Permanently Positively Charged Stable Isotope Labeling Agents and Its Application in the Accurate Quantitation of Alkylphenols Migrated from Plastics to Edible Oils

Article abstract of DOI:10.1021/acs.jafc.0c03413

A new permanently positively charged stable isotope labeling (SIL) agent pair, 4-(((2,5-dioxopyrrolidin-1-yl)oxy)carbonyl)-N,N,N-Trimethylbenzenaminium iodide(DPTBA) and its deuterated counterpart d3-DPTBA, was designed and synthesized. The SIL agents wer

Full text of DOI:10.1021/acs.jafc.0c03413

pubs.acs.org/JAFC
Article
Permanently Positively Charged Stable Isotope Labeling Agents and
Its Application in the Accurate Quantitation of Alkylphenols
Migrated from Plastics to Edible Oils
Chong Ma, Shijuan Zhang,* Xia Wu, and Jinmao You*
Cite This: https://dx.doi.org/10.1021/acs.jafc.0c03413
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ABSTRACT: A new permanently positively charged stable isotope labeling (SIL) agent pair, 4-(((2,5-dioxopyrrolidin-1-
yl)oxy)carbonyl)-N,N,N-trimethylbenzenaminium iodide(DPTBA) and its deuterated counterpart d3-DPTBA, was designed and
synthesized. The SIL agents were applied to the liquid chromatography−tandem mass spectrometry analysis of alkylphenols. Light
labeled standards and heavy labeled samples were mixed and analyzed simultaneously. Matrix effect which mainly occurred during
the ionization process was minimized because of the identical ionization processes between samples and standards. Meanwhile,
derivatization made alkylphenols be positively charged, and thus the sensitivity was enhanced. The limits of detection were in the
range of 1.5−1.8 ng/L, and the limits of quantitation were in the range of 4.8−6.1 ng/L. The developed method was applied to
analyze alkylphenols migrated from plastics to edible oils. The recoveries for all analytes were in the range of 88.6−95.3%, while the
matrix effects for all analytes were in the range of 96.2−99.6%.
KEYWORDS: stable isotope labeling, alkylphenols, matrix effect, HPLC−MS/MS
number of studies indicate that the method accuracy is greatly
influenced by the matrix effect.13−15 The matrix effect can be
reduced by a dilution of the sample,14 but this strategy might
not work well because the sensitivity of different instruments
differs greatly. Another often used method is the application of
an internal standard (IS) which coelutes with the analytes and
thus compensates for the alteration in the LC−MS/MS
signal,16−19 but it is expensive to use IS for all analytes, and IS
is not always available. The matrix-matched calibration curve
has also been used to enhance method accuracy, but it is
difficult to find identical matrices and more contaminants
might be introduced in to the MS instrument during this
process.20 The stable isotope labeling (SIL) technique provides
an alternative strategy to overcome the matrix effect.21
In the SIL method, there is a pair of stable isotope labeling
agents which have identical functional groups and differ only in
isotopic composition.22,23 Light and heavy SIL agents react
with the standard and analytes, respectively, and then they are
mixed and analyzed in the same run.24 Analytes and standards
elute simultaneously, and thus the matrix effect which mainly
occurs during the ionization process is overcome. It is desirable
that the sensitivity of MS be enhanced simultaneously during
this process. In such conditions, samples can be injected in
small volume, and fewer matrices are introduced into the
1. INTRODUCTION
Plastics have been widely used in food packaging because of
their stable, flexible, and low density properties.1,2 The
production of plastics needs many compounds such as
monomers, stabilizers, plasticizers, ultraviolet light absorbers,
lubricants, and so on.1,3 Besides, impurities of raw materials
might also be introduced into plastics.2 Alkylphenols might be
used as raw materials of plastics, and some of them exist in the
form of contamination or impurities.3 They showed high
incidence of migrating into oil samples because of their good
solubility. Alkylphenols can bring about adverse effect on our
hormonal system and are regarded as endocrine disrupting
compounds.3−5 Some of them can cause immune system
damage and induce tumor or cancer at low concentrations.6,7
A
large proportion of oil samples are packaged in plastic materials
in the Chinese market, which renders a big health threat to
local people. It is urgent to study the level of alkylphenols
migrating from plastics to oils.
