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This standard supersedes “Determination of Total Mercury and Organic-mercury in Foods” (GB/T 5009.17-2003).
There are some significant changes in this standard over GB/T 5009.17-2003:
- the name of this standard was revised as "National Food Safety Standard - Determination of Total Mercury and Organic-mercury in Foods";
- dithizone colorimetry for determination of total mercury, gas chromatography and cold-vapor atomic absorption method for determination of organic mercury were deleted;
- liquid chromatogram - atomic fluorescence spectrometry (LC-AFS) for determination of methyl mercury was added.
Contents
Foreword i
1 Scope 1
2 Principles 1
3 Reagents and Materials 1
4 Instruments and Apparatus 2
5 Analytical Procedures 3
6 Calculation (Expression) of Analytic Result 5
7 Precision 5
8 Others 5
9 Principle 6
10 Reagents and Materials 6
11 Instruments and Apparatus 7
12 Analytical Procedures 7
13 Calculation (Expression) of Analytical Result 8
14 Precision 8
15 Others 9
16 Principle 9
17 Reagents and Materials 9
18 Instruments and Apparatus 11
19 Analytical Procedures 11
20 Calculation (Expression) of Analytical Result 12
21 Precision 12
22 Others 13
Appendix A Reference Condition of Microwave Digestion 14
Appendix B Chromatogram 15
National Food Safety Standard
Determination of Total Mercury and Organic-mercury in Foods
食品安全國家標(biāo)準(zhǔn)
食品中總汞及有機(jī)汞的測定
1 Scope
Volume I of this standard specifies method for determination of total mercury in foods.
Volume I of this standard is applicable to the determination of total mercury in foods.
Volume II of this standard specifies the liquid chromatogram - atomic fluorescence spectrometry (LC-AFS) for determination of methyl mercury content in foods.
Volume II of this standard is applicable to the determination of methyl mercury content in foods.
Volume I Determination of Total Mercury in Foods
Method 1 Atomic Fluorescence Spectrometry
2 Principles
After being heated and digested in acid, the mercury in the specimen will be reduced to the atomic mercury by the potassium borohydride (KBH4) or sodium borohydride (NaBH4) in acid medium and is carried into the atomizer by the carrier gas (argon gas), the mercury atoms at ground state will be activated to the super-high energy state with the irradiation of the hollow-cathode lamp of special mercury; when the mercury atoms are deactivated to the ground state and eradiate out the fluorescent of characteristic wavelength, the fluorescence intensity is proportional to the mercury content and shall be quantified by comparing with the standard series solution.
3 Reagents and Materials
Note: Unless otherwise specified, reagents used in this method are all super pure, and 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;
3.2 Reagent preparation
3.2.1 Nitric acid solution (1+9): measure 50mL nitric acid, slowly pour it into 450mL water.
3.2.2 Nitric acid solution (5+95): measure 5mL nitric acid and slowly pour it into 95mL water.
3.2.3 Potassium hydroxide solution (5g/L): weigh 5.0g potassium hydroxide and dissolve it in pure water, dilute the solution to 1 000mL and mix it uniformly.
3.2.4 Potassium borohydride solution (5g/L): weigh 5.0g potassium borohydride and dissolve it in 5g/L potassium hydroxide solution, dilute the solution to 1 000mL and mix it uniformly, this reagent is prepared freshly before use.
3.2.5 Nitric acid solution of potassium dichromate (0.5g/L): weigh 0.05g potassium dichromate and dissolve it in 100mL nitric acid solution (5+95).
3.2.6 Nitric acid - perchloric acid mixed solution (5+1): measure 500mL nitric acid and add in 100mL perchloric acid, and mix it uniformly.
3.3 Standard sample
Mercuric chloride (HgCl2): purity ≥99%.
3.4 Preparation of standard solution
3.4.1 Standard stock solution of mercury (1.00mg/mL): accurately weigh 0.1354g dried mercuric chloride, dissolve it in the nitric acid solution of potassium dichromate (0.5g/L), transfer the liquid into a 100mL-volumetric flask and dilute it to the scale, mix it uniformly finally. Concentration of this solution is 1.00mg/mL. Being protected from light in 4℃ refrigerator, it may be preserved for 2 years. Or standard solution material approved and awarded with reference material certificate by the nation shall be purchased.
