International Journal of Geosciences, 2011, 2, 267-273
doi:10.4236/ijg.2011.23029 Published Online August 2011 (http://www.SciRP.org/journal/ijg)
Copyright © 2011 SciRes. IJG
Rapid Lab-Scale Microwave-Assisted Extraction and
Analysis of Anthrop o genic Organic Chemicals in River
Thomas J. Brown, Chad A. Kinney
Chemistry Department, Colorado State University-Pueblo, Pueblo, United States of America
Received June 16, 2011; revised July 19, 2011; accepted August 4, 2011
An Ethos EZ Microwave Lab Station is employed in the development of a robust and efficient microwave
extraction method for organic contaminants of anthropogenic origin in river sediments. The extraction method
is designed for a small, representative set of target compounds encompassing a range of physicochemical
properties. Listed in order of gas chromatography elution they are para-cresol, indole, 4-tert-octylphenol,
phenanthrene, triclosan, bisphenol-A, carbamazepine, and benzo[a]pyrene. The sediments samples are ex-
tracted wet, which reduces preparation time, and allows the ambient moisture of the sediments to aid in mi-
crowave energy absorption and the extraction process. The microwave can hold up to 12 samples that can be
simultaneously extracted allowing for rapid sample preparation. Utilizing the pressurized vessels, microwave
energy, and a unique mixture of three organic solvents allows for multiple samples to be extracted rapidly
with minimal solvent consumption. The final extracts are quantified by gas chromatography/mass spectro-
metry. Recoveries of the 8 target compounds in sediment range from 49% to 113%, and method detection
limits range between 14 and 114 μg kg–1, which are comparable with other more time consuming methods.
Keywords: Microwave Assisted Extraction, Para-Cresol, Phenanthrene, Bisphenol-A, Triclosan,
Surface waters have historically been burdened with a
variety of pollutants including suspended solids, nutri-
ents and pathogens . Other historic classes of indus-
trial pollutants include heavy metals, pesticides, PCB’s,
dioxins, volatile organics and polycyclic aromatic com-
pounds. There are also “emerging pollutants” which in-
clude pharmaceuticals, personal care products, surfac-
tants, flame-retardants, plasticizers and other endocrine
disrupting compounds that may not be effectively re-
moved by conventional wastewater treatment plants.
These anthropogenic organic compounds (AOCs) find
their way into the environment in a number of different
ways. Some AOCs, such as the polycyclic aromatic hy-
drocarbons (PAHs) phenanthrene and benzo[a]pyrene,
are the result of combustion process. Once airborne,
PAHs may eventually deposited on the ground through
precipitation, and therefore make their way into water-
ways by urban run-off . Urban runoff may be a source
of other AOCs such as para-cresol, which can originate
from road building (asphalt construction) or from wood
preservation products [3,4]. Many AOCs including
PAHs, pharmaceuticals and personal care products, de-
tergent metabolites, and more enter surface water in the
effluent discharged from wastewater treatment plants
[5,6]. AOCs are routinely detected in sediments at the
bottom of creeks, rivers, lakes and marine harbors
[3,7-12]. AOCs that make their way into sediments are
known to have longer half-lives than in soil, water or air,
because of the usually low temperatures and mostly an-
aerobic environment [13,14]. AOCs with large octanol
water partition coefficients tend to preferentially parti-
tion into the sediment from the water , and may bio-
concentrate or biomagnify in living organisms and their
predators, respectively .
The classic method still widely used to separate an-
thropogenic organic compounds from sediments and
other solid or semisolid matrices is by Soxhlet extraction,
invented in 1879 . It involves refluxing and recycling
T. J. BROWN ET AL.
an organic solvent through the sample continuously for 3
to 48 hours to dissolve the targeted compounds into the
organic solvent . In the last two decades there has
been call for newer more automated methods that offer
shorter extraction intervals and smaller and less toxic
solvent loads . Several competing methods have
been developed to meet this demand. They include su-
percritical fluid extraction, pressurized liquid extraction,
and microwave-assisted extraction.
Supercritical fluid extraction (SFE) typically utilizes
supercritical carbon dioxide with or without a co-solvent
such as methanol, to extract the target compounds from
the solid matrix. It is an environmentally benign tech-
nique, and technologically advanced, but there are nu-
merous factors that must be optimized, particularly in
analyte collection SFE extraction takes between 10 to 60
minutes to complete [18,19].
Pressurized liquid extraction (PLE) is another tech-
nique that lends itself to automation. Utilizing PLE, the
sample and solvent are pressurized and heated. The main
advantages of this method are fast extraction times and
limited solvent use. Interfering compounds such as lipids,
pigments and sterols can be co-extracted . Unless
these compounds are removed in a subsequent cleanup
step, these compounds may impair the efficiency of a
chromatographic column and quantitative analysis .
