Some standard content:
ICS67.040
National Standard of the People's Republic of China
GB/T5009.42-2003
Replaces GB/T5009.42--1996
Method for analysis of hygienic standard of table salt
Promulgated on August 11, 2003
Ministry of Health of the People's Republic of China
Standardization Administration of the People's Republic of China
Implementation on January 1, 2004
GB/T5009.42—2003
This standard replaces GB/T5009.42—1996≤Method for analysis of hygienic standard of table salt". Compared with GB/T5009.42-1996, this standard has been modified as follows: The structure of the original standard has been modified in accordance with GB/T20001.4-2001 Standard Writing Rules Part 4: Chemical Analysis Methods.
This standard is proposed and managed by the Ministry of Health of the People's Republic of China. This standard was drafted by the Food Hygiene Supervision and Inspection Institute of the Ministry of Health, Beijing Municipal Health and Epidemic Prevention Station, Lianyungang City Health and Epidemic Prevention Station of Jiangsu Province, Hunan Provincial Health and Epidemic Prevention Station, Mianyang District Health and Epidemic Prevention Station of Sichuan Province, Guangdong Provincial Health and Epidemic Prevention Station, and Sichuan Provincial Health and Epidemic Prevention Station. This standard was first issued in 1985 and revised for the first time in 1996. This is the second revision. 334
1 Scope
Analysis methods for hygienic standards for salt
This standard specifies the analysis methods for various hygienic indicators of salt. This standard is applicable to the analysis of various hygienic indicators of salt. GB/T5009.42—2003
The minimum detection concentration of fluorine by colorimetric determination is 1.0 mg/kg, and the minimum detection concentration of sulfate by determination is 0.050 g/100 g. 2 Normative references
The clauses in the following documents become clauses of this standard through reference in this standard. For all referenced documents with an undated date, all subsequent amendments (excluding errata) or revisions are not applicable to this standard. However, the parties who reach an agreement based on this standard are encouraged to study whether the latest versions of these documents can be used. For all referenced documents without an undated date, the latest versions shall apply to this standard. GB/T5009.4 Determination of moisture in food
GB/T5009.11 Determination of total arsenic and inorganic arsenic in foodGB/T5009.12 Determination of lead in food
GB/T5009.13 Determination of copper in food
GB/T5009.14 Determination of zinc in food
GB/T5009.15 Determination of thiophene in food
GB/T5009.17 Total mercury and organic arsenic in food Determination of GB/T5009.18—2003 Determination of fluoride in food GB/T5009.33 Determination of nitrite and nitrate in food GB/T5009.39-2003 Analytical method of sauce hygiene standard 3 Sensory inspection
3.1 Spread the sample evenly on a piece of white paper and observe its color. It should be white, or white with light gray or light yellow. The one with anti-caking agent potassium ferric phosphate should be light blue. Due to its different sources, it should not contain foreign mechanical impurities visible to the naked eye. 3.2 Take about 20g of the sample and grind it in a porcelain mortar. Check it immediately. There should be no odor. 3.3 Take about 5g of the sample and dissolve it in 100mL of warm water. The aqueous solution should have a pure taste without other odors. 4 Physical and chemical inspection
4.1 Moisture
Operate according to the direct drying method in GB/T5009.4. 4.2 Water-insoluble matter
4.2.1 Reagents
Silver nitrate solution (50g/1)
4.2.2 Analysis steps
4.2.2.1 Take $12.5cm (or 9cm) Xinhua rapid quantitative filter paper in advance, fold it and put it in a high-type weighing bottle, and bake the filter paper and weighing bottle at 100℃±5℃ to constant weight.
4.2.2.2 Weigh 25.00g of sample, cover it in a 400mL beaker, add about 200ml of water, heat it in a boiling water bath, and stir it with a glass rod at all times to make it completely dissolved.
