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PAPER IN FOREFRONT
Micro-solid phase equilibrium extraction with highly ordered
TiO2 nanotube arrays: a new approach for the enrichment
and measurement of organochlorine pesticides at trace level
in environmental water samples
Qingxiang Zhou & Yunrui Huang & Junping Xiao &
Guohong Xie
Received: 29 November 2010 /Revised: 4 February 2011 /Accepted: 7 February 2011 /Published online: 23 February 2011# Springer-Verlag 2011
Abstract Ordered TiO2 nanotube arrays have been widely
used in many fields such as photocatalysis, self-cleaning,
solar cells, gas sensing, and catalysis. This present study
exploited a new functional application of the ordered TiO2
nanotube arrays. A micro-solid phase equilibrium extrac-
tion using ordered TiO2 nanotube arrays was developed for
the enrichment and measurement of organochlorine pesti-
cides prior to gas chromatography-electron capture detec-
tion. Ordered TiO2 nanotube arrays exhibited excellent
merits on the pre-concentration of organochlorine pesticides
and lower detection limits of 0.10, 0.10, 0.10, 0.098,
0.0076, 0.0097, 0.016, and 0.023 μ g L−1 for α -HCH, β-
HCH, γ-HCH, δ-HCH, p, p’-DDE, p, p’-DDD, o, p’-DDT,
and p, p’-DDT, respectively, were achieved. Four real water
samples were used for validation, and the spiked recoveries
were in the range of 78 – 102.8%. These results demonstrat-
ed that the developed micro-solid phase equilibrium
extraction using ordered TiO2 nanotube arrays would be
very constructive and have a great beginning with a brand
new prospect in the analysis of environmental pollutants.
Keywords Ordered TiO2 nanotube array. Organochlorine
pesticides . Micro-solid phase equilibrium extraction . Gas
chromatography-electron capture detection
Introduction
TiO2 has been widely used in many applications ranging
from anticorrosion, self-cleaning coatings, paints to solar
cells, and photocatalysts due to its high photocatalytic
activity, chemical stability, non-toxicity, and relatively low
cost [1 – 4]. Recently, TiO2 nanotubes have received
considerable attention because of their higher surface area,
better adsorption ability, and higher photocatalytic activity
in comparison with TiO2 powders [5 – 8]. However, it was
difficult to separate and reuse the TiO2 nanotubes from the
solution. Therefore, the aim became to align the TiO2
nanotubes on a substrate or template. Zwelling and cow-
orkers [9] made a first attempt and successfully achieved
ordered TiO2 nanotubes arrays through a simple anodiza-
tion process. Grimes and coworkers firstly utilized the
Electronic supplementary material The online version of this article
(doi:10.1007/s00216-011-4788-7) contains supplementary material,which is available to authorized users.
Q. Zhou (*) : Y. Huang
Henan Key Laboratory for Environmental Pollution Control,
Key Laboratory for Yellow River and Huaihe River Water
Environment and Pollution Control, Ministry of Education,
School of Chemistry and Environmental Sciences,
Henan Normal University,
Xinxiang 453007, China
e-mail: [email protected]
e-mail: [email protected]
Q. Zhou
State Laboratory of Petroleum Resource and Prospecting, Key
Laboratory of Earth Prospecting and Information Technology,College of Geosciences, China University of Petroleum Beijing,
Beijing 102249, China
J. Xiao
Department of Chemistry,
University of Science and Technology Beijing,
Beijing 100083, China
G. Xie
College of Resources and Environment,
Henan Institute of Science and Technology,
Xinxiang 453003, China
Anal Bioanal Chem (2011) 400:205 – 212
DOI 10.1007/s00216-011-4788-7
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highly ordered TiO2 nanotube array film to fabricate the
solar cell [10]. Afterwards, many related preparation
methods and applications of TiO2 nanotubes arrays were
reported, which made it easy to obtain needed TiO2 nano-
tubes arrays for many important engineering applications.
Nowadays, TiO2 nanotubes arrays have been employed in
many fields including photoelectrochemical hydrogen gen-
eration [11 – 15], solar cells [16 – 18], hydrogen storage [19],gas sensing [20 – 22], templates for growth of compound
semiconductor nanowires for radiation sensing [23], sub-
strate for high interfacial bond strength hydroxyl apatite
coating in implants [24, 25], biomedical applications [26],
and catalyst supports [27]. In environmental field, TiO2
nanotubes arrays have also been reported for organic
contaminant degradation based on its photoelectrocatalytic
activity [28 – 32]. However, to the best of our knowledge,
there has been no report using TiO2 nanotube array for the
goal of enrichment of environmental pollutants.
