Journal of Environmental Protection, 2011, 2, 198-203
doi:10.4236/jep.2011.22023 Published Online April 2011 (
Copyright © 2011 SciRes. JEP
Hollow-Fiber Microporous Membrane
Liquid-Liquid Extraction for Determination
of Polybrominated Diphenyl Ethers at
Trace Levels in Sewage Sludge with Gas
Chromatography-Electron Capture Detection
Azadeh Sharifi Aghili, Jan Åke Jönsson
Center for Analysis and Synthesis, Department of Chemistry, Lund University, Lund, Sweden.
Received January 20th, 2010; revised February 3rd, 2011; accepted March 16th, 2011.
A two-phase hollow-fiber (HF) liquid-phase microextraction (LPME) method followed by gas chromatography was
developed for quantification of 8 major polybrominated diphenyl ethers at trace level in sewage sludge. In this method
the porous polypro pylene hollow fib ers filled with a few microliters of organic so lvent, were immersed in aqueous sam-
ples of wet sludge which were spiked with the PBDEs at ng/l level. Parameters such as salt concentration, stirring
speed, extraction time and pH were optimized and the optimum extraction conditio ns were then applied to the determi-
nation of PBDEs in sewage sludge from Källby sewage treatment plant in Lund. The optimized method allowed detec-
tion of 5.1 µg kg–1 and 0.43 µg kg–1 of BDE-47 and 183, respectively, in dried sludge. The findings were compatible
with the results from recent research on PBDEs level in sewage sludge samples from Sweden. Although BDE-209 was
expected to have the highest level, it was not detected. Limit of detection, photodegradation or/and biodegradation of
BDE-209 during treatment or experiment are major reasons. Low organic solvent consumption, low sample volume
requirement, high preconcentration factor, simplicity without using expensive instrument for extraction and excellent
sample clean-up are some important factors that make this sample preparation technique very useful for determination
of PBDEs in sludge.
Keywords: PBDE, Gas Chromatography, Sewage Sludge, Membrane Extraction, LPME
1. Introduction
Of all the pollutants released into the environment every
year, persistent organic pollutants (POPs) are among the
most dangerous chemical pollutants. These are used as
pesticides, used by industry, or generated unintentionally
as by-products of industrial processes. They accumulate
through the food chain in environmental and biota sam-
ples [1-9] and pose a risk of causing adverse effect to
human health and environment. Polybrominated diphenyl
ethers (PBDEs) are a group of persistent organic pollut-
ants, which are used as flame retardants in plastics in
consumer products such as computers, television sets and
polyurethane foam. Animal studies have shown that
PBDEs cause very serious health effects such as estro-
genic [10] and, neurobehavioral [8,11] effects, thyroid
dysfunctions [12] and cancer [13,14]. Exponential in-
crease of PBDEs in human [4] and biota samples as well
as their adverse health effects on animals have raised
concerns over potential health effects of PBDEs in hu-
mans and many studies have been conducted to deter-
mine these persistent pollutants in environmental sam-
ples such as sewage sludge and treatment plant effluents,
which are major sources of contamination by PBDEs.
Conventional methods for extraction of PBDEs from
sewage sludge such as Soxhlet extraction or accelerated
solvent extraction (ASE) need a clean-up step prior to
analysis by chromatographic methods and consume a lot
of time and extraction solvent, which leads to a signifi-
cant expense. Hollow fiber microporous membrane liq-
uid-liquid extraction (HF-MMLLE) [15] also known as
Hollow-Fiber Microporous Membrane Liquid-Liquid Extraction for Determination of
Polybrominated Diphenyl Ethers at Trace Levels in Sewage Sludge with Gas Chromatography-Electron Capture Detection
liquid phase micro-extraction (LPME) is an alternative
technique that can be used for extraction of contamina-
tion from different types of matrices.
Depending on the analyte hydrophobicity, a two or
three phase extraction system is applied. In two-phase
LPME that is also called microporous membrane liq-
uid-liquid extraction (MMLLE), the organic solvent
filled in the lumen and the pores of the hollow fiber acts
as acceptor phase and is used to extract hydrophobic
analytes from an aqueous sample which is donor phase.
The acceptor phase can then be analyzed with gas chro-
matography or HPLC in the normal phase mode. The
three phase system (aq/org/aq), or supported liquid
membrane (SLM) extraction, involves extraction of polar
compounds from an aqueous sample matrix, through an
organic phase in the pores of the hollow fiber into a new
aqueous phase inside the lumen of the hollow fiber.
