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National food safety standard - Determination of Iodine in foods
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National Food Safety Standard -- Determination of Iodine in Foods
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GB 5009.267-2020: PDF in English
GB 5009.267-2020
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
National food safety standard - Determination of
iodine in foods
ISSUED ON: SEPTEMBER 11, 2020
IMPLEMENTED ON: MARCH 11, 2021
Issued by: National Health Commission of PRC;
State Administration for Market Regulation.
Table of Contents
Foreword ... 4
1 Scope ... 5
2 Principle ... 5
3 Reagents and materials ... 6
4 Instruments and equipment... 7
5 Analytical procedures ... 7
6 Expression of analysis results ... 9
7 Precision ... 10
8 Others ... 10
9 Principle ... 10
10 Reagents and materials ... 11
11 Instruments and equipment ... 12
12 Analytical procedures ... 13
13 Expression of analysis results ... 13
14 Precision ... 14
15 Others ... 14
16 Principles ... 14
17 Reagents and materials ... 15
18 Instruments and equipment... 16
19 Analytical procedures ... 17
20 Expression of analysis results ... 18
21 Precision ... 18
22 Others ... 19
23 Principles ... 19
24 Reagents and materials ... 19
25 Instruments and equipment... 20
26 Analytical procedures ... 20
27 Expression of analysis results ... 22
28 Precision ... 23
29 Others ... 23
Appendix A Gas chromatogram of iodine standard derivative ... 24
National food safety standard - Determination of
iodine in foods
1 Scope
This standard specifies the determination method of iodine content in food.
The method 1 Inductively coupled plasma mass spectrometry is suitable for the
determination of iodine in food.
The method 2 Redox titration is suitable for the determination of iodine in algae
and its products.
The method 3 Arsenic-cerium catalytic spectrophotometry is suitable for the
determination of iodine in food, vegetables, fruits, beans and their products,
milk and their products, meat, fish and eggs.
The method 4 Gas chromatography is applicable to the determination of
nutritional fortifier iodine in infant formula foods and dairy products (except
infant formula foods for special medical purposes and formula foods for special
medical purposes).
Method 1 -- Inductively coupled plasma mass
spectrometry (ICP-MS)
2 Principle
The iodine in the specimen is extracted by tetramethylammonium hydroxide
solution and measured by inductively coupled plasma mass spectrometer. It is
qualitatively determined by the specific mass of iodine element 127 (mass-to-
charge ratio, m/z), the mass spectrometry signal intensity ratio between iodine
element and internal standard element which is proportional to the
concentration of the iodine element is used for quantification, to determine the
iodine content in the specimen.
standard intermediate solution. Use diluent to make its volume reach to 100 mL.
3.4.4 Iodine series standard solution: Respectively, pipette appropriate volume
of iodine standard solution. Use the diluent to make a series standard solution
which has the concentration of 0 μg/L, 0.100 μg/L, 1.00 μg/L, 5.00 μg/L,10.0
μg/L, 15.0 μg/L, 20.0 μg/L. It may also adjust the concentration range of the
series standard solution according to the iodine concentration in the sample
solution.
3.4.5 Internal standard element standard solution (1000 mg/L): Tellurium (Te),
indium (In), rhodium (Rh), rhenium (Re) and any other single-element or multi-
element internal standard stock solution.
3.4.6 Internal standard solution: First use water to dilute the internal standard
element standard solution 10 times or 100 times. Then take an appropriate
amount of the solution and use the diluent to prepare an internal standard
solution of appropriate concentration. The internal standard solution can be
added manually and quantitatively to the standard series and sample solutions;
it can also be added online by the instrument. After the internal standard is
mixed with the sample solution, the reference concentration of the internal
standard is about 10 μg/L ~ 100 μg/L.
Note: For samples with complex matrices, an appropriate amount of isopropanol can
be added to the internal standard, to make the volume fraction 1% ~ 2%.
4 Instruments and equipment
4.1 Inductively coupled plasma mass spectrometer (ICP-MS).
4.2 Analytical balance: Sensitivity is 0.1 mg and 1 mg.
4.3 Constant temperature drying oven or constant temperature water bath
shaker.
4.4 Sample crushing equipment: Homogenizer, high-speed crusher.
4.5 Centrifuge: The speed is greater than 3000 r/min.
4.6 Vortex mixer.
5 Analytical procedures
5.1 Preparation of specimen
5.1.1 Solid samples
cell gas He gas flow rate 4 mL/min ~ 5 mL/min; when each sample is measured,
the flushing time of the sample injection system is greater than 60 s.
5.3.2 Measurement reference conditions
After the tuning instrument meets the measurement requirements, edit the
measurement method and select the iodine isotope (127I) and the internal
standard tellurium isotope (125Te, 130Te) or 103Rh or 115In or 185Re.