Microwave extraction entails immersing and heating
the sample in a liquid capable of absorbing microwave
radiation. There are two types of microwave extraction
techniques; one using closed vessels known as micro-
wave-assisted extraction (MAE) and the other technique
using open vessels known as focused microwave assisted
solvent extraction (FMASE). FMASE typically requires
a slightly longer extraction time since the temperature of
the extraction is limited by the boiling point of the sol-
vent system. In addition to low solvent volumes and fast
extraction times, microwave extraction offers the impor-
tant advantage of the ability to perform simultaneous
extractions of multiple samples. Typically solvent mix-
tures or systems are employed that combine two or more
solvents together in different ratios to achieve the desired
solvent properties .
2. Materials and Methods
Organic solvents were all HPLC grade or better. Di-
chloromethane (DCM) and acetone were from Mallin-
ckrodt Chemicals and ethyl acetate (EtOAc) was from
EMD Chemicals. Sodium sulfate was purchased from
Fisher Scientific. Solid phase extraction (SPE) tubes (6
mL) containing 1 g of Florisil with stainless steel frits
were purchased from Supelco Analytical (Supelclean™
ENVI™ Florisil®). The internal standard (phenanthrene-
d10) was purchased from Isotec through Sigma Aldrich.
N, O-bis-(trimethylsilyl) trifluoroacetamide (BSTFA) was
purchased from TCI America. Analytical standards of
the target compounds were purchased from Sigma Al-
2.2. Microwave Assisted Extraction
Samples were extracted without stirring in a Milestone
Ethos EZ Microwave Lab Station equipped with 100 mL
Teflon vessels rated to withstand 30 bar of internal pres-
sure. Prior to use the Teflon vessels were cleaned with a
solution of water and Alconox. This is followed by mi-
crowaving with 8.5 mL of DI water, 1.0 mL concentrated
nitric acid and 0.5 mL of 30% hydrogen peroxide to
110˚C for ten minutes to rid the vessels of residual or-
ganics. This is followed by microwaving with 2 mL of
concentrated NaOH and 8 mL of water to 110˚C to neu-
tralize any residual acid that could react at elevated tem-
perature and pressure with the sediments. Finally, just
prior to use the vessels are rinsed with acetone.
Sediment samples are prepared by pouring off any su-
pernatant layer of water and then homogenized. Any
obvious foreign material such as large rocks, sticks or
leaves were then eliminated prior to extraction. About 5
g of wet sediments are placed in the microwaveable ves-
sels enough DI water is added to bring the sediment to
24% moisture. Water was also added to the dry sand
used during the method development. The local heating
of water facilitated by microwave energy is thought to
help liberate target molecules [22,23]. A 30 mL volume
of a 1:1:1 mixture of DCM /EtOAc/acetone was then
added to the sediment or sand in the extraction vessel.
The vessel is sealed and shaken vigorously for a few
seconds. The microwave parameters are a 10-min ramp
to 110˚C, hold for 10 min, then cool the vessels in the
microwave for 30 min to <50˚C prior to further process-
ing. Prior to opening, each vessel is again shaken vigor-
2.3. Sample Cleanup and Preconcentration
A 58 degree short stem glass funnel loaded with a tab of
baked glass wool to trap the sediment. The funnel is set
loosely on top of the 60 mL plastic BD Luer-Lok syringe
with the plunger removed. A 25 mm 0.2 mm PTFE sy-
ringe filter is attached to the bottom of the syringe. The
filter is connected by a union to a 6 mL Florisil SPE car-
tridge (1 g Supelclean ENVI made by Supelco) precon-
ditioned with 10 mL of the 1:1:1 mixture of DCM/
EtOAc/acetone solvent and filled with approximately 4 g
of anhydrous sodium sulfate. The extract is poured
through the funnel into the syringe. The funnel is re-
Copyright © 2011 SciRes. IJG
T. J. BROWN ET AL.269
moved and the extract is then passed through this
cleanup system by positive pressure using the syringe
plunger directly into the evaporation glassware (LAB-
CONCO RapidVap 600 mL glass evaporative tube). The
microwave container was then rinsed with 6 mL of 1:1:1
DCM/EtOAc/acetone that is passed through the cleanup
system generating about 36 mL of total extract.
