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GB 5009.123-2023 English PDF (GB5009.123-2023)

GB 5009.123-2023 English PDF (GB5009.123-2023)

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GB 5009.123-2023: National food safety standard - Determination of chromium in foods

This Standard specifies the method for the determination of chromium in foods by graphite furnace atomic absorption spectrometry and inductively coupled plasma mass spectrometry. This Standard is applicable to the determination of chromium in foods. Method I - Graphite Furnace Atomic Absorption Spectrometry
GB 5009.123-2023
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
National Food Safety Standard - Determination of
Chromium in Foods
ISSUED ON: SEPTEMBER 6, 2023
IMPLEMENTED ON: MARCH 6, 2024
Issued by: National Health Commission of the People’s Republic of China; State Administration for Market Regulation.
Table of Contents
Foreword ... 3
1 Scope ... 4
Method I - Graphite Furnace Atomic Absorption Spectrometry ... 4
2 Principle ... 4
3 Reagents and Materials ... 4
4 Instruments and Equipment ... 5
5 Analytical Procedures ... 6
6 Expression of Analysis Results ... 8
7 Precision ... 9
8 Others ... 9
Method II - Inductively Coupled Plasma Mass Spectrometry ... 9
Appendix A Microwave Digestion Temperature Rise Program and Instrument
Reference Conditions of Graphite Furnace Atomic Absorption Spectrometry ... 10 National Food Safety Standard - Determination of
Chromium in Foods
1 Scope
This Standard specifies the method for the determination of chromium in foods by graphite furnace atomic absorption spectrometry and inductively coupled plasma mass spectrometry. This Standard is applicable to the determination of chromium in foods.
Method I - Graphite Furnace Atomic Absorption
Spectrometry
2 Principle
After the specimen is digested, atomize it in a graphite furnace, at 357.9 nm, determine the absorbance. Within a certain concentration range, the absorbance value of chromium is proportional to the chromium content. Conduct quantitative comparison with standard series solutions.
3 Reagents and Materials
Unless it is otherwise specified, the reagents used in this Method are all excellent-grade pure, and the water is Grade-2 water specified in GB/T 6682.
3.1 Reagents
3.1.1 Nitric acid (HNO3).
3.1.2 Perchloric acid (HClO4).
3.1.3 Ammonium dihydrogen phosphate (NH4H2PO4).
3.2 Preparation of Reagents
3.2.1 Nitric acid solution (5 + 95): measure-take 50 mL of nitric acid, slowly add it to 950 mL of water and evenly mix it.
3.2.2 Nitric acid solution (1 + 1): measure-take 50 mL of nitric acid, slowly add it to 50 mL of water and evenly mix it.
3.2.3 Ammonium dihydrogen phosphate solution (20 g/L): weigh-take 2 g of ammonium dihydrogen phosphate, add a small amount of nitric acid solution (5 + 95) to dissolve it, then, use nitric acid solution (5 + 95) to reach a constant volume of 100 mL, and evenly mix it. 3.3 Reference Material
Potassium dichromate (K2Cr2O7, CAS No.: 7778-50-9): purity > 99.99%, or a standard substance certified by the state and awarded a reference material certificate. 3.4 Preparation of Standard Solutions
3.4.1 Chromium standard stock solution (1,000 mg/L): accurately weigh-take 0.2829 g of potassium dichromate (110 C, bake for 2 h), dissolve it in water, then, transfer into a 100 mL volumetric flask. Use nitric acid solution (5 + 95) to dilute it to the scale and evenly mix it. The mass concentration of chromium in this solution is 1,000 mg/L.
3.4.2 Chromium standard intermediate solution (1,000 g/L): accurately draw 1.00 mL of chromium standard stock solution (1,000 mg/L) into a 10 mL volumetric flask, add nitric acid solution (5 + 95) to the scale, and evenly mix it. Then, accurately draw 1.00 mL of the above- mentioned solution into a 100 mL volumetric flask, add nitric acid solution (5 + 95) to the scale, and evenly mix it. The mass concentration of chromium in this solution is 1,000 g/L. 3.4.3 Chromium standard series of solutions: respectively and accurately draw 0 mL, 0.150 mL, 0.400 mL, 0.800 mL, 1.20 mL and 1.60 mL of chromium standard intermediate solution into a 100 mL volumetric flask. Add nitric acid solution (5 + 95) to the scale, and evenly mix it. The mass concentration of chromium in this series of solutions is 0 g/L, 1.50 g/L, 4.00 g/L, 8.00 g/L, 12.0 g/L and 16.0 g/L. Prepare them right before use.
NOTE: the mass concentration of chromium in the standard series of solutions can be determined in accordance with the sensitivity of the instrument and the actual chromium content in the sample.
4 Instruments and Equipment
NOTE: all glassware and polytetrafluoroethylene digestion inner tanks need to be soaked in nitric acid solution (1 + 5) overnight, repeatedly rinsed with tap water, and finally, thoroughly rinsed with water.
4.1 Atomic absorption spectrometer: equipped with graphite furnace atomizer and chromium hollow cathode lamp.
4.2 Electronic balance: with a division value of 0.1 mg and 1 mg.
4.3 Adjustable electric heating plate or adjustable electric stove.
