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Paper spray ionization mass spectrometry for rapid
quantification of illegal beverage dyes†
Tianyang Guo,ab Zezhen Zhang,a Karen E. Yannell,a Yiyang Dongb
and R. Graham Cooks *a
A rapid method is described for quantification of six illegal colorants in beverages, i.e., soft beverages,
energy beverages, alcoholic beverages, teas, and fruit juices. Paper spray (PS) ionization combined with
tandem mass spectrometry (MS/MS) allowed detection of particular dyes in times of less than 1 min per
sample. Samples where diluted in methanol and isotopically-labeled internal standards were utilized to
obtain linear responses over ranges of two or three orders of magnitude. The LODs were below 1.5 ng
mL1 and LOQs were below 5 ng mL1. Quality control experiments gave accuracies that ranged
between 80% and 120%. Matrix effects were evaluated for different samples but had little effect given the
use of the dilution method.
1. Introduction
Dyes are added to specic products to provide attractive visual
effects. In the case of foods, food dyes can compensate for color
loss, enhance natural colors, or add color to colorless food.1
Synthetic food dyes, synthesized from coal tar or petroleum byproducts,
2 are widely used, owing to their ease of production,
low cost, high stability, and good coloring properties.3 During
the 1900s, some 80 different food dyes were used in the United
States, but over the years, most of them have been taken off the
market because of safety concerns.2 Currently, only nine
synthetic colorings are allowed for food use by the U.S. Food
and Drug Administration (FDA), and these are subject to
certication.4
Although maximum use levels for these dyes have been listed
by the FDA, their use still requires careful consideration. For
example, Fast Green, Orange B and Citrus Red 2 are legal in the
US, but they are not permitted in other countries, e.g., China5
and the European Union.6 Some studies showed that synthetic
food dyes may have a negative effect on the behavior of children,
such as hyperactivity.1,2,7 Furthermore, use of multiple synthetic
food colors is also a challenge for food safety, because of
potential synergistic effects.8
The addition to food of some industrial dyes, e.g., Sudan
dyes, Disperse dyes, Rhodamine B and Malachite Green, is
forbidden due to their genotoxic and carcinogenic activity.9
However, some producers still add these illegal non-food colors
to the product.10,11 Therefore, a sensitive method to screen both
legal and illegal dyes in food is required for food safety.
Conventional mass spectrometry-based methods for detection
of dyes require complex pretreatment process, including
drying, extraction, and purication.12,13 These treatments avoid
matrix interferences from various mono-, di- and polysaccharides
and modied starch, and from compounds with
the same molecular weight as the analyte as well as minimizing
ionization suppression.14,15 These advantages come with the
need for time-consuming chromatographic separation
processes.12–14,16 Ambient ionization mass spectrometry17–19 is an
alternative way to rapidly ionize samples without or with only
minimal pretreatment. The ESI-related method of desorption
electrospray ionization (DESI)20 and APCI-related direct analysis
in real time (DART),21 as well as many other ambient ionization
techniques, have been applied widely in food safety,19,22 environmental
analysis,23 forensics24 and clinical diagnosis.25
As for dyes, several ambient ionization methods have been
used for identication or quantication. Four Sudan dyes in
chili powder were quantied at the mgmL1 level by DART-MS,26
although DART has proved less successful with those dyes
which are salts. Four dyes in aqueous solution were detected by
DESI-MS at the ng mL1 level.27 Dyes with different structures
were identied at pg mL1 level in wool samples by surface
acoustic wave nebulization (SAWN) mass spectrometry,
although degradation of certain analytes was observed.28
Paper spray (PS) ionization is a representative ESI-related
ambient ionization method which allows rapid and direct
analysis of an untreated sample from paper or other porous
(occasionally non-porous29) media which include a ne tip. This
technique requires neither elevated temperature nor gas ow so
it is particularly appropriate for use with portable MS systems.30
In several application areas, it has been demonstrated to allow
aDepartment of Chemistry, Purdue University, West Lafayette, IN 47907, USA
bCollege of Life Science and Technology, Beijing University of Chemical Technology,
Beijing 100029, China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c7ay02241g
Cite this: DOI: 10.1039/c7ay02241g
Received 18th September 2017
Accepted 25th October 2017
DOI: 10.1039/c7ay02241g
rsc.li/methods
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quantication of analytes in complex matrices with the use of
internal standards.31,32 Most such applications focus on biological
samples, such as blood, urine and tissue. However, this
technique is useful also in the food safety domain, because of
the complexity of food matrix and the requirement for trace
residue detection.33–37 Some azo dyes at mgmL1 level have been
examined in powdered chili pepper by PS-MS/MS.38
In this paper, we establish a PS-MS/MS method using
multiple reaction monitoring (MRM) to quantify illegal dyes in
liquid beverages. Minimal sample preparation was used and
internal standards were investigated and optimized. LOD and
LOQ at ng mL1 level, accuracy and precision were calculated
using matrix-matched calibration curves. As a nal test, real
samples were screened to ensure the usefulness of this method.
2. Experimental
2.1 Reagents and materials
Analytical standards of Sudan I, Sudan II, Malachite Green (as
chloride), Rhodamine B (as chloride), Crystal Violet (as chloride)
and Methylene Blue (as chloride) were purchased as
powders from Sigma-Aldrich (St. Louis, MO), and stored at
20 C. The D5 isotopically labeled internal standards Sudan Id5
and Malachite Green-d5 picrate were also purchased from
Sigma-Aldrich, and stored at 20 C. HPLC grade methanol,
acetic acid, and ammonium acetate were purchased from
Sigma-Aldrich (St. Louis, MO). Twenty-one colorless and twenty
colored beverage samples were purchased from three local
supermarkets in West Lafayette, Indiana (Walmart, Meijer,
Fresh City Market). They included so beverages, energy
beverages, alcoholic beverages, teas, and fruit juices.
2.2 Analytes and internal standards
Illegal food dyes of two molecular types were investigated:
neutral molecules and salts with complex cations. Most neutral
molecule dyes produce the protonated molecule [M + H]+ in
positive ion mode, while not being ionized in the negative ion
mode. Compounds of this neutral molecule class, including
Sudan and related dyes, are usually oil-soluble. Two representatives
Sudan dyes (Table 1) were selected to assess the
performance of rapid determination by paper spray (PS) as
described in this article. The complex cation salt dyes, ionize
with relatively high efficiency to give the intact cation [C]+ in the
positive mode. The examples of this class examined were Malachite
Green, Rhodamine B, Crystal Violet and Methylene Blue
(Table 1).