The extract is concentrated by evaporation under a ni-
trogen blanket (13,800 Pa) at 70˚C to a final volume of 1
mL using a LABCONCO RapidVap N2 Evaporation
System. The vortex mixing action of the evaporation
system is left off for most of the evaporative process to
yield the best recovery of the compounds. When the ex-
tract is less than 2 mL and is contained in the stem of the
tube the vortex is turned on at the lowest setting of 24%.
If the concentrated extract is nearly clear or light am-
ber in color the extract is transferred into a 2 mL GC vial
and 50 µL of the 100 ng/µL internal standard phenan-
threne-d10 is added. When the extract is a dark orange or
brown in color, indicating the potential presence of hu-
mic interferences. The extract is pipetted into a small 15
mL centrifuge tube and centrifuged at 1500 rpm for 30
seconds. The supernatant is pipetted into a 2 mL GC vial
and the internal standard is added. The vial is mixed on a
Baxter Super Mixer II for 10 seconds prior to GC/MS
2.4. Gas Chromatography/Mass Spectrometry
The AOCs in the concentrated extracts were quantified
on an Agilent 6890N/5973N GC/MSD. It was operated
using positive electron impact ionization (70 eV) and in
the full-scan mode from 45 - 450 mass/charge ratio (m/z).
The GC/MS was equipped with a 30 meter Restek RTX-
5Sil MS w/Integra Guard with a 0.25 mm ID and 0.25
µm film thickness. A 2 µL volume was injected in
splitless mode. The injection port temperature was 290˚C,
the purge flow was 6.1 mL/min, and the transfer line was
maintained at 250˚C. The oven temperature was pro-
grammed as follows: 40˚C (hold 3 min), ramped at
8˚C/min to 100˚C (hold 4.50 min), then ramped at 9˚C
/min to 290˚C and (hold 2 min) with pressure control set
for a constant flow of helium carrier gas of 3.0 mL/min.
As a measure of quality control, lab blanks were run to
guard against laboratory contamination and compound
carryover. An injection internal standard, 5.00 ng/µL of
phenanthrene-d10 is used for quantification purposes.
Multiple ion monitoring of the mass spectra along with
retention time was used for target compound identifica-
2.5. MAE Method Validation
Ashed (400˚C for 4 hours) Ottawa reagent-sand (Fisher
Scientific, Fairlawn, NJ USA) and 4 stream sediment
samples from Fountain Creek near Colorado Springs and
Pueblo, Colorado were utilized in the validation of the
method. Eight samples (5 g) of each were spiked with 10
g of each compound. Also, three unfortified blank sam-
ples of both sand and sediment were extracted for quality
control purposes. The sand serves as a method blank to
prevent and alert against laboratory contamination. The
sediment samples were stored at 4˚C prior to extraction.
Sand samples were spiked just prior to placing them in
the microwave for extraction. The sediment samples
were spiked, mixed and allowed to equilibrate at room
temperature for 24 hours before MAE. The unfortified
sediment samples contained trace but quantifiable
amounts of phenanthrene and benzo[a]pyrene which
were subtracted from the spiked sample results. The ini-
tial method detection limits (IMDL) were determined
according to the procedure outlined by the U.S. Envi-
ronmental Protection Agency .
While not part of the final reported and applied method,
to help provide a more sensitive analysis of some of the
target compounds, especially bisphenol-A and triclosan,
extract derivatization with a silylation was tested. After
mixing the final extract, 50 µL of the extract was pipet-
ted into another 2 mL GC vial containing a 350 µL, coni-
cal pulled point insert. Then 50 µL of N, O-bis-(trime-
thylsilyl) trifluoroacetamide (BSTFA) is added to the
extract, close the vial and heat at 70˚C for 30 minutes for
derivatization. The derivatization of the calibration stan-
dard solutions is conducted simultaneously using the
same protocol. All compounds with active hydrogens can
2.7. Sample Sites
Sediments from four sites along upper (UF) and lower
(LF) Fountain Creek near Colorado Springs, Colorado
were collected on March 25th 2009 with approximate
locations of between 38˚51- 48'N latitude and 104˚55 –
47'W longitude. The four sites were 46.32 km (LF-2),
53.83 km (LF-1), 65.46 km (UF-2), and 77.57 km (UF-1)
from the confluence of Fountain Creek and the Arkansas
River. Fountain Creek was originally ephemeral, flowing
only from snowmelt and precipitation, but base flow is
currently dominated by wastewater effluent and flow
year around. A 2.54 cm PVC pipe was punched 10 cm
into the sediment five times in a transect across the creek
at each site to collect a composite sediment sample. The
samples were stored at 4˚C until extraction.
