GB 5009.267-2020National food safety standard - Determination of iodine in foods (English PDF)

3.1 Reagent

3.1.1 25% Tetramethylammonium hydroxide [(CH3)4NOH] aqueous solution.

the English abbreviation name TMAH.

3.1.2 Isopropanol. Chromatographically pure.

3.1.3 Argon (Ar). Argon (>= 99.995%) or liquid argon.

3.1.4 Helium (He). Helium (>= 99.995%).

3.2 Preparation of reagents

3.3 Standard product

Potassium iodide (KI) or potassium iodate (KIO3). Reference reagent.

3.4 Preparation of standard solution

3.4.1 Iodine standard stock solution (1000 mg/L). Weigh 0.1685 g of potassium

iodate that has been dried at 180 °C +/- 2 °C to a constant weight. Use water to dissolve and make its volume reach to 100 mL. Or weigh 0.1307 g of potassium iodide which had been dried in a silica gel dryer for 24 hours. Use water to dissolve and dilute it to 100 mL. Store it in a brown bottle. It may also use the iodine standard solution certified nationally and awarded with a certificate of standard material.

3.4.2 Iodine standard intermediate solution (10.0 mg/L). Pipette 1.00 mL of

iodine element standard stock solution. Use diluent to make its volume reach to 100 mL.

3.4.3 Iodine standard solution (100 ug/L). Pipette 1.00 mL of iodine element

standard intermediate solution. Use diluent to make its volume reach to 100 mL.

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.

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.

4.6 Vortex mixer.

5.1 Preparation of specimen

5.1.1 Solid samples

5.1.1.1 Dry sample

For samples of beans, grains, fungi, tea, dried fruits, baked foods, etc., take the edible part; use a high-speed grinder to crush it; stir until uniform. For solid dairy products, protein powders, flour and other homogeneous powder samples, shake it uniformly.

5.1.1.2 Fresh sample

Wash and drain samples of vegetables, fruits, aquatic products, etc., if necessary; homogenize the edible part. For samples of meat and eggs, homogenize the edible part.

5.1.1.3 Quick frozen and canned food

Homogenize the edible part of the thawed quick-frozen food and canned food samples to homogeneity.

5.1.2 Liquid sample

Shake the samples of soft drinks, condiments, etc., uniformly.

5.2 Specimen processing

Weigh 0.2 g ~ 1 g (accurate to 0.001 g) of the specimen in a 50 mL plastic centrifuge tube which is resistant to 110 °C temperature. Add 5 mL of extraction solution. Vortex for 1 min, to make the sample fully dispersed.

5.3 Instrument reference conditions

5.3.1 Reference working conditions for instrument operation

Radio frequency power 1550 W; plasma gas flow rate 15 L/min; carrier gas flow rate 0.80 L/min ~ 0.90 L/min; auxiliary gas flow rate 0.30 L/min ~ 0.40 L/min;

pump speed during analysis.

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.

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.

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.

10.2.6 Sodium formate solution (200 g/L). Weigh 20.0 g of sodium formate. Use

water to dissolve and dilute it to 100 mL.

10.3 Preparation of standard solution

10.3.1 Standard stock solution of sodium thiosulfate (0.1 mol/L). Weigh 26 g of

sodium thiosulfate (Na2S2O3 - 5H2O). Add 0.2 g of anhydrous sodium carbonate.

Dissolve it in 1000 mL water. Slowly boil it for 10 min. Cool it down. Filter and calibrate after being placed for two weeks.