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This standard replaces GB 5009.267-2016 National food safety standard—Determination of iodine in foods and SN/T 3154-2012 Determination of iodine content in algae plant for export—Inductively coupled plasma mass spectrometry method.
The following main changes have been made with respect to GB 5009.267-2016:
—Inductively coupled plasma mass spectrometry has been introduced as Method I;
—The redox titration method has been revised and designated as Method II, with its applicability modified and a low concentration standard solution introduced;
—The As(III)–Ce(IV) catalytic spectrophotometry has been revised and designated as Method III, with its applicability and accuracy modified;
—The gas chromatography has been revised and designated as Method IV, with its applicability and accuracy modified.
National food safety standard—
Determination of iodine in foods
1 Scope
This standard specifies methods for determination of iodine content in foods.
Method I—inductively coupled plasma mass spectrometry is applicable to determination of iodine in foods.
Method II—redox titration is applicable to determination of iodine in algae and their products.
Method III—As(III)–Ce(IV) catalytic spectrophotometry is applicable to determination of iodine in grains, vegetables, fruits, beans and bean products, milk and milk products, meat, fish and eggs.
Method IV—gas chromatography is applicable to determination of iodine for food fortification purposes in infant formula and milk products, except for infant formula for special medical purposes and formula for special medical purposes.
Method I—inductively coupled plasma mass spectrometry (ICP-MS)
2 Principle
Iodine in the specimen is extracted by tetramethyl ammonium hydroxide solution and determined by inductively coupled plasma mass spectrometer. The content of iodine in the specimen is determined through qualitative analysis with by qualification with the specific mass number (127) of the iodine element (mass-to-charge ratio, m/z) and quantitative analysis with the intensity ratio of mass spectrum signal ratio of the iodine element to the internal standard element in proportion to the concentration of iodine.
3 Reagents and materials
Unless otherwise specified, all reagents used in this method are of guaranteed grade, and the water of Grade I as specified in GB/T 6682 or of high grade of purity for instrumental analysis purposes are used.
3.1 Reagents
3.1.1 25% tetramethylammonium hydroxide [(CH3)4NOH] solution: TMAH.
3.1.2 Isopropanol: Chromatographic grade.
3.1.3 Argon (Ar): Gaseous argon (≥99.995%) or liquid argon.
3.1.4 Helium (He): Gaseous helium (≥99.995%).
3.2 Preparation of reagents
3.2.1 Extracting solution (5% TMAH): Take 100 mL of 25% TMAH solution and dilute with water to 500 mL for sample preparation.
3.2.2 Diluent (0.5% TMAH): take 10 mL of 25% TMAH solution and dilute with water to 500 mL for preparation of standard solutions and dilution of the sample.
3.3 Standards
Potassium iodide (KI) or potassium iodate (KIO3):Reference reagent.
3.4 Preparation of standard solutions
3.4.1 Iodine standard stock solution (1,000 mg/L): Weigh 0.1685 g of potassium iodate dried to constant weight at 180°C±2°C, dissolve in water till 100 mL; alternatively, weigh 0.1307g of potassium iodide dried with silica gel desiccator for 24 h, dissolve in water till 100 mL, and keep it in a brown bottle; or use an iodine standard solution nationally approved and granted with the Reference Material Certificate.
3.4.2 Iodine standard intermediate solution (10.0 mg/L): Pipette 1.00 mL of iodine standard stock solution and dilute with the diluent to 100 mL.
3.4.3 Iodine standard working solution (100 μg/L): Pipette 1.00 mL iodine standard intermediate solution and dilute with the diluent to 100 mL.
3.4.4 Iodine series standard solutions: Separately pipette appropriate volumes of iodine standard working solution, and prepare with the diluent into series standard solutions at 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 and 20.0 μg/L; and the concentration range of the series standard solutions may be adjusted according to the concentration of the iodine element in the sample solution.
3.4.5 Standard solution of internal standard element (1,000 mg/L): Internal standard stock solution with single element or multiple elements of tellurium (Te), indium (In), rhodium (Rh), rhenium (Re) etc.
3.4.6 Internal standard working solution: Dilute the standard solution of internal standard element 10 or 100 times with water, and then take appropriate amount of solution from it and prepare it with diluent into the internal standard working solution at appropriate concentration. The internal standard solution may be manually added by fixed volume to the standard series and sample solution, or be added by the instrument. After mixing the internal standard with the sample solution, the reference concentration of the internal standard is about 10 μg/L–100 μg/L.
Note: For samples of complex matrices, the internal standard may be added with an appropriate amount of isopropanol to make the volume fraction of 1% to 2%.
4 Apparatus
4.1 Inductively coupled plasma mass spectrometer (ICP-MS).
4.2 Analytical balance, with a sensitivity of 0.1 mg and 1 mg.
4.3 Desiccator with thermostat or water bath shaker with thermostat.
4.4 Sample grinding device: Homogenizer and high speed disintegrator.
4.5 Centrifuge, with rotation speed greater than 3,000 r/min.
4.6 Vortex mixer.
5 Analysis procedure
5.1 Preparation of specimen
5.1.1 Solid samples
5.1.1.1 Dry sample
For samples such as beans, grains, fungi, tea, dried fruit and bakery products, take their edible parts, and grind and stir them with high speed disintegrator until uniform; for solid dairy products and such powder samples in a homogeneous form as albumen powder and flour, shake well.
5.1.1.2 Fresh sample
For samples such as vegetables, fruits and aquatic products, clean and drain them, take their edible parts and homogenize until uniform; for samples such as meat and eggs, take their edible parts and homogenize until uniform.
Foreword i
1 Scope
2 Principle
3 Reagents and materials
4 Apparatus
5 Analysis procedure
6 Expression of analysis results
7 Accuracy
8 Miscellaneous
9 Principle
10 Reagents and materials
11 Apparatus
12 Analysis procedure
13 Expression of analysis results
14 Accuracy
15 Miscellaneous
16 Principle
17 Reagents and materials
18 Apparatus
19 Analysis procedure
20 Expression of analysis results
21 Accuracy
22 Miscellaneous
23 Principle
24 Reagents and materials
25 Apparatus
26 Analysis procedure
27 Expression of analysis results
28 Accuracy
29 Miscellaneous
Annex A Gas chromatogram of iodine standard derivative
