GB 5009.17-2021 English PDF

GB 5009.17-2021: Determination of total mercury and organic-mercury in foods
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GB 5009.17-2021
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
National Food Safety Standard - Determination of
Total Mercury and Organic-mercury in Food
ISSUED ON: SEPTEMBER 7, 2021
IMPLEMENTED ON: MARCH 7, 2022
Issued by: National Health Commission of the People’s Republic of China;
State Administration for Market Regulation.
Table of Contents
Foreword ... 4 
1 Scope ... 5 
Part 1 - Determination of Total Mercury in Food ... 5 
Method 1 - Atomic Fluorescence Spectrometry ... 5 
2 Principle ... 5 
3 Reagents and Materials ... 5 
4 Instruments and Equipment ... 7 
5 Analytical Procedures ... 7 
6 Expression of Analytical Results ... 10 
7 Precision ... 11 
8 Others ... 11 
Method 2 - Direct Injection Method for Mercury Determination ... 11 
9 Principle ... 11 
10 Reagents and Materials ... 12 
11 Instruments and Equipment ... 13 
12 Analytical Procedures ... 13 
13 Expression of Analytical Results ... 14 
14 Precision ... 15 
15 Others ... 15 
Method 3 - Inductively Coupled Plasma Mass Spectrometry ... 15 
Method 4 - Cold Atomic Absorption Spectrometry ... 15 
16 Principle ... 15 
17 Reagents and Materials ... 16 
18 Instruments and Equipment ... 17 
19 Analytical Procedures ... 17 
20 Expression of Analytical Results ... 18 
21 Precision ... 19 
22 Others ... 19 
Part 2 - Determination of Methyl Mercury in Food ... 19 
Method 1 - Liquid Chromatography - Atomic Fluorescence Spectrometry ... 19 
23 Principle ... 19 
24 Reagents and Materials ... 19 
25 Instruments and Equipment ... 22 
26 Analytical Procedures ... 23 
27 Expression of Analytical Results ... 25 
28 Precision ... 25 
29 Others ... 25 
Method 2 - Liquid Chromatography - Inductively Coupled Plasma Mass
Spectrometry... 26 
30 Principle ... 26 
31 Reagents and Materials ... 26 
32 Instruments and Equipment ... 28 
33 Analytical Procedures ... 29 
34 Expression of Analytical Results ... 30 
35 Precision ... 31 
36 Others ... 31 
Appendix A Reference Conditions of Microwave Digestion ... 32 
Appendix B Reference Conditions of Instruments ... 33 
Appendix C Chromatograms of LC-AFS Method ... 35 
Appendix D Chromatograms of LC-ICP-MS Method ... 38 
National Food Safety Standard - Determination of
Total Mercury and Organic-mercury in Food
1 Scope
Part 1 of this Standard specifies the methods for the determination of total mercury in
food.
Part 1 of this Standard is applicable to the determination of total mercury in food.
Part 2 of this Standard specifies the methods for the determination of methyl mercury
in food.
Part 2 of this Standard is applicable to the determination of methyl mercury in aquatic
animals and their products, as well as rice and edible fungi.
Part 1 - Determination of Total Mercury in Food
Method 1 - Atomic Fluorescence Spectrometry
2 Principle
After the specimen is heated and digested by acid, in the acidic medium, the mercury
in the specimen is reduced to atomic-state mercury by potassium borohydride or
sodium borohydride, which is brought into the atomizer by the carrier gas (argon).
Under the irradiation of mercury hollow cathode lamp, the ground-state mercury atoms
are excited to a high-energy state. When they return from the high-energy state to the
ground-state, they emit fluorescence with a characteristic wavelength. The
fluorescence intensity is directly proportional to the mercury content, which is
quantified by the external standard method.
3 Reagents and Materials
Unless it is otherwise specified, the reagents used in this Method are of top-grade
purity, and the water is Grade-1 water specified in GB/T 6682.
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.
3.2.4 Potassium borohydride solution (5 g/L): weigh-take 5.0 g of potassium
borohydride; use potassium hydroxide solution (5 g/L) to dissolve it and dilute to 1,000
mL; mix it up. Prepare it right before use.
3.2.5 Nitric acid solution of potassium dichromate (0.5 g/L): weigh-take 0.5 g of
potassium dichromate; use nitric acid solution (5 + 95) to dissolve it and dilute to 1,000
mL; mix it up.
