A simplified fabric phase sorptive extraction method for the determination of amphetamine drugs in water samples using liquid chromatography-mass spectrometry

Article abstract of DOI:10.1039/c9ra10138a

Fabric phase sorptive extraction (FPSE) can directly extract the target analytes and simultaneously determine many similar substances from complicated sample matrices. Also, it has very high chemical stability. Therefore, we used fabric phase sorptive extraction to analyze three amphetamine drugs (amphetamine (AM), methamphetamine (MAM), and 3,4-methylenedioxymethamphetamine (MDMA)) in water. This was coupled with ultrahigh-performance liquid chromatography and tandem mass spectrometry. The effects of different sorbent chemistries such as sorption time, ratios of back-extraction solvents, back-extraction time, and the salt effect on the extraction efficiency were studied; the optimum operation conditions were determined. Medium polarity polar polymer-coated FPSE media were created using short-chain poly (tetrahydrofuran) (PTHF). This is the most efficient extraction media for the analytes of interest. Under the optimized conditions, the linear range of the three amphetamine drugs were 0.1-150.0 (AM, MAM) and 0.5-200 ng mL^-1 (MDMA). The correlation coefficients (γ) were 0.9947 (AM), 0.9925 (MAM), and 0.9918 (MDMA). The detection limits (LOD) were 0.025 ng mL^-1 for AM, 0.029 ng mL^-1 for MAM, and 0.01 ng mL^-1 for MDMA. The corresponding limit of quantification values (LOQ) were 0.083 ng mL^-1, 0.097 ng mL^-1, and 0.031 ng mL^-1, respectively. The recoveries were 73.4-91.6%, 82.6-95.4%, and 92.7-95.3%, respectively, and the relative standard deviations (RSD) were 1.65-6.88%, 1.38-6.11%, and 1.58-7.34%, respectively. Moreover, our method can be successfully applied for the analysis of amphetamines in wastewater samples, and at the same time, lays the foundation for the future detection of such substances.

Full text of DOI:10.1039/c9ra10138a

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A simplified fabric phase sorptive extraction
method for the determination of amphetamine
drugs in water samples using liquid
Cite this: RSC Adv., 2020, 10, 10854
chromatography-mass spectrometry
*
Xiaomeng Ruan, Limei Xing,
Ju Peng, Shiying Li, Yiqun Song and Qianqian Sun
Fabric phase sorptive extraction (FPSE) can directly extract the target analytes and simultaneously
determine many similar substances from complicated sample matrices. Also, it has very high chemical
stability. Therefore, we used fabric phase sorptive extraction to analyze three amphetamine drugs
(amphetamine (AM), methamphetamine (MAM), and 3,4-methylenedioxymethamphetamine (MDMA)) in
water. This was coupled with ultrahigh-performance liquid chromatography and tandem mass
spectrometry. The effects of different sorbent chemistries such as sorption time, ratios of back-
extraction solvents, back-extraction time, and the salt effect on the extraction efficiency were studied;
the optimum operation conditions were determined. Medium polarity polar polymer-coated FPSE media
were created using short-chain poly (tetrahydrofuran) (PTHF). This is the most efficient extraction media
for the analytes of interest. Under the optimized conditions, the linear range of the three amphetamine
drugs were 0.1–150.0 (AM, MAM) and 0.5–200 ng mLꢀ1 (MDMA). The correlation coefficients (g) were
0.9947 (AM), 0.9925 (MAM), and 0.9918 (MDMA). The detection limits (LOD) were 0.025 ng mLꢀ1 for AM,
0.029 ng mLꢀ1 for MAM, and 0.01 ng mLꢀ1 for MDMA. The corresponding limit of quantification values
(LOQ) were 0.083 ng mLꢀ1, 0.097 ng mLꢀ1, and 0.031 ng mLꢀ1, respectively. The recoveries were 73.4–
91.6%, 82.6–95.4%, and 92.7–95.3%, respectively, and the relative standard deviations (RSD) were 1.65–
6.88%, 1.38–6.11%, and 1.58–7.34%, respectively. Moreover, our method can be successfully applied for
the analysis of amphetamines in wastewater samples, and at the same time, lays the foundation for the
future detection of such substances.
