GB 5009.17-2021Determination of total mercury and organic-mercury in foods (English PDF)

3.1 Reagents

3.1.1 Nitric acid (HNO3).

3.1.2 Hydrogen peroxide (H2O2).

3.1.3 Sulfuric acid (H2SO4).

3.1.4 Potassium hydroxide (KOH).

3.1.5 Potassium borohydride (KBH4). analytically pure.

3.1.6 Potassium dichromate (K2Cr2O7).

3.2 Preparation of Reagents

3.2.1 Nitric acid solution (1 + 9). measure-take 50 mL of nitric acid; slowly add it to 450

mL of water; mix it up.

3.2.2 Nitric acid solution (5 + 95). measure-take 50 mL of nitric acid; slowly add it to

950 mL of water; mix it up.

3.2.3 Potassium hydroxide solution (5 g/L). weigh-take 5.0 g of potassium hydroxide;

use water to dissolve it and dilute to 1,000 mL; mix it up.

3.3 Standard Substance

Mercury chloride (HgCl2, CAS No.. 7487-94-7). purity >= 99%.

3.4 Preparation of Standard Solutions

4.1 Atomic fluorescence spectrometer. equipped with a mercury hollow cathode lamp.

4.2 Electronic balance. with a division value of 0.01 mg, 0.1 mg and 1 mg.

4.3 Microwave digestion system.

4.4 Pressure digester.

4.5 Constant-temperature drying oven (50 °C ~ 300 °C).

4.6 Temperature-controllable electric heating plate (50 °C ~ 200 °C).

4.7 Ultrasonic water bath.

4.8 Homogenizer.

4.9 High-speed pulverizer.

5.1 Pre-treatment of Specimens

5.2 Digestion of Specimens

5.2.1 Method of microwave digestion

Weigh-take 0.2 g ~ 0.5 g of solid specimen (accurate to 0.001 g; for samples with relatively more water content, the sampling amount may be properly increased to 0.8 g), or accurately weigh-take 1.0 g ~ 3.0 g of liquid specimen (accurate to 0.001 g). For samples that are difficult to digest, for example, vegetable oils, weigh-take 0.2 g ~ 0.5 g (accurate to 0.001 g). Place it in a digestion tank; add 5 mL ~ 8 mL of nitric acid; put on the lid and let it stand for 1 h. For samples that are difficult to digest, add 0.5 mL ~

1 mL of hydrogen peroxide; tightly screw the lid; in accordance with the standard operating procedures of the microwave digestion apparatus (please refer to Table A.1 in Appendix A for the reference conditions of microwave digestion), conduct the digestion. After cooling it down, take it out; slowly open the lid of the tank to exhaust air;

5.2.2 Method of pressure tank digestion

Weigh-take 0.2 g ~ 1.0 g of solid specimen (accurate to 0.001 g; for samples with relatively more water content, the sampling amount may be properly increased to 2 g), or accurately weigh-take 1.0 g ~ 5.0 g of liquid specimen (accurate to 0.001 g). For samples that are difficult to digest, for example, vegetable oils, weigh-take 0.2 g ~ 0.5 g (accurate to 0.001 g). Place it in a digestion tank; add 5 mL of nitric acid; let it stand for 1 h or overnight. Put on the inner lid; tightly screw the stainless steel enclosure; put it in a constant-temperature drying oven; at 140 °C ~ 160 °C, maintain for 4 h ~ 5 h.