Various methods have been developed for the analysis of
alkylphenols.3,8,9 Liquid chromatography and gas chromatog-
raphy distinguished themselves from these methods because of
their high selectivity and sensitivity.10 However, misidenfica-
tion often occurs because of the coelution of the interferences
with the analytes. Gas chromatography−mass spectrometry
(GC-MS) and liquid chromatography−tandem mass spec-
trometry (LC−MS/MS) methods can provide not only
retention time data but also molecular weight and fragment
ion information.11 They greatly decreased the misidentification
ratio and were often used in the analysis of samples with
complex matrices.12 However, there are still great challenges in
accurate GC−MS and LC−MS/MS quantification. The matrix
effect is one of the most important drawbacks, and a large
Received: May 30, 2020
Revised: July 19, 2020
Accepted: July 22, 2020
Published: July 22, 2020
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© XXXX American Chemical Society
A

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Figure 1. Synthesis route for DPTBA (A) and the derivatization scheme for alkylphenols(B). X = H or D.
instrument.25 Phenolic compounds were usually analyzed in
negative mode, the sensitivity of which was regarded to be
lower than that in positive mode.26 It is desirable that charge
reverse be achieved during the derivatization process.
In this study, a pair of permanently positively charged SIL
agents were designed and synthesized to enhance the MS
sensitivity, and to overcome the matrix effect too. This SIL
strategy showed the following merits: (1) charge reverse
derivatization which enable the analysis of alkylphenols in
more sensitive positive mode; (2) overcome of matrix effect
because of the coelution of the analytes and standards; and (3)
multiple reaction monitoring (MRM) identification of
unknown analytes because of the identical MRM conditions
for all analytes. This strategy can be well applied in the
accurate analysis of alkylphenols in complex matrices.
263.1, in good accordance with the theoretical molecular weight
(Figure S1).
2.2.2. Synthesis of DPTBA and Its Deuterated Counterpart d3-
DPTBA. The final products were synthesized based on the reaction of
tertiary amine with iodomethane.28 Then 0.1 g of 2,5-dioxopyrrolidin-
1-yl 4-(dimethylamino)benzoate was dissolved in 20 mL of
acetonitrile, meanwhile iodomethane (0.5 g, 15 mmol) or iodo-
methane-d3 (0.5 g, 15 mmol) was dissolved in 10 mL of acetonitrile.
The former solution was added dropwise into the latter solution
under stirring. Then, the mixed solution was further reacted at 60 °C
for 12 h. After removing excess solvent under reduced pressure, a
crude product was obtained. Finally, it was recrystallized from ethanol
to obtain a pure product, yield 0.11 g (70%). The m/z value for
DPTBA was 277.1 (Figure S2), in good accordance with the [M]+ of
the DPTBA, indicating the positive charge of DPTBA. The m/z value
for d3-DPTBA was 280.1, and the synthesis route was depicted in
Figure 1A. DPTBA ethanol solution could react with AgNO3 to afford
a yellow precipitate, which further confirmed the ionic property of
DPTBA (Figure S3).
2. MATERIALS AND METHODS
2.3. Sample Extraction. 2.3.1. Migration Test. A migration test
was performed using edible peanut oil according to the dietary habit
of China. Plastics made of polyethylene terephthalate (PET),
polycarbonate (PC), polyvinyl chlorid (PVC), polystyrene (PS),
high density polyethylene (HDPE), polyethylene (PE), and
polypropylene (PP) were chosen as examples because they were
frequently used in the packaging of oils. Plastics (0.6 dm2) were
purchased from supermarket and cut to squared rectangles. They were
immersed in 100 mL of oil samples and incubated at 70 °C for 2 h.
After cooling to room temperature, 30 mL of the liquid oil sample was
transferred to 50 mL centrifuge tubes.
2.3.2. Liquid−Liquid Extraction (LLE) of the Analytes from Oil
Migrant. NaHCO3 buffer, aquatic NaOH solution, and NaOH
methanol solutions with concentrations of 0.1 mol/L were used to
extract acidic alkylphenols from oil samples. They were added into oil
samples containing 100 ng/L of alkylphenols, respectively. The
mixture was vortexed vigorously for 3 min to achieve the LLE process.
