Some standard content:
ICS 67.040
National Standard of the People's Republic of China
GB/T5009.123—2003
Replaces GB/T14962—199
Determination of chromium in foods
Determination of ehromium in foodDS2003-08-11Promulgated
Ministry of Health of the People's Republic of China
National Standardization AdministrationbzxZ.net
2004-01-01Implementation
GB/T5009.123—2003
This standard replaces GB/T14962—1994 Determination of chromium in foods. Compared with GB/T14562-1994, this standard has the following major adjustments: The Chinese name of the standard has been modified, and the Chinese name of the standard has been changed to "Determination of cobalt in food according to GB/T20001.1-20014 standard writing rules Part 4: Chemical analysis method 3" The original standard has been modified.
This standard was proposed by the Ministry of Health of the People's Republic of China. The drafting units of the first method of this standard are: Hebei Provincial Health and Epidemic Prevention Station, Runan Provincial Food Hygiene Supervision and Control Institute, West China University of Medical Sciences, Nanjing Medical College,
The drafting units of the second method of this standard are: Huasi Medical University, Chinese Academy of Preventive Medicine and Institute of Health, the main drafters of the first method of this standard are Zhang Xinxie, Tu Zhunzhou, Tian Yongke, and Jiang Zhao. The main drafters of the second method of this standard are Wang Guangjian, Tian Qiubi, and Wang Zhunzhou. The original standard was first issued in 10, and this is the first time. 112
Determination of chromium in food
This standard specifies the determination of total chromium content in food by atomic absorption oscillographic method and oscillographic polarography. This standard is applicable to the determination of total chromium content in various foods. The limit of this standard is: 0.2g/mL for whole oscillographic sheet: 1/mL for each oscillographic sheet. Method 1: Atomic absorption oscillographic method
2: Principle
CB/T5009.123—2003
After the test is digested, wash with deionized water and adjust to a certain volume. Take the appropriate sample and atomize it in the graphite furnace atomizer. Under the selected instrument parameters, the absorption wavelength of chromium is 357,91, and its absorbance is proportional to the chromium content. 3.2 Test: 3.3 Hydrogen peroxide, 3.4 1.0 1/L nitric acid, 3.5 Chromium standard solution, weigh 1.4 13 of high-grade pure potassium hydroxide (110 ° C drying for 3 hours) and add it to water, and add a volumetric flask to 5C5mL. This solution contains 1. D mg-ml of chromium as the standard stock solution. When used, the standard stock solution is diluted with 1. 3 mol/L nitric acid to make a standard working solution containing 10cng/ml of lead.
4 Spectrometer
The glass collector and the polytetraoxyethylene used for high-pressure digestion must be soaked in hot salt (1-1 μg) for 1 hour before each use. Soak in high-pressure acid (1.1 μg) for 1 hour, then rinse with water and use 4.1 Absorption spectrophotometer. A qualified hollow cathode lamp must be used. 4.2 Product protection:
4.3 High-pressure digestion,
4.4 Machine-resistant electric oven.
5 Analysis steps
5.1 Pretreatment of samples
5.1.1 Food, u. Remove impurities, powder, alcohol, pass through a 20-sieve, and store in a plastic bottle for later use. 5.1.2 Wash and dry vegetables, fruits, etc., take the edible parts, crush them, and set aside. 5.1, 3 Wash fish, etc., take the edible parts, and use them. 5.2 Sample Digestion (depending on the experimental conditions, you can choose one of the following methods for digestion) 5.2. 1-way digestion method
Weigh the food sample 0, = * ~ 1.0 in a glass, add 1mL. ~ 2mL of high-grade pure acid, soak for more than 1h, put the sample on an electric furnace, carefully ignite it, and incubate it until it is no longer fuming, transfer it to a high-temperature furnace, incubate it at 550℃ for 2h, absorb it. After cooling, add a few drops of concentrated nitric acid to the sample. Transfer it to a high-temperature furnace at 50℃ and continue to incubate it for 1h ~ 2h. When the sample is in a ash state, take it out from the high-temperature furnace and put it in 111
CB/T 5009.123—2003
After cooling, add nitric acid (1% of the total weight) to the test solution. Transfer the solution quantitatively into a mL or \mL volume bottle, mix thoroughly after adjusting the volume, and then make the test solution. At the same time, perform the test according to the above method. 5.2.2 High-pressure digestion method
Add 0.3M~3,5n to the test tank with the highest ethylene content. Add 1.0mL of acid and 4.0mL of hydrogen peroxide solution, gently remove the cover, and put it into a constant temperature box. Start timing when the temperature rises to 40°C, maintain constant humidity for 1h, and evacuate the test solution. Take out the digestion end and wait for it to cool naturally, then open the cover and transfer the digestion solution into a 10mL bottle. , select the digestion water. Combine the washed water and sieve with water until the mark, mix, and the test is ready. 5.2.3 Preparation of standard curves