4.2.2.3 Filter the solution in 4.2.2.2 through constant weight filter paper, collect the filtrate in a 500mL volumetric flask, repeatedly rinse the precipitate and 335
GB/T5009.42-2003
filter paper with hot water until no chloride ion reacts (until no white turbidity is found after adding 1 drop of silver nitrate solution). Add water to the scale, mix well, and keep this solution for determination of other items.
4.2.2.4 Place the precipitate and filter paper in a high-type weighing bottle that has been dried to a constant weight, and dry to a constant weight at 100℃±5℃. The first drying is 1h, and each subsequent drying is 0.5h. Take it out and place it in a desiccator for 0.5h, and weigh it until the difference between the two weighed masses does not exceed 0.0010g. 4.2.3 Calculation of results
The content of water-insoluble matter in the sample is calculated according to formula (1). X=ml=m2×100
Wherein:
X is the content of water-insoluble matter in the sample, in grams per hundred grams (g/100g); m
is the mass of the weighing bottle and the filter paper with water-insoluble matter, in grams (g); the mass of the weighing bottle plus the filter paper, in grams (g); the mass of the sample, in grams (g).
The calculation result shall be rounded to two significant figures.
4.2.4 Precision
The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 5% of the arithmetic mean. 4.3 Salt (measured as sodium chloride)
4.3.1 Principle, reagents, instruments
Same as 4.3.1 to 4.3.3 of GB/T5009.39-2003. 4.3.2 Analysis steps
(1)
Pull 25.0mL of the filtrate in 4.2.2.3 into a 250mL volumetric flask, add water to the mark and mix well. Then take 25.0mL and place it in a 200mL conical flask, add water to 50mL, and operate according to 4.3.4 of GB/T5009.39-2003 starting from adding 1mL potassium chromate solution (50g/L).
4.3.3 Calculation of results
The salt content (as sodium chloride) in the sample (on a dry basis) is calculated according to formula (2). X-(Vi-V)XcX0.0585
m××250
Where:
5×100/(!A)
X-the salt content (as sodium chloride) in the sample (on a dry basis), in grams per hundred grams (g/100g); A-the water content in the sample, g/g;||t t||m—mass of sample, in grams (g);
V1V2c, 0.0585—respectively the same as V..Vz, c in 4.3.5 of GB/T5009.39-2003. The calculation result shall be rounded to three significant figures.
4.3.4 Precision
Under repeatability conditions, the absolute difference in the volume of the standard titrant for two parallel titrations shall not exceed 0.10mL. 4.4 Sulfate (barium chromate method)
4.4.1 Principle
Barium chromate is dissolved in dilute hydrochloric acid and can form barium sulfate precipitate with sulfate in the sample. After the solution is neutralized, the excess barium chromate and the generated barium sulfate are in a precipitated state and are removed by filtration, while the filtrate contains chromium replaced by sulfate. Acid ions. Quantitative comparison with the standard series. 4.4.2 Reagents
4.4.2.1 Chromic acid lock suspension: Weigh 19.44g potassium chromate and 24.44g barium chloride (BaClz·2H2O) and dissolve them in 1000mL water respectively, and heat to boiling. Pour the two liquids into a 3000ml beaker to generate a yellow barium chromate precipitate. After the precipitate settles, pour out the upper liquid, and then rinse the precipitate with 1000mL of water for about 5 times each time. Finally, add water to 1000mL to form a suspension, and mix well before each use. 336
4.4.2.2 Hydrochloric acid (1+4).
4.4.2.3 Ammonia water (1+2).
GB/T5009.42--20 03
4.4.2.4 Sulfate standard solution: Accurately weigh 1.4787g of dried anhydrous sodium sulfate or 1.8141g of dried anhydrous potassium sulfate, dissolve in a small amount of water, transfer to a 1000mL volumetric flask, and dilute to the mark with water. This solution contains 1.0mg sulfate per milliliter. 4.4.3 Instrument
Spectrophotometer.