After centrifugation, the oil phase was discharged, and the methanol
phase was adjusted to neutral with 6 mol/L HCl aqueous solution.
The extract was evaporated to dryness for later derivatization. Each
sample was analyzed in three parallels.
2.1. Chemicals. 4-Propylphenol (C3), 4-butylphenol (C4), 4-
pentylphenol (C5), 4-n-hexylpheno (C6), 4-n-heptylphenol (C7), 4-t-
octylphenol (C8), and 4-n-nonylphenol (C9) were purchased from
national standard material research center of China. Methanol, 1-
ethyl-3-(3-(dimethylamino)propyl)-carbodiimide hydrochloride
(EDC), dichloromethane (DCA), N-hydroxysuccinimide (NHS), 4-
dimethylaminobenzoic acid, n-hexane, and acetonitrile were of high
performance liquid chromatography (HPLC) grade and purchased
from Sigma-Aldrich (U.S.A.). Dichloromethane (DCM) and dansyl
chloride (DNS-Cl) were purchased from Aladdin Company
(Shanghai, China). Pure water was purchased from Watsons
(Guangzhou, China).
2.2. Synthesis of 4-(((2,5-Dioxopyrrolidin-1-yl)oxy)-
carbonyl)-N,N,N-trimethylbenzenaminium iodide(DPTBA)
and D3-DPTBA. 2.2.1. Synthesis of 2,5-Dioxopyrrolidin-1-yl 4-
(dimethylamino)benzoate. The synthesis of 2,5-dioxopyrrolidin-1-yl
4-(dimethylamino)benzoate was based on the reaction of carboxylic
acid with NHS.27 NHS (1 g) and 4-dimethylaminobenzoicacid (1 g)
were dissolved in 40 mL of DCM and then cooled to 0 °C in an ice
bath. Then 20 mL of DCM solution of EDC (100 g/L) was then
added slowly into the mixture through a constant pressure dropping
funnel. The mixture was stirred at room temperature for 24 h. After
the completion of the reaction, the solvent was removed under
reduced pressure to obtain a crude product. The crude product was
purified by silica gel column chromatography to obtain the target
product, and the yield was 75%. The [M]+ of the product was m/z
2.4. Derivatizaiton of Alkylphenols. Alkylphenols were
derivatized under basic condition, and the derivatization scheme
was shown is Figure 1B. Briefly, dried sample extract, 100 μL of
acetonitrile, 100 μL of 500 mg/L d3-DPTBA acetonitrile solution, and
100 μL of 0.1 mol/L pH 9 Na2CO3 buffer were mixed and react in a
B
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Figure 2. Illustration of the generation path of the production ions for DPTBA-C6 (A) and DPTBA-C8 (B).
water bath at 70 °C for 10 min. Standard samples were derivatized
under the same conditions with DPTBA as labeling reagent. After the
reaction was completed, the mixture was cooled to room temperature.
Then heavy labeled samples and light labeled standards were mixed
and analyzed by LC−MS/MS in three replicates.
studied. Experimental peak abundance ratio between light and heavy
labeled standard, was compared with the theoretical concentration
ratio to obtain the linearity information. The six ratio levels were 12:1,
9:1, 6:1, 3:1, 1:1, and 1:3, respectively. Recoveries obtained by the
comparison between determined value and spiked value were used to
evaluate the accuracy of the method. They were carried out by spiking
blank oil samples with standard solutions, and the concentrations of
the analytes in oil samples were 10, 30, and 100 ng/L, respectively.
Intraday precision was performed with six replicates, and interday
precision was calculated with three replicates on three different days.
They were carried out at the same three levels with those of
recoveries. The relative standard deviations of the parallel results were
used to evaluate the precision. The matrix effect was evaluated by
comparing the MS responses of alkylphenols in blank oil migrants to
those of an equivalent amount in a neat standard solution. They were
calculated by the formula of (determined value of standard in
migrant/determined value of neat standard) × 100. All spiked samples
were heavy labeled and standard samples were light labeled. Samples
and standard were mixed in equal volume before HPLC−MS/MS
analysis. If the peak abundance ratios obtained were beyond the linear
range, the volume ratio of the sample and standard were adjusted, and
the new mixture was analyzed again to obtain accurate results.