Pipette the standard sample (10gmL>9.10.0.50, 0.50, 0.70, 1.30, 1.50m.) into a 20m volumetric volume, add 1.01ul/L nitric acid to the scale, and mix. 5.3 Determination
5.3.1 Instrument test data
Should be based on: the best state of each instrument, test conditions: sample length 567.9m; drying 11045$ashing 1000℃ 305℃ chemical 28UV5s back calibration sea effect or light
5. 3.2 Determination
After adjusting the original absorption spectrophotometer to the optimal state, the standard series with the same amount of interference as the test sample should be injected for determination. The injection volume is 200 μL. For the sample with interference, the same amount of 2% phosphate buffer as the test sample should be added (the same applies to the standard series). 6 Accumulative calculation: Calculate according to the formula: X_A.)X1900: The content of the sample before, the unit is grams per kilogram/gA: The concentration in the sample solution, the unit is nanograms per liter (sample/mL): The concentration of the blank, the unit is grams per liter (g/) The volume of the sample is determined by the digestion volume, the unit is liter (mL); Take the sample, the unit is the point (g>
7 Precision: The absolute difference between two independent determination results obtained under the condition of multiplexing shall not exceed 1/56 of the technical mean. Method 2: Oscillographic polarography
Principle
After the sample is treated with acid-peroxide, the complex will react with ammonia-oxidation to produce a sensitive polarographic wave at 1.4V. The polarization voltage is proportional to the complex content. It is quantitatively compared with the standard series. 9 Reagents
9.1 Standard solution
9.1.1 Reserve solution
GD/T5009.123—2003
Accurately weigh 1.4:3511nT of high-purity heavy potassium hydroxide (K2O), dilute to 500L in water, and mix 1 tablespoon of this solution. ml. Contains 1.nm Cr (> 1.1nm Cr).
9.1.2 Application solution
Collect the reserve solution and dilute it to 1mL containing 0.1Cr (> 1.1nm Cr), 9.2 acid (chemical 9.4 ol/sulphuric acid.
9.3 Pass through a flask.
9.4 0.1% chlorinated blue indicator (1g/) Weigh 0.1g of monohydrate, dissolve in 2U% acetic acid and dilute to 100ml. 9.5 1mD/E sodium hydroxide solution,
9.6 Ammonium chloride solution
Weigh 53.5g of ammonium hydroxide (fresh) in water. Add 7.2mL of ammonia water (fresh> add water to dissolve to 25UL), 9.7 u-bipyridine solution
9.7.1 1×10-1nol/1, a-bipyridine (analytical grade) Weigh 0.157g of α-dipyridine precipitate (analytical grade) in water and dilute to 10). It can be stored in the refrigerator for a long time. 9.7.2 1x13*mal/La.a-bipyridine solution: Take 10.nmT.1×10-\mnl/1.4a-bipyridine solution, add water to dilute to 100ml. Mix and store in the refrigerator.
10 Preparation
10.1 Polarograph.
10.2 Heat the electric heating plate.
11 Analysis steps
11.1 Accurately weigh 1g~2g of representative sample in a 150ml diagonal flask and add 3.0ml.Alkali, 20ml-30mL hydrogen peroxide, heat on the grid at 160℃~21℃ to digest until a colorless and transparent solution is obtained (if necessary, add peroxide), continue heating until hydrogen peroxide is completely decomposed, and carbon dioxide (SO) appears in the bottle, remove and cool. 12ml2 drops of water, 100% formic acid indicator, neutralize with 1mol/sodium hydroxide, until the foil turns blue, add 20 drops, 2mol/sodium hydroxide, and place on the hot plate Heat the solution at 16 °C to 2 °C. After most of the hydrogen peroxide is decomposed, add 1% potassium hydroxide solution and continue to heat until the hydrogen peroxide is completely decomposed. Remove the solution and cool. Transfer to a 59 ml volumetric plate with water. Set the plate to the engraved position and take 5% of this solution into a 25 ml colorimetric plate for analysis. At the same time, make a digestion blank: 11.2 standard lines are added into 25 ml colorimetric plates and 0. 00, 0.20, 0.50, 1.00, 2.00, 3.0c1, 30mL standard should be reduced in the cabinet. 0, 0.02.0.05, 5.10, 0.20, 0.3C and 0.40ugCr>, 1.0mL5,4mol/L, 1 drop of 100-type blue indicator core in the oxygen solution: when the solution turns blue, refill and mix. 11.3 Determination of the sample and To the standard series tubes, add 2.1 ml of fluorine-chloride buffer, 1.0 mL of 1x10 mol/1.α, c-bipyridine solution, 1.1 L of 6 mm/s sodium nitrate solution, dilute to 25 ml, mix well, and place on the oscillographic polarogram. Use two electrodes, cathode polarization, origin potential -1.2 V, read the second-order peak height of the absorption peak of zirconium, and calculate the result according to (3):
GB/T 5009.123—2003
x—the content of zirconium in the sample, in milligrams (mg/kg/L); A—the content of zirconium in the sample digestion solution for determination, in micrograms; the total volume of the sample digestion, in milliliters (mL); --the volume of the digestion solution for determination, in milliliters (mL); --the mass or volume of the test group, in grams (mL); 13
Precision seat
The absolute value of each of the two independent determination results obtained under the condition of gravity shall not exceed 15% of the screening average value, 174
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