective detector
for the analysis of p-aminohippuric acid, a trichloroanisole, the compound responsible operated in scanning mode. The analytical
uremic toxin related to renal dysfunction. for the musty odour and taste in wine, at conditions are identical to the conditions
The native compound is very polar (free very low nanograms-per-litre levels in wine used for the retention-time-locked analysis
amino and acid function, log Ko/w 0.3), samples. of pesticides.37 Samples analysed under
but after derivatization with ethyl Several applications have shown the these conditions can thus be screened for
chloroformate into the N-ethoxycarbonyl determination of pesticides in food the pesticides present in the Agilent RTL
ethyl ester (log Ko/w 3), Tienpont and matrices.33 35 Recently, we presented a pesticide screener library. Based on the
colleagues18 obtained an efficient multiresidue screening method for non- log Ko/w values of the 567 compounds
extraction. fatty foods; that is, fruits and vegetables.36 present in the library, we have calculated
Food analysis: Another successful The method is based on stir-bar sorptive that 374 pesticides can be extracted
application area of stir-bar sorptive extraction of a diluted methanol extract efficiently and screened using this method.
extraction is the determination of minor followed by thermal desorption and The sensitivity of the method allows the
food ingredients and food contaminants. GC MS analysis. Typically, we extracted a detection of pesticides in the low parts-per-
Stir-bar sorptive extraction has been used 15 g sample with 30 mL of methanol. From billion range. For most compounds and
for the determination of flavour and off- the extract, we diluted 1 mL with 10 mL of matrices, the limits of detection are less
flavour compounds in different food water and then extracted that solution than 10 ppb.
matrices, including non-alcoholic and with a stir bar for 60 min. After extraction, Figure 5 is an example of this pesticide
alcoholic beverages and dairy we washed the stir bar with a few millilitres screening. We detected tolylfluanid,
products.25 30 Food preservatives have also of water to remove adsorbed sugars or endosulphan sulphate and bromopropylate
been analysed.31 In general, analysts non-volatile material, dried it on a clean in the extract of a pear sample. The
encounter no problems with different food tissue, and inserted it into a thermal- measured concentrations were 59 ppb,
matrices if the fat content is less than desorption tube. Thermal desorption is 3 ppb and 190 ppb, respectively. This
2 3%. In other instances, dilution is performed at 280 �C for 5 min. The application also demonstrates that stir-bar
necessary. For samples that contain high compounds are trapped in the sorptive extraction can be used for the
levels of alcohol, dilution to a maximum programmed-temperature vaporizing inlet analysis of solid samples after a preliminary
ethanol concentration of 10% is necessary. at 250 �C and then injected by extraction with a water-miscible solvent.
Finally, stir-bar sorptive extraction has programming to 280 �C at 600 �C/min.
also been used for the determination of The analysis is performed on an Quantification in Stir-Bar Sorptive
contaminants in food. Hoffmann and Agilent 6890 gas chromatograph and an Extraction
Quantification in stir-bar sorptive extraction
can be performed in different ways, and
Figure 5: Extracted ion chromatograms showing the presence of pesticides in a pear
the selection of the method is mainly
sample. Stir-bar sorptive extraction was done using a 10 mm 0.5 mm Twister stir
dictated by the complexity of the sample.
bar on a 1 mL sample (methanol macerate) that was diluted in 10 mL of water. The
For example, both external standardization
analysis was performed by GC MS in scanning mode.
and internal standard addition can be used
for tap water because matrix effects that
Br
O
contribute to the equilibrium are absent.
O
For samples in which matrix effects
OH
contribute to the equilibrium  biological
fluids, wastewater, beverages, fruits and
Br
3 vegetables  different methods can be
O
O
1.2
used, including single-level calibration with
S
N
N a standard at a concentration close to that
Cl
S
1.0 of the estimated concentration and
Cl
F
1
prepared in a blank matrix to compensate
for matrix effects, internal standard
0.8
addition of deuterated or 13C-labeled
target solutes and standard addition at
0.6
three to six concentration levels. The first
method requires a blank sample to
Cl
0.4
Cl S compensate for matrix effects, but, as
Cl
O
Cl
strange as this may seem, these samples
Cl S
are often difficult to obtain. For the second
0.2
Cl
approach, labeled standards are
2
commercially available for only a few
0.0
solutes such as deuterated PAHs and
5.00 9.00 13.00 17.00 21.00 25.00 29.00 33.00
13
C PCBs. The last method is by far the
Time (min) easiest to use in a routine environment,
and it has been applied in the determination
of dicarboximide fungicides in wines35 and
Peaks: 1 tolylfluanid, 2 endosulphan sulphate, 3 bromopropylate.
