Rapid and Sensitive Determination of Acesulfame in Vinegar

Appli cat i on N ote 1 1 0 4
Rapid and Sensitive Determination of
Acesulfame in Vinegar
Ran Liangji,1 Jin Yan,1 Xu Qun,1 and Jeffrey Rohrer2
1
Thermo Fisher Scientific, Shanghai, People’s Republic of China;
2
Thermo Fisher Scientific, Sunnyvale, CA, USA
Key Words
HPLC, Acesulfame k, Acclaim Mixed-Mode WAX-1 Column, Artificial
Sweetener, Sugar Substitute, Food Additive, Food Safety, Food Analysis
Goal
To develop an efficient high-performance liquid chromatography (HPLC)
method for the rapid and sensitive determination of acesulfame in vinegar,
in compliance with the Chinese National Standard regulation
Introduction
Acesulfame (structure shown in Figure 1), a synthetic
sweetener 200 times sweeter than sucrose, has been
extensively used as a sugar substitute in foods and
beverages. The Standardization Administration of China
allows acesulfame to be added to fermented vinegar
products, but limits the added amount to no more than
4 µg/mL.1 Therefore, it is necessary to establish efficient
methods to sensitively and rapidly determine acesulfame
in fermented vinegar.
The typical method for determination of acesulfame
in vinegar uses HPLC, which is also recommended in
China GB/T 5009.140-2003.1-3 Table 1 lists details of
three methods for determining acesulfame in food and
beverages, each using either ammonium sulfate or
ammonium acetate as a mobile phase component. Use of
ammonium sulfate and ammonium acetate mobile phase
buffers with UV detection at ~220 nm may result in less
stable baselines than when using other HPLC mobile
phases. In addition, the polar compounds present in
vinegar samples may interfere with the separation of
acesulfame on a C18 stationary phase. To address these
issues, the authors investigated using other stationary
and mobile phases for this application.
0
H3C
Figure 1. Structure of acesulfame.
Table 1. Methods for determining acesulfame in food products.
Method
Sample
Column
Mobile Phase
Detection
GB/T 5009.140-20031
Beverage
C18
0.02 M Ammonium Sulfate/
Methanol/Acetonitrile, 10%
UV, 214 nm
Literature2
Food
C18
0.02 M Ammonium Acetate/
Methanol (90:10, v/v)
UV, 230 nm
Literature3
Liquid
Seasoning
C18
0.02 M Ammonium Acetate/
Methanol (93:7, v/v)
UV, 230 nm
N–
K+
S
0
0
0
2
Equipment, Software, and Consumables
• Thermo Scientific™ Dionex™ UltiMate™ 3000 Rapid
Separation LC (RSLC) system, including:
– LPG-3400RS Quaternary Pump (P/N 5040.0036)
– SRD-3400 Integrated Solvent and Degasser Rack
(P/N 5035.9245)
– WPS-3000TRS Well Plate Sampler, Thermostatted
(P/N 5840.0020), with 25 µL sample loop
(P/N 6820.2415)
– TCC-3000RS Thermostatted Column Compartment
(P/N 5730.0000)
Conditions
Column:
Thermo Scientific™ Acclaim™ Mixed-Mode
WAX-1, 3 µm, 3 × 150 mm (P/N 070088)
Mobile Phase:
Acetonitrile/100 mM ammonium phosphate
(dissolve 13.6 g of ammonium phosphate in 1 L
of DI water, adjust pH to 6.8 with 50% NaOH
solution), 20:80 (v/v)
Flow Rate:
0.8 mL/min
Injection Volume: 10 µL (partial-loop injection mode)
Temperature:
30 °C
– DAD-3000RS Diode Array Detector (P/N 5082.0010),
with 2.5 µL flow cell (P/N 6082.0300)
Detection:
UV, 227 nm
• Thermo Scientific™ Dionex™ Chromeleon™ Chromatography Data System software, version 7.1 or above
Preparation of Standard Solutions
• Thermo Scientific™ Target2™ Nylon Syringe Filters,
0.45 μm, 30 mm (P/N F2500-1)
Reagents and Standards
• Deionized (DI) water, 18.2 MΩ-cm resistivity, generated
from the Thermo Scientific™ Barnstead™ GenPure™ Pro
ultrapure water system (P/N 50131948)
• Acetonitrile, HPLC Grade (Fisher Scientific
P/N AC610010040)
• Ammonium phosphate monobasic, HPLC Grade,
(Fisher Scientific P/N A685-500)
• Sodium hydroxide (NaOH) solution, 50%
w/w/Certified (Fisher Scientific P/N SS254-500)
• Acesulfame potassium (Fisher Scientific
P/N NC0525062)
Stock Standard 1
Dissolve 0.01 g of acesulfame potassium standard in
10 mL of DI water. The concentration of Stock Standard 1
will be 1000 µg/mL.
