Electrochemically deposited conductive composite sorbent
for highly efficient online solid-phase microextraction of
jasmonates in plant samples
Xu Linga,b, Zilin Chen *a,b
aKey Laboratory of Combinatorial Biosynthesis and Drug Discovery (Wuhan
University), Ministry of Education, and Wuhan University School of Pharmaceutical
Science, Wuhan 430071, ChinabState Key Laboratory of Transducer Technology, Chinese Academy of Sciences,
Beijing 10080, China
Corresponding authorDr. Zilin ChenLuojia Chair Professor Vice Dean and Institute Director School of Pharmaceutical Sciences, Wuhan UniversityWuhan, 430071CHINAPhone: 86-27-68759893Fax: 86-27-68759850Email: [email protected]
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Supplementary data
The Supplementary data provides additional relevant details of this work, including:
Optimization of the polymerization conditions
Optimization of parameters for online solid-phase microextraction-HPLC
Figure. S1. Liquid chromatograms of jasmonic acid and methyl jasmonate
after SPME with PEDOT-SG and PEDOT respectively
Figure. S2. Cyclic voltammogram of electropolymerization
Figure. S3. Optimization for polymerization
Figure. S4. SEM image of pure PEDOT on carbon fiber bundle
Figure. S5. Optimization for extraction
Table. S1. Table S1. Comparison of PEDOT-Sulfonated graphene based
SPME-HPLC for jasmonates with other current Methods
Table S2. Recoveries of jasmonic acid and methyl jasmonate by online
SPME-HPLC
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Optimization of polymerization conditions
The polymerization process of the sulfonated graphene-PEDOT hybrid composite on
carbon fiber may be strongly influenced by many factors, such as monomer and
supporting analyte concentration, scan rates. To obtain higher extraction efficiency,
several main affecting factors were investigated as discussed as follows.
Effect of sulfonated graphene concentration. Sufficient sulfonated graphene in the
supporting electrolyte solution is a key factor for the extraction of analytes. Therefore,
it is necessary to investigate the effect of sulfonated graphene concentration on
extraction performance. In general, the solubility of sulfonated graphene in aqueous
solution is 2 mg⋅mL⁻¹. In our experiment we investigated five different
concentrations gradient and triple respectively for each concentration. From the result
shown in Figure. S2A, we can see that when the concentration is blew 2 mg⋅mL⁻¹,
the extraction efficiency kept increasing gradually. However, concentration of higher
than 2 mmol⋅L⁻¹ cannot dissolve and uniformly distribute in the solution, which may
cause waste of synthesized sulfonated graphene. As a result, we chose 2 mg⋅mL⁻¹ of
sulfonated graphene for our experiment.
Effect of scan rates. Scanning rates is a vital kinetic parameter, which helps to
increase the homogeneity of the coating obviously, thus improving extraction
efficiency and reducing extraction time. The effect of the scanning rate (0.025, 0.05,
0.075, 0.1, 0.2 V⋅s⁻¹) on the extraction efficiency of jasmonates was investigated.
Results in Figure. S2B shows that the peak areas for both jasmonic acid and methyl
jasmonate reached its maximum amounts at a scan rate of 0.025 V⋅s⁻¹. The results
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revealed that slow scan rate leads to better the extraction efficiency. However, it
would take longer time to coat the fiber bundle. Therefore, slower scan rates less than
0.025 V⋅s⁻¹ were not tested and it was chosen as an optimal option.
Effect of scan segments. The thickness of the electro-polymerized hybrid
membrane is influenced by scan segments in cyclic voltammetry. When it was varied
between 70 and 130, the extraction efficiency varied slice as Figure. S2C showed.
When scan segments increased from 130 to 150, the extraction efficiency increased
sharply simultaneously. We deduce that an increase of cyclic voltammetry segments
up to 150 gave rise to a rougher surface of the hybrid film on the fiber bundle, as
more sulfonated graphene are immobilized during polymerization. Concerning about
the time for modification, we choose 150 scan segments for next step.
Optimization of parameters for online solid-phase microextraction-HPLC
The sorption of jasmonates molecules onto the surface of modified fibers is mainly
due to the hydrophobic interaction, hydrogen bonds and π-πelectrostatic force, which
may be affected by pH of the solution to a great extent. Therefore, pH value of sample
solution is an important parameter for SPME. The pH values among 3.0-8.0 were
investigated, and the pH value was adjusted by 0.01 mol⋅L⁻¹ NaOH and HCl solution.