in the quantification of pesticides in
www.lcgceurope.com 6
6
Abundance ( 10
)
Sample Preparation Perspectives
Chromatography (IOPMS, Kortrijk, Belgium,
vegetables, fruits and baby food.36 Frank David is R&D manager at the
CD-ROM, 2002).
23.) K. Desmet et al.,  Analysis of Polycyclic Research Institute for Chromatography,
Aromatic Hydrocarbon Metabolites in Urine
Conclusion President Kennedypark 20, B-8500,
Using in-situ Derivatisation Stir Bar Sorptive
Stir-bar sorptive extraction is a solventless Kortrijk, Belgium, e-mail
Extraction CGC/MS, paper D13, Proceedings
extraction and concentration technique [e-mail].
of the 25th International Symposium on
Capillary Chromatography (IOPMS, Kortrijk,
that can be used successfully to determine Bart Tienpont is a Ph.D. student at the
Belgium, CD-ROM, 2002).
low traces of organic compounds in Laboratory of Organic Chemistry, University
24.) T. Benijts et al., J. Chromatogr. B 755, 137
aqueous matrices, including water samples, of Ghent, Krijgslaan 281 S4, B-9000
(2001).
biological fluids and food samples. We 25. A.G.J. Tredoux et al., J. High Resolut. Ghent, Belgium.
Chromatogr. 23, 644 (2000).
have obtained sensitivities of less than Pat Sandra is director of the Research
26. J.C.R. Demyttenaere et al.,  Flavour Analysis
1 ng/L, depending upon the solutes Institute for Chromatography and a
of Greek White Wine Using Solid Phase Micro-
(log Ko/w), sample volume, stir bar professor at the University of Ghent.
extraction Capillary GC/MS, paper P35,
Proceedings of the 25th International
dimensions and GC MS sensitivity.
Symposium on Capillary Chromatography
(IOPMS, Kortrijk, Belgium, CD-ROM, 2002).
References  Column Watch editor Ronald E. Majors
27. A. Hoffmann and A.C. Heiden,
 Determination of Flavor and Off Flavor
1. C.L. Arthur and J. Pawliszyn, Anal. Chem. 62, is the business development manager,
Compounds in Dairy Products using Stir Bar
2145 (1990).
consumables and accessories business unit,
Sorptive Extraction and Thermal Desorption
2. E. Baltussen et al., J. Microcol. Sep. 11, 737
Agilent Technologies, Wilmington,
GC/MSD/PFPD, paper D34, Proceedings of
(1999).
the 23rd International Symposium on Capillary Delaware, USA and is a member of LC" GC
3. E. Baltussen, C.A. Cramers and P. Sandra,
Chromatography (IOPMS, Kortrijk, Belgium,
Anal. Bioanal. Chem. 373, 3 (2002).
Europe Editorial Advisory Board.
CD-ROM, 2000).
4. K. Grob and G. Grob, J. High Resolut.
Direct correspondance about this column
28. A. Hoffmann, A.C. Heiden and E. Pfannkoch,
Chromatogr. 6, 133 (1983).
to LC" GC Europe, Advanstar House,
 Flavor Profiling of Beverages by Stir Bar
5. C. Bicchi et al., Flavour Fragrance J. 2, 49
Sorptive Extraction and Thermal Desorption
(1987).