Received 4th December 2019
Accepted 3rd February 2020
DOI: 10.1039/c9ra10138a
rsc.li/rsc-advances
signicance for the timely and effective planning of anti-drug
work. The Sewage Analysis Act was rst proposed by the
American scholar Daughton CG5 in 2001 and was rst imple-
1. Introduction
At present, the abuse of narcotic drugs and psychotropic
substances, and drug crimes worldwide are serious threats to
human health and social stability, and present other global
hazards.1,2 As drug abuse has become increasingly serious,
illegal addition and the loss of various psychotropic drugs have
become increasingly threatening to social stability. It has been
reported that the drug abuse rate in South Korea and China has
steadily increased since the 1980s. Amphetamines are common
synthetic addiction agents in Iran, Taiwan, and even the United
States, and are, thus, a cause of great concern.3 In 2015, about
2.1 million young people around the world used “ecstasy” and
1.3 million people used amphetamine (AM) and methamphet-
amine (MAM). The 2016 World Drug Report showed that
amphetamine drug consumption is on the rise, and it is the
second largest illegal drug.4 Therefore, mastering the patterns,
extents, types, and other information of drug abuse is of great
mented in 2005 by Zuccato et al. in Italy. The method, based on
human drug abuse, is discharged through the body's metabolic
pathways and enters the urban sewage treatment system. By
monitoring the concentration of drugs and metabolites in
sewage combined with the population of the service area and
the ow rate of the sewage treatment plant, drug abuse in the
service area is evaluated. In 2016, Been Fred et al. evaluated the
differences in drug abuse in different regions by collecting
samples from 19 sewage treatment plants in Germany and
Switzerland.6 In 2016, Thai PK and other methods used sewage
analysis to detect the use of 4-methylmethacinone and 2-
methylamino-1-(3,4-methylenedioxyphenyl)-1-propanone
in
Queensland, Australia.7 Therefore, it is of practical signicance
to detect amphetamine drugs in sewage.
A large number of literature reports have been published on
various instrumental methods for measuring such compounds in
biological samples and water samples for successfully analyzing
drug samples; the methods include gas chromatography-mass
Criminal Investigation Police University of China, China. E-mail: xinglimei1@sina.
com; Tel: +86 13898164819
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spectrometry (GC-MS),8–11 capillary electrophoresis (CE),12–14 and transfer coefficient increases with the pores of the medium,28 so
liquid chromatography-mass spectrometry (HPLC-MS).15–17 GC- the extraction can reach equilibrium quickly. FPSE is a simple
MS is oen used because of its sensitivity. However, samples sample pretreatment technique that consists of two main steps:
oen require derivatization and higher costs limit their use. (1) adsorption of the target substance: the sample is in contact
Therefore, LC-MS is now widely used for analyzing various trace with the FPSE medium and the analytical substance is retained
small molecules in biological matrices and water samples. on the adsorbent; (2) desorption of the target: the FPSE medium
Compared to GC, LC-MS does not require derivatization and can (in which the target is adsorbed) is fully immersed in the
be used for analyzing non-volatile or semi-volatile compounds.
organic solvent and the target analyte is back-extracted into the
Although the indexes and functions of modern analytical organic solvent.
instruments are improving day by day, such aspects are not
In addition, the medium can use a large number of different
suitable for direct use in detection instruments for complex adsorbent types, including sol–gel polydimethylsiloxane
samples in the original state; trace target analysis materials (PDMS), sol–gel polydimethyldiphenylsiloxane (PDMDPS), sol–
must be extracted and separated via sample pretreatment gel polydiphenylsiloxane, sol–gel C18, sol–gel C8, sol–gel gra-
methods because of the complex composition and low content phene, sol–gel polytetrahydrofuran (PTHF), sol–gel poly-
of target analyte materials. It is only aer enrichment and ethylene glycol (PEG), sol–gel carbowax 20M, and sol–gel
purication that trace target analysis can be carried out using polyethylene glycol–polyethylene glycol–polyethylene glycol
instrument detection and analysis. Therefore, sample pre- (PEG–PEG–PEG),27 thereby adsorbing compounds of different
processing is very important for analysis and testing in instru- polarities.
mental analysis. Sample pre-processing is related to the integ-
In the sample preparation process, the FPSE medium of the
rity of the evidence chain of an entire case and plays an adsorbed target can be directly introduced into the container
important role in the nal determination of criminal facts. with the stripping agent and then, the stripping agent is
Therefore, sample pretreatment is the research content to introduced into GC/LC-MS or another analytical instrument
which every worker in the eld of forensic science attaches great using a syringe. Thus, FPSE is a simpler process as the number
importance for a tribunal.