Sample solutions of 10 mL were loaded onto the polymer sorbent at a constant flow
rate (1 mL⋅min⁻¹). Total peak areas were calculated at each pH value and the results
are shown in Figure. S4A. The extraction efficiency of both jasmonic acid and methyl
jasmonate increased along with the increase of pH in the range of 3.0–6.0. A
maximum for jasmonic acid was observed in pH 6 and for methyl jasmonate it was
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pH 7. Higher pH value over 7 would result in lower extraction efficiency. This can be
explained by the dissociation state of carboxyl group on jasmonic acid molecules and
sulfonic acid group of sulfonated graphene. Acidic condition will restrain the
dissociation of acid group, making the analytes and the sulfonated graphene to be in
the electro-neutral state. As a result, the hydrophobic heterocyclic rings of the
jasmonates molecule were absorbed onto the conjugate carbon backbone. Concerning
insolubility, partial acidic condition may be advantageous for the hydrophobic
interaction. Dissociation of the jasmonates molecules would increase its solubility and
electrostatic force, but the hydrogen bonds may be destroyed in strong solution. In
general, mild aqueous condition is advantageous for the formation of hydrogen bonds
between jasmonates and sulfonated graphene. In our experiment we noticed that
jasmonates were better extracted in aqueous solution than in acetonitrile. However,
anions such as OH− are easy to react with jasmonic acid and help for dissociation of
sulfonic group. The extraction efficiency is the result of equilibrium of these three
kinds of interactions. With all factors taken into consideration, pH 6.0 is selected in
the following studies.
The pre-extraction solution is pushed through the packed PEEK tube loop, thus the
sample flow rate has potential effect on the contact between jasmonates and the
adsorbent. In our experiment, the effect of sample flow rate was studied; the values
were ranged from 0.5 to 0.9 mL⋅min⁻¹ controlled by a syringe pump. As shown in
Figure. S4B, peak areas fell off gradually in the examined sample flow rate, indicating
that sample flow rate has big influence on extraction efficiency. Considering analysis
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time and pressure, which might increase along with the flow rate, 0.5 mL⋅min⁻¹ of
flow rate was applied for further studies.
In-tube SPME based on packed sorbents is a nonequilibrium absorption process
and the extraction efficiency is closely related to sample volume. Volumes of pre-
extraction solution in the range of 2.5–25 mL were loaded onto the PEEK tube
separately, and the extraction efficiencies were investigated. As shown in Figure. S4C,
the peak areas increase rapidly along with increase of the sample volume from 2.5 to
20 mL and increased slowly from 20 to 25 mL. Sample volume of 20 mL was selected
for ultimate extraction.
Figure. S1. Liquid chromatograms of jasmonic acid and methyl jasmonate after SPME with PEDOT-SG and PEDOT respectively. Sample: 500 ng⋅mL⁻¹ pH 7 standard aqueous solution, 20 mL loaded at 0.8 mL⋅min⁻¹. Peak identification: 1 jasmonic acid, 2 methyl jasmonate.
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Figure. S2. Cyclic voltammogram of modification. (monomer
concentration:5 mmol⋅L⁻¹, scan rate: 0.025 V⋅s⁻¹, 150 scan
segments)
Figure. S3. Optimization for polymerization: (A) sulfonated graphene concentration, (B) scan rates, (C) scan segments. 20 ml sample solution
(10 ng⋅mL⁻¹, pH 7) was loaded at 1 mL⋅min⁻¹ by syringe pump.
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Figure. S4. SEM image of pure PEDOT on carbon fiber bundle
Figure. S5. Optimization for extraction: (A) Sample pH, (B) Sample flow rates, (C) Sample volume.
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Table S1. Comparison of PEDOT-Sulfonated graphene based SPME-HPLC
for jasmonates with other current Methods
Method Sorbents LOD (ng⋅mL⁻¹)
This method PEDOT-sulfonated graphene 0.01-0.1
Film Extraction-GC [4] Polydimethylsiloxane 0.2
PMME-HPLC [7] MAA-EGDMA 0.5-2.0
SPE-HPLC [10] β-CD modified silica, 4-VP-EGDMA 2.0-3.0
HSPME-GC-MS [11] Polydimethylsiloxane 1.3
Table S2. Recoveries of jasmonic acid and methyl jasmonate by online
SPME-HPLC
*Mean value. N=6.
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AnalytesConcentration
(ng⋅mL⁻¹)Added
(ng⋅mL⁻¹)Found*
(ng⋅mL⁻¹) Recovery %RSD%
Jasmonic acid 60.7 10.0 69.9 92.4 1.84
Methyl jasmonate 26.3 10.0 36.1 98.9 2.96
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