Internal standards (IS) were used to improve accuracy and
precision, as well as to establish the robustness of the method
for the various complex matrices. In ambient ionization mass
spectrometry analysis, IS use is highly desirable.39,40 Commonly,
two types of IS are used: structural analogues and stable-isotope
labeled forms of analyte. Isotopically labeled IS's have performed
very well in past ambient ionization mass spectrometry
analyses, owing to similar ionization efficiency and similar
transport along the paper substrate.31,32 However, the higher
cost of isotopically labeled standards makes their use for each
individual analyte impractical. Therefore, two IS's were selected
to allow detection of multiple analytes. The IS Sudan I-d5 was
chosen for the neutral molecule class and Malachite Green-d5
picrate for the complex salt class (Table 1).
2.3 Instruments and devices
All MS experiments were performed using PS ionization
combined with triple quadruple mass spectrometry. PS was performed
using a toothless copper clip, obtained from Muller
Electric (Akron, OH), and Whatman 1ET-Chr paper, obtained
from GE Healthcare Life Sciences (Chicago, IL). The paper
substrate was cut into a small triangle (8  10, mm), and clamped
with the copper clip. High voltage was supplied to the clip
and the solvent methanol was pipetted onto the paper triangle.
The mass spectrometer used was a TSQ Quantum Access
MAX (Thermo Fisher Scientic, Waltham, MA). Full scan mode
was used to observe the precursor ion of each analyte/IS pair,
while the multiple reaction monitoring (MRM) mode was used
for quantication of the analytes and IS. The most abundant
fragment of the precursor ion was used in the MRM quanti-
cation (“quantier”); a second abundant fragment was used in
a separate qualitative check of the quality of the data (“quali-
er”). The optimized fragmentation results are summarized in
Table 1.
Table 1 Information and fragment results on specific dyes in foods and their internal standards
Analytes Molecular formulaa Exact massb Precursor ion Tube lens (V)
Precursor ion > product ion
Quantier CEc Qualier CEc
Sudan I C16H12N2O 248.09 [M + H]+ 85 249.1 > 93.2 26 249.1 > 232.0 33
Sudan II C18H16N2O 276.13 [M + H]+ 85 277.1 > 121.1 18 277.1 > 260.2 12
Sudan I-d5 C16D5H7N2O 253.13 [M + H]+ 85 254.1 > 98.2 30 — —
Malachite Green C23H25N2
+ 329.20 [C]+ 100 329.2 > 313.1 35 329.2 > 208.1 32
Rhodamine B C28H31N2O3
+ 443.23 [C]+ 100 443.2 > 399.1 42 443.2 > 355.1 58
Crystal Violet C25H30N3
+ 372.24 [C]+ 100 372.2 > 356.2 36 372.2 > 251.1 31
Methylene Blue C16H18N3S+ 284.12 [C]+ 90 284.1 > 268.0 34 284.1 > 240.2 32
Malachite Green-d5 C23D5H20N2
+ 334.23 [C]+ 100 334.2 > 318.2 34 — —
a For neutral molecule (M) or complex cation (C+) depending on which form analyte takes. b For neutral molecule (M) or complex cation (C+)
depending on which form analyte takes. c CE – collision energy.
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These data were recorded using optimized parameters of the
PS source and MS as follows: ionization mode, positive; spray
voltage, 3500 V; capillary temperature, 300 C; collision pressure,
1.5 mTorr; peak width, 0.010 Th (Thomson, unit of m/z);
scan time, 0.100 s; Q1 peak width (FWHM), 0.70 Th.
Data acquisition and data processing utilized Thermo Fisher
Xcalibur soware (version 3.0). Data for the ion transitions were
separately acquired in two segments, because of the relative
high intensity difference between them. Peaks were automatically
integrated aer acquisition, and quantication was performed
with a set of concentrations (x-axis) and the area ratios
of analyte and internal standards (y-axis). Limits of detection
(LODs) and limits of quantication (LOQs) were calculated as 3
times and 10 times, respectively, of the standard deviation of
[blank signal/IS signal] for seven blank samples containing IS in
known amount, divided by the slope of the trend line in
concentration units. This IUPAC denition41 does not consider
chemical noise42 which is an important consideration in mass
spectrometry. However, chemical noise (intrinsic signal at the
m/z value being measured due to contamination and other
sources) will result in a non-zero intercepts in the calibration
curves and this was not the case in the present study.
2.4 Sample preparation
The colorless negative beverage samples were selected as the
matrix. If carbonated, the liquid sample was degassed by sonication
for ve minutes. If it had pulp, the liquid partition of the
beverage sample was taken. Aer that, two simple sample
treatment methods were used and compared:
Method 1 (M1). Degassed liquid samples were diluted with
spray solvent, methanol, spiked with mixed IS, and sprayed
from the paper substrate to introduce the sample into the mass
spectrometer.
Method 2 (M2). Degassed liquid samples were spiked with
mixed IS, pipetted and dried on the paper, and then sprayed
with added spray solvent methanol to introduce the sample into
mass spectrometer.
Both methods required optimization of the spray solvent. In
M1, dilution ratio and spray volume were also optimized; in M2,
pipet volume and spray volume were also optimized.
2.5 Screening and quantication
For M1, quantication was carried out using internal standards
and matrix-matched calibration curves. All degassed noncolored
samples (N ¼ 21) were mixed together as a pooled
matrix solution. Individual standard stock solutions were
prepared using powdered dye standards dissolved in methanol
and/or toluene to a concentration of 1000 mg mL1, and the
resulting standard solutions were stored in the dark at 4 C.
Calibration curves of peak area vs. concentration (ng mL1)
were established by spiking dye standards into the pooled
matrix solution to nal concentrations of 0.25, 0.5, 1, 2.5, 5, 10,
25, 50, 100, 250, 500, and 1000 ng mL1. The corresponding
solutions were also made up in water rather than the matrix to
examine the effect of matrix. The best dilution solvents for the
calibration curves were found by examining methanol/beverage
mixtures over a range of proportions (v/v) when using M1.