3.4.2 Standard intermediate solution of mercury (10μg/mL): pipet 1.00mL standard stock solution of mercury (1.00mg/mL) to a 100mL-volumetric flask, dilute the solution to the scale with nitric acid solution of potassium dichromate (0.5g/L), mix it uniformly finally. Concentration of this solution is 10μg/mL. Being protected from light in 4℃ refrigerator, it may be preserved for 2 years.
3.4.3 Standard working solution of mercury (50ng/mL): pipet 0.50mL standard intermediate solution of mercury (10μg/mL) to a 100mL-volumetric flask, dilute the solution to the scale with nitric acid solution of potassium dichromate (0.5g/L), mix it uniformly finally. This solution concentration is 50ng/mL, and is prepared freshly before use.
4 Instruments and Apparatus
Note: Both the glassware and polytetrafluoroethylene digestion inner tank require to be soaked in nitric acid solution (1+4) for 24h, washed with water repeatedly, and finally washed cleanly with deionized water.
4.1 Atomic fluorescence spectrometer.
4.2 Balance: with sensibility of 0.1mg and 1mg.
4.3 Microwave digestion system.
4.4 Pressure digester.
4.5 Constant-temperature drying oven, (50℃~300℃).
4.6 Temperature control electric hot plate (50℃~200℃).
4.7 Ultrasonic water bath.
5 Analytical Procedures
5.1 Pretreatment of specimen
5.1.1 The specimen shall be protected against contamination during the sampling and preparing process.
5.1.2 After the sundries are removed from such samples as grain and bean, the sample shall be uniformly grinded and put into clean polyethylene bottle; seal and preserve it for standby.
5.1.3 As for such fresh samples as vegetables, fruits, fish, meats and eggs, clean them and dry them in the air, take the homogenate of the edible part and put it into clean polyethylene bottle, seal the bottle and put it into 4℃ refrigerator for standby.
5.2 Specimen digestion
5.2.1 Pressure tank digestion method
Weigh 0.2g~1.0g (to the nearest of 0.001g) of solid specimen, 0.5g~2.0g of fresh sample or take 1mL~5mL (to the nearest of 0.001g) of liquid specimen, put it into digestion inner tank, and add into 5mL of nitric acid and soak overnight. Cover the inner cap and screw stainless steel enclosure, put inside constant-temperature drying oven at 140℃~160℃ for 4h~5h, and cool it to room temperature naturally. Then, slowly unscrew the stainless steel enclosure, take out the digestion inner tank, wash the inner cap with a small amount of water, put it on temperature control electric hot plate or in ultrasonic water bath at 80℃ or ultrasonic degas for 2min~5min to force brown gas out. Take out the digestion inner tank, transfer the digestive solution into a 25mL-volumetric flask, wash the inner tank for 3 times with a small amount of water, merge the washing solutions to volumetric flask, scale the volume to the scale and mix it uniformly for standby; Blank test is conducted simultaneously.
5.2.2 Microwave digestion method
Weigh solid specimen of 0.2g~0.5g (to the nearest 0.001g), fresh sample of 0.2g~0.8g or liquid specimen of 1mL~3mL, put it to digestion tank, and add into 5mL~8mL nitric acid, cover the cap and place overnight, screw the tank cover, conduct the digestion according to standard operating procedure of the microwave digestion instrument (see Table A.1 of Appendix A for reference condition of digestion). Take out the tank after it being cooled, slowly uncover it, wash the inner cap with a small amount of water, put the digestion tank on temperature control electric hot plate or in ultrasonic water bath at 80℃ or ultrasonic degas for 2min~5min to force brown gas out. Take out the digestion inner tank, transfer the digestive solution into a 25mL-plastic volumetric flask, wash the inner tank for 3 times with a small amount of water, merge the washing solutions to volumetric flask , scale the volume to the scale and mix it uniformly for standby; Blank test is conducted simultaneously.
Foreword i
1 Scope
2 Principles
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 Analytical Result
14 Precision
15 Others
16 Principle
17 Reagents and Materials
18 Instruments and Apparatus
19 Analytical Procedures
20 Calculation (Expression) of Analytical Result
21 Precision
22 Others
Appendix A Reference Condition of Microwave Digestion
Appendix B Chromatogram