Organochlorine pesticides (OCPs) have been widely
used for the control of pests in agriculture and cities because of its low cost and effectiveness all over the world.
A huge amount of organochlorinated compounds is
continuously being released into the environment with the
extensive use of OCPs and herbicides, and discharge of
wastewater from bleaching of pulp and municipal waste-
water treatment. Environmental contamination by OCPs has
been a major concern over the past several decades in the
world because of their persistence, long-distance transport,
biological effects, and bioaccumulation along the food
webs. Nowadays, OCPs are known as one of the most
persistent organic pollutants in the environment and have
absorbed much attention from most of the governments all
over the world. To date, most of the developed and
developing countries have already banned or restricted the
production and usage of OCPs, such as dichlorodi-phenyl-
trichloroethanes (DDTs), hexachlorocyclohexanes (HCHs),
hexachlorobenzene, polychlorinated biphenyls, etc. The US
Environmental Protection Agency (EPA) has identified 12
priority persistent bioaccumulative and toxic compounds of
special interest [33], which includes DDT and its break-
down products, DDE and DDD. Some of them were listed
in the Stockholm Convention on Persistent Organic
Pollutants. However, recent studies have reported the
presence of organochlorine pesticides in different sites
[34 – 36]. Therefore, it is necessary to monitor the amounts
and distribution of OCPs and evaluate their effects on the
environment. Thus, simple and highly sensitive analytical
techniques are required to detect and quantify OCPs at trace
levels. Usually, to achieve the necessary level of sensitivity,
an enrichment step is needed before analysis. A variety of
enrichment steps had been established for separation and
preconcentration of OCPs such as solvent cooling-assisted
dynamic hollow-fiber-supported headspace liquid-phase
microextraction [37], dispersive liquid – liquid microextrac-
tion [38, 39], solid phase extraction [40], solid phase
microextraction [41, 42], etc. Solid phase extraction has
distinguished from many extraction techniques because of
its advantages of lower cost, higher enrichment factor, and
less consumption of organic solvents.
The aim of present work was to establish a novel,
effective, reusable, simple, and sensitive determinationmethod for OCPs with TiO2 nanotube arrays. Used as
adsorbents, TiO2 nanotube arrays would avoid the low flow
rate of the conventional solid phase extraction with TiO2
nanotubes cartridge and the difficulty in separation from
dispersion in solution and make it easy to reuse. This new
protocol is to establish a convenient micro-solid phase
equilibrium extraction (μ SPEE) with TiO2 nanotube arrays
for the enrichment of OCPs and to enlarge the application
field of TiO2 nanotube arrays.
Experimental
Reagents and materials
A working stock solution (10.00 mg L−1) of OCPs was
prepared in HPLC-grade methanol with mixed standards
containing α -hexachlorocyclohexane (α -HCH), β-
hexachlorocyclohexane (β-HCH), γ-hexachlorocyclohexane
( γ-HCH), δ-hexachlorocyclohexane (δ-HCH), dichlorodi-
phenyltrichloroethane (o, p’-DDT, p, p’-DDT), dichlorodi-
p h e n y l d i c h l o r o e t h y l e n e ( p , p ’ - D D E ) , a n d
dichlorodiphenyldichloroethane ( p, p’-DDD) from Beijing
Yingtianyi Chemical Science and Technology Co., Ltd.
(Beijing, China). All the standard solutions were stored at
4 °C in the refrigerator and protected from light. The
aqueous solutions were prepared daily by diluting the
standard mixture with ultrapure water. HPLC-grade meth-
anol and acetonitrile were obtained from Jiangsu Guoda
Chemical Reagent Co., Ltd. (Huaian, China). Ultrapure
water was prepared in the laboratory using a Millipore
(Billerica, MA, USA) water generator system, and all the
other solvents were of analytical reagent grade unless
stated. One percent sodium hydroxide and 1 mol L−1
hydrochloric acid were used for adjusting the pH value of
the water samples.
