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GB 5009.267-2020: National food safety standard - Determination of Iodine in foods
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 don...