To further validate the utility of the MAE method, 8
Copyright © 2011 SciRes. IJG
T. J. BROWN ET AL.
sediment samples from Sacramento River were acquired
and analyzed. The sediment samples were taken every
two miles from the mouth of the river starting at mile
two and ending at mile sixteen. The Sacramento River
sediments were generally finer than the course grain
Fountain Creek sediments. Sacramento River sediments
averaged 28% moisture, and average organic carbon
content of 0.57%, while Fountain Creek had an average
of 14% water and 0.16% organic carbon. Organic carbon
was estimated by loss on ignition and using the universal
correction factor 0.58 .
3. Results and Discussion
3.1. Microwave Assisted Extraction Method
The initial consideration for method optimization in-
volved the choice of solvent, which can influence both
sample extraction and cleanup efficiency. Hexane, tolu-
ene, acetonitrile, methanol, acetone, ethyl acetate, dichlo-
romethane and diethyl ether were considered as possible
solvents. The performance of solvent mixtures during
final extract evaporation step was considered first. A
mixture of methanol and acetone proved to be a poor
solvent during the evaporation step. We hypothesize that
this is because of hydrogen bonding between the protic
and aprotic solvents in preference of interactions with
other organic compounds [26,27]. Hexane and acetone in
a 1:1 through a 3:1 mix respectively provided excellent
recovery during evaporation, but resulted in co-extra-
ction of background compounds leading to noisy chro-
matographic baselines during MAE experiments using
real sediments. A 7:3 DCM/EtOAc was substituted for
the hexane/acetone resulting in improved recovery of the
target compounds and a reduction in background noise.
Extraction efficiency was improved when acetone was
added to this mixture. The final 1:1:1 mixture of the
three solvents provided the best and most consistent re-
covery of these target compounds.
The extract evaporation parameters were considered
next. Different evaporation temperatures were tested. 30
mL of extraction solvent was spiked with 100 µg of each
target compound then immediately evaporated to 1 mL
and subsequently analyzed by GC/MS. The highest
available temperature setting, 70˚C, and thus the shortest
evaporation time resulted in the greatest compound re-
covery (Figure 1). It has been reported that the nitrogen
evaporation step may results in up to a 15% loss of ana-
lytes . Therefore, evaporation is an important step to
optimize but commonly neglected. Greater recovery dur-
ing evaporation was observed when the delivery of N2
was decreased from 10 to 2 PSI. Better recoveries were
also observed when the vortex mixing feature on the on
the LABCONCO RapidVap N2 Evaporation System was
left off until the solvent was 2 mL or less and entirely
contained in the finger of the evaporation glassware.
Microwave parameters were optimized next. Initial
temperature range was set at between 95˚C to 145˚C.
Sediment to solvent ratio was bracketed between 10 to
30 percent. The time range was set between 5 and 25
minutes. A series of experiments (100 µg spike) with real
sediments was conducted to determine the optimized
parameters (Table 1). The optimized heating parameters
are 10 minute ramp to 110˚C, and then hold for 10 min-
utes, followed by a 30 minute cooling period. Finally, the
benefits of compound derivatization was tested, but was
not incorporated in final method tested. The reason for
this is because three compounds, bisphenol-A, triclosan,
and carbamazepine, had limited sensitivity during the
GC/MS analysis compared to other target compounds.
Derivatized has been reported to improve results for bis-
phenol-A [29-32] and triclosan [33,34]. Without deriva-
tization, we observed partial degradation of carbamaze-
pine to iminostilbene in the injection port leading to a de-
crease in sensitivity . Derivatization of carbamaze-
pine can increase stability and sensitivity , which is
consistent with the observations of this study, but this did
not completely alleviate the problem. Derivatization im-
Figure 1. Compound recovery during solvent evaporation
(30 mL solvent was spiked with a 100µg of each target com-
pound and evaporated to approximately 1 mL).
Table 1. Optimization of Microwave Oven Parameters.