Stock Standard 2
Dilute 400 μL of Stock Standard Solution 1 to 10 mL with
DI water. The concentration of Stock Standard 2 will be
40 µg/mL.
Stock Standard 3
Dilute 500 μL of Stock Standard Solution 2 to 10 mL with
DI water. The concentration of Stock Standard 3 will be
2 µg/mL.
Standard Solutions for Calibration
For calibration, prepare eight working standard solutions
with different concentrations by diluting the proper
amount of the stock standard solutions with DI water.
The volumes of each solution needed to make the
calibration standards are shown in Table 2.
Table 2. Preparation of calibration standards.
Acesulfame Stock Std
for Calibration, Concn
(µg/mL)
Stock Standard 2,
40
Stock Standard 3,
2
Volume of Acesulfame Stock
Std for Calibration
(mL)
Volume of
DI Water
(mL)
5.0
5.0
2.5
7.5
Final Volume of
Calibration Std
(mL)
Final Concn of
Calibration Std
(µg/mL)
20
10
10
1.25
8.75
0.625
9.375
5.0
5.0
5.0
1.0
2.5
7.5
0.5
0.25
9.75
0.125
9.875
2.0
10
0.05
0.025
Preparation of Samples
3
1.5
Two vinegar samples were purchased from a supermarket
in Chengdu, People’s Republic of China.
1.0
Dilute 1 mL of the vinegar sample to 100 mL with DI
water in a 100 mL volumetric flask. Pass the sample
through a 0.45 μm syringe filter prior to injection.
Dilute 5 mL of the 10 μg/mL calibration standard and
1 mL of the vinegar sample with DI water in a 100 mL
volumetric flask. The spiked concentration of acesulfame
in the vinegar sample will be 0.5 µg/mL. Pass the sample
through a 0.45 μm syringe filter prior to injection.
Peak: 1. Acesulfame
0.5
mAU
1
0
Results and Discussion
Here, ammonium acetate/ammonium phosphate mobile
phase buffers and methonal/acetonitrile mobile phase
solvents were evaluted using an Acclaim Mixed-Mode
WAX-1 column. Compared to ammonium acetate and
methanol, ammonium phosphate/acetonitrile yielded
better peak symmetry, a smoother baseline, and a faster
separation of acesulfame. Therefore, an acetonitrile/
ammonium phosphate mobile phase was used in
this work.
In addition, investigations of the concentration and pH
value of the mobile phase buffer showed that a 0.1 M
buffer concentration at pH 6.8 yielded a reproducible
separation of acesulfame in vinegar samples. Figure 2
shows a chromatogram of a 0.025 µg/mL acesulfame
standard under the optimized chromatographic
conditions.
Reproducibility, Linearity, and Detection Limit
Short-term method reproducibility was estimated by
making seven consecutive injections of a vinegar sample
spiked with acesulfame to a concentration of 0.5 µg/mL.
The retention time RSD was 0.1 and the peak area RSD
was 0.4, demonstrating good short-term precision for this
HPLC method.
–0.5
0
1
2
3
4
Minutes
5
6
7
8
Figure 2. An acesulfame standard.