Analytical techniques such as reversed phase HPLC and
capillary electrophoresis can be used for analysis of ex-
tracts from three-phase LPME [16,17]. In the present
study a two phase hollow fiber microextraction method is
applied to extract PBDEs from sewage sludge samples
and gas chromatography (GC) with electron capture de-
tector was used as final analysis. The aim was to propose
an inexpensive and simple method for environmental
laboratories, where thousands of samples are analyzed
2. Material and Methods
2.1. Reagents and Standards
The PBDE congeners 28, 47, 99, 100, 153, 154, 183 and
209 were obtained from Accustandard (BDE-EPA-SET;
New Haven, CT, USA) as stock solutions (50 µg mL-1 )
in isooctane. They were stored in refrigerator and pro-
tected against light. Acetone and n-undecane (analytical
grade) were from Sigma-Aldrich (Steinheim, Germany).
Sulfuric acid (> 95%) and sodium hydroxide were pur-
chased from Acros (New Jersey, USA) and Scharlau
(Barcelona, Spain) respectively. Sodium chloride was
from Merck (Darmstadt, Germany). Working solutions
were prepared by appropriate dilution of stock solutions
in acetone. All aqueous solutions for optimization pro-
cedure were prepared by using reagent water purified by
a Milli-Q system (Millipore, Bedford, MA, USA). A
standard solution containing 4000 µg·L1 BDE-209 and
2000 µg·L1 of the remaining seven BDEs was prepared
in acetone and was used to spike into aqueous sample
solutions containing sludge. Solutions were stored in
dark at 4˚C.
2.2. Instruments
Sample analyses were carried out using a Hewlett-Pack-
ard 6890 series (Agilent, Palo Alto, CA, USA) gas
chromatograph system equipped with a Hewlett-Packard
6890 autosampler and a DB-5MS fused silica capillary
column 15 m × 0.25 mm × 0.1 µm (J&S Scientific, Fol-
som, CA, USA) connected to a siltek deactivated reten-
tion gap from Restek Corp (Bellefonte, PA, USA) (5 m ×
0.32 mm) by a siltek deactivated universal glass press-fit
connector (Restek Corp, Bellefonte, PA, USA). The
temperature program was: 50˚C hold 2 min; rate 20 to
final temperature of 325˚C, hold 15 min. Injection was
made on-column. The injection volume was set at 3 µL.
Helium was used as a carrier gas at a flow rate of 30 cm/s.
The µECD (Hewlett Packard) temperature was 350˚C
and nitrogen was used as make-up gas at a flow of 60
The Q3/2 Accurel PP Q3/2 polypropylene hollow-fiber
membranes (HF) (200 μm wall-thickness, 600 μm inner
diameter, 0.2 μm pore size) obtained from Membrana
GmbH (Wuppertal, Germany) were used to extract
PBDEs from sludge. The effective length of the mem-
brane was 5.5 cm. LC Microsyringes with 50 μl volume
from Agilent Technology were applied to inject the or-
ganic solvent (n-undecane) in the lumen of hollow fibers
which were sealed from one side and to keep the mem-
brane in extraction solutions. The membrane pores were
impregnated un-decane by dipping the hollow fiber
pieces in it for 15 min. The solution pH was measured
with a 211 microprocessor pH-meter (Hanna instruments,
Kungsbacka, Sweden). A five-position magnetic stirrer
(RO 5 power, IKA-WERKE GmbH & Co. KG, Staufen,
Germany) was used to stir the samples during extrac-
2.3. Sample Collection
The sludge sample was collected during May 2009 from
Källby sewage treatment plant which treats sewage from
the city of Lund in the south of Sweden and kept in dark
condition at 4˚C until analysis. The waste water treat-
ment in STP consists of four steps: a primary mechanical
pre-treatment, a biological treatment step, a chemical
treatment step and a sludge treatment step. The aim of
mechanical treatment is to remove different types of
suspended solids. In the biological process activated
sludge which contains large amount of microorganisms is
added to waste water to degrade organic matter in water
and in chemical treatment process phosphate is removed
by addition of iron or aluminum salt. Finally in the
sludge treatment process, the sludge collected from the
first step (sedimentation) undergoes dewatering; an an-
aerobic digestion process and various dewatering proc-
esses for reducing the amount of sludge.
Copyright © 2011 SciRes. JEP
Hollow-Fiber Microporous Membrane Liquid-Liquid Extraction for Determination of
Polybrominated Diphenyl Ethers at Trace Levels in Sewage Sludge with Gas Chromatography-Electron Capture Detection
3. Results and Discussion
3.1. Analytical Challenges
Analysis of high molecular weight PBDE (nona- and
decaBDE) congeners poses some problems. These com-
pounds are sensitive to light and adsorb to glass surfaces
and small dust particles. In general, the photochemical
reaction rate increases with increasing number of bro-
mine substituent, so PBDE-209 is the most sensitive. To
avoid photochemical degradation, samples should be
kept in dark and UV filters may be placed at windows
and below fluorescent lights. In addition, all glassware
should be covered with aluminum foil to prevent adsorp-
tion of dust. They are also sensitive to temperature and
degrade at high temperature required for GC analysis.