Note: If the ICP-MS instrument changes from an acidic injection system to an
alkaline system, it is recommended to replace all injection pump tubes and
clean the injection system with 0.5% TMAH solution for 1 h ~ 2 h, until the 127I
signal is stable.
5.4 Preparation of standard curve
Inject iodine standard solution into ICP-MS. Measure the signal response value
of iodine element and internal standard element. Take the mass concentration
of iodine element as the abscissa, the ratio of the response signal value of
iodine element and the selected internal standard element as the ordinate, to
draw standard curve.
5.5 Measurement of sample solution
Inject the blank and sample solution into the inductively coupled plasma mass
spectrometer, respectively. Measure the signal response values of the iodine
element and the selected internal standard element. Calculate the ratio of the
response signal value of the iodine element and the selected internal standard
element. Obtain the mass concentration of iodine in the liquid to be measured
according to the standard curve.
6 Expression of analysis results
The iodine content in the specimen is calculated according to formula (1):
Where:
X - The content of iodine in the specimen, in milligrams per kilogram (mg/kg);
ρ - The mass concentration of iodine element in the sample solution, in
micrograms per liter (μg/L);
ρ0 - The mass concentration of iodine element in the sample blank solution,
in micrograms per liter (μg/L);
10 Reagents and materials
Unless otherwise specified, the reagents used in this method are all analytically
pure; the water is grade-3 water as specified in GB/T 6682.
10.1 Reagents
10.1.1 Anhydrous sodium carbonate (Na2CO3).
10.1.2 Liquid bromine (Br2).
10.1.3 Sulfuric acid (H2SO4).
10.1.4 Sodium formate (CHNaO2).
10.1.5 Sodium thiosulfate (Na2S2O3 • 5H2O).
10.1.6 Potassium iodide (KI): Reference substance.
10.1.7 Methyl orange.
10.1.8 Soluble starch.
10.2 Reagent preparation
10.2.1 Sodium carbonate solution (50 g/L): Weigh 5 g of anhydrous sodium
carbonate. Use water to dissolve it and make its volume reach to 100 mL.
10.2.2 Saturated bromine water: Measure 5 mL of liquid bromine and place it in
a brown glass bottle with a stopper which is coated with Vaseline. Add 100 mL
of water. Shake it sufficiently to make it a saturated solution (a small amount of
liquid bromine is left at the bottom of the solution; the operation shall be done
in ventilation hood).
10.2.3 Sulfuric acid solution (3 mol/L): Measure 180 mL of sulfuric acid and
slowly pour it into a beaker containing 700 mL of water. Keep stirring. Cool to
room temperature. Use water to dilute it to 1000 mL. Mix well.
10.2.4 Sulfuric acid solution (1 mol/L): Measure 57 mL of sulfuric acid and slowly
pour it into a beaker containing 700 mL of water. Keep stirring. Cool to room
temperature. Use water to dilute it to 1000 mL. Mix well.
10.2.5 Potassium iodide solution (150 g/L): Weigh 15.0 g of potassium iodide.
Use water to dissolve and dilute it to 100 mL. Store it in a brown bottle. Prepare
it before use.
10.2.6 Sodium formate solution (200 g/L): Weigh 20.0 g of sodium formate. Use
11.9 Brown acid burette: 25 mL; the minimum scale is 0.1 mL.
11.10 Micro acid burette: 1 mL or 5 mL; the minimum scale is 0.01 mL.
12 Analytical procedures
12.1 Specimen preparation
Same as 5.1.
12.2 Specimen analysis
12.2.1 Weigh 2 g ~ 5 g of the specimen (accurate to 0.01 g). Place it in a 50 mL
porcelain crucible. Add 5 mL ~ 10 mL of sodium carbonate solution to fully
infiltrate the specimen. Let it stand for 5 min. Place it in a 101 °C ~ 105 °C
constant temperature drying oven to dry it. Take it out.
12.2.2 Heat and carbonize the dried specimen until it is smoke-free. Place it in
a muffle furnace at 550 °C ± 25 °C for 40 minutes. Cool to room temperature.
Take it out. Add a small amount of water to grind it. Transfer the solution and
residue into a 250 mL beaker. Use water to rinse the crucible several times and
merge it into the beaker. The total volume of solution in the beaker is about 150
mL ~ 200 mL. After boiling for 5 min, use filter paper to filter it into a 250 mL
iodine flask while it is hot, to prepare for use.