Internal standards at the nal concentration 100 ng mL1
were also spiked into the above solutions. Quality control
accuracy was determined by calculating the ratio between the
determined value of analyte and the known value of the analyte
in the initial sample. Experiments were done working with
concentrations of 3.2, 16, 80, 400 ng mL1 as well as 100 ng
mL1 IS.
For M2, quantication again used IS but at a nal concentration
of 400 ng mL1. The analytes in this method had nal
concentrations of 1 to 5000 ng mL1. The solvent used was
methanol. Addition of formic acid (0.1–1%) was found not to
improve the performance.
3. Results and discussion
3.1 Optimization of spray method
Methanol has oen been used for PS ionization,31,32 so it was
tested rst. In method 1 (M1), the dilution ratio (v/v) was optimized
by examining
methanol þ beverage sample
beverage sample
ratios of 6, 7,
8, 9, 10, 15, and 20. The data are shown in Fig. 1. The solvent of
most samples was water, while for some alcoholic beverage, the
solvent was water with a small proportion of ethanol. The
results showed that for some analytes such as Malachite Green,
there was no signicant difference when using different dilution
ratios. In the cases of other analytes, e.g., Rhodamine B, the
results of different dilution ratios were quite different. When
the proportion of water (aqueous beverage) was higher than
10%, poor spray ionization efficiency was found. The ratio 10%
aqueous 90% methanol provided a stable spray. On the other
hand, if the proportion of water was less than 10%, the spray
ionization efficiency did not increase, but more solvent was
needed. Therefore, we chose the 10 times dilution ratio of
aqueous beverage with methanol. The corresponding optimization
experiment for method 2 (M2), led to methanol alone
being added to the dried analyte on the paper.
A spray solvent volume of 30 mL was used to cover the entire
paper triangle for a consistent spray for a few tens of seconds.
Fig. 1 Optimization of dilution ratio of Malachite Green and Rhodamine
B in method 1 (M1). Malachite Green showed no significant
difference using different dilution ratio in the spray solvent while
Rhodamine B had better spray ionization efficiency when the methanol
dilution ratio was larger than 10.
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To obtain a consistent peak intensity and peak area, a sufficient
number of points in each peak was necessary. Thus, 10 points
per analyte was selected, achieving a balance between analytical
speed and stability.
In an attempt to improve ionization efficiency in M1, the weak
acids, i.e., acetic acid and formic acid, and the salts of a weak acid
and weak base, i.e., ammoniumacetate and ammoniumformate,
were added to the spray solvent. However, the results did not
provide any improvement in ionization efficiency.
3.2 Optimization of sample preparation method
Two simple sample preparation methods (M1 and M2)
mentioned above were compared. The calibration curves were
established for the analytes in a mixture of the colorless
beverages (N ¼ 6) (Fig. 2a, b, d and e, S1a, b, d, e, h, i, k and l†) as
well as in water (n ¼ 4) (Fig. 2c and f, S1c, f, j, m and S2†). In the
case of Malachite Green, both methods showed good linear
responses, and the RSDs were low (<6%) (Fig. 2d and f), which
might be due to the use of the isotopically labeled compound as
IS and the type of cation structure. Sudan I showed good linear
respond and RSD with M1 (<14%) (Fig. 2a), but poor reproducibility
with M2 (RSD > 80%) (Fig. 2b). However, when Sudan
I was diluted in water (i.e., no beverage matrix) using M2, it
showed an acceptable RSD (<11%) (Fig. 2c), which proved that
the poor RSD with M2 was associated with the sample matrix
not the paper substrate. Although the corresponding IS was
used, M2 exhibited poor matrix effects while M1 appears to help
to minimize matrix effects. Although dyes were redissolved in
M2, the concentration of matrix apparently was not low enough
to avoid matrix effects. In the case of the other dyes with noncorresponding
internal standard, the results also showed that
M1 was better than M2 in terms of matrix effects (Fig. S1 and
S2†). Thus, we selected M1, the simpler method and more
precise method, for sample analysis from this point forward.
3.3 Calibration curve and quality control
Matrix-matched calibration curves of six analytes as well as IS in
mixed beverage solutions (n ¼ 6) with M1 were recorded (Fig. 3).
The linear ranges of analytes were rescaled (Table 2). In
particularly, the Malachite Green was examined over a wide
linear range, i.e., 0.25–1000 ng mL1. The coefficients of variation
(R2) of all the analytes were higher than 0.999. The LODs of
all analytes were less than 1.5 ng mL1, and the LOQs were less
than 5 ng mL1 (Table 2). Note that the LOQ of Malachite Green
was under 0.5 ng mL1, mainly due to the use of the isotopically
labeled internal standard Malachite Green-d5. For quality
control assessment, the accuracies and RSDs for six analytes
over a range of concentrations were calculated (Table 2). These
results demonstrate that the linear concentration ranges for
detection of six illegal beverage dyes were acceptable, and the
whole quantication process, including sample dilution preparation
and PS-MS/MS detection, was appropriately accurate.
Sudan dyes have been examined previously38 by PS-MS/MS and
the performance achieved in the present study is similar to that
shown there.
3.4 Real sample detection
The developed method was applied to the real liquid food
sample screening. A total of twenty-one samples were examined
using M1. The results showed no detectable signal in any of the
samples, shown in Table S1.† These results demonstrated the
safety of these particular products in terms of the six dyes
analyzed.
Fig. 2 Comparative results for dyes Sudan I (a)–(c) and Malachite Green (d)–(f) as judged by slopes and standard deviations of analyte/IS
response ratio in beverage and water matrices, respectively. Error bars are based on six measurements. Sudan I performed poorly in the beverage
matrix when using M2 compared to M1. Malachite Green performed well by both methods.
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4. Conclusions
In this study, a rapid method of quantication was developed
and validated for six illegal food dyes (i.e., Sudan I, Sudan II,
Malachite Green, Rhodamine B, Crystal Violet and Methylene
Blue) in various beverages. An analysis time of less than 1 min
per sample was achieved by paper spray (PS) ionization with
triple quadruple mass spectrometry (MS/MS) in the multiple
reaction monitoring mode. Calibration curves were established
over linear ranges of two or three orders of magnitude. LODs
ranged between 0.1–1.4 ng mL1 and LOQs ranged between 0.3–
4.8 ng mL1. The accuracy of the assay was between 80–120%.