of sample processing preparation steps further reduces the
Sample preparation is oen required before instrumental potential risks of analyte loss and experimental error. FPSE has
analysis. Solid phase extraction (SPE),12,18 solid phase micro- a large contact surface area and can quickly adsorb the target
extraction (SPME),19,20 and liquid–liquid extraction (LLE)20,21 are analytes. Because of the low viscosity of the organic solvent that
traditional technologies and are currently widely used as is used, it is usually possible to extract the target analyte in 2–
pretreatment techniques. Two of these techniques are currently 10 min and less organic solvent is required. Thus, the target
used for analyzing amphetamines but all the three technologies analyte can be back-extracted from the FPSE medium faster and
have certain limitations. SPE requires small particle size lters without potential residual risk. In addition, any organic solvent
to prevent clogging of the adsorbent carrier, and this requires can be used for the reverse-extraction of target analysis and
a long time and consumes a large amount of organic solvents in strong chemical bonding between the adsorbent and the fabric
the process of resolution.22 In contrast, SPME has a lower cost matrix allow the fabric phase to be exposed to any selected
but the sorbent loading is low and extraction equilibrium time organic solvent and to harsh chemical conditions (high acid–
is relatively long. The adsorbent-coated extraction head in base).29
SPME equipment may be bent or damaged during operation,
The advantages of FPSE are as follows: (1) the operation is
resulting in decreased performance with aging.23 Also, the simple, the device is cheap, adsorption is fast, and the solvent
number of commercially available sorbent coatings is limited in content is low. (2) the fabric phase can be directly introduced
SPME; instability of the coating layer in organic solvents, into the sample and the original sample can be absorbed by the
swelling, fracture, and other factors greatly limit the application target substance. (3) Any organic solvent can be chosen for
of SPME in instrumental analysis.24 LLE also has some short- elution. (4) There are fewer sample processing steps, which
comings. For example, most of the organic solvents used are thereby reduces the potential sources of errors and the cost of
toxic and easily emulsify, which prolongs the extraction cycle sample preparation. (5) Hundreds of new sol–gel coatings can
and causes sample loss.25
be used as adsorbents. (6) The chemical bond between the
As early as the 1990s, Malik et al. developed a sol–gel coating adsorbent and the fabric matrix provides high chemical
technique for the microextraction of adsorbents to extract stability of the fabric phase.22
complex microsamples.26 In 2014, Kabir and Furton used this
This technique is used to test amphetamine drugs in water
technology to develop a new sample extraction technology samples, including AM, MAM, and 3,4-methylenediox-
called fabric phase sorptive extraction (FPSE).27 FPSE is an ymethamphetamine (MDMA). Table 1 shows the chemical
adsorption extraction technique that uses a sol–gel coating structures and basic properties of these three drugs. Drugs such
technique to form an ultra-thin coating on a natural or synthetic as amphetamine have been included in the scope of illicit drugs
fabric and then uniformly coats the fabric substrate. Aer the but because of illegal and prevalent drug abuse, illegal drug
sol–gel adsorbent coating is applied, the permeability of the trafficking, new drug abuse, and various drug criminal activities
substrate remains unchanged and this ensures the uidity of involving amphetamines, the concentration of amphetamines
the sample solution in the extraction system as the point of in the environment has reached a very serious level, even in
adsorbent on the coating surface is limited and the mass sewage and wastewater. A certain number of drugs can be
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Table 1 Chemical structures of the amphetamine drugs
Compound
Abbreviation
Chemical structure
pKa
log KOW
Amphetamine
AM
9.8
1.79
Methamphetamine
MAM
9.5
9.9
2.27
2.75
3,4-Methylenedioxymethamphetamine
MDMA
detected30 and thus, the accurate, simple, and rapid detection of Dual-Frequency Numerical Control Ultrasonic Cleaner (Kun-
amphetamines using scientic means is of great signicance shan Ultrasonic Instrument Co., Ltd.), an HJ-3 Digital Display
for combating drug abuse and maintaining social stability. In Thermostatic Magnetic Stirrer (Gongyi Yuhua Instrument Co.,
addition, a variety of microextraction methods for determining Ltd.), and a PH-10/100 pen-type acidity meter (Shanghai Lichen
amphetamines drugs have been published in the literature and Bangxi Instrument Technology Co., Ltd.). Also, 100 and 1000 mL
most of these are based on adsorbent-based microextraction pipettes (Gilson, United States) and a 10 mL liquid chromatog-
techniques such as SPE, SPME, and LLE (as mentioned above). raphy micro sampler (Shanghai, China, Pigeon) were used.
Therefore, compared to conventional sample preparation
techniques, two new FPSE media were selected for this experi-
ment: sol–gel polytetrahydrofuran (sol–gel PTHF) and sol–gel
polyethyleneglycol (sol–gel PEG). These media were evaluated in
the extraction process of amphetamines in water samples.
2.3. Preparation of standards
The stock standard solution (1 mg mLꢀ1) was prepared in
methanol. The stock solution was used within 3 months of
preparation, was stored at low temperature (ꢀ4 ꢁC), and was
protected from light. Working standard solutions were
prepared by further dilutions of the stock solution to obtain
varying concentrations. The dilutions were made using distilled
water over the entire linear range and were freshly prepared at
the time of use. The concentrations of the working standards
ranged from 0.5 to 200 ng mLꢀ1. Aliquots of 10 mL were injected
into the LC-MS column and quantitative analysis was based on
peak area ratio measurements.
2. Experimental
2.1. Chemicals and materials
AM, MAM, and MDMA were purchased from the China Food
and Drug Testing Institute. Make a storage solution of 1 mg
mꢁlꢀ1 with methanol and store the sample in a refrigerator at
4 C.
Methyltrimethoxysilane (purity 98%), polyethylene (average
molecular weight 200), and polytetrahydrofuran (average
molecular weight 850) were purchased from Shanghai Aladdin
Biochemical Technology Co., Ltd. Triuoroacetic acid was
purchased from Tianjin Kemi European Chemical Reagent and
cotton fabric was purchased from Guangzhou Airou Non-woven
Fabrics Co., Ltd.