Therefore relatively short columns should be used for the
GC analysis of nona- and decaBDEs [18].
The injection technique, type of retention gap, press-fit
connector and stationary phase also significantly affect
the yield of PBDEs from chromatographic systems.
Concerning these aspects the recommendations given in
the literature were followed. [19].
3.2. Optimization of Extraction Procedure
The optimization step was performed using four variable
factors, involving pH of donor phase, salt (NaCl) addi-
tion, stirring speed and extraction time. The choice of
organic solvent (n-undecane) as the acceptor phase was
based on selection of the best solvent with high stability
and selectivity in extraction of PBDEs (high hydropho-
bicity) in a previous study on environmental water [20].
To study the extraction process the variable taken as re-
sponse was extraction efficiency E, that is the ratio of the
number of moles of analyte in the acceptor phase (nA)
after extraction to that initially present in the donor phase
Enn (1)
To evaluate the effect of parameters on extraction effi-
ciency, a series of 100 ml aqueous slurry samples con-
taining 1 g of wet sludge were spiked to final concentra-
tions of 0.100 µg·L1 of BDE-209 and 0.050 µg·L1 of
each the remaining seven BDEs and then pH was ad-
justed at 5.1 according to a preliminary experiment.
Spiked slurry samples were stirred for 5 min before
starting the extraction procedure. All determinations and
experiments were performed in triplicate and the pre-
sented results are the average values of three determina-
3.3. Influence of Ionic Strength
The use of salting-out effects may greatly enhance the
extraction efficiency of various organic compounds from
aqueous solutions and thereby sensitivity and precision
of their determination. This effect can be especially sig-
nificant for hydrophobic analytes, which bind well to
particles with high organic carbon content in sewage
sludge. In this study different amounts of NaCl (0 - 20%
W/V) were added to aqueous solutions containing sludge
and spiked with 0.100 µg·L1 of BDE-209 and 0.050
µg·L1 of remaining BDEs with pH adjusted at 5.1. Fig-
ure 1 depicts that optimal extraction condition was ob-
tained at 10% NaCl for all analytes.
Addition of NaCl to sample solution will alter the par-
tition coefficient of the analytes between dissolved or-
ganic matter content of sludge and water and also be-
tween water and acceptor phase based on the change of
ionic strength and viscosity [21]. Changes in ionic strength
can alter macromolecular structure of humic substances
(HSs) which exist in sewage sludge. At lower ionic
strength HSs have long and flexible structure with avail-
able region for binding to hydrophobic organic molecules
(HOMs) whereas at higher ionic concentrations HSs
forms rigid spherical shape molecules with the hydro-
philic surface and hydrophobic interior where is less ac-
cessible for binding of hydrophobic organic molecules
(HOCs). Therefore an increase in ionic strength results in
a decrease in sorption of HOMs [22,23].
Moreover the high content of salt in water affects hy-
dration and causes decrease in water solubility. It seems
that in 5% NaCl, the solution does not have sufficient
ionic strength required for efficient partitioning to the
organic solvent in the fiber and increased viscosity of the
aqueous phase negatively influences the kinetics of the
process. Lower extraction efficiency at higher ionic
strength (15% and 20% of NaCl) can also be related to
high viscosity and adsorption of analytes to glassware or
polymer [24]. Therefore, the maximum extraction effi-
ciency in selected concentration for experiments at 10%
of NaCl is due to the combined effects of ionic strength
and viscosity.
Figure 1. Effect of donor salt addition on E (%). Stirring
speed 1200, extraction time 60 min, pH 5.1.
Copyright © 2011 SciRes. JEP
Hollow-Fiber Microporous Membrane Liquid-Liquid Extraction for Determination of
Polybrominated Diphenyl Ethers at Trace Levels in Sewage Sludge with Gas Chromatography-Electron Capture Detection
3.4. Stirring Speed
The stirring speed has an important effect on transport of
analytes in LPME system thereby reducing extraction
time to reach thermodynamic equilibrium. The stirring of
donor phase was carried out from dial settings 4 to 10
(480 to 1200 rpm). Figure 2 shows the E value for all
PBDE congeners studied and indicates that extraction
efficiency decreases at lower speeds. Therefore, the
highest speed was selected as optimum for subsequent
3.5. Extraction Time
The effect of extraction time was evaluated for slurry
solutions stirred with stirring at 1200 rpm and adjusted to
pH at 5.1 with 10% NaCl during 20, 60, 120, 180 and
300 min. As seen in Figure 3, the concentration in the
fiber increased with time for all PBDEs up to 60 min and
then remained rather constant during an hour, indicating
that equilibrium was attained. A decrease in extraction
efficiency observed during prolonged extraction time
most probably was due to solvent losses at the high stir-
ring speed (1200 rpm). On the basis of these finding, we
selected 60 min as optimum extraction time.
