GB 5009.297-2023 PDF English
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National food safety standard - Determination of molybdenum in foods
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GB 5009.297-2023: PDF in English GB 5009.297-2023
GB
NATIONAL STANDARD OF THE
PEOPLE'S REPUBLIC OF CHINA
National food safety standard - Determination of
molybdenum in food
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
1 Scope ... 3
2 Principle ... 3
3 Reagents and materials ... 3
4 Instruments and equipment ... 4
5 Analysis steps ... 5
6 Presentation of analysis results ... 7
7 Precision ... 8
8 Others ... 8
Appendix A Instrument reference conditions ... 9
National food safety standard - Determination of
molybdenum in food
1 Scope
This standard specifies the methods for the determination of molybdenum in foods by
using graphite furnace atomic absorption spectrometry and inductively coupled plasma
mass spectrometry.
This standard applies to the determination of molybdenum in food.
Method I - Graphite furnace atomic absorption spectrometry
2 Principle
After digestion treatment, the sample is atomized in a graphite furnace, and the
absorbance value is measured at 313.3 nm. Within a certain concentration range, the
absorbance value of molybdenum is proportional to the molybdenum content, and the
external standard method is used for quantitative analysis.
3 Reagents and materials
Unless otherwise stated, the reagents used in this method are guaranteed reagents and
the water is secondary water specified in GB/T 6682.
3.1 Reagents
3.1.1 Nitric acid (HNO3).
3.1.2 Perchloric acid (HClO4).
3.1.3 Calcium chloride (CaCl2).
3.2 Reagent preparation
3.2.1 Nitric acid solution (5:95, volume fraction): Measure 50 mL of nitric acid, slowly
add it to 950 mL of water, and mix well.
3.2.2 Calcium chloride solution (1.00 g/L): Weigh 0.100 g of calcium chloride, dissolve
it in a small amount of water, then make the volume up to 100 mL with the nitric acid
solution (5:95, volume fraction), and mix well.
3.2.3 Nitric acid solution (1:5, volume fraction): Measure 100 mL of nitric acid, slowly
add it to 500 mL of water, and mix well.
3.3 Standard product
Ammonium molybdate (H8MoN2O4, CAS number: 13106-76-8): purity of ≥99.98%, or
a standard solution with national authentication and a Reference Material Certificate.
3.4 Preparation of standard solutions
3.4.1 Molybdenum standard stock solution (1000 mg/L): Accurately weigh 2.0430 g
(accurate to 0.0001 g) of ammonium molybdate, dissolve it in 50 mL of water, transfer
it to a 1000 mL volumetric flask, add the nitric acid solution (5:95, volume fraction) to
make the volume up to the mark, and mix well. This solution can be stored refrigerated
for 12 months.
3.4.2 Molybdenum standard intermediate solution (10.0 mg/L): Accurately draw 1.00
mL of molybdenum standard stock solution (1000 mg/L) into a 100 mL volumetric flask,
add the nitric acid solution (5:95, volume fraction) to the mark, and mix well. This
solution can be stored and refrigerated for 1 month.
3.4.3 Molybdenum standard solution (1.00 mg/L): Accurately pipette 10.0 mL of
molybdenum standard intermediate solution (10.0 mg/L) into a 100 mL volumetric
flask, add the nitric acid solution (5:95, volume fraction) to the mark, and mix well.
Prepare the solution fresh just before use.
3.4.4 Molybdenum standard series working solution: Take 0 mL, 0.10 mL, 0.25 mL,
0.50 mL, 1.00 mL, and 2.50 mL of molybdenum standard solution (1.00 mg/L) into 100
mL volumetric flasks, add nitric acid solution (5:95, volume fraction) to the mark, and
mix well. The mass concentrations of this molybdenum standard series solution are 0
μg/L, 1.00 μg/L, 2.50 μg/L, 5.00 μg/L, 10.0 μg/L and 25.0 μg/L. Prepare the solution
fresh just before use.
NOTE: The mass concentration of molybdenum in the standard series working solution can be
determined based on the sensitivity of the instrument and the actual content of molybdenum in the sample.
4 Instruments and equipment
All glassware and polytetrafluoroethylene digestion inner tanks need to be soaked in
nitric acid solution (1:5, volume fraction) overnight, rinsed repeatedly with tap water,
and finally rinsed with water.