Temperature Time Solvent
110˚C 10 min 33 mL 93%
95˚C 20 min 33 mL 86%
110˚C 10 min 22 mL 84%
110˚C 10 min 16.5 mL 83%
95˚C 10 min 33 mL 76%
125˚C 10 min 33 mL 72%
140˚C 20 min 16.5 mL 52%
Copyright © 2011 SciRes. IJG
T. J. BROWN ET AL.271
proved calibration sensitivity for the bisphenol-A, and
triclosan by a factor of 6.6 and 3.3, respectively. In fact,
the calibration sensitivity of all the derivatized com-
pounds improved to some extent with the exception of
indole, which contains a difficult to derivatize secondary
3.2. MAE Method Performance
The performance of the MAE and GC/MS quantification
method reported here (Table 2) is comparable to other
extraction/quantification methods, including other MAE
based methods, employed for organic contaminants in
sediments and other solid samples. For example Lopez-
Avila et al. reported recoveries of PAHs in an opti-
mized microwave method of 101% for benzo [a] pyrene
and 81.9% for phenanthrene for a soil-sediment suspen-
sion, which is comparable with this MAE method of
113% recovery for benzo[a]pyrene and 62% recovery of
phenanthrene in sediment. Seven out of the eight com-
pounds included in this study were included in a pres-
surized liquid extraction (PLE) based method developed
by Burkhardt et al. . Overall the recoveries of target
analytes using this MAE method are slightly better than
those reported by Burkhardt et al. , and the IMDLs are
comparable. In particular the recovery of bisphenol-A
was improved using MAE compared to PLE. EPA
method 1694 has LC/MS/MS reported a detection limit
for carbamazepine of 1.6 µg/kg and for triclosan of 56
µg/kg The detection limit of our MAE method for car-
bamazepine 64.6 µg/kg is much greater than the EPA
method, but our triclosan IMDL of 66.8 µg/kg was very
close to the EPA method .
Because of its proven capability to extract compounds
with a wide range of physico-chemical properties from
sediments, there is a high likelihood that other emerging
AOCs could be added or substituted with the eight ana-
lytes in this study. The major advantage of this MAE
method over some other possible extraction procedures is
the ability to perform 12 extractions simultaneously and
a quick clean-up step thereby dramatically reducing the
time required for sample preparation. The primary limi-
tation that occurred during the development of the
method reported here is the larger than desired standard
deviations for some compounds that ultimately results in
higher detection limits, which may be improved with a
microwave oven that includes a stirring provision.
3.3. AOCs in Sediments
As a test of the MAE method reported here, a small set
of sampling of the Fountain Creek Watershed was con-
ducted on March 25, 2009. Some portions of Fountain
Creek, particularly those in the Lower Fountain Creek
below Colorado Springs, CO are dominated by waste-
water effluent. The results are summarized in Figure 2.
Many of the target compounds were detected below the
calculated method detection limits, which are designated
with an “a” in Figure 2. In such instances all reporting
criteria with the exception of the IMDL were met. In
those instances where compounds were detected below
the IMDLs the estimated concentrations have been in-
cluded. This may in part reflect the paucity of organic
matter present in Fountain Creek sediment. Sample UF-1
was extracted in triplicate to assess method precision.
The precision for the detected compounds are good ex-
cept for triclosan, which was only quantified in one of
the three samples extracted.
To further test the reported method, 8 sediment sam-
ples from the Sacramento River were also extracted and
analyzed. Of the target compounds included in this me-
thod, only the two PAHs, phenanthrene and benzo [a]
pyrene were detected in the Sacramento River sediments.
Benzo[a]pyrene was detected in all of the Sacramento
Table 2. MAE Method Recoveries and IMDLs.
p-cresol 128.8 175.0 83.6 85.9
indole 89.3 27.3 48.9 44.3
4-tert-octylphenol98.6 27.9 59.5 100.8
phenanthrene 98.5 36.7 62.0 13.9
triclosan 97.8 139.7 97.1 66.8
bisphenol-A 96.5 110.4 100.9 113.7
carbamazepine 105.0 79.9 110.1 64.6
benzo[a]pyrene 111.1 45.0 112.9 71.6
Figure 2. Concentrations of target compounds in sediments
collected on March 25, 2009 along Upper Fountain (UF)
Creek and Lower Fountain (LF). Creek near Colorado
Springs, Colorado. The capped black lines represent ± 1
standard deviation of triplicate extractions of UF-1. The
“a” indicates an estimated concentration that falls below
the 99% confidence MDLs.
Copyright © 2011 SciRes. IJG
T. J. BROWN ET AL.
sediments tested three of which were above the IMDL.
The concentration ranged from an estimated 61.1 µg/kg
to 185.1 µg/kg. Phenanthrene was positively identified in
six of the sample sites only one sample came close to the
detection limit of 13.9 µg/kg.
The microwave extraction method reported here is a
rapid, low cost extraction method that lends itself to si-
multaneous screening of multiple samples. The MAE
method proved to reliable measure eight physicochemi-
cally diverse organic compounds in river sediments. The
sensitivity of the quantitation method and therefore de-
tection limits may be improved by addition of a derivati-
zation step or operation of the GC/MS in the single ion
monitoring (SIM) mode. However, even without deri-
vatization or SIM, this MAE method had similar per-
formance to other accepted extraction methods. The
method was successfully applied to the detection and
measurement of several target compounds in two differ-
ent set of sediment samples.
This research was supported by the College of Science
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