Titanium sheets (99.6% purity) from Beijing Hengli
Taiye Co., Ltd. (Beijing, China), Pt electrode was obtained
from Shanghai Ruosull Technology Co., Ltd., 30 V
potentiostat (JWY-30 G, Shijiazhuang, China)
Preparation and identification of TiO2 nanotube array
Titanium sheets (0.2 mm thick, 10×20 mm size) with
99.6% purity (Beijing, China) were polished with metallo-
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graphic abrasive paper and were then degreased by
sonicating in acetone, isopropanol, and methanol, respec-
tively. The sheets were air-dried after rinsing with ultrapure
water. The anodic oxidation was accomplished by using
titanium sheet as anode and platinum as cathode. The
distance between two electrodes was 3 cm in all experi-
ments. The electrolyte was composed of 0.14 M NaF and
0.5 M H3PO4 [43]. The anodic oxidation was carried out at 20 V for 1 h. After electrolysis, a titanium sheet was rinsed
with ultrapure water and then air-dried. The TiO2 nanotube
arrays prepared were then analyzed with a field emission
scanning electron microscope (S-4800 FESEM, Hitachi,
Japan; see Fig. 1).
μ SPEE procedure
The TiO2 nanotube array sheet was directly immersed in
10 mL solution with a constant depth and then sealed in
the sample vial. The extraction conditions were the same
as that of the optimized conditions. The stirring rate of the magnetic stirrer was set at 500 rpm. After the
equilibrium between adsorption and desorption was
basically reached, the TiO2 nanotube array sheet was
taken out and rinsed with distilled water in order to
remove co-adsorbed matrix substances, then air-dried and
eluted for the desorption of analytes. TiO2 nanotube array
sheet was directly immersed in a small amount of
dichloromethane for complete desorption in an interval
of 7 min. After that, the TiO2 nanotube array sheet wasremoved, and the dichloromethane was dried with mild
stream of nitrogen gas. Then, the residue was dissolved in
100 μ L methanol. Finally, 1 μ L of the solution was
injected for gas chromatography (GC) analysis.
GC analysis
GC analyses were performed on an Agilent 7890A gas-
chromatographic system, equipped with an electron capture
detector (ECD). Separations were carried out using a HP-5
column (30 m× 0.32 mm×0.25μ m). Nitrogen (99.999%) was
employed as the carrier gas (0.6 mL min−1). The 1.0 μ L of astandard solution or sample solution was injected in the
splitless mode at 250 °C using the following program of
80 °C (held 1 min), then 25 °C min−1 ramp to 200 °C held
for 2 min, and then 10 °C min−1 ramp to 300 °C held for
5 min. Total run time was 22.8 min. The ECD was
maintained at 300 °C.
Water samples
In this work, four environmental water samples such as tap
water, melted snow water, lake water, and reservoir water
were collected for validating the proposed method. Tap water
sample was collected from our own laboratory after it was
flowing for 10 min at a very fast rate. A snow sample was
collected from Henan Normal University, Xinxiang, Henan
Province, 12 Nov 2009. Lake water sample was collected
from Shouxihu Lake, Yangzhou, Jiangsu Province, China.
Reservoir water sample was taken from Xiaoshangzhuang
reservoir, Xinxiang, Henan Province, China. All the collect-
ed water samples were filtered through 0.45-μ m micropore
membranes after sampling and were maintained in glass
containers, and then stored at 4 °C.
Results and discussion
The effect of equilibrium between sample solution
and TiO2 nanotube array
In this μ SPEE procedure, the extraction is affected by
several factors. The analytes, which exist as molecular form
in the solution, would be enriched, and the enriched amount
of analytes was related to the amount of analytes existing asFig. 1 FESEM images of TiO2 nanotube arrays. a Top view; b
cross-view
Micro-solid phase equilibrium extraction 207
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molecular form in the solution. However, two procedures
will occur in the extraction process and influence the
amount of molecular analytes in the solution, further
influencing the enrichment performance. First, the analytes
would migrate between gas and liquid phases due to the
vapor pressure for the volatile or half volatile compounds.
This procedure will reach equilibrium. This equilibrium
obeys Henry’s law when the concentrations of analytes arevery low,
pB ¼ kH xB ð1Þ
where pB is the partial pressure of the (analytes) in the gas
above the solution; xB is the concentration of the (analytes),
and kH is known as the Henry's law constant, which depends
on the solute (analytes), the solvent, and the temperature.