12.2.3 Add 2 ~ 3 drops of methyl orange solution to the iodine measuring flask.
Use 1 mol/L sulfuric acid solution to adjust it o red. Add 5 mL of saturated
bromine water. Heat and boil until the yellow color disappears. After cooling
slightly, add 5 mL of sodium formate solution. Heat to boil for 2 minutes. Use
water bath to cool to below 30 °C. Then add 5 mL of 3 mol/L sulfuric acid
solution and 5 mL of potassium iodide solution. Cover the bottle cap and place
it in the dark for 10 minutes. Use sodium thiosulfate standard solution to titrate
the solution until it becomes light yellow. Add 1 mL of starch solution. Continue
titration until the blue color just disappears. At the same time, do a blank test
and record the consumed sodium thiosulfate standard solution volume.
13 Expression of analysis results
The iodine content in the specimen is calculated according to formula (2):
Where:
In the reaction system, Ce4+ is yellow and Ce3+ is colorless. The absorbance
value of the remaining Ce4+ is measured by a spectrophotometer. The iodine
content is linearly related to the logarithm of the absorbance value, to calculate
the total iodine content in the food.
17 Reagents and materials
Unless otherwise specified, the reagents used in this method are analytically
pure; the water is grade-2 water as specified in GB/T 6682.
17.1 Reagent
17.1.1 Anhydrous potassium carbonate (K2CO3).
17.1.2 Zinc sulfate (ZnSO4 • 7H2O).
17.1.3 Potassium chlorate (KClO3).
17.1.4 Sulfuric acid (H2SO4): Premium grade pure.
17.1.5 Sodium hydroxide (NaOH).
17.1.6 Arsenic trioxide (As2O3).
17.1.7 Sodium Chloride (NaCl): Premium grade pure.
17.1.8 Ammonium cerium sulfate [(Ce(NH4)4(SO4)4 • 2H2O) or (Ce(NH4)4 (SO4)4
• 4H2O)].
17.1.9 Potassium iodide (KI): Reference substance.
17.2 Reagent preparation
17.2.1 Potassium carbonate-sodium chloride mixed solution: Weigh 30 g of
anhydrous potassium carbonate and 5 g of sodium chloride. Dissolve them in
100 mL of water. It can be stored for 6 months at room temperature.
17.2.2 Zinc sulfate-potassium chlorate mixed solution: Weigh 5 g of potassium
chlorate in a beaker. Add 100 mL of water. Heat to dissolve. Add 10 g of zinc
sulfate. Stir to dissolve. It can be stored for 6 months at room temperature.
17.2.3 Sulfuric acid solution (2.5 mol/L): Measure 140 mL of sulfuric acid and
slowly pour it into a beaker containing 700 mL of water. Stir continuously. Cool
to room temperature. Use water to dilute to 1000 mL. Mix well.
17.2.4 Arsenious acid solution (0.054 mol/L): Weigh 5.3 g of arsenic trioxide,
18.5 Constant temperature drying oven.
18.6 Adjustable electric furnace: 1000 W.
18.7 Vortex mixer.
18.8 Analytical balance: Sensitivity is 1 mg and 0.1 mg.
18.9 Stopwatch timer
19 Analytical procedures
19.1 Specimen preparation
Same as 5.1.
19.2 Ashing of specimen
Accurately pipette 0.5 mL of iodine standard application series solutions (with
iodine content of 0 ng, 25 ng, 50 ng, 100 ng, 150 ng, 200 ng, 250 ng); weigh
0.3 g ~ 1.0 g (accurate to 0.001 g) of specimen in a porcelain crucible. Add 1
mL ~ 2 mL of water to the solid specimen (liquid sample, homogenized sample
and standard solution do not need to add water). Respectively add 1 mL of
potassium carbonate-sodium chloride mixed solution and 1 mL of zinc sulfate-
potassium chlorate mixed solution and stir well. Iodine standard series and
specimens are placed in a constant temperature drying oven at 103 °C ± 2 °C
and dried for 3 hours. Then the dried specimens are carbonized on an
adjustable electric furnace for about 30 min in a fume hood (the iodine standard
series do not need to be carbonized). During carbonizing, cover the porcelain
crucible but leave a gap, until the specimen no longer smokes. Then put the
iodine standard series and the carbonized specimen in the muffle furnace, to
ash it at 600 °C for 4 hours. After the furnace temperature drops to room
temperature, take it out. The ashed specimen shall have uniform white or light
gray-white.
