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This standard replaces GB 5009.17-2014 National food safety standard — Determination of total mercury and organic-mercury in foods
The following main modifications have been made with respect to GB 5009.17-2014:
Volume I Determination of total mercury in foods
——The name of Method I has been modified as “Atomic fluorescence spectrometry”, and the relevant content of sample digestion and annexes also modified;
——“Direct injection mercury measurement” has been added as Method II, and “Inductively coupled plasma mass spectrometry” added as Method III;
——“Cold-vapour atomic absorption spectrometry” has been modified as Method IV.
Volume 2 Determination of methyl mercury in foods
——“Liquid chromatography-atomic fluorescence spectrometry” as well as its application scope have been modified as Method I.
——“Liquid chromatogram-inductively coupled plasma mass spectrometry” has been added as Method II.
National food safety standard — Determination of total mercury and organic-mercury in foods
1 Scope
Volume I of this standard specifies the determination method of total mercury in grains.
Volume I of this standard is applicable to the determination of total mercury in grains.
Volume II of this standard specifies the determination method of methyl mercury in grains.
Volume II of this standard is applicable to the determination of methyl mercury in aquatic animals and their products, rice and edible fungi.
Volume I Determination of total mercury in foods
Method I Atomic fluorescence spectrometry
2 Principle
After the sample is heated and digested by acid, in the acidic medium, the mercury in the sample is reduced to atomic mercury by potassium borohydride or sodium borohydride, which is brought into an atomizer by carrier gas (argon gas). Under the irradiation of a mercury hollow cathode lamp, ground-state mercury atoms are stimulated to high-energy state, and when returned to the ground-state from high-energy state, they emit fluorescence with characteristic wavelength, and the fluorescence intensity is proportional to the mercury content, which is quantified by the external standard method.
3 Reagents and materials
Unless otherwise specified, super pure reagents and Grade 1 water (defined in GB/T 6682) are adopted for the purpose of this method.
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): Take 50 mL of nitric acid, and pour it slowly into 450 mL of water and mix well.
3.2.2 Nitric acid solution (5+95): Take 50 mL of nitric acid, and pour it slowly into 950 mL of water and mix well.
3.2.3 Potassium hydroxide solution (5 g/L): Weigh 5.0 g of potassium hydroxide, dissolve it in water, dilute to 1000 mL, and mix well.
3.2.4 Potassium borohydride solution (5 g/L): Weigh 5.0 g of potassium borohydride, dissolve it with 5 g/L potassium hydroxide solution, dilute to 1000 mL, and mix well. Freshly prepare before use.
3.2.5 Nitric acid solution of potassium dichromate (0.5 g/L): Weigh 0.5 g potassium dichromate, dissolve it with nitric acid solution (5+95), dilute to 1000 mL, and mix well.
Note: Sodium borohydride may also be used as reducing agent in this method: weigh 3.5 g of sodium borohydride, dissolve it with sodium hydroxide solution (3.5 g/L), dilute to 1000 mL, and mix well. Freshly prepare before use.
3.3 Standard sample
Mercury chloride (HgCl2, CAS No.7487-94-7): purity ≥ 99%.
3.4 Preparation of standard solution
3.4.1 Mercury standard stock solution (1000 mg/L): Accurately weigh 0.1354 g of mercuric chloride, dissolve it with nitric acid solution of potassium dichromate (0.5 g/L), transfer it to a 100 mL volumetric flask, dilute it to the scale, and mix well. Being protected from light in 2°C-8°C refrigerator, it may be preserved for 2 years. Or a nationally recognized and certified mercury standard solution.
3.4.2 Mercury standard intermediate solution (10.0 mg/L): Accurately pipet 1.00 mL of the mercury standard stock solution (1000 mg/L) in a 100 mL volumetric flask, dissolve it with nitric acid solution of potassium dichromate (0.5 g/L), dilute it to the scale, and mix well. Being protected from light in the refrigerator at 2°C-8°C, it may be preserved for 1 year.
3.4.3 Mercury standard working solution (50.0 μg/L): Accurately pipet 1.00 mL of the mercury standard intermediate solution (10.0 mg/L) in a 200 mL volumetric flask, dissolve it with nitric acid solution of potassium dichromate (0.5 g/L), dilute it to the scale, and mix well. Freshly prepare before use.
3.4.4 Mercury standard series solution: Respectively pipet 0.00 mL, 0.20 mL, 0.50 mL, 1.00 mL, 1.50 mL, 2.00 mL and 2.50 mL of mercury standard working solution (50.0μg/L) into a 50 mL volumetric flask, dilute with nitric acid solution (1+9), dilute to the scale, and mix well, which is equivalent to that the mercury concentration is 0.00μg/L, 0.20μg/L, 0.50μg/L, 1.00μg/L, 1.50μg/L, 2.00μg/L and 2.50μg/L. Freshly prepare before use.
4 Instruments and apparatus
4.1 Atomic fluorescence spectrometer: equipped with a mercury hollow-cathode lamp.
4.2 Electronic balance: sensitivity is 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 control electric hot plate (50°C~200°C).
4.7 Ultrasonic water bath.
4.8 Homogenizer.
4.9 High speed disintegrator.
Note: Both the glassware and polytetrafluoroethylene digestion inner tank require to be soaked in nitric acid solution (1+4) for 24 h, flushed with water repeatedly, and finally washed cleanly with water.
5 Analytical procedures
5.1 Sample pretreatment
5.1.1 Grain, beans and other samples shall be crushed evenly after removing edible parts, put into clean polyethylene bottles and sealed for later use.
5.1.2 For such fresh samples as vegetables, fruits, fish, meats and eggs, clean them and dry them in the air, take their edible parts and homogenize uniformly, put them into clean polyethylene bottles, seal the bottles and put them into the refrigerator at 2°C~8°C for later use.
5.1.3 After milk and milk products are homogenated or homogenized, put them into clean polyethylene bottles, and seal them in a refrigerator at 2°C~8°C for later use.
Foreword iii
1 Scope
2 Principle
3 Reagents and materials
4 Instruments and apparatus
5 Analytical procedures
6 Calculation (expression) of analytic result
7 Precision
8 Others
9 Principle
10 Reagents and materials
11 Instruments and apparatus
12 Analytical procedures
13 Calculation (expression) of analytic result
14 Precision
15 Others
16 Principle
17 Reagents and materials
18 Instruments and apparatus
19 Analytical procedures
20 Calculation (expression) of analytic result
21 Precision
22 Others
23 Principle
24 Reagents and materials
25 Instruments and apparatus
26 Analytical procedures
27 Calculation (expression) of analytic result
28 Precision
29 Others
30 Principle
31 Reagents and materials
32 Instruments and apparatus
33 Analytical procedures
34 Calculation (expression) of analytic result
35 Precision
36 Others
Annex A Reference condition of microwave digestion
Annex B Reference condition of instruments
Annex C Chromatogram of LC-AFS
Annex D Chromatogram of LC-ICP-MS