4.1 Atomic absorption spectrometer: equipped with a graphite furnace atomizer and a
Weigh 0.3 g~0.8 g of the sample (accurate to 0.001 g) or accurately pipette 0.500
mL~3.00 mL of the liquid sample into the microwave digestion tank, add 5 mL~10 mL
of nitric acid, and digest the sample according to the operating steps of the microwave
digestion system. Please refer to Table A.1 in Appendix A for reference conditions of
the instrument. After cooling, take it out and reduce the acid to about 1 mL on the
electric hot plate at 150 ℃~170 ℃. Remove the digestion tank, cool it, and transfer the
digestion liquid to a 10 mL or 25 mL volumetric flask. Wash the digestion tank 2 to 3
times with a small amount of water. Combine the washing liquid in the volumetric flask
and make the volume up to the mark with water, mix well for later use. Do a blank test
at the same time.
5.2.2 Wet digestion method
Weigh 0.5 g~3.0 g of the sample (accurate to 0.001 g) or accurately pipette 0.500
mL~5.00 mL of the liquid sample into the digestion tube, add 10 mL of nitric acid and
0.5 mL of perchloric acid, and digest on the adjustable electrothermal furnace
(Reference conditions: rise the temperature to 120 °C and hold for 0.5 h~1 h, rise the
temperature to 180 °C and hold for 2 h~4 h, and rise the temperature to 200 °C~220 °C
until digestion is complete). If the digestive fluid is brown, add a small amount of nitric
acid, and digest until white smoke is emitted; if the digestive fluid is still brown,
repeatedly add a small amount of nitric acid to make the digestive fluid colorless and
transparent or slightly yellow, and reduce the acid to about 1 mL, then take the digestive
tube out. After cooling, transfer the digestive fluid to a 10 mL or 25 mL volumetric flask,
wash the digestive tube 2 to 3 times with a small amount of water, combine the washing
fluids in the volumetric flask, make to volume up to the mark with water, mix well for
later use. Do a blank test at the same time. An Erlenmeyer flask can be used also to
perform wet digestion on an adjustable electric hot plate according to the above
operation method.
5.2.3 Pressure tank digestion method
Weigh 0.2 g~1.0 g of the sample (accurate to 0.001 g) or accurately pipette 0.500
mL~5.00 mL of the liquid sample into the digestion tank, add 5 mL~10 mL of nitric
acid, cover the inner cap, tighten the stainless-steel jacket, put the digestion tank in a
constant temperature drying oven, and keep it at 150 ℃~170 ℃ for 4 h~5 h. After
cooling, slowly unscrew the outer jacket, take out the inner digestion tank, and reduce
the acid to about 1 mL on an electric hot plate at 150 °C~170 °C. Remove the digestion
tank, cool it, and transfer the digestion fluid to a 10 mL or 25 mL volumetric flask.
Wash the digestion tank 2 to 3 times with a small amount of water, combine the washing
liquid in the volumetric flask, make the volume up to the mark with water, and mix well
for later use. Do a blank test at the same time.
5.3 Instrument reference conditions
Adjust to the best condition according to the performance of each instrument. For
instrument operating conditions, see Table A.2 in Appendix A.
5.4 Preparation of standard curve
Inject the molybdenum standard series working solutions into the graphite furnace in
order of mass concentration from low to high, and measure the absorbance value after
atomization. Draw a standard curve with the mass concentration as the abscissa and the
absorbance value as the ordinate.
5.5 Determination of sample solution
Under the same test conditions as measuring the standard solution, inject the blank
solution or sample solution (it can be appropriately diluted according to the
concentration of the sample solution before it is tested on the machine) into the graphite
furnace, measure its absorbance value after atomization, and compare quantitatively
with the standard series solutions.
For samples with interference, the matrix modifier shall be injected simultaneously
during the preparation of the standard curve and the measurement of the sample solution.
6 Presentation of analysis results
The molybdenum content in the sample is calculated according to formula (1).
where:
X -- the molybdenum content in the sample, in milligrams per kilogram or
milligrams per liter (mg/kg or mg/L);
ρ -- the mass concentration of molybdenum in the sample solution, in micrograms
per liter (μg/L);
ρ0 -- the mass concentration of molybdenum in the blank solution, in micrograms
per liter (μg/L);
V -- the metered volume of the sample digestion fluid, in milliliters (mL);
f -- dilution factor of the sample;
m -- the sampling volume or pipetting volume of the sample, in grams or milliliters
(g or mL);
1000 -- conversion factor.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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