The second procedure is the adsorption of analytes onto the
adsorbents, and it is also a reversible procedure. Some of the
HCHs and DDTs may adsorb on the surface of the adsorbents,
and some of them will be desorbed at the same time. Finally,
they will reach equilibrium. This equilibrium obeys the
Freundlich equation (Freundlich adsorption isotherm):
lg Q ¼ lg K F þ 1=nð Þ lg xB ð4Þ
Where Q is the weight adsorbed per unit area of TiO2
nanotubes array sheet, k F and (1/ n) are constants for a given
adsorbate and adsorbent at a particular temperature, and pBis the partial pressure of the (analytes) in the gas above the
solution. We substituted Eq. 1 into Eq. 4:
lgQ ¼ lg K F À 1=nð Þ lg kH þ 1=nð Þ lg pB ð5Þ
In general, these three steps will reach equilibrium, and
the best enrichment will be achieved (see Fig. 2).
On the other hand, if the concentrations of analytes are
larger, which does not make them obey Henry’s law,
suppose the amount of volatile part as C v, so:
lg Q ¼ lg K F þ 1=nð Þ lg C 0 À C vð Þ ð6Þ
The primary experiments have proved that it was
right that the peak areas of HCHs were very small due
to the relatively high vapor pressure or lower compet-
itive adsorption. As the nonvolatile compounds are
concerned, the adsorption obeys the Eq. 4. Beside these,
the parameters including the kind of organic solvents,
sample pH, extraction time, and desorption time would
give rise to influence the enrichment efficiency. In order
to obtain appropriate extraction efficiency, a procedure
for optimization was necessary. Hence, we performed a
series of experiments for obtaining optimal enrichment
conditions.
The effect of other factors on μ SPEE
Effect of the kind organic solvents
In a μ SPEE procedure, different desorption efficiency
would be obtained when different solvents are used due to
the different physical and chemical properties of the organic
solvents and characteristics of the target analytes. In this
experiment, there are five types of solvents such as
methanol, acetonitrile, acetone, hexane, and dichlorome-
Fig. 2 Adsorption equilibrium
of TiO2 nanotube arrays as
adsorbents for analytes
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thane which were used for desorption of OCP pesticides. It
was found that dichloromethane was the most effective
solvent of the eight analytes, so it was used as the solvent
for desorption.
Effect of sample pH
Sample pH plays an important role in the extraction procedure because pH value determines the existing form
of the analytes, and then the pH of the sample solution
affects the extraction efficiency. In this experiment, the
effect of sample pH on the enrichment of OCPs was
evaluated in a range of pH 3.0~ 8.0 (see Fig. 3). As can be
seen, the peak area of four HCHs decreased with the
increase of pH value, and the peak area of DDTs, DDD, and
DDE reached the maximum at the pH 6.0. The extent of
peak area decrease of HCHs was very small. Hence, pH 6
was used in the following experiments.
Effect of salting-out effect
Salting-out effect is often an important factor in the extraction
procedure. In these experiments, it was optimized in the range
of 0~30% (w/ v ). The peak areas of the HCHs increased a little
with the increase of NaCl concentration and the peak areas of
DDTs, DDD, and DDE decrease significantly when the NaCl
concentration is in the range of 0~30%. The reason may be
that addition of salt suppresses the thickness of electrical
adsorption layer at the TiO2 solution interface, which leads to
the decrease of mixed hemimicelles formed on the TiO2
surface. Based on these results, NaCl was not added.
Effect of equilibrium time
Equilibrium time is an important parameter in the μ SPEE
procedure, which determines the enrichment performance
better or not. In order to achieve a reasonable extraction
time, a series of experiments were designed for investiga-
tion of the effects of extraction time in the range of 20~
90 min. The results were shown in Fig. 4. From the figure,
we can see that the adsorption of HCHs reached the
equilibrium rapidly and DDT, DDD, and DDE needed more
time. So, the peak areas of DDT, DDD, and DDE increased
straightly in the time interval. However, the extraction
efficiency improved significantly with increasing equilibri-um time up to 40 min; after that, the extraction efficiency
increased slightly. Hence, for time saving in subsequent
experiments, 40 min was used as the equilibrium time.
Effect of desorption time
In the μ SPEE procedure, two steps are very important; one
is the adsorption of analytes on the surface of adsorbents,
and the other is desorption of analytes from the adsorbents.
Ideally, these two procedures are very rapid. In fact, the
procedure may be various due to different conditions.
Desorption of OCPs from the TiO2 nanotube array sheet with the dichloromethane is controlled by the time. In order
to achieve complete desorption of OCPs, the desorption
time was investigated in the range of 1~9 min. The results
indicated that the desorption of HCHs was rapid and had no
significant differences in the time interval, but the DDT and
DDD reached the best desorption level in 7 min; DDE
needed longer time for desorption. However, there were
very limited peak area increases with the time over 7 min.