Figure 2. Effect of stirring speed on E (%). Extraction time
60 min, 10% NaCl, pH 5.1.
Figure 3. Effect of extraction time on E (%). Stirring speed
1200 rpm, 10% NaCl, pH 5.1.
3.6. Effect of Sample pH
The pH can be an important factor in membrane extrac-
tion especially when analytes of interest are ionisable. It
was found that sludge pH increases with stirring, espe-
cially at lower pH. So to determine the influence of pH
on extraction efficiency, the initial pH of samples was
adjusted to pH 4, 5, 6.6, 7.5 and 9 using H2SO4 and
NaOH. Figure 4 shows the effect of initial pH on the
extraction efficiency of all analytes. Samples with acidic
and basic pH showed lower recoveries but higher and
similar results were achieved for samples with pH values
of 5, 6 and 7.5. Lower recoveries at acidic and basic con-
ditions can be related to changes in sludge properties.
The chromatogram is shown in Figure 5. Among the
analytes, the more hydrophobic compounds (BDE-183,
BDE-209) showed a significant increase in extraction
efficiency when the pH was changed from 5 to 6.6.
Therefore pH 6.6 was selected as optimum pH for sam-
ple preparation of real samples.
3.7. Application to Real Sample
The extraction method developed in this study was applied
to sewage sludge from Källby sewage treatment plant in
Lund (Sweden). 100 ml of spiked and non spiked aqueous
samples containing 1 g of wet sludge (considering of 70%
water content) and 10% NaCl (w/v) were prepared and pH
was adjusted at 6.6 for each sample. Extractions were per-
formed with 5.5 cm polypropylene hollow-fiber at 1200
rpm stirring speed for 1 hour and the amounts of PBDEs
per dry weight were calculated on the basis of 70% water
in wet sludge using a standard addition calibration proce-
dure. It was found that the sludge contained 5.1 µg·kg1 of
BDE-47 and 0.43 µg·kg1 of BDE-183. No other conge-
ners were found. The relative standard deviation of the
results was about 15%.
Also, the extraction efficiency of the native PBDE in
the sludge was calculated from the standard addition data.
It was found to be 23% - 32%, which is compensated for
by the standard addition procedure.
Figure 4. The effect of pH on E (%). Stirring speed 1200
rpm, extraction time 60 min, 10% NaCl.
Copyright © 2011 SciRes. JEP
Hollow-Fiber Microporous Membrane Liquid-Liquid Extraction for Determination of
Polybrominated Diphenyl Ethers at Trace Levels in Sewage Sludge with Gas Chromatography-Electron Capture Detection
Copyright © 2011 SciRes. JEP
Figure 5. Chromatogram obtained by the developed method for sludge sample spiked with 0.100 µg L-1 of BDE-209 and 0.050
µg L-1of remaining BDEs. Stirring speed 1200 rpm, extraction time 60 min, 10% NaCl, pH 6.6.
An overview of distribution and levels of brominated
flame retardants in sewage sludge samples from 22
wastewater treatment plants in Sweden shows that the
concentration of PBDEs were in the range of n.d. –450
µg·kg1 wet weight [25]. Previous studies on 9 sewage
sludge samples in Germany also showed total amounts of
tri- to hepta BDEs between 0.49 and 16.25 µg·kg1 dry
weight sludge [26]. Extraction techniques applied to
these analyses were centrifugation and Soxhlet extraction
respectively, and the concentrations of PBDEs are com-
patible with the results obtained for BDE-47 and 183 by
membrane extraction in this study although BDE-209
which was expected to have the highest level was not
detected. The major reason may be the limit of detection
but photodegradation or/and biodegradation during treat-
ment or experiment are other explanations. On the other
hand there is a correlation between PBDE levels and vi-
cinity of industrial areas, especially textile and electrical
industries (which is not the case in Lund) as significant
local sources of PBDEs. This causes important variation
among different municipal wastewater treatment plants.
4. Conclusions
A simple and novel method has been developed for de-
termination of 8 major polybrominated diphenyl ethers at
trace level in sewage sludge. The method was based on
two phase HF-MMLLE for extraction and gas chroma-
tography analysis. The investigation was focused on the
optimization of the extraction parameters such as salt
concentration, stirring speed, extraction time and initial
pH of donor phase. The employed extraction method
minimizes the consumption of organic solvents (microli-
ters) which are expensive and toxic for environment. In
addition, cheap piece of hollow fiber, no additional
preconcentration prior to final analysis and no require-
ment for sample clean-up step by expensive instruments
make the method simple and more economic for deter-
mination of PBDEs in sewage sludge.
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