None of the six dyes was detected in 20 actual locally-sourced
beverage samples.
Conflicts of interest
There are no conicts to declare.
Acknowledgements
Support of TY through the CSC Scholarship Program, from
BUCT, the Key Program of a Synchronized Detection Research
and Risk Assessment for Radionuclides in Foods of Beijing
Fig. 3 Matrix-matched calibration curves of Sudan I (a), Sudan II (b), Malachite Green (c), Crystal Violet (d), Methylene Blue (e) and Rhodamine B
(f) as well as IS in mixed beverage solution (n ¼ 6). Error bars denote the standard deviation (SD). The equation, coefficient of variation (R2), and
zoomed-in calibration curves are shown.
Table 2 Linear range, LOD, LOQ, accuracy and precision for six analytes in colorless beverage liquid
Analytes
Linear range
(ng mL1)
LOD
(ng mL1)
LOQ
(ng mL1)
Accuracy (%) and precision (% RSD) (N ¼ 4)
3.2 ng mL1 16 ng mL1 80 ng mL1 400 ng mL1
Sudan I 2.5–250 1.4 4.8 92.4 7.2 108.1 7.9 102.0 8.6 — —
Sudan II 2.5–250 1.1 3.7 97.6 9.2 82.1 4.0 82.9 12.0 — —
Malachite Green 0.25–1000 0.1 0.3 113.3 2.4 108.6 1.8 98.3 7.7 95.8 2.6
Rhodamine B 1–500 0.6 2.1 91.5 9.4 103.3 21.4 108.9 19.1 98.9 11.7
Crystal Violet 1–500 0.8 2.5 76.0 3.3 109.8 5.6 107.9 7.5 107.8 5.0
Methylene Blue 0.5–500 0.2 0.8 108.5 9.1 104.7 6.1 103.1 11.7 96.9 9.6
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Municipal Science & Technology Commission
(D161100002116002), NSFC grant (51673012), and the National
Key Research and Development Program of China
(2016YFF0203703), is acknowledged. We thank Qiang Ma,
Chinese Academy of Inspection and Quarantine, for helpful
advice.
References
1 P. Amchova, H. Kotolova and J. Ruda-Kucerova, Health safety
issues of synthetic food colorants, Regul. Toxicol. Pharmacol.,
2015, 73, 914–922.
2 L. J. Stevens, J. R. Murgess, M. A. Stochelski and T. Kuczek,
Amounts of articial food colors in commonly consumed
beverages and potential behavioral implications for
consumption in children, Clin. Pediatr., 2014, 53(2), 133–140.
3 V. Oreopoulou, V. Psimouli, D. Tsimogiannis, T. K. Anh,
N. M. Tu, U. Uygun, H. Koksel, V. Gokmen, C. Crews,
S. Tomoskozi, L. Domotor, G. Balazs, L. Zhang, H. Liu,
Y. Cui, B. Liu, D. Wenping, W. Xingguo, H. Weining,
H. Ozer, L. Zhongdong and M. El-Nawawy, Assessing food
additives: the good, the bad and the ugly, Qual. Assur. Saf.
Crops Foods, 2009, 1(2), 101–110.
4 FDA, Summary of Color Additives for Use in the United
States in Foods, Drugs, Cosmetics, and Medical Devices,
http://www.fda.gov/ForIndustry/ColorAdditives/
ColorAdditivesinSpecicProducts/InFood/ucm130054.html.
5 GB2760-2014, http://down.foodmate.net/standard/sort/3/
42543.html.
6 CODEX, GENERAL STANDARD FOR FOOD ADDITIVES
CODEX STAN 192-1995, http://www.fao.org/fao-whocodexalimentarius/
sh-proxy/en/?lnk¼1&url¼https%253A%
252F%252Fworkspace.fao.org%252Fsites%252Fcodex%
252FStandards%252FCODEX%2BSTAN%2B192-1995%
252FCXS_192e.pdf.
7 L. J. Stevens, T. Kuczek, J. R. Burgess, M. A. Stochelski,
L. E. Arnold and L. Galland, Mechanisms of behavioral,
atopic, and other reactions to articial food colors in
children, Nutr. Rev., 2013, 71(5), 268–281.
8 M. Oplatowska-Stachowiak and C. T. Elliott, Food colors:
existing and emerging food safety concerns, Crit. Rev. Food
Sci. Nutr., 2017, 57, 524–548.
9 IARC Monographs on the Evaluation of the Carcinogenic
Risk of Chemicals to Man, 1975, 8, IARC, Lyon.
10 Food and Drug Administration, http://www.fda.gov.ph/
advisories/food/114164-fda-advisory-on-products-positiveon-
rhodamine.
11 Food Standards Agency (FSA), http://www.fda.gov.ph/
advisories/food/114164-fda-advisory-on-products-positiveon-
rhodamine.
12 F. Feng, Y. Zhao, W. Yong, L. Sun, G. Jiang and X. Chu,
Highly sensitive and accurate screening of 40 dyes in so
drinks by liquid chromatography-electrospray tandem
mass spectrometry, J. Chromatogr. B: Anal. Technol. Biomed.
Life Sci., 2011, 879, 1813–1818.
13 H. Gao, M. Yang, M. Wang, Y. Zhao, Y. Cao and X. Chu,
Determination of 30 Synthetic Food Additives in So
Drinks by HPLC/Electrospray Ionization-Tandem Mass
Spectrometry, J. AOAC Int., 2013, 96(1), 110–115.
14 X. Chen, Y. Zhao, H. Shen, L. Zhou, S. Pan and M. Jin, Fast
determination of seven synthetic pigments from wine and
so drinks using magnetic dispersive solid-phase
extraction followed by liquid chromatography-tandem
mass spectrometry, J. Chromatogr. A, 2014, 1346, 123–128.
15 P. L. L´opez-de-Alba, W. Wr´obel-Kaczmarczyk, K. Wr´obel,
L. L´opez-Mart´ınez and J. A. Hern´andez,
Spectrophotometric determination of Allura Red (R40) in
so drink powders using the universal calibration matrix
for partial least squares multivariate method, Anal. Chim.
Acta, 1996, 330, 19–29.