So, 7 min was optioned in subsequent experiments.
Analytical performance
In this experiment, some important quantitative parameters
of the proposed method such as linear range, correlation
coefficients, limits of detection (LODs), and relative
standard deviation (RSD) were evaluated by enriching
10 mL standard solutions, and the results were listed in
Fig. 3 Effect of sample pH equilibrium time, 40 min; NaCl, 0%;
desorption time, 5 min; spiked sample concentration, 1 μ g L−1 for
each compound. (■) α -HCH ( ) β-HCH ( ) γ-HCH ( ) δ-HCH
( ) p,p’-DDE ( ) p,p’-DDD ( ) o,p’-DDT ( ) p,p’-DDT
Fig. 4 Effect of equilibrium time. pH, 6; desorption time, 5 min;
spiked sample concentration, 1 μ g L−1 for each compound (■) α -HCH
( )β-HCH ( ) γ-HCH ( ) δ-HCH ( ) p,p’-DDE ( ) p,p’-DDD
( ) o,p’-DDT ( ) p,p’-DDT
Micro-solid phase equilibrium extraction 209
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Table 1. Calibration curves were performed using 10 mL
ultrapure water spiked with 0.1~100 μ g L−1 each of the
OCPs. Each analyte exhibited good linearity with correla-
tion coefficient ( R2)>0.99 in the studied range. The limits
of detection, calculated on the basis of signal-to-noise ratio
of 3 (S/N=3) were in the range of 0.062~0.212 μ g L−1.
The precision of analytical method was investigated usingsix replicate experiments with 10 mL standard solution
containing each of the OCPs at 1.0 μ g L−1, and the RSD of
below 10.0% was obtained.
Analysis of real water samples
To demonstrate the applicability of the TiO2 nanotube array
sheet as μ SPEE adsorbents, the proposed procedure has
been carried out on four real environmental water samples,
and the results were shown in Table 2. The results indicated
that no OCPs were found in water samples; maybe, it was
due to the limited sample volume which the too-lowconcentration of OCPs could not provide enough amount
for detection. So, these samples were then spiked with
OCPs at three different concentration levels to investigate
the effect of sample matrices. The spiked recoveries were
satisfied in the range of 78~102.8%. The typical chromato-
grams of real water sample were demonstrated (see Fig. S1,
Electronic Supplementary Material).
Comparison with SPE
In order to validate the proposed method, comparisons with
conventional solid-phase equilibrium (SPE) and dispersive
liquid-liquid microextraction (DLLME) were performed. The
four environmental water samples were preconcentrated with
SPE using C18 and TiO2 nanotubes as the adsorbents, and
their amounts were 200 and 100 mg, respectively. The
enrichment conditions were as that reported in reference
[44]. Sample volume is 50 mL. Dispersive liquid – liquid
microextraction was carried out under the conditions as
reported in [45], and the sample volume is 10 mL. Theresults (see Table S1, Electronic Supplementary Material)
Compound Linear range (μ gL−1) R2 Precision (RSD%, n=6) LOD (μ gL−1)
α -HCH 0.1 – 40 0.9947 9.12 0.10
β-HCH 0.1 – 40 0.9915 7.91 0.10
γ-HCH 0.1 – 40 0.9973 7.32 0.10
δ-HCH 0.1 – 40 0.9989 8.94 0.098
p, p’-DDE 0.1 – 100 0.9950 8.01 0.0076
p, p’-DDD 0.1 – 100 0.9951 7.00 0.0097
o, p’-DDT 0.1 – 100 0.9966 9.88 0.016
p, p’-DDT 0.1 – 100 0.9952 9.58 0.023
Table 1 Linear range, correla-
tion coefficient, precision, and
detection limits (S/N=3)
Table 2 Recoveries of real water samples spiked at three concentration levels with proposed method
Water samples Blank Added levels
(μ gL−1)
α -HCH β-HCH γ-HCH δ-HCH p, p’-DDE p, p’-DDD o, p’-DDT p, p’-DDT
Tap water ND 0.2 79.2 ±3.4 80.2 ±2.9 82.1 ±4.8 80.5 ±3.4 95.8 ±6.1 95.8 ±1.8 95.6 ±2.8 100.2 ±5.2
ND 1 78.0± 2.5 78.6±6.1 83.5±5.9 89.6± 2.9 96.2±4.3 99.8± 3.8 96.9±8.1 98.9±2.1
ND 5 88.2± 5.1 80.1±4.2 86.7±2.8 87.6± 5.6 98.6±6.1 102.5± 2.1 99.2±2.8 99.8±4.9
Snow water ND 0.2 80.1 ±1.9 82.5 ±5.4 79.8 ±2.1 88.2 ±6.2 92.8 ±2.9 98.5 ±8.1 99.8 ±2.9 99.6 ±6.4