NOTE: this method may also use sodium borohydride as a reducing agent: weigh-take 3.5
g of sodium borohydride; use sodium hydroxide solution (3.5 g/L) to dissolve it and
reach a constant volume of 1,000 mL; mix it up. Prepare it right before use.
3.3 Standard Substance
Mercury chloride (HgCl2, CAS No.: 7487-94-7): purity ≥ 99%.
3.4 Preparation of Standard Solutions
3.4.1 Standard stock solution of mercury (1,000 mg/L): accurately weigh-take 0.1354
g of mercury chloride; use nitric acid solution of potassium dichromate (0.5 g/L) to
dissolve it and transfer to a 100 mL volumetric flask; dilute it to 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 2 years. Or a mercury standard solution certified by the country
and awarded with a standard substance certificate.
3.4.2 Standard intermediate solution of mercury (10.0 mg/L): accurately draw 1.00 mL
a clean polyethylene bottle; seal and store it for later use.
5.1.2 In terms of fresh samples, such as: vegetables, fruits, fish, meat and eggs, wash
and dry them; take the edible part and homogenize it; put it into a clean polyethylene
bottle; seal it; store it at 2 °C ~ 8 °C in the refrigerator for later use.
5.1.3 In terms of milk and dairy products, after homogenizing it, put it into a clean
polyethylene bottle; seal it; store it at 2 °C ~ 8 °C in the refrigerator for later use.
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; use a small amount of water to rinse the inner lid. Place the digestion tank on a
temperature-controllable electric heating plate or in the ultrasonic water bath; at 80 °C,
heat it up or ultrasonically degas for 3 min ~ 6 min to drive off the brown gas. Take out
the digestion inner tank; transfer the digestion solution to a 25 mL volumetric flask. Use
a small amount of water to rinse the inner tank in 3 times; combine the washing liquid
in a volumetric flask and reach a constant volume to the scale; mix it up for later use.
Meanwhile, conduct a blank test.
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.
Let it naturally cool down to room temperature; slowly loosen the stainless steel
enclosure. Take out the digestion inner tank; use a small amount of water to rinse the
inner lid. Put the digestion tank on a temperature-controllable electric heating plate or
in the ultrasonic water bath; at 80 °C, heat it up or conduct ultrasonic degassing for 3
min ~ 6 min to drive off the brown gas. Take out the digestion inner tank; transfer the
digestion solution to a 25 mL volumetric flask; use a small amount of water to rinse the
inner tank in 3 times; combine the washing liquid in a volumetric flask and reach a
constant volume to the scale; mix it up for later use. Meanwhile, conduct a blank test.
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.
5.2.3.2 Vegetable oils and animal fats
Weigh-take 1.0 g ~ 3.0 g (accurate to 0.001 g) of specimen; place it in a conical flask
of the digestion device. Add several glass beads; add 7 mL of sulfuric acid; carefully
mix it up, until the solution turns brown, then, add 40 mL of nitric acid. 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”.
5.2.3.3 Potatoes and soy 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, 30 mL of nitric acid and 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”.
5.2.3.4 Meat and eggs
Weigh-take 0.5 g ~ 2.0 g (accurate to 0.001 g) of specimen; place it in a conical flask
of the digestion device. Add several glass beads, 30 mL of nitric acid and 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”.
5.2.3.5 Milk and dairy products
mg/L, 2.0 mg/L, 3.0 mg/L, 4.0 mg/L and 6.0 mg/L.
NOTE: in accordance with the type and measuring range of the detector configured in the
instrument, or the actual content of mercury in the sample, the range of mass
concentration of mercury in the standard series solutions may be determined.
11 Instruments and Equipment
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%).
11.7 Sieve: particle size ≤ 425 μm (or sieve opening ≥ 40 mesh).
NOTE: the glassware needs to be soaked in nitric acid solution (1 + 4) for 24 h; use tap
water to repeatedly rinse it, and finally, use water to thoroughly rinse it.
12 Analytical Procedures
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 μm 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.
12.1.3 In terms of quick-frozen and canned food, thawed quick-frozen food and canned
food samples, 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.
12.1.4 For milk and dairy products, shake them well.
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 pro...