4.4 Microwave digestion system: equipped with polytetrafluoroethylene digestion inner tank. digestion tube with scale. For samples containing ethanol or carbon dioxide, firstly heat them at a low temperature to remove ethanol or carbon dioxide, add 10 mL of nitric acid and 0.5 mL of perchloric acid, and digest on an adjustable electric furnace (reference conditions: at 120 C, maintain for 0.5 h ~ 1 h, raise to 180 C, maintain for 2 h ~ 4 h, raise to 200 C ~ 220 C). If the digestion solution is brown, after cooling, add a small amount of nitric acid and digest it, until it emits white smoke, and the digestion solution turns colorless, transparent or slightly yellow. Drive acid to about 0.5 mL, take out the digestion tube, cool it and use water to reach a constant volume of 10 mL or 25 mL, evenly mix it and reserve it for later use. Meanwhile, conduct a blank test. Alternatively, a conical flask can also be used; on an adjustable electric heating plate, in accordance with the above-mentioned operation method, perform wet digestion. 5.2.1.2 Microwave digestion method
For solid specimens, weigh-take 0.2 g ~ 0.5 g (accurate to 0.001 g; for samples containing relatively high-water content, the sampling size can be appropriately increased to 1 g). For liquid specimens, accurately transfer-take or weigh-take 0.500 mL (g) ~ 3.00 mL (g) (accurate to 0.001 g) into a microwave digestion tank. For samples containing ethanol or carbon dioxide, firstly heat them at a low temperature to remove ethanol or carbon dioxide, add 5 mL ~ 10 mL of nitric acid, in accordance with the operation procedures of microwave digestion, digest the specimen. For the digestion conditions, refer to Table A.1 in Appendix A. When necessary, after adding acid, cover and let it stand for 1 h or overnight, then, in accordance with the operation procedures of microwave digestion, digest the specimen. After cooling, take out the digestion tank; at 140 C ~ 160 C, drive acid to about 1 mL. After the digestion tank cools, transfer the digestion solution into a 10 mL of 25 mL volumetric flask. Use a small amount of water to wash the digestion tank 2 ~ 3 times, combine the washing liquid in the volumetric flask and use water to reach a constant volume to the scale; evenly mix it and reserve it for later use. Meanwhile, conduct a blank test.
5.2.1.3 Pressure tank digestion method
For solid specimens, weigh-take 0.2 g ~ 1 g (accurate to 0.001 g; for samples containing relatively high-water content, the sampling size can be appropriately increased to 2 g). For liquid specimens, accurately transfer-take or weigh-take 0.500 mL (g) ~ 5.00 mL (g) (accurate to 0.001 g) into a digestion inner tank. For samples containing ethanol or carbon dioxide, firstly heat them at a low temperature to remove ethanol or carbon dioxide and add 5 mL ~ 10 mL of nitric acid. Properly put on the inner cover, tighten the stainless-steel jacket, put it into a constant-temperature drying oven; at 140 C ~ 160 C, maintain for 4 h ~ 5 h. When necessary, after adding acid, cover and let it stand for 1 h or overnight, then, tighten the stainless-steel jacket and put it into a constant-temperature drying oven to digest the specimen. After cooling, slowly unscrew the stainless-steel jacket, take out the digestion inner tank; at 140 C ~ 160 C, drive acid to about 1 mL. After cooling, transfer the digestion solution to a 10 mL or 25 mL volumetric flask, use a small amount of water to wash the inner tank and inner cover for 2 ~ 3 times, combine the washing liquid in the volumetric flask and use water to reach a constant volume to the scale; evenly mix it and reserve it for later use. Meanwhile, conduct a blank test. 5.2.1.4 Dry digestion method
X---the chromium content in the specimen, expressed in (mg/kg) or (mg/L); ρ---the mass concentration of chromium in the specimen digestion solution, expressed in (g/L); ρ0---the mass concentration of chromium in the blank solution, expressed in (g/L); f---dilution factor;
V---the constant volume of the specimen digestion solution, expressed in (mL); m---the mass or volume of the specimen, expressed in (g) or (mL);
1,000---conversion factor.
When the chromium content is  1 mg/kg (mg/L), the calculation results shall retain 3 significant figures. When the chromium content is < 1 mg/kg (mg/L), the calculation results shall retain 2 significant figures.
7 Precision
When the chromium content in the specimen is > 1 mg/kg (mg/L), the absolute difference between the results of two independent determinations obtained under repeatability conditions shall not exceed 10% of the arithmetic mean. When 0.1 mg/kg (mg/L) < chromium content in the specimen  1 mg/kg (mg/L), the absolute difference between the results of two independent determinations obtained under repeatability conditions shall not exceed 15% of the arithmetic mean. When the chromium content in the specimen is  0.1 mg/kg (mg/L), the absolute difference between the results of two independent determinations obtained under repeatability conditions shall not exceed 20% of the arithmetic mean.
8 Others
When the sampling size is 0.5 g or 2 mL and the constant volume is 10 mL, the detection limit of this Method is 0.01 mg/kg or 0.003 mg/L, and the quantitation limit is 0.03 mg/kg or 0.008 mg/L.
Method II - Inductively Coupled Plasma Mass Spectrometry
See Method I of GB 5009.268.

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