To achieve the sufficient labeling of the analytes, derivatization
conditions including DPTBA concentration, reaction temperature,
reaction time, and pH of buffer solutions were optimized in detail.
2.5. HPLC−MS/MS Analysis. An Agilent 6460 Triple Quadru-
pole LC/MS System (Agilent, Santa Clara, U.S.A.) coupled with an
Agilent 1290 series HPLC system was used for the HPLC−MS/MS
analysis. An Agilent Jet Stream electrospray ionization source (ESI
source) was used as ionization source. HPLC separation was achieved
using an Eclipse Plus C18 column (2.1 × 50 mm, 1.8 μm i.d.,
Agilent). Mobile phase A was distilled water containing 5%
acetonitrile, and 100% acetonitrile was used as the mobile phase B.
The column flow rate was set at 0.15 mL/min, and the column
temperature was kept at 30 °C. The elution conditions were as
follows: 40%−95% B from 0 to 5 min and then hold for 2 min. The
first 1.5 min was operated in the “to waste” mode to make the excess
labeling reagent be discharged. The injection volume was 2 μL. The
derivatives were permanently positively charged and was analyzed in a
positive ion mode for the monitoring of [M]+. The ESI source
conditions were capillary voltage, +4.0 kV; nebulizer pressure, 40 psi;
dry gas flow rate, 11.0 L/min; dry gas temperature, 300 ◦C; sheath gas
temperature, 280 ◦C; sheath gas flow rate, 10 L/min. The MRM
conditions were fragmentor, 140 V; collision energy, 40 V. The
precursor ions were 298.2 (C3), 312.2 (C4), 326.2 (C5), 340.3 (C6),
354.2 (C7), 368.3 (C8), and 382.4 (C9). The production ions for
lighted labeled alkylphenols were m/z 135.1, 120.1, and 148.1, and
the production ions for heavy labeled ones were m/z 138.1, 123.1,
and 151.1.
3. RESULT AND DISCUSSION
3.1. Confirmation of the Derivatives. DPTBA is
vulnerable to fragmentation, and thus it can produce common
production ions for different derivatives. As shown in Figure 2,
the DPTBA-C6 (m/z 340.3) and DPTBA-C8 (m/z 368.3)
derivatives had identical production ions, i.e., m/z 148.1, 135.1,
and 120.1. The production ion of m/z 148.1 comes from the
breaking of the C−O bond and a methyl group of DPTBA,
while the ion with m/z of 120.1 comes from the further
breaking of the chemical bond between the benzene ring and
the CO bond. The production ion of m/z 135.1 comes from
2.6. Method Validation. Limits of detections (LODs) which
were defined as signal-to-noise (S/N) ratio of 3 were evaluated first,
and then limits of quantitation (LOQs) based on S/N = 10 were
C
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Table 1. Linearity, Detection Limits, Precision, and Matrix Effect
intraday
precision
(RSD%)
interday
LOD
LOQ spiked level
precision
matrix effect
matrix effect of
control group (%)
analyte
C3
linearity
R2
(ng/L) (ng/L)
(ng/L)
(RSD%)
recovery (%)
(%)
a
b
Y = 1.1176X
− 0.0536
0.9980
1.7
1.6
1.5
1.8
1.7
1.7
1.8
5.5
5.0
4.8
6.1
5.6
5.6
6.0
10
30
100
10
30
100
10
30
100
10
30
100
10
30
100
10
30
100
10
30
3.5
3.3
3.5
3.4
3.1
2.9
3.4
3.1
3.2
3.1
2.8
3.2
3.4
3.1
3.3
3.6
3.4
3.5
3.3
3.1
3.4
5.2
4.8
4.6
5.0
4.7
4.5
4.5
4.6
4.2
4.3
4.6
4.2
4.7
4.2
4.1
4.5
4.3
4.4
4.8
4.6
4.5
95.2 2.5
95.1 2.6
95.3 2.8
93.1 3.0
93.6 2.6
93.4 2.5
92.6 3.1
92.4 3.2
92.3 3.1
91.2 2.6
91.5 2.8
91.6 2.9
90.3 3.0
90.6 2.9
90.2 2.7
89.5 3.1
89.8 2.8
89.6 3.2
88.6 3.0
88.8 2.9
88.9 2.6
96.8 2.9
96.2 2.5
96.4 2.7
97.3 2.6
97.2 2.8
97.5 2.9
99.3 2.8
98.8 3.0
98.7 2.6
99.0 2.8
99.6 2.5
99.2 2.4
98.7 3.1
98.4 2.9
98.5 2.7
99.4 2.5
99.5 2.8
99.6 2.7
98.6 2.8
98.5 2.6
98.7 2.5
86.4 2.6
86.2 2.8