5.2.3 Method of reflux digestion

5.2.3.1 Grains

Weigh-take 1.0 g ~ 4.0 g (accurate to 0.001 g) of specimen; place it in a conical flask of the digestion device. Add several glass beads; add 45 mL of nitric acid and 10 mL and sulfuric acid; rotate the conical flask to prevent local carbonization. After installing the condenser pipe, heat it up at a low temperature. When it starts foaming, stop heating. After foaming stops, heat to reflux for 2 h. If the solution turns brown during the heating process, add 5 mL of nitric acid and continue to reflux for 2 h. Conduct digestion, until the sample is completely dissolved, which is generally pale yellow or colorless. After cooling, carefully add 20 mL of water from the upper end of the condenser pipe; continue to heat and reflux for 10 min. After leaving it to cool down, use an appropriate amount of water to rinse the condenser pipe; incorporate the rinsing liquid into the digestive fluid. Filter the digestive fluid through glass wool into a 100 mL volumetric flask; use a small amount of water to wash the conical flask and filter.

Incorporate the washing liquid into the volumetric flask; add water to the scale; mix it up for later use. Meanwhile, conduct a blank test.

5.2.3.5 Milk and dairy products

Weigh-take 1.0 g ~ 4.0 g (accurate to 0.001 g) of specimen, place it in a conical flask of the digestion device. Add several glass beads and 30 mL of nitric acid; for milk, add

10 mL of sulfuric acid; for dairy products, add 5 mL of sulfuric acid. Rotate the conical flask to prevent local carbonization. The subsequent steps are the same as 5.2.3.1 “After installing the condenser pipe, heat it up with a small fire... Meanwhile, conduct a blank test”.

5.3 Determination

10.1 Reagents

10.2 Preparation of Reagents

10.3 Standard Substance

Mercury chloride (HgCl2, CAS No.. 7487-94-7). purity >= 99%.

10.4 Preparation of Standard Solutions

10.4.1 Standard stock solution of mercury (1,000 mg/L). same as 3.4.1.

10.4.2 Standard intermediate solution of mercury (100 mg/L). accurately draw 10.0 mL

of the standard stock solution of mercury (1,000 mg/L) in a 100 mL volumetric flask;

10.4.3 Standard working solution of mercury (10.0 mg/L). accurately draw 10.0 mL of

the standard intermediate solution of mercury (100 mg/L) into a 100 mL volumetric flask; use nitric acid solution of potassium dichromate (0.5 g/L) to dilute it and reach a constant volume to the scale; mix it up. Store it at 2 °C ~ 8 °C in the refrigerator; keep away from light; it shall remain valid for 1 year.

11.1 Direct mercury meter.

11.2 Electronic balance. with a division value of 0.01 mg, 0.1 mg and 1 mg.

11.3 Homogenizer.

11.4 High-speed pulverizer.

11.5 Sample boat. nickel boat or quartz boat.

11.6 Carrier gas. oxygen (99.9%) or air; argon-hydrogen mixture (9.1, volume ratio)

(99.9%).

12.1 Pre-treatment of Specimens

12.1.1 In terms of grains and beans, take the edible part and evenly crush it, with a

particle size of 425 um or less (equivalent to 40 mesh or more). Put it into a clean polyethylene bottle; seal and store it for later use.

12.1.2 In terms of samples with relatively more water content, for example, vegetables, if necessary, wash and drain them; take the edible part and homogenize it. For samples like aquatic products, meat and eggs, take the edible part and homogenize it. Put it in a clean polyethylene bottle; seal it; store it at 2 °C ~ 8 °C in the refrigerator for later use.

12.2 Determination

12.2.1 Reference conditions of instrument

In accordance with the performance of the used direct mercury meter, adjust to the optimum state. The reference conditions of catalytic pyrolysis gold amalgam cold atomic absorption mercury meter are shown in Table B.1 in Appendix B; the reference conditions of catalytic pyrolysis gold amalgam atomic fluorescence mercury meter are shown in Table B.2; the reference conditions of pyrolysis cold atomic absorption mercury meter are shown in Table B.3.

12.2.2 Sample boat purification

After the sample ash remaining in the sample boat is cleaned up, adopt the built-in heating program of the instrument or muffle furnace to conduct high-temperature burning (600 °C ~ 800 °C) for more than 20 min to remove the mercury residue.