16 F. Gosetti, U. Chiuminatto, E. Mazzucco, R. Mastroianni and
E. Marengo, Ultra-high-performance liquid
chromatography/tandem high-resolution mass
spectrometry analysis of sixteen red beverages containing
carminic acid: Identication of degradation products by
using principal component analysis/discriminant analysis,
Food Chem., 2015, 167, 454–462.
17 R. J. Fussell, D. Chan and M. Sharman, An assessment of
atmospheric-pressure solids-analysis probes for the
detection of chemicals in food, Trends Anal. Chem., 2010,
29(11), 1326–1335.
18 J. L. Nizzia, A. E. O'Leary, A. T. Ton and C. C. Mulligan,
Screening of cosmetic ingredients from authentic
formulations and environmental samples with desorption
electrospray ionization mass spectrometry, Anal. Methods,
2013, 5(2), 394–401.
19 T. Guo, W. Wei, Y. Jin, L. Zhang, J. Liu, W. Wang, Q. Chen,
Y. Dong, H. Su and T. Tan, Applications of DART-MS for
food quality and safety assurance in food supply chain,
Mass Spectrom. Rev., 2017, 136(2), 161–187.
20 N. E. Manicke, J. M. Wiseman, D. R. Ifa and R. G. Cooks,
Desorption electrospray ionization (DESI) mass
spectrometry and tandem mass spectrometry (MS/MS) of
phospholipids and sphingolipids: Ionization, adduct
formation, and fragmentation, J. Am. Soc. Mass Spectrom.,
2008, 19(4), 531–543.
21 T. Guo, P. Fang, J. Jiang, Z. Feng, W. Yong, J. Liu and
Y. Dong, Rapid screening and quantication of residual
pesticides and illegal adulterants in red wine by direct
analysis in real time mass spectrometry, J. Chromatogr. A,
2016, 1471, 27–33.
22 J. S. Wiley, J. F. Garcia-Reyes, J. D. Harper, N. A. Charipar,
Z. Ouyang and R. G. Cooks, Screening of agrochemicals in
foodstuffs using low-temperature plasma (LTP) ambient
ionization mass spectrometry, Analyst, 2010, 135, 971–979.
23 C. Jiang, S. Sun, Q. Zhang, J. Liu, J. Zhang, Y. Zong and J. Xie,
Fast determination of 3-ethenylpyridine as a marker of
environmental tobacco smoke at trace level using direct
atmospheric pressure chemical ionization tandem mass
spectrometry, Atmos. Environ., 2013, 67, 1–7.
24 D. N. Correa, J. M. Santos, L. S. Eberlin, M. N. Eberlin and
S. F. Teunissen, Forensic Chemistry and Ambient Mass
Spectrometry: A Perfect Couple Destined for a Happy
Marriage?, Anal. Chem., 2016, 88(5), 2515–2526.
Anal. Methods This journal is The Royal Society of Chemistry 2017
Analytical Methods Paper
Published on 26 October 2017. Downloaded by Beijing University of Chemical Technology on 07/11/2017 15:34:28.
View Article Online
25 C. R. Ferreira, K. Yanne, A. Jarmusch, V. Pirro, Z. Ouyang and
R. G. Cooks, Ambient ionization mass spectrometry for
point-of-care diagnostics and other clinical measurements,
Clin. Chem., 2016, 62(1), 99–110.
26 Z. Li, Y. Zhang, Y. Zhang, Y. Bai and H. Liu, Rapid analysis of
four Sudan dyes using direct analysis in real time-mass
spectrometry, Anal. Methods, 2015, 7, 86–90.
27 J. L. Nizzia, A. E. O'Leary, A. T. Ton and C. C. Mulligan,
Screening of cosmetic ingredients from authentic
formulations and environmental samples with desorption
electrospray ionization mass spectrometry, Anal. Methods,
2013, 5, 394–401.
28 A. Astefanei, M. van Bommel and G. L. Corthals, Surface
acoustic wave nebulisation mass spectrometry for the fast
and highly sensitive characterisation of synthetic dyes in
textile samples, J. Am. Soc. Mass Spectrom., 2017, 28, 2108–
2116.
29 J. Jiang, H. Zhang, M. Li, M. T. Dulay, A. J. Ingram, N. Na Li,
H. You and R. N. Zare, Droplet Spray Ionization from a Glass
Microscope Slide: Real-Time, Anal. Chem., 2015, 87, 8057–
8062.
30 F. P. M. Jjunju, S. Maher, D. E. Damon, R. M. Barrett,
S. U. Syed, R. M. A. Heeren, S. Taylor and A. K. Badu-
Tawiah, Screening and quantication of aliphatic primary
alkyl corrosion inhibitor amines in water samples by paper
spray mass spectrometry, Anal. Chem., 2016, 88, 1391–1400.
31 R. D. Espy, S. F. Teunissen, N. E. Manicake, Y. Ren,
Z. Ouyang, A. V. Asten and R. G. Cooks, Paper spray and
extraction spray mass spectrometry for the direct and
simultaneous quantication of eight drugs of abuse in
whole blood, Anal. Chem., 2014, 86(15), 7712–7718.
32 K. E. Yannell, K. R. Kesely, H. D. Chien, C. B. Kissinger and
R. G. Cooks, Comparison of paper spray mass spectrometry
analysis of dried blood spots from devices used for in-eld
collection of clinical samples, Anal. Bioanal. Chem., 2016,
409(1), 121–131.
33 C. Black, O. P. Chevallier and C. T. Elliott, The current and
potential applications of ambient mass spectrometry in
detecting food fraud, Trends Anal. Chem., 2016, 82, 268–278.
34 E. V. D. Hee, Y. J. C. Bolck, B. Beumer, A. W. J. M. Nijrolder,
A. A. M. Stolker and M. W. F. Nielen, Full-scan accurate mass
selectivity of ultra-performance liquid chromatography
combined with time-of-ight and orbitrap mass
spectrometry in hormone and veterinary drug residue
analysis, J. Am. Soc. Mass Spectrom., 2009, 20(3), 452–463.
35 L. Li, B. Feng, J. Yang, C. Chang, Y. Bai and H. Liu,
Applications of ambient mass spectrometry in highthroughput
screening, Analyst, 2013, 138, 3097–3103.
36 Q. Ma, H. Bai, W. Li, C. Wang, X. Li, R. G. Cooks and
Z. Ouyang, Direct identication of prohibited substances
in cosmetics and foodstuffs using ambient ionization on
a miniature mass spectrometry system, Anal. Chim. Acta,
2016, 912(17), 65–73.