86.9 2.4
90.7 3.2
90.5 2.9
91.1 3.4
92.5 3.3
92.7 3.2
92.1 2.8
96.3 2.7
96.1 2.9
96.7 2.6
95.2 3.4
95.8 3.6
95.1 2.6
98.8 3.2
98.2 3.5
99.2 3.6
92.4 3.2
92.9 2.8
93.4 3.1
C4
C5
C6
C7
C8
C9
Y = 1.0494X − 0.9995
0.0292
Y = 1.0193X − 0.9990
0.0290
Y = 1.0032X − 0.9993
0.0253
Y = 1.0587X − 0.9996
0.0244
Y = 1.0249X − 0.9991
0.0537
Y = 1.0727X − 0.9993
0.055
100
a
X, theoretic concentration ratio of light/heavy labeled alkylphenols; Y, experimental mass spectrometric peak intensity ratio of light/heavy labeled
b
alkylphenols. data are expressed as mean value.
the breaking of the chemical bond between benzene ring and
the carboxylate ester. These common production ions from
different derivatives confirmed the successful derivatization of
the analytes.
The peak abundance ratio of the production ions showed
obvious correlations with the alkyl substituent of alkylphenols.
For compounds with linear alkyl substituent, m/z 120.1 ion
was more abundant. When the abundance of m/z 148.1 was set
as 100, the abundance of m/z 120.1 was in the range of 9.06−
9.31, while the abundance of m/z 135.1 was lower than 3. For
C8 with branched alkyl substituent, the m/z 135.1 ion was
more abundant. The peak abundance ratios of all DPTBA
derivatives were listed in Table S1, while the production ion
chromatograms were shown in Figures S4 and S5.
3.2. Optimization of Derivatization Condition.
3.2.1. Effect of DPTBA Concentration on Derivatization.
According to our previous experience in derivatization,29
DPTBA was studied in the concentration level of 200 to 800
mg/L with acetonitrile as solvent. The results indicated that
the peak abundance reached the maximum when DPTBA
concentration was 500 mg/L. Further increasing the
concentration of DPTBA beyond this level had no obvious
influence on peak abundance. As a result, the labeling reagent
was prepared at a concentration of 500 mg/L.
3.2.2. Effect of pH on Derivatization. The derivatization of
DPTBA was carried out in basic acetonitrile condition.
Na2CO3/NaHCO3 buffer was studied in the pH range of 8−
11. As shown in Figure S6A, the highest peak abundance was
obtained when the pH was 9, further increasing pH beyond
this level, the peak abundance decreased. Therefore, the
subsequent derivatization was carried out in 0.1 mol/L
Na2CO3/NaHCO3 buffer with pH of 9.
influence of temperature on derivatization was studied in the
temperature range of 50−90◦C with the reaction time fixed at
30 min. The results showed that the derivatization could be
quickly finished at 70 °C (Figure S6B). Further increasing the
temperature to 80 °C, the signal abundance decreased
obviously. The reaction time was further studied when
temperature was fixed at 70 °C, and the results indicated
that stable peak abundance was obtained at 10 min. As a result,
the derivatization was carried out at 70 °C for 10 min.
3.3. Optimization of the Extraction Method. Most of
the migration test was performed using food simulates.
Although food simulate is easier to analyze, the migration
behavior in food simulate might be different from that in real
food samples. Therefore, it is ideal to use real food samples to
study the migration behavior.30 However, food matrices are
usually much more complex than those of food simulate, and
thus efficient sample preparation and analysis skills are
necessary. In this study, the migration test was carried out
using peanut oil, a kind of preferred edible oil in China. The oil
matrices were removed by a simple but effective LLE method.