19.3 Preparation of standard curve and determination of sample solution
Add 8 mL of water to the crucible after ashing. Let it stand for 1 hour to fully
infiltrate the ash sintered on the crucible. Stir to dissolve salt substances. Then
stand for at least 1 hour to completely precipitate the ash (the standing time
shall not exceed 4 hours). Pipette 2.0 mL of the supernatant into a test tube
(Caution: Do not pipette the sediment). Iodine standard series solutions are
arranged in order from high concentration to low concentration. Add 1.5 mL of
arsenous acid solution to each tube. Use a vortex mixer to mix it thoroughly, to
release the gas. Then place it in a 30 °C ± 0.2 °C constant temperature water
bath for 15 min.
is less than or equal to 1 mg/kg and greater than 0.1 mg/kg, the absolute
difference between two independent determination results obtained under
repeatability conditions shall not exceed 15% of the arithmetic mean. When it
is less than or equal to 0.1 mg/kg, the absolute difference between two
independent determination results obtained under repeatability conditions must
not exceed 20% of the arithmetic mean.
22 Others
When calculated with a sampling volume of 0.3 g, the method quantification
limit is 0.1 mg/kg.
Method 4 -- Gas chromatography
23 Principles
The iodine in the specimen reacts with methyl ethyl ketone under sulfuric acid
conditions to generate methyl ethyl ketone and iodine derivatives, which are
separated by gas chromatography, detected by an electron capture detector,
quantified by an external standard method.
24 Reagents and materials
Unless otherwise stated, all reagents in this method are of analytical grade. The
water is the grade-1 water as specified in GB/T 6682 or the high-purity water
used in instrument analysis as specified in GB/T 33087-2016.
24.1 Reagent
24.1.1 Amylase: Enzyme activity ≥ 1.5 U/mg.
24.1.2 Potassium iodide (KI) or potassium iodate (KIO3): Reference substance.
24.1.3 Hydrogen peroxide (H2O2).
24.1.4 Potassium ferrocyanide [K4Fe(CN)6 • 3H2O].
24.1.5 Zinc acetate [Zn(CH3COO)2].
24.1.6 Butanone (C4H8O): Chromatographically pure.
24.1.7 Sulfuric acid (H2SO4): Supreme grade pure.
26.1.1 According to the identification of the ingredient list in the product
label, the specimen containing no starch
Weigh 5 g of uniformly mixed solid specimen or 20 g of liquid specimen
(accurate to 0.01 g) in a 150 mL conical flask. Use about 25 mL of hot water at
about 40 °C to dissolve the solid specimen.
26.1.2 According to the identification of the ingredient list in the product
label, the specimen containing starch
Weigh 5 g of uniformly mixed solid specimen or 20 g of liquid specimen
(accurate to 0.01 g) into a 150 ml conical flask. Add 0.2 g of amylase. Use 25
ml of hot water at about 40 °C to dissolve the solid specimen. Enzymatically
hydrolyze in a constant temperature drying oven at 60 °C for 30 minutes. Take
it out to cool.
26.2 Preparation of specimen test solution
26.2.1 Precipitation
Transfer the above-treated sample solution into a 100 mL volumetric flask. Add
5 mL of potassium ferrocyanide solution and 5 mL of zinc acetate solution. Use
water to make its volume reach to the mark. Shake well and let stand for 10
minutes. Filter it. Pipette 10 mL of the filtrate into a 100 mL separatory funnel.
Add 10 mL of water.
26.2.2 Derivation and extraction
Add 0.7 mL of sulfuric acid, 0.5 mL of methyl ethyl ketone, 2.0 mL of hydrogen
peroxide solution to the separatory funnel. Mix well and keep it at room
temperature for 20 minutes. Add 20 mL of n-hexane. Shake and extract for 2
minutes. After standing for stratification, transfer the aqueous phase into
another separatory funnel. Perform the second extraction. Combine the organic
phases and use water to wash it for 2 ~ 3 times. After filtering and dehydrating
through anhydrous sodium sulfate, transfer it into a 50 mL volumetric flask. Use
n-hexane to make the volume reach to the mark. This is the sample
measurement solution. Perform the reagent blank at the same time.
26.3 Preparation of working solution for determination of iodine standard
Pipette 1.0 mL, 2.0 mL, 4.0 mL, 8.0 mL, 12.0 mL of iodine standard working
solution, which is equivalent to 1.0 μg, 2.0 μg, 4.0 μg, 8.0 μg, 12.0 μg of iodine.
Other analysis steps are processed simultaneously with the specimen.
26.4 Instrument reference conditions
The instrument reference conditions are as follows:
......
| Standard ID | GB 5009.267-2020 (GB5009.267-2020) | | Description (Translated English) | National food safety standard - Determination of Iodine in foods | | Sector / Industry | National Standard | | Classification of Chinese Standard | X09 | | Word Count Estimation | 16,150 | | Date of Issue | 2020-09-11 | | Date of Implementation | 2021-03-11 | | Older Standard (superseded by this standard) | GB 5009.267-2016; SN/T 3154-2012 | | Regulation (derived from) | National Health Commission Announcement No. 7 (2020) of the State Administration for Market Regulation |
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