37 P. P´erez-Ortega, F. J. Lara-Ortega, B. Gilbert-L´opez,
D. Moreno-Gonz´alez, J. F. Garc´ıa-Reyes and A. Molina-D´ıaz,
Screening of Over 600 Pesticides, Veterinary Drugs, Food-
Packaging Contaminants, Mycotoxins, and Other
Chemicals in Food by Ultra-High Performance Liquid
Chromatography Quadrupole Time-of-Flight Mass
Spectrometry (UHPLC-QTOFMS), Food Analytical Methods,
2017, 10(5), 1216–1244.
38 D. Taverna, L. Di Donna, F. Mazzotti, B. Policicchio and
G. Sindona, High-throughput determination of Sudan azodyes
within powdered chili pepper by paper spray mass
spectrometry, J. Mass Spectrom., 2013, 48(5), 544–547.
39 J. Liu, R. G. Cooks and Z. Ouyang, Enabling quantitative
analysis in ambient ionization mass spectrometry: internal
standard coated capillary samplers, Anal. Chem., 2013, 85,
5632–5636.
40 N. E. Manicke, B. J. Bills and C. Zhang, Analysis of biouids
by paper spray MS: advances and challenges, Bioanalysis,
2016, 8(6), 589–606.
41 International union of pure and applied chemistry (IUPCA)
Gold book, https://goldbook.iupac.org/html/L/L03540.html.
42 K. A. Cox, J. D. Williams, R. G. Cooks and R. E. Kaiser,
Quadrupole ion trap mass spectrometry: Current
applications and future directions for peptide analysis,
Biol. Mass Spectrom., 1992, 21(5), 226–241.


Original text

Paper spray ionization mass spectrometry for rapid
quantification of illegal beverage dyes†
Tianyang Guo,ab Zezhen Zhang,a Karen E. Yannell,a Yiyang Dongb
and R. Graham Cooks *a
A rapid method is described for quantification of six illegal colorants in beverages, i.e., soft beverages,
energy beverages, alcoholic beverages, teas, and fruit juices. Paper spray (PS) ionization combined with
tandem mass spectrometry (MS/MS) allowed detection of particular dyes in times of less than 1 min per
sample. Samples where diluted in methanol and isotopically-labeled internal standards were utilized to
obtain linear responses over ranges of two or three orders of magnitude. The LODs were below 1.5 ng
mL1 and LOQs were below 5 ng mL1. Quality control experiments gave accuracies that ranged
between 80% and 120%. Matrix effects were evaluated for different samples but had little effect given the
use of the dilution method.



  1. Introduction
    Dyes are added to specic products to provide attractive visual
    effects. In the case of foods, food dyes can compensate for color
    loss, enhance natural colors, or add color to colorless food.1
    Synthetic food dyes, synthesized from coal tar or petroleum byproducts,
    2 are widely used, owing to their ease of production,
    low cost, high stability, and good coloring properties.3 During
    the 1900s, some 80 different food dyes were used in the United
    States, but over the years, most of them have been taken off the
    market because of safety concerns.2 Currently, only nine
    synthetic colorings are allowed for food use by the U.S. Food
    and Drug Administration (FDA), and these are subject to
    certication.4
    Although maximum use levels for these dyes have been listed
    by the FDA, their use still requires careful consideration. For
    example, Fast Green, Orange B and Citrus Red 2 are legal in the
    US, but they are not permitted in other countries, e.g., China5
    and the European Union.6 Some studies showed that synthetic
    food dyes may have a negative effect on the behavior of children,
    such as hyperactivity.1,2,7 Furthermore, use of multiple synthetic
    food colors is also a challenge for food safety, because of
    potential synergistic effects.8
    The addition to food of some industrial dyes, e.g., Sudan
    dyes, Disperse dyes, Rhodamine B and Malachite Green, is
    forbidden due to their genotoxic and carcinogenic activity.9
    However, some producers still add these illegal non-food colors
    to the product.10,11 Therefore, a sensitive method to screen both
    legal and illegal dyes in food is required for food safety.
    Conventional mass spectrometry-based methods for detection
    of dyes require complex pretreatment process, including
    drying, extraction, and purication.12,13 These treatments avoid
    matrix interferences from various mono-, di- and polysaccharides
    and modied starch, and from compounds with
    the same molecular weight as the analyte as well as minimizing
    ionization suppression.14,15 These advantages come with the
    need for time-consuming chromatographic separation
    processes.12–14,16 Ambient ionization mass spectrometry17–19 is an
    alternative way to rapidly ionize samples without or with only
    minimal pretreatment. The ESI-related method of desorption
    electrospray ionization (DESI)20 and APCI-related direct analysis
    in real time (DART),21 as well as many other ambient ionization
    techniques, have been applied widely in food safety,19,22 environmental
    analysis,23 forensics24 and clinical diagnosis.25
    As for dyes, several ambient ionization methods have been
    used for identication or quantication. Four Sudan dyes in
    chili powder were quantied at the mgmL1 level by DART-MS,26
    although DART has proved less successful with those dyes
    which are salts. Four dyes in aqueous solution were detected by
    DESI-MS at the ng mL1 level.27 Dyes with different structures
    were identied at pg mL1 level in wool samples by surface
    acoustic wave nebulization (SAWN) mass spectrometry,
    although degradation of certain analytes was observed.28
    Paper spray (PS) ionization is a representative ESI-related
    ambient ionization method which allows rapid and direct
    analysis of an untreated sample from paper or other porous
    (occasionally non-porous29) media which include a ne tip. This
    technique requires neither elevated temperature nor gas ow so
    it is particularly appropriate for use with portable MS systems.30
    In several application areas, it has been demonstrated to allow
    aDepartment of Chemistry, Purdue University, West Lafayette, IN 47907, USA
    bCollege of Life Science and Technology, Beijing University of Chemical Technology,
    Beijing 100029, China
    † Electronic supplementary information (ESI) available. See DOI:
    10.1039/c7ay02241g
    Cite this: DOI: 10.1039/c7ay02241g
    Received 18th September 2017
    Accepted 25th October 2017
    DOI: 10.1039/c7ay02241g
    rsc.li/methods
    This journal is © The Royal Society of Chemistry 2017 Anal. Methods
    Analytical
    Methods
    PAPER
    Published on 26 October 2017. Downloaded by Beijing University of Chemical Technology on 07/11/2017 15:34:28.