12
10
Peak Area (µS * min)
Optimization of Chromatographic Conditions
Three columns with different stationary phases were
evaluted for the separation of acesulfame: the Acclaim
120 C18, Acclaim PolarAdvantage II (PA2), and the
Acclaim Mixed-Mode WAX-1 columns. Under the
recommended chromatographic conditions shown in
References 1–3, the acesulfame peak tailed with weak
retention (close to the void volume) on the Acclaim PA2
column. When using the Acclaim 120 C18 column, the
elution of some compounds from a vinegar sample
required a long time (nearly 20 min). The Acclaim
Mixed-Mode WAX-1 column—which has been applied
to the determination of additives including acesulfame in
beverages—showed good separation of acesulfame from
other compounds found in vinegar samples and was,
therefore, used in this application.4
0.025 µg/mL
8
6
4
2
0
0
5
10
15
20
25
Concentration (µg/mL)
Figure 3. Calibration curve for acesulfame.
Calibration linearity for UV detection of acesulfame was
investigated by making three consecutive 10 µL injections
of a standard prepared at eight different concentrations
(i.e., 24 total injections). Linearity was observed from
0.025 to 20 μg/mL when plotting the concentration vs
peak area (calibration curve shown in Figure 3). The
linear regression equation was A = 0.4874c (forced to the
origin), where A represents peak area and c represents
analyte concentration. The coefficient of determination
was 1.000. This calibration curve was used to quantify
acesulfame in vinegar samples.
Five replicate injections of an acesulfame standard
with a concentration of 0.025 μg/mL were used for
estimating the method detection limit (MDL) using
a signal-to-noise ratio = 3. The measured MDL of
acesulfame was 0.008 μg/mL. The detection limit of
acesulfame in a vinegar sample is 0.8 μg/mL (100-fold
dilution of the sample), which is much lower than the
4 μg/mL that is specified in GB/T 5009.140-2003.1
18.8
Peak:
15.0
10.0
mAU
1
5.0
b
Conclusion
This work describes an efficient HPLC method using a
mixed-mode column with UV detection for a rapid and
sensitive determination of acesulfame in vinegar. This
approach offers the advantages of simple sample
preparation, good method reproducibility, and a wide
linear calibration range.
References
1.GB/T 5009.140-2003: Determination of Acesulfame K
in Beverages; Standardization Administration of China
(SAC), General Administration of Quality Supervision,
Inspection and Quarantine of the People’s Republic of
China: Beijing, 2003.
0
a
–5.0
0
1
2
3
4
Minutes
5
3.Dong, M. Simultaneous Determination of Acesulfame,
Benzoic Acid, Sorbic Acid and Saccharin Sodium in
Compound Liquid Seasoner by Reversed Phase High
Performance Liquid Chromatography. Commodities
and Quality (Shang pin yu zhi liang) 2013, 3, 244, 252.
4.Dionex (now part of Thermo Scientific) Application
Note 193: Determination of Additives in Carbonated
Beverages. Sunnyvale, CA, 2007. [Online] www.
thermoscientific.com/content/dam/tfs/ATG/CMD/
CMD%20Documents/AN-193-DeterminationAdditive-Carbonated-Beverages-LPN1961.pdf
(accessed July 30, 2014).
www.thermofisher.com/chromatography
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7
Figure 4. A vinegar sample (a) and the same sample spiked with 0.5 μg/mL of
acesulfame standard (b).
2.Chen, Y.; Xie, X.F.; Di, J.W. Determination of
Acesulfame, Benzoic Acid, Sorbic Acid and Saccharin
Sodium in Food by HPLC. PTCA (Part B: Chem. Anal.)
2007, 43, 887–888. [Online] www.doc88.com/
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1. Acesulfame
Appli cat i on N ote 1 1 0 4
Analysis of Vinegar Samples
Acesulfame was not found in either vinegar sample.
Figure 4 shows chromatograms of a vinegar sample and
the same sample spiked with acesulfame. To judge method
accuracy, three injections were made of the two vinegar
samples spiked with a 0.5 μg/mL acesulfame standard.
The average recoveries were 90 and 96%, respectively,
demonstrating good method accuracy.
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