Methanol, acetonitrile, and acetone were chromatographi-
cally pure and were purchased from Shandong Yuwang Indus-
trial Co., Ltd. Dichloromethane was chromatographically pure
and was purchased from Tianjin Fuyu Fine Chemical Co., Ltd.
Hydrochloric acid, NaOH, and NaCl were analytical reagent
grade and were purchased from Beijing Chemical Plant. The
experimentally used water was deionized water and the blank
water sample was distilled water.
2.4. Chromatography and mass spectrometry
The samples were separated and detected using high-
performance liquid chromatography (equipped with a diode
array detector (DAD)). A Thermo Gold ODS (150 mm ꢂ 2.1 mm
ꢂ 5 mm) was used separately and the column heater remained at
35 ꢁC. The mobile phase was a solution of methanol : 0.1%
acetic acid (80 : 20, v/v) and the ow rate was 0.200 mL minꢀ1
.
For the mass spectroscopic measurements, an electrospray
ionization source (ESI), positive ion mode detection, full ion
scanning mode (50–500 m/z), and a capillary temperature of
350 ꢁC were used. The atomized gas, heating auxiliary gas, and
purge gas ow rates were 33.00, 8.00, and 2.00 L minꢀ1
,
respectively. The source voltage was 5.00 kV.
2.2. Instrumentation
2.5. Fabric phase sorptive extraction sample preparation
process
The instruments used were a Finnigan Surveyor liquid chro-
matograph with an electrospray ion source, an LXQ linear ion The substrate selection for the sol–gel coating depends
trap mass spectrometer (Thermo Fisher, USA), a KQ-200VDE primarily on: (a) the hydrophilicity or hydrophobicity of the
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target analyte and (b) the strategy for analyte stripping aer
preconcentration onto the FPSE media.31 This experiment
used solvent back extraction, which is known to be hydro-
philic, so the fabric substrate selected was cellulose.
The fabric was pretreated before it was coated with the
sorbent to remove residues of external dirt, particulates, and
fabric nishing chemicals, and to activate the surface hydroxyl
groups. First, the fabric was soaked in a large amount of
deionized water for 15 min and the clean fabric was then placed
in a 1 M NaOH solution for 1 h under sonication to activate the
silanol groups on the fabric surface. The base treated fabric was
then washed several times with a large amount of deionized
water. It was then treated with 0.1 M HCl solution for 1 h under
sonication to neutralize the hydroxides on the surface. The
treated fabric was then rinsed with a copious amount of
deionized water and nally placed in a clean beaker with
tweezers and dried overnight in a stream of inert gas at a proper
temperature. The dried fabrics are were kept in a clean, sealed
bottle until the next day.
A coating layer was prepared using a sol–gel method. Briey,
10 mL of polytetrahydrofuran, 10 mL of sol–gel precursor
methyltrimethoxysilane (MTMS), and 20 mL of dichlor-
omethane : acetone (v : v ¼ 50 : 50) were added sequentially to
a beaker. Then, 4 mL of triuoroacetic acid (containing 5%
water) was added as the sol–gel catalyst. The mixture was stirred
well and then vortexed for 3 min, centrifuged for 5 min, and
ultrasonicated for 2 min. The treated sol–gel solution was
transferred to a brown glass bottle.
The pretreated fabrics were immersed in a sol–gel solution
and the solution was le for a certain period of time to form
the sol–gel coating on the fabrics. The coating was removed
and rinsed with dichloromethane : acetone (50 : 50, v/v)
under ultrasonication for 30 min to remove the unreacted
contents. When the coating cycle was complete, the solution
was discharged from the bottle and the remaining contents of
the bottle were then piped into another bottle, which was
sealed. A small hole was made during the sealing process to
allow nitrogen to circulate and the bottle was placed in an
oven. The oven was kept at 40 ꢁC for 12 h. The oven was then
closed for 12 ꢁh and kept at room temperature. Then, it was
opened at 60 C for 12 h. The temperature was then adjusted
to 50 ꢁC and held for 12 h at a constant temperature. The
coated fabric was extracted using dichloromethane and
acetone (50 : 50, v/v) sequentially. Before extraction using
fabric phase adsorption, the fabric was rinsed with ultrasonic
treatment for 30 min to remove non-reactive substances and
residual sol–gel solutions from the coated surfaces. The fabric
was then dried at 50 ꢁC and stored in an inert atmosphere for
1 h. Finally, the coated fabric was cut into pieces that were
Fig. 1 Scheme for describing FPSE.
2.6. FPSE procedure
A 10 mL sample containing 5 ng mLꢀ1 target analyte was prepared.