The extraction was based on the weak acidic property of
alkylphenols. NaHCO3 buffer which had been used to extract
bromophenols from biological matrices was tried first,31 but
the recoveries were lower than 40% for most of the analytes.
Then aquatic NaOH solution with stronger basic property was
applied, but the recoveries were still not satisfying. The poor
recoveries were due to the low solubility of alkylphenols in
water. In consideration of the immiscibility of methanol with
oil samples, 0.1 M NaOH methanol solution was applied to
extract the analytes from the oil migrants, and good recoveries
were obtained. As shown in Table 1, the obtained recoveries
were in the range of 88.6−95.3%.
3.2.3. Effect of Temperature on Derivatization. Derivatiza-
tion can be accelerated at high reaction temperature, but
decomposition of the derivatives might also occur. The
3.4. Evaluation of Matrix Effect. Matrix effect was
reported to be mainly caused by the ionization competition
form matrices,16,32 and a severe matrix effect (40%−65%) of
D
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Figure 3. Extracted ion chromatograms of light (blue chromatogram) and heavy (red chromatogram) labeled alkylphenols.
oil samples have been reported.33 In this study, two strategies
were applied to overcome matrix effect. The first one is the
permanent positive charge of the SIL agents. The derivatives
were permanently positively charged, and thus they did not
suffer from the ionization competition from matrices. More-
over, all samples were analyzed using neutral mobile phase, but
not the traditional acidic mobile phase. This change in mobile
phase greatly restrained the ionization of neutral matrices and
thus lowered the matrix effect. The second strategy is the SIL
method during which light labeled standard and heavy labeled
samples eluted simultaneously (Figure 3). Sample and
standard experienced the same evaporation and ionization
process, which further eliminated the matrix effect. In this
study, standard samples were added in oil extract, but the
matrix effect could be neglected. The obtained values of spiked
standards were about 96.2−99.6% of that in neat standard
solutions (Table 1). The performance of the developed
method was also compared with previously reported methods.
As shown in Table 2, the recoveries and matrix effect was
obviously improved in comparison with normal MS
method.34−37
chloride (DNS-Cl), a commercially available labeling reagent.
OP and NP were selected as examples, and the derivatization
and MS conditions for DNS-Cl derivatives were shown in
section S1 and S2. The DPTBA and DNS-Cl derivatives were
mixed and analyzed in a single run. As shown in Figure S7, the
sensitivity obtained using DPTBA as the derivative was much
higher than that of DNS-Cl derivatives. Meanwhile the
background noise was lowered. The detection limit (signal-
to-noise ratio of 3) was lowered by 11 and 16 times for OP and
NP, respectively, further validating the MS enhancement effect
of the positively charged DPTBA.
3.6. Method Validation. The proposed method was
validated based on the method described in experimental
section. As shown in Table 1, the correlation coefficients (R2)
for all analytes were higher than 0.998, indicating the good
linearity of the SIL method. LODs were in the range of 1.5−
1.8 ng/L, while LOQs were in the range of 4.8−6.1 ng/L.
Recoveries were in the range of 88.6−95.3%, and the matrix
effects were in the range of 96.2−99.6%. Intraday precision was
in the range of 2.8−3.6%, while interday precision ranged from
4.1% to 5.2%.
3.7. Sample Analysis. The proposed method was applied
to the analysis of alkylphenols in the oil migrants from different
plastic materials. All standard samples were light labeled and all
migrants were heavy labeled, and they were mixed in equal
volume before MS analysis. As shown in Table 3, C9 was
detected in all samples with a concentration higher than 10 μg/
L, while the other alkylphenols were detected in some samples.