    View Article Online
    View Journal
    quantication of analytes in complex matrices with the use of
    internal standards.31,32 Most such applications focus on biological
    samples, such as blood, urine and tissue. However, this
    technique is useful also in the food safety domain, because of
    the complexity of food matrix and the requirement for trace
    residue detection.33–37 Some azo dyes at mgmL1 level have been
    examined in powdered chili pepper by PS-MS/MS.38
    In this paper, we establish a PS-MS/MS method using
    multiple reaction monitoring (MRM) to quantify illegal dyes in
    liquid beverages. Minimal sample preparation was used and
    internal standards were investigated and optimized. LOD and
    LOQ at ng mL1 level, accuracy and precision were calculated
    using matrix-matched calibration curves. As a nal test, real
    samples were screened to ensure the usefulness of this method.

  2. Experimental
    2.1 Reagents and materials
    Analytical standards of Sudan I, Sudan II, Malachite Green (as
    chloride), Rhodamine B (as chloride), Crystal Violet (as chloride)
    and Methylene Blue (as chloride) were purchased as
    powders from Sigma-Aldrich (St. Louis, MO), and stored at
    20 C. The D5 isotopically labeled internal standards Sudan Id5
    and Malachite Green-d5 picrate were also purchased from
    Sigma-Aldrich, and stored at 20 C. HPLC grade methanol,
    acetic acid, and ammonium acetate were purchased from
    Sigma-Aldrich (St. Louis, MO). Twenty-one colorless and twenty
    colored beverage samples were purchased from three local
    supermarkets in West Lafayette, Indiana (Walmart, Meijer,
    Fresh City Market). They included so beverages, energy
    beverages, alcoholic beverages, teas, and fruit juices.
    2.2 Analytes and internal standards
    Illegal food dyes of two molecular types were investigated:
    neutral molecules and salts with complex cations. Most neutral
    molecule dyes produce the protonated molecule [M + H]+ in
    positive ion mode, while not being ionized in the negative ion
    mode. Compounds of this neutral molecule class, including
    Sudan and related dyes, are usually oil-soluble. Two representatives
    Sudan dyes (Table 1) were selected to assess the
    performance of rapid determination by paper spray (PS) as
    described in this article. The complex cation salt dyes, ionize
    with relatively high efficiency to give the intact cation [C]+ in the
    positive mode. The examples of this class examined were Malachite
    Green, Rhodamine B, Crystal Violet and Methylene Blue
    (Table 1).
    Internal standards (IS) were used to improve accuracy and
    precision, as well as to establish the robustness of the method
    for the various complex matrices. In ambient ionization mass
    spectrometry analysis, IS use is highly desirable.39,40 Commonly,
    two types of IS are used: structural analogues and stable-isotope
    labeled forms of analyte. Isotopically labeled IS's have performed
    very well in past ambient ionization mass spectrometry
    analyses, owing to similar ionization efficiency and similar
    transport along the paper substrate.31,32 However, the higher
    cost of isotopically labeled standards makes their use for each
    individual analyte impractical. Therefore, two IS's were selected
    to allow detection of multiple analytes. The IS Sudan I-d5 was
    chosen for the neutral molecule class and Malachite Green-d5
    picrate for the complex salt class (Table 1).
    2.3 Instruments and devices
    All MS experiments were performed using PS ionization
    combined with triple quadruple mass spectrometry. PS was performed
    using a toothless copper clip, obtained from Muller
    Electric (Akron, OH), and Whatman 1ET-Chr paper, obtained
    from GE Healthcare Life Sciences (Chicago, IL). The paper
    substrate was cut into a small triangle (8  10, mm), and clamped
    with the copper clip. High voltage was supplied to the clip
    and the solvent methanol was pipetted onto the paper triangle.
    The mass spectrometer used was a TSQ Quantum Access
    MAX (Thermo Fisher Scientic, Waltham, MA). Full scan mode
    was used to observe the precursor ion of each analyte/IS pair,
    while the multiple reaction monitoring (MRM) mode was used
    for quantication of the analytes and IS. The most abundant
    fragment of the precursor ion was used in the MRM quanti-
    cation (“quantier”); a second abundant fragment was used in
    a separate qualitative check of the quality of the data (“quali-
    er”). The optimized fragmentation results are summarized in
    Table 1.
    Table 1 Information and fragment results on specific dyes in foods and their internal standards
    Analytes Molecular formulaa Exact massb Precursor ion Tube lens (V)
    Precursor ion > product ion
    Quantier CEc Qualier CEc
    Sudan I C16H12N2O 248.09 [M + H]+ 85 249.1 > 93.2 26 249.1 > 232.0 33
    Sudan II C18H16N2O 276.13 [M + H]+ 85 277.1 > 121.1 18 277.1 > 260.2 12
    Sudan I-d5 C16D5H7N2O 253.13 [M + H]+ 85 254.1 > 98.2 30 — —
    Malachite Green C23H25N2

    • 329.20 [C]+ 100 329.2 > 313.1 35 329.2 > 208.1 32
      Rhodamine B C28H31N2O3

    • 443.23 [C]+ 100 443.2 > 399.1 42 443.2 > 355.1 58
      Crystal Violet C25H30N3

    • 372.24 [C]+ 100 372.2 > 356.2 36 372.2 > 251.1 31
      Methylene Blue C16H18N3S+ 284.12 [C]+ 90 284.1 > 268.0 34 284.1 > 240.2 32
      Malachite Green-d5 C23D5H20N2

    • 334.23 [C]+ 100 334.2 > 318.2 34 — —
      a For neutral molecule (M) or complex cation (C+) depending on which form analyte takes. b For neutral molecule (M) or complex cation (C+)
      depending on which form analyte takes. c CE – collision energy.
      Anal. Methods This journal is © The Royal Society of Chemistry 2017
      Analytical Methods Paper
      Published on 26 October 2017. Downloaded by Beijing University of Chemical Technology on 07/11/2017 15:34:28.