The pH of the solution was adjusted and then the sample was
placed in a vial. The treated sol–gel polytetrahydrofuran-coated
FPSE medium was placed in the vial using a tweezer (Fig. 1),
and the sample solution was stirred at 1500 rpm and heated at
38 ꢁC to extract the target analyte therein. Aer 60 min, the FPSE
was removed from the vial, immersed in 1 mL of the elution
solvent, and le to stand for a while. It was then sonicated for 8
minutes and a clear solution was obtained. The concentrated
solution was ltered and 10 mL of the ltered solution was injected
into a high-performance liquid chromatograph-mass spectrom-
eter, which was used for detection.
2.7. Method validation
The effectiveness of the method was veried in terms of line-
arity and precision. The data was assessed using least squares
linear regression analysis over the working range. The formula
S/N ¼ 3 was used to calculate the limit of detection (LOD) and
the formula S/N ¼ 10 was used to calculate the limit of quan-
titation (LOQ) (in each of these equations, S ¼ is the signal
and N ¼ is the noise). The relative standard deviation (RSD%) of
repeated measurements was calculated to assess the precision
of this method and the concentrations of different standard
amphetamines were analyzed to determine the accuracy.
3. Results and discussion
3.1. Chemistry of the substrate and sol–gel PTHF coating
2.0 cm ꢂ 2.0 cm and the pieces were stored in a closed glass Currently, many adsorbents use different porous substrates as
container to prevent contamination. Compared with a blank the support because the fabrics themselves are porous substrates.
ber (0.0197 g) of the same size, the FPSE weighed 0.0501 g Also, there are many sol–gel reactive functional groups on the
and the sorbent loading per device was 0.0076 g cmꢀ2. The surface of the fabrics and thus, the sol–gel solution can be rmly
same method was used to prepare the sol–gel polyethylene coated on the fabrics. Kabir and coworkers developed micro-
glycol coating.
extraction sorbents that use fabrics as the matrix.32 In just a few
years, hundreds of kinds of sol–gel solutions with different uses
have been reported.
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Fig. 2 Schematic diagram of (a) sol–gel PTHF and (b) sol–gel PTHF-coated FPSE media.
The preparation of sol–gel polytetrahydrofuran (PTHF) incorporation of the sol–gel PTHF to the sol–gel network, and
coatings on the fabrics involves the following reactions: chemical xation of the grown sol–gel network to the exible
hydrolysis of sol–gel precursors catalyzed by MTMS, polymeri- cellulose substrate via condensation. The sol–gel PTHF can be
zation of MTMS aer hydrolysis (resulting in the formation of coated on the fabrics via chemical bonding.
a three-dimensional sol–gel network on the fabrics), random
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Fig. 3 SEM images of (a) uncoated substrate surface at 320ꢂ magnification and of (b) coated substrate surface at 300ꢂ magnification.
During the polycondensation process, the grown sol–gel coating is not limited to the surface of the cellulose substrate; it
PTHF network reacts with hydroxyl groups on the surface of the also occurs in the three-dimensional matrix. The sol–gel coating
fabrics and this results in a covalently bonded sol–gel poly- does not block the pores and this allows the sample matrix to
tetrahydrofuran coating that is uniformly distributed penetrate through the body, and such a structure helps to
throughout the fabric. The coating is chemically stable, and has complete the feature extraction balance in a short period of
good selectivity for efficient and fast analyte extraction. The time.
chemical representation of the sol–gel PTHF coated cellulose
substrate reaction scheme is shown in Fig. 2.
3.2.2. FT-IR spectroscopy. In infrared spectroscopy, a beam
of infrared light that has a continuous wavelength is trans-
mitted through the molecules of a substance. When the vibra-
tional frequency of a certain functional group in the molecules
of a particular substance is the same as the frequency of the
infrared light and a vibrational dipole moment occurs, the
vibrational level of the molecules is activated. The transition of
this energy level results in a molecular spectrum.
3.2. Characterization of sol–gel PTHF-coated FPSE media
Scanning electron microscopy (SEM) and Fourier transform-
infrared spectroscopy (FT-IR) were used to characterize the
sol–gel short-chain polytetrahydrofuran-coated FPSE medium.
The surface morphology of the sol–gel tetrahydrofuran network
and chemical integration of the fabric substrate were studied
using these methods.
In this experiment, we used FT-IR to analyze the structural
changes in the FPSE medium before and aer coating. For these
tests, the sample tested was placed directly on the OMNIC
sampler germanium crystal and the spectrum was scanned in
3.2.1. SEM. Scanning electron microscopy uses a very ne
electron beam to scan a sample and to excite secondary elec-
trons on the surface of the sample. The secondary electrons are
then collected by the detector and converted into an optical
signal. A photomultiplier tube and an amplier are used to then
convert this signal into an electrical signal. Thus, a scanned
image is synchronized with the electron beam and is displayed
on the screen. Because the generation of secondary electrons is
related to the surface structure of the sample, a scanning elec-
tron microscope can be used to observe the morphological
characteristics of the particles on the fabric. Fig. 3a shows
a scanning electron micrograph at 320ꢂ magnication of the
uncoated surface of a cellulosic textile substrate and Fig. 3b
shows a micrograph at 300ꢂ magnication of the sol-poly PTHF
coated FPSE medium surface.