Sealand Road, Chester CH1 4RN, UK,
6. J. Roeraade and S. Blomberg, J. High Resolut. GC/MS/PFPD, Part II: Non-Alcoholic
e-mail [e-mail]
Chromatogr. 11, 457 (1988). Beverages, paper M33, Proceedings of the
7. B.V. Burger and Z. Munro, J. Chromatogr. 370, 23rd International Symposium on Capillary
449 (1986). Chromatography (IOPMS, Kortrijk, Belgium,
8. C.L. Arthur et al., J. High Resolut. Chromatogr. CD-ROM, 2000).
15, 741 (1992). 29. C. Bicchi et al.,  Headspace Sorptive
9. Y. Yang et al., Anal. Chem. 70, 1866 (1998). Extraction in the Headspace Analysis of
10. E. Baltussen et al., Anal. Chem. 71, 5213 Aromatic and Medicinal Plants, paper D45,
(1999). Proceedings of the 23rd International
11. B. Tienpont et al., J. Microcol. Sep. 12, 577 Symposium on Capillary Chromatography
(2000). (IOPMS, Kortrijk, Belgium, CD-ROM, 2000).
12. B. Kolahgar, A. Hoffmann and A.C. Heiden, 30. P. Sandra, F. David and J. Vercammen, in
 Evaluation of the Method of Stir Bar Sorptive Advances in Flavours and Fragrances, K.A.D.
Extraction for the Determination of Polycyclic Swift, Ed. (Royal Society of Chemistry,
Aromatic Hydrocarbons (PAH) in Water Cambridge, United Kingdom, 2002), p. 27.
Samples, paper M16, Proceedings of the 31. N. Ochiai et al., Anal. Bioanal. Chem. 373, 56
25th International Symposium on Capillary (2002).
Chromatography (IOPMS, Kortrijk, Belgium, 32. A. Hoffmann et al.,  Corkiness in Wine 
CD-ROM, 2002). Trace Analysis of 2,4,6-Trichloroanisole by Stir
13. P. Popp, C. Bauer and L. Weinrich, Anal. Chim. Bar Sorptive Extraction and Thermal
Acta 436, 1 (2001). Desorption GC/MS, paper D35, Proceedings
14. N. Ochiai et al., Analyst 126, 1652 (2001). of the 23rd International Symposium on
15. D. Benanou et al., Anal. Bioanal. Chem., in Capillary Chromatography (IOPMS, Kortrijk,
press (2003). Belgium, CD-ROM, 2000).
16. J. Vercauteren et al., Anal. Chem. 73, 1509 33. F. David et al.,  Determination of
(2001). Contaminants in Wine Using Stir Bar Sorptive
17. B. Tienpont, C. P�rŁz, F. David and P. Sandra, Extraction, paper M35, Proceedings of the
unpublished results. 23rd International Symposium on Capillary
18. B. Tienpont, F. David and P. Sandra, Anal. Chromatography (IOPMS, Kortrijk, Belgium,
Bioanal. Chem. 373, 46 (2002). CD-ROM, 2000).
19. H.G. Wahl et al.,  Analysis of Drugs in Human 34. C. Bicchi et al.,  Stir Bar Sorptive Extraction in
Body Fluids by Stir Bar Sorptive Extraction and Sample Preparation from Heterogeneous
Thermal Desorption GC/MS, paper L15, Matrices: Determination of Pesticide Residues
Proceedings of the 23rd International in Pear Pulp at ppb Level, paper D19,
Symposium on Capillary Chromatography Proceedings of the 25th International
(IOPMS, Kortrijk, Belgium, CD-ROM, 2000). Symposium on Capillary Chromatography
20. B. Tienpont et al., J. Pharm. Biomed. Anal., in (IOPMS, Kortrijk, Belgium, CD-ROM, 2002).
press (2003). 35. P. Sandra et al., J. Chromatogr. A 928, 117
21. H.G. Wahl et al.,  Analysis of Plasticizers and (2001).
Their Metabolites in Body Fluids and Infusates 36. P. Sandra, B. Tienpont, and F. David, J.
by Stir Bar Sorptive Extraction and Thermal Chromatograph. A, in press (2003).
Desorption GC/MS, paper D28, Proceedings 37. C. Kai Meng,  Agilent Application Note 5988-
of the 23rd International Symposium on 4392 EN, Agilent Technologies, Inc.
Capillary Chromatography (IOPMS, Kortrijk, (Wilmington, Delaware, USA 2001).
Belgium, CD-ROM, 2000).
22.) H.A. Soini et al.,  Quantification of Volatiles in
Mammalian Urine by Stir Bar Sorptive
Extraction Techniques and Gas
Chromatography, paper Q37, Proceedings of
the 25th International Symposium on Capillary
7 LC" GC Europe July 2003