      View Article Online
      These data were recorded using optimized parameters of the
      PS source and MS as follows: ionization mode, positive; spray
      voltage, 3500 V; capillary temperature, 300 C; collision pressure,
      1.5 mTorr; peak width, 0.010 Th (Thomson, unit of m/z);
      scan time, 0.100 s; Q1 peak width (FWHM), 0.70 Th.
      Data acquisition and data processing utilized Thermo Fisher
      Xcalibur soware (version 3.0). Data for the ion transitions were
      separately acquired in two segments, because of the relative
      high intensity difference between them. Peaks were automatically
      integrated aer acquisition, and quantication was performed
      with a set of concentrations (x-axis) and the area ratios
      of analyte and internal standards (y-axis). Limits of detection
      (LODs) and limits of quantication (LOQs) were calculated as 3
      times and 10 times, respectively, of the standard deviation of
      [blank signal/IS signal] for seven blank samples containing IS in
      known amount, divided by the slope of the trend line in
      concentration units. This IUPAC denition41 does not consider
      chemical noise42 which is an important consideration in mass
      spectrometry. However, chemical noise (intrinsic signal at the
      m/z value being measured due to contamination and other
      sources) will result in a non-zero intercepts in the calibration
      curves and this was not the case in the present study.
      2.4 Sample preparation
      The colorless negative beverage samples were selected as the
      matrix. If carbonated, the liquid sample was degassed by sonication
      for ve minutes. If it had pulp, the liquid partition of the
      beverage sample was taken. Aer that, two simple sample
      treatment methods were used and compared:
      Method 1 (M1). Degassed liquid samples were diluted with
      spray solvent, methanol, spiked with mixed IS, and sprayed
      from the paper substrate to introduce the sample into the mass
      spectrometer.
      Method 2 (M2). Degassed liquid samples were spiked with
      mixed IS, pipetted and dried on the paper, and then sprayed
      with added spray solvent methanol to introduce the sample into
      mass spectrometer.
      Both methods required optimization of the spray solvent. In
      M1, dilution ratio and spray volume were also optimized; in M2,
      pipet volume and spray volume were also optimized.
      2.5 Screening and quantication
      For M1, quantication was carried out using internal standards
      and matrix-matched calibration curves. All degassed noncolored
      samples (N ¼ 21) were mixed together as a pooled
      matrix solution. Individual standard stock solutions were
      prepared using powdered dye standards dissolved in methanol
      and/or toluene to a concentration of 1000 mg mL1, and the
      resulting standard solutions were stored in the dark at 4 C.
      Calibration curves of peak area vs. concentration (ng mL1)
      were established by spiking dye standards into the pooled
      matrix solution to nal concentrations of 0.25, 0.5, 1, 2.5, 5, 10,
      25, 50, 100, 250, 500, and 1000 ng mL1. The corresponding
      solutions were also made up in water rather than the matrix to
      examine the effect of matrix. The best dilution solvents for the
      calibration curves were found by examining methanol/beverage
      mixtures over a range of proportions (v/v) when using M1.
      Internal standards at the nal concentration 100 ng mL1
      were also spiked into the above solutions. Quality control
      accuracy was determined by calculating the ratio between the
      determined value of analyte and the known value of the analyte
      in the initial sample. Experiments were done working with
      concentrations of 3.2, 16, 80, 400 ng mL1 as well as 100 ng
      mL1 IS.
      For M2, quantication again used IS but at a nal concentration
      of 400 ng mL1. The analytes in this method had nal
      concentrations of 1 to 5000 ng mL1. The solvent used was
      methanol. Addition of formic acid (0.1–1%) was found not to
      improve the performance.


  3. Results and discussion
    3.1 Optimization of spray method
    Methanol has oen been used for PS ionization,31,32 so it was
    tested rst. In method 1 (M1), the dilution ratio (v/v) was optimized
    by examining
    methanol þ beverage sample
    beverage sample
    ratios of 6, 7,
    8, 9, 10, 15, and 20. The data are shown in Fig. 1. The solvent of
    most samples was water, while for some alcoholic beverage, the
    solvent was water with a small proportion of ethanol. The
    results showed that for some analytes such as Malachite Green,
    there was no signicant difference when using different dilution
    ratios. In the cases of other analytes, e.g., Rhodamine B, the
    results of different dilution ratios were quite different. When
    the proportion of water (aqueous beverage) was higher than
    10%, poor spray ionization efficiency was found. The ratio 10%
    aqueous 90% methanol provided a stable spray. On the other
    hand, if the proportion of water was less than 10%, the spray
    ionization efficiency did not increase, but more solvent was
    needed. Therefore, we chose the 10 times dilution ratio of
    aqueous beverage with methanol. The corresponding optimization
    experiment for method 2 (M2), led to methanol alone
    being added to the dried analyte on the paper.
    A spray solvent volume of 30 mL was used to cover the entire
    paper triangle for a consistent spray for a few tens of seconds.
    Fig. 1 Optimization of dilution ratio of Malachite Green and Rhodamine
    B in method 1 (M1). Malachite Green showed no significant
    difference using different dilution ratio in the spray solvent while
    Rhodamine B had better spray ionization efficiency when the methanol
    dilution ratio was larger than 10.
    This journal is © The Royal Society of Chemistry 2017 Anal. Methods
    Paper Analytical Methods
    Published on 26 October 2017. Downloaded by Beijing University of Chemical Technology on 07/11/2017 15:34:28.
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    To obtain a consistent peak intensity and peak area, a sufficient
    number of points in each peak was necessary. Thus, 10 points
    per analyte was selected, achieving a balance between analytical
    speed and stability.
    In an attempt to improve ionization efficiency in M1, the weak
    acids, i.e., acetic acid and formic acid, and the salts of a weak acid
    and weak base, i.e., ammoniumacetate and ammoniumformate,
    were added to the spray solvent. However, the results did not
    provide any improvement in ionization efficiency.
    3.2 Optimization of sample preparation method
    Two simple sample preparation methods (M1 and M2)
    mentioned above were compared. The calibration curves were
    established for the analytes in a mixture of the colorless
    beverages (N ¼ 6) (Fig. 2a, b, d and e, S1a, b, d, e, h, i, k and l†) as
    well as in water (n ¼ 4) (Fig. 2c and f, S1c, f, j, m and S2†). In the
    case of Malachite Green, both methods showed good linear
    responses, and the RSDs were low (

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