As seen in these SEM images, each of the fabrics is composed
of many microfabrics and is designed from macroscopic pores
that are generated during the weaving process. Because the low
viscosity sol solution enters the fabric matrix, a sol–gel PTHF-
coated ultrathin lm is uniformly formed on the surface of
the cellulose microfabric. Therefore, as seen from the SEM
image of the sol–gel PTHF-coated extraction medium, the
the range of 4000–500 cmꢀ1
.
Fig. 4 depicts the FT-IR spectra of an uncoated cellulose
substrate (top) and a sol–gel polytetrahydrofuran-coated FPSE
medium (bottom). The FT-IR spectra of uncoated cellulose
fabrics show characteristic absorptions between 3343 cmꢀ1
,
2900 cmꢀ1, and 1428 cmꢀ1. The characteristic absorptions of
–OH association, –CH2 symmetry extension, and –CH2 defor-
mation vibrations are observed. The characteristic absorptions
of C–O stretching and C–H bending vibrations were also
observed at 1107 cmꢀ1, 1056 cmꢀ1, and 1033 cmꢀ1. Because of
the functional groups of polytetrauoroethylene combined
with the –OH groups on the fabric, there are, therefore, no
characteristic bands for the sol–gel polytetrauoroethylene
coating at about 3000 cmꢀ1, 2942 cmꢀ1, and 2864 cmꢀ1 (cor-
responding to –CH2 antisymmetric scaling), at 2805 cmꢀ1 and
2334 cmꢀ1 (both corresponding to –CH2 symmetric scaling), or
–CH2 at 1491 cmꢀ1, 1373 cmꢀ1, and 1270 cmꢀ1 (corresponding
to deformation vibrations). These observations strongly
suggest the presence of sol–gel PTHF coatings.33 The sol–gel-
polytetrahydrofuran-coated FPSE medium has clean bands in
the FT-IR spectrum at 1107 cmꢀ1 and 1029 cmꢀ1, and these
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Fig. 4 FT-IR spectra of uncoated cellulose substrate (top) and sol–gel poly-THF coated FPSE medium (bottom).
indicate SiO–C–C bonding, which may be derived from the affect the efficiency of the method. These parameters include
sol–gel PTHF network and cellulose in the successful combi- the extraction time, back-extraction solvent, back-extraction
nation of substrates.34
time, and the salt effect. The maximum value of peak area
was used to evaluate the extraction efficiency of amphetamines
in the water samples. Each factor was assessed three times and
all of the experiments were performed at 1500 rpm with
stirring.35
3.3. Optimization of FPSE conditions
Developing methods for the determination of amphetamines
using FPSE-LC-MS requires the optimization of parameters that
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increases and becomes almost constant at 60 min. Thus, an
extraction time of 60 min was selected as the optimized exper-
imental condition for further experiments.
3.3.3. Optimization of pH. Adjusting the pH of an aqueous
drug solution can change the morphology of the target drug in
water. Amphetamines contain amino groups and thus, they are
alkaline drugs. In acidic conditions, they are mainly in the form
of ions and in alkaline conditions, they are mainly in the
molecular form; this is more conducive for their retention on
non-polar adsorbents. This section examines the effect of buffer
solutions with pH values in the range of 9–12 on the adsorption
of FPSE. In this experiment, a buffer solution with pH 11.0 was
selected to adjust the pH of the aqueous drug solution and then
the FPSE operation was performed.
Fig. 5 Effects of extraction time.
3.3.4. Optimization of back-extraction solvent. Different
solvents and different solvent ratios were used to reversely
extract the analytical substance in a FPSE medium. In this
research, it was found that mixed solvents have better perfor-
mance than their pure counterparts. Methanol and acetonitrile
solvents were mixed to obtain a homogeneous single-phase
solvent system, which had a good effect on the elution of the
target analyte (Fig. 6). Since the mixed solvent can better exert
the solubility characteristics of methanol and acetonitrile,
amphetamine originally dissolved in methanol was easily dis-
solved. The best ratio for the back-extraction solvents is aceto-
nitrile : methanol ¼ 3 : 7. The volume of the extracted solvent
was xed at 1.0 mL for all further experiments.
3.3.5. Optimization of back-extraction time. The back-
extraction time was optimized by placing the FPSE medium in
a mixture of acetonitrile : methanol (in the ratio of 3 : 7) for 4 to
12 min. The largest number of amphetamine-type drugs can be
laundered in 8 min (Fig. 7). Therefore, a back-extraction time of
8 min was optimal and was used for further experimentation.
3.3.6. Effects of added salt. Studies have shown that ionic
strength is an important parameter in these kinds of experi-
ments. For compounds with log KOW < 3, ionic strength can have
3.3.1. Effects of the type of fabric phase. In the existing
literature, it has been reported that static FPSE techniques have
been used to extract contaminants from environmental water
samples. In that study, information about the following FPSE
media coated with different polar sorbents was reported: non-
polar sol–gel PDMDPS, medium polar sol–gel PTHF, and polar
sol–gel PEG.35
Because of the polarity of amphetamine drugs, we chose sol–
gel PTHF and sol–gel PEG as the coating layers. We determined
from our experiment that sol–gel PTHF provides a high recovery
rate for the analyte. Therefore, the sol–gel PTHF-coated fabric
phase was selected as the optimized experimental operation.