The determined concentrations were in the range of 0.17−33.2
μg/L, and a representative MRM chromatogram was shown in
Figure 4. These concentrations were lower than some reported
median inhibitory concentrations (IC 50) of alkylphenols (199
and 44 μg/L for OP and NP, respectively).38 However, there
are various intake routes of alkylphenols, and their total
concentration might exceed these levels and pose an adverse
effect on our body. Although alkylphenols can cause obvious
adverse effect at low levels, there is still a great lack of
regulations on them.6 It is good to see that some regulations
3.5. MS Enhancement Effect. It is commonly regarded
that the MS sensitivity is higher in the positive mode than that
in the negative mode, especially for phenolic compounds
which do not dissociate completely in aqueous solution. To
illustrate the mass enhancement effect of the positively charged
DPTBA, a comparison was made between DPTBA and dansyl
Table 2. Comparison of the Accuracy of This Method with
Previously Reported Methods
NO
method
matrix
recovery
matrix effect
73−121%
ref
1
2
3
4
5
GC−MS
GC−MS
LC−MS
LC−MS
LC−MS
water
water
water
soil
73−107%
83.6−118.6%
57−136%
67−114%
88.6−95.3%
34
35
36
37
43−138%
80.8−82.5%
96.2−99.6
oil
this article
E
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Table 3. Concentrations of Alkylphenols Determined in Peanut Oil Migrants
plastic type
plastic character
C3 (μg/L)
C4 (μg/L)
C5 (μg/L)
C6 (μg/L)
C7 (μg/L)
C8 (μg/L)
C9 (μg/L)
HDPE
PET/PE
PET
PP
PC
PVC
PS
white, rigid, and semitransparent
opaque and flexible
rigid and transparent
rigid and transparent
rigid and transparent
rigid and white
a
a
a
a
1.52
0.49
1.36
a
a
a
a
0.19
a
0.18
a
a
a
a
0.25
0.18
0.31
17.7
5.72
2.43
4.92
a
a
a
a
a
0.18
0.17
0.19
1.63
2.81
a
a
0.20
a
11.5
14.8
13.4
11.3
33.2
16.1
14.5
a
a
rigid and white
a
a
Not detected.
Figure 4. MRM chromatogram of light labeled standard (A) and heavy labeled sample (B).
on them are being made now. For example, there is a local
standard for C9 in food contacting materials in China, and the
national standard is in the consultation process.39 European
Union will forbid the use of nonylphenol ethoxylates after 3
Feburary 2021.40
migrated from plastics to edible oil, and little matrix effect was
observed. It also showed great potential in the MRM
identification of unknown phenolic compounds.
ASSOCIATED CONTENT
■
3.8. Application in the MRM Identification of New
Compounds. DPTBA is more vulnerable to fragmentation
than alkylphenols, and thus all of the analytes showed common
production ions. Since these ions come from the breaking of
the same chemical bond, thus the collision energy needed for
these ions was also equal. This means that all of the
alkylphenols derivatives can be analyzed in the same MRM
condition. Even if there is no standard sample available, as long
as the molecular information is available, the compounds can
still be analyzed in MRM mode, which is much more sensitive
than the scan mode. In this study, we found 4-dodecylphenol
in the absence of corresponding standard using the common
MRM conditions (Figure S8A). The compound eluted after
C9, and its precursor ion was m/z 427.3, in good accordance
with the character of 4-dodecylphenol. To verify our
predication, the standard sample of 4-dodecylphenol was
purchased and analyzed. As shown in Figure S8B, the retention
time and MRM information on the standard and sample were
identical, validating the MRM identification result.
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.jafc.0c03413.
Derivatization of OP and NP with DNS-Cl, the MRM
conditions for DNS-Cl derivatives, the mass spectrum of
2,5-dioxopyrrolidin-1-yl 4-(dimethylamino)benzoate,
the picture for DPTBA, AgNO3 and a mixture of
DPTBA and AgNO3, the mass spectrum of DPTBA (A)
and D3-DPTBA (B), the production ion chromatograms
for all alkylphenol derivatives, the influence of pH (A)
and temperature (B) on derivatization, the MRM
chromatogram of DPTBA and DNS-Cl derivatized
alkylphenols, MRM chromatogram of 4-dodecylphenol
detected by the established MRM method (A) and
standard MRM chromatogram of 4-dodecylphenol (B),
peak abundance ratio of the DPTMA derivatives (PDF)
AUTHOR INFORMATION
■
In conclusion, permanently positively charged SIL agents,
DPTBA and d3-DPTBA, were designed and synthesized. The
derivatives were positively charged, and thus the MS sensitivity
was enhanced. Samples and standards were mixed before
HPLC−MS/MS analysis, and thus they experienced the same
electrospray process, which minimized the matrix effect. The
developed method was applied to the analysis of alkylphenols
Corresponding Authors
Shijuan Zhang − Shandong Province Key Laboratory of Life-
Organic Analysis and Key Laboratory of Pharmaceutical
Intermediates and Analysis of Natural Medicine, Qufu Normal
University, Qufu, PR China; orcid.org/0000-0001-9245-
1877; Phone: +86 537 4456305; Email: sjzhang156@
163.com; Fax: +86 537 4456305
F
https://dx.doi.org/10.1021/acs.jafc.0c03413
J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Journal of Agricultural and Food Chemistry
pubs.acs.org/JAFC
Article
(11) Omar, T. F. T.; Ahmad, A.; Aris, A. Z.; Yusoff, F. M. Endocrine
disrupting compounds (EDCs) in environmental matrices: Review of
analytical strategies for pharmaceuticals, estrogenic hormones, and
alkylphenol compounds. TrAC, Trends Anal. Chem. 2016, 85, 241−
259.