ND 1 82.3± 5.5 83.6±2.9 82.6±5.6 86.7± 3.2 96.5±4.2 92.6± 6.1 100.2±5.2 98.5±5.3
ND 5 80.5± 3.1 80.9±2.8 81.8±5.6 89.5± 4.6 98.5±3.3 96.2± 2.8 99.8±1.8 101.5±8.1
Shouxihu Lake water ND 0.2 80.2 ± 2.3 82.3 ± 3.2 85.6 ± 4.2 88.9 ± 6.1 95.8 ± 5.2 98.2 ± 4.6 99.8 ± 5.2 99.8 ± 5.6
ND 1 79.8± 4.1 81.4±3.7 87.8±4.6 89.1± 2.9 98.6±3.2 97.8± 4.1 98.6±4.6 98.6±6.8
ND 5 81.5± 3.2 82.3±4.8 86.6±2.7 90.1± 1.9 99.4±6.2 101.2± 7.1 102.8±2.5 102.3±2.2
Xiaoshangzhuang
wastewater
ND 0.2 81.5± 2.9 81.2±3.1 80.6±5.2 82.5± 2.8 98.6±6.1 98.2± 2.6 99.8±5.1 99.8±3.8
ND 1 79.2± 3.5 80.6±5.5 79.8±7.1 83.2± 2.9 99.2±6.4 97.8± 4.1 101.2±5.2 98.9±3.7
ND 5 81.4± 2.9 80.9±3.1 81.5±4.1 85.1± 2.8 97.9±5.1 98.6± 5.2 100.1±3.7 101.2±4.2
ND not detected
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showed that the enrichment performance was different for
different target analytes, different sample matrices, and
different initial concentrations of the analytes. In contrast,
the spiked recoveries of the target analytes in wastewater and
lake water were better than that in tap water and snow water;
this was due to the high ionic strength in these two water
matrices. The detection limits of these target analytes in real
water samples (see Table S2, Electronic SupplementaryMaterial) exhibited that the sensitivity of proposed method
was the same as that of DLLME and was lower than that
obtained with C18 and TiO2 nanotubes SPE. The results were
predicted because of two reasons. One is the sample volume,
which was five times higher than that of proposed method.
This accounted for a part of the results. The other is the
different amount of the adsorbents. The effective amount of
TiO2 nanotube arrays for μ SPEE was far lower than that for
SPE. Because the TiO2 nanotube array sheet was 400 mg,
and the thickness was 200 μ m. The length of TiO2 nanotube
was about 400 – 500 nm, and there had one layer each side on
the titanium sheet. Hence, the thickness of TiO2 nanotubearrays were about 1 μ m, and the amount of TiO2 nanotube
arrays was about 0.5% of the amount of titanium sheet.
Based on the LODs in Table S2 (see S2, Electronic
Supplementary Material), we can predict that the practice
sensitivity of proposed method will be much higher than that
of SPE if the sample volume, and the amount of adsorbent
were as the same. All these results indicated that the
developed μ SPEE provided relative stable and excellent
results and was a new, robust, and good mode for the
determination of such compounds.
Conclusions
TiO2 nanotube array as a novel nanomaterial has gained
much more attention in many fields. However, its merits
have not been utilized completely. This work demonstrated
for the first time that TiO2 nanotube array could be used as
effective μ SPEE materials for the enrichment of OCPs in
four different environmental water samples. The proposed
method provided good linear range, reproducibility, and
detection limits. Based on the experimental results, a simple
and reliable determination method for OCPs was developed
based on the μ SPEE. According to the physical and
chemical properties of TiO2 nanotube array and the
different preparation method, different TiO2 nanotube
arrays with good structure would be achieved easily. It is
expected that they would have better enrichment capacity
for selected analytes. TiO2 nanotube array will give a much
higher enrichment performance with the same effective
amount of adsorbents than the established methods. TiO2
nanotube array can be potentially applied to the enrichment
and determination of many other pollutants.
Acknowledgements This work was supported by the Natural
Science Foundation of China (20877022), the Natural Science
Foundation of Henan Province (082102350022), and the Personal
Innovation Foundation of Universities in Henan Province ([2005]126).
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