3.3.2. Optimization of extraction time. The amount of
analyte of interest that was adsorbed in the FPSE medium is
related to three things: (1) the distribution constant between the
fabric and the solution, (2) the surface area of the adsorbed
phase, and (3) the diffusion coefficient of the target analyte.
These parameters are different for different target analytes and
the analyte reaches equilibrium at a certain time. This experi-
ment was performed with extraction times in the range from 30
to 120 min. As seen from Fig. 5, when the extraction time
increases, the extraction of target analytes into the FPSE fabric
Fig. 6 Effects of elution solvent ratio.
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Fig. 7 Effects of back extraction time.
a great impact on extraction.35–38 Therefore, salt effect can facili- at 3 : 7 as the back-extraction solvent. The enrichment factor
tate the movement of a target analyte in the PTHF direction. achieved using these conditions was more than 10.
Different amounts of NaCl were added to the aqueous solution to
analyze the effects of the analyte on the adsorption of the FPSE
media. The concentrations of NaCl in the aqueous solution
varied from 0% to 3% (w/v). However, the recovery value changed
sharply with the adsorption characteristics when NaCl was
3.4. Matrix effects
Since the matrix oen signicantly interferes with the analysis
of analytes and affects the accuracy of the results, it is necessary
to determine the matrix effect of amphetamine drugs in urban
added. Other authors have reported in the related literature that
river water. Matrix effects are considered to be suitable in the
ionic strength does not improve efficiency.19,38 Some scholars
range from 80% to 120% because they indicate that the matrix
have explained that this is because NaCl helps to move analytes
effects in this experiment are small. Standard solutions of the
to the surface of water and this makes their interaction with the
three amphetamine drugs were measured and the peak area of
fabric PTHF weaker.19 Also, higher NaCl content may increase
each analyte was recorded as A. Water samples from different
sources were processed by FPSE, then the standard analytes
electrostatic interaction between the analyte and salt ions, which
can also reduce the extraction efficiency. Because NaCl can have
a negative impact on the extraction efficiency, we chose not to
add NaCl in our experiment.
In summary, the employed conditions for the FPSE procedure
were as follows: 60 min of extraction time, no added salt, pH 11,
back-extraction time of 8 min, and 1 mL of acetonitrile : methanol
were added, and the peak area for each analyte was recorded as
B. Matrix effect (ME%) ¼ A/B ꢂ 100%.39 The results show that
the matrix effect values of AM, MAM, and MDMA are between
0.8872 and 1.2041 in the selected municipal wastewater; thus,
matrix effects are not signicant.
3.5. Method validation
A blank water sample was tested as described above. Secondary
ion chromatograms of 5 ng mLꢀ1 AM, MAM, and MDMA
Table 2 Recoveries and RSD of amphetamine drugs from aqueous
samples
Concentration
Recovery
(%, n ¼ 5)
RSD
(%, n ¼ 5)
Analyte
(ng mLꢀ1
)
Amphetamine
5
73.4
92.3
91.6
82.6
89.5
95.4
92.7
94.7
95.3
6.88
5.30
1.65
6.11
4.97
1.38
7.34
6.32
1.58
50
150
5
50
150
5
Methamphetamine
3,4-Methylenedioxy-
methamphetamine
50
150
Fig. 8 The chromatographic behavior of AM, MAM, MDMA after FPSE
(from top to bottom).
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Table 3 Mean linear calibration curve parameters determined using weighted-linear least-squares regression analysis of five independent
calibrations in water samples
Analyte
Regression equation
Linear range (ng mLꢀ1
)
R2
LOD (ng mLꢀ1
)
LOQ (ng mLꢀ1
)
AM
MAM
MDMA
Y ¼ 283X + 29.123
0.1–150.0
0.1–150.0
0.5–150.0
0.9986
0.9925
0.9918
0.025
0.029
0.010
0.083
0.097
0.031
Y ¼ 1244.6X + 204.36
Y ¼ 1763.2X + 291.16
Table 4 Analytical performance data of different other methods
Sample preparation
methoda
Analytical
instrument
Analytes
Matrix
LOD
0.31–4.29 ng mLꢀ1
LOQ
Reference
AM and its
derivates
AM
MAM
MDMA
MDA
Urine
SPE
CE-MS
GC-MS
1.00–13.98 ng mLꢀ1
13
19
Water urine
SPME
0.4–2 ng Lꢀ1
,
10.4–6.8 ng Lꢀ1
0.3–0.6 ng Lꢀ1
,
0.09–0.2 ng Lꢀ1
MDEA
AM
Saliva
LPE
GC-MS
1–5 mg Lꢀ1
10 mg Lꢀ1
21
MAM
MDMA
MDA
AM
AM
Oral uid
Water
MIP
FPSE
UHPLC-MS
LC-MS
0.03–1.3 mg Lꢀ1
—
40
0.01–0.025 ng mLꢀ1
0.031–0.083 ng mLꢀ1
This work
MAM
MDMA
a
SPE: solid phase extraction; SPME: solid phase microextraction; LPE: liquid phase extraction; MIP: molecular imprinting.