(12) De Silva, R.; De Menezes, M. G.G.; De Castro, R. C.; De
Nobre, C.; Milhome, M. A.L.; Do Nascimento, R. F. Efficiency of ESI
and APCI ionization sources in LC-MS/MS systems for analysis of 22
pesticide residues in food matrix. Food Chem. 2019, 297, 124934.
(13) Kaczynski, P. Clean-up and matrix effect in LC-MS/MS
analysis of food of plant origin for high polar herbicides. Food Chem.
2017, 230, 524−531.
Jinmao You − Shandong Province Key Laboratory of Life-
Organic Analysis and Key Laboratory of Pharmaceutical
Intermediates and Analysis of Natural Medicine, Qufu Normal
University, Qufu, PR China; Phone: +86 537 4456305;
Email: jmyou6304@163.com; Fax: +86 537 4456305
Authors
Chong Ma − Shandong Province Key Laboratory of Life-Organic
Analysis and Key Laboratory of Pharmaceutical Intermediates
and Analysis of Natural Medicine, Qufu Normal University,
Qufu, PR China
Xia Wu − Shandong Province Key Laboratory of Life-Organic
Analysis and Key Laboratory of Pharmaceutical Intermediates
and Analysis of Natural Medicine, Qufu Normal University,
Qufu, PR China
(14) Van Eeckhaut, A.; Lanckmans, K.; Sarre, S.; Smolders, I.;
Michotte, Y. Validation of bioanalytical LC-MS/MS assays: evaluation
of matrix effects. J. Chromatogr. B: Anal. Technol. Biomed. Life Sci.
2009, 877 (23), 2198−207.
(15) McManus, M. M.; Oates, R. P.; Subbiah, S.; Klein, D.; Canas-
Carrell, J. E. Matrix-matched standards in the liquid chromatography-
mass spectrometry determination of neonicotinoids in soil and
sediment. J. Chromatogr. A 2019, 1602, 246−252.
(16) Chamberlain, C. A.; Rubio, V. Y.; Garrett, T. J. Impact of
matrix effects and ionization efficiency in non-quantitative untargeted
metabolomics. Metabolomics 2019, 15 (10), 135.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.jafc.0c03413
Notes
The authors declare no competing financial interest.
(17) Dawson, D. D.; Martin, R. W. Investigation of Chocolate
Matrix Interference on Cannabinoid Analytes. J. Agric. Food Chem.
2020, 68 (20), 5699−5706.
(18) Gao, Y.; Xia, B.; Qin, Y.; Huang, K.; Yang, C.; Yang, Q.; Zhao,
L. Online Scavenging of Trace Analytes in Complex Matrices for Fast
Analysis by Carbon Dioxide Bubbling Extraction Coupled with Gas
Chromatography-Mass Spectrometry. J. Agric. Food Chem. 2020, 68
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(19) Koller, D.; Vaitsekhovich, V.; Mba, C.; Steegmann, J. L.;
Zubiaur, P.; Abad-Santos, F.; Wojnicz, A. Effective quantification of
11 tyrosine kinase inhibitors and caffeine in human plasma by
validated LC-MS/MS method with potent phospholipids clean-up
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ACKNOWLEDGMENTS
■
The work was supported by National Natural Science
Foundation of China (Nos. 31801624 and 21976105) and
Natural Science Foundation of Shandong Province
(ZR2018MC031).
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