solutions were compared to examine the effects of matrix was performed to determine the regression equation. From the
components on the test. The parent ion of MAM is m/z 150 and tting results (Table 3), the linear range for the quantitative
the secondary ion is m/z 119. The parent ion of AM is m/z 136 analysis of AM and MAM in water is 0.1–150.0 ng mLꢀ1 and that
and the secondary ion is m/z 119. The parent ion of MDMA is m/ for the quantitative analysis of MDMA is 0.5–200.0 ng mLꢀ1
.
z 194 and the secondary ion of m/z 163. Aer treatment with The linear equation correlation coefficients (g) are higher than
FPSE, each of the drugs (AM, MAM, and MDMA) have good 0.99. This shows that the working curves for the three
chromatographic behavior, the peak shape is symmetrical amphetamine drugs in water that were established using this
(Fig. 8), and the matrix impurities in the water sample do not method have a good linear relationship within the concentra-
interfere with the determinations made using the optimized tion range studied.
conditions.
The LODs of the three drugs were calculated using a S/N ratio
The samples were spiked with standard solutions of different of 3. Similarly, the LOQs were estimated as the S/N ratio of 10 (S/
concentrations of three amphetamine drugs, and the relative N ¼ 10, n ¼ 5). Also, as seen in Table 3, the LODs for AM, MAM,
recoveries and precisions of the same measured object in and MDMA in water were 0.025, 0.029, and 0.01 ng mLꢀ1
parallel at 5 different time points in a day were calculated. The respectively. The LOQs were 0.083, 0.097, and 0.031 ng mLꢀ1
results are shown in Table 2 for the adsorption and extraction respectively.
,
,
efficiency and the stability of the test method. The recoveries of
AM, MAM, and MDMA in the water samples were all higher than
70% when FPSE was used with the optimized experimental
conditions. The relative standard deviation is less than 10% and
this indicates that the method is reliable for the quantitative
analysis of three drugs.
The optimized FPSE-LC-MS conditions that were established
above were used to prepare calibration curves for the analytes
spiked with the concentrations of 0.5, 1.0, 2.0, 5.0, 10.0, 15.0,
20.0, 40.0, 50.0, 100.0, 150.0, and 200.0 ng mLꢀ1. Using the
experimental method described above, the values of peak area
were plotted versus drug concentration and linear regression
3.6. Method comparison
In terms of the LOD and LOQ values, the newly developed and
validated FPSE-LC-MS method was used to compare the detec-
tion of amphetamine drugs with other reported methods. The
comparative data are listed in Table 4. In these existing studies,
component extraction was performed by conventional extrac-
tion techniques, such as SPE and SPME. The LOD and LOQ of
amphetamine drugs in this study are basically higher than
those reported in these literatures. Only one paper has lower
data than the procedure of this study but SPME has some
disadvantages (see Introduction). Therefore, the FPSE-LC-MS
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program selected in this study does not require complicated
On the basis of this research, it can provide the basis for the
equipment conguration, and the obtained LOD and LOQ detection of other sample types (such as urine, blood, hair,
values are low.
saliva, and other biological samples) using FPSE-LC-MS,
thereby establishing a more efficient and applicable sample
pretreatment method. Additionally, GC, GC-MS, HPLC-MS, and
other analytical instruments were used to examine the drug-
4. Application to sewage samples
To further evaluate the method's applicability, real water detecting effect of the biological samples that were pretreated
samples were also used. The FPSE-LC-MS method was applied with FPSE; thus, the application range of FPSE was expanded. In
to 100 mL of non-spiked wastewater samples to measure three future, research will have the challenge to develop new coatings
of the studied analytes. The water samples were taken from and materials to determine any analytes in complex sample
municipal sewage outlets of Xinkaihe River in Huanggu matrices.
District and from Weigong Nullah in Tiexi District (City in
northern China). The measured concentration for AM in the
Xinkai River water sample was 123.2 ng Lꢀ1, that for MAM was
169.6 ng Lꢀ1, and that for MDMA was 72.5 ng Lꢀ1. Although
AM and MAM were not detected in the Weigong open channel
water sample, where the concentration for MDMA was
Conflicts of interest
We declare that we do not have any commercial or associative
interest that represents a conict of interest in connection with
the work submitted.
63.4 ng Lꢀ1
.
5. Conclusions
References
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and efforts are being made to develop more efficient and
selective methods for sample preparation. Conventional
pretreatment methods are gradually being replaced by micro-
extraction techniques to reduce the volume of sample and
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