4.4.4 Analysis steps
Pull 10.0mL~20.0mL of 4.2.2.3 filtrate into a 150mL conical flask and add water to 50mL. Pipette 0, 0.50, 1.0, 3.0, 5.0, 7.0mL of sulfate standard solution (equivalent to 00.50, 1.0, 3.0, 5.0, 7.0mL)0mg sulfate), placed in 150mL conical flasks, add water to 50mL each. Add 3 to 5 glass beads (to prevent boiling) and 1mL hydrochloric acid (1+4) to each bottle, heat and boil for 5min. Then add 2.5mL barium chromate suspension respectively, boil for about 5min, so that barium chromate and sulfate form barium sulfate precipitation. Remove the conical flasks and cool, add ammonia water (1+2) dropwise into each bottle, and neutralize until it turns lemon yellow. Then filter into 50mL stoppered colorimetric tubes (the filtrate should be transparent), wash with water three times, collect the washing liquid in the colorimetric tube, and finally dilute with water to the scale, use a 1cm colorimetric cup with a zero tube to adjust the zero point, measure the absorbance at a wavelength of 420nm, and draw a standard curve for comparison. 4.4.5 Calculation of results
The content of sulfate in the sample (in terms of sulfate) is calculated according to formula (3). X
mz×50×1000
Wherein:
X-sulfate content in the sample (calculated as sulfate), in grams per 100 grams (g/100g); V-volume of sample dilution during determination, in milliliters (mL); my
mass of equivalent sulfate in the sample for determination, in milligrams (mg), mass of the sample, in grams (g).
The calculation result shall retain two significant figures.
4.4.6 Precision
The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 10% of the arithmetic mean. 4.5 Magnesium
4.5.1 Titration
4.5.1.1 Principle
(3)wwW.bzxz.Net
Calcium and magnesium ions can react with disodium ethylenediaminetetraacetic acid to form soluble chromium complexes. Eriochrome black T indicator reacts with calcium and magnesium ions to form tartar red. When titrated to the endpoint, disodium ethylenediaminetetraacetic acid and calcium and magnesium form colorless complexes, which frees chromium black T. The solution changes from red to bright blue. The total amount of calcium and magnesium and the amount of calcium are measured according to the different pH values of the solution and different indicators. The difference between the two is the magnesium content. 4.5.1.2 Reagents
4.5.1.2.1 Standard titration solution of disodium ethylenediaminetetraacetic acid [c(CoHuN,OgNaz·2H,O)=0.010mol/L]. 4.5.1.2.2 Ammonium violurate mixed indicator (2%): Take 10g dry coal sodium chloride and 0.2g ammonium violurate, mix in a glass mortar, grind finely, and store in a brown wide-mouth bottle for later use.
4.5.1.2.3 Sodium hydroxide solution (80g/L): Take 8g sodium hydroxide and dissolve in water and dilute to 100mL. 4.5.1.2.4 Ammonia buffer solution: Take 20g ammonium chloride and dissolve in 300mL water, add 100mL ammonia water, and then dilute to 1000mL with water and store in a brown bottle.
4.5.1.2.5 Chrome black T mixed indicator (1%): Take 10g dry sodium chloride and grind finely, add 0.10g Chrome black T in a glass mortar, mix and grind finely, and store in a brown wide-mouth bottle for later use. 337
GB/T5009.42—2003
4.5.1.3 Apparatus
10ml microburette.
4.5.1.4 Analytical steps
Pipette 50ml of the filtrate from 4.2.2.3 and place it in a 250ml conical flask. Add 2ml of sodium hydroxide solution (80g/L) and about 5mg of ammonium violurate mixed indicator (2%), stir to dissolve, and immediately titrate with disodium ethylenediaminetetraacetic acid standard solution until the solution changes from red to blue-purple, and record the number of milliliters of solution consumed. Pipette another 50ml of the filtrate from 4.2.2.3 and place it in a 250ml conical flask, add 5ml of ammonia buffer solution and about 5mg of chrome black T mixed indicator, stir to dissolve, and immediately titrate with disodium ethylenediaminetetraacetic acid standard solution until the solution changes from tartrate red to bright blue. Record the number of milliliters of solution consumed. 4.5.1.5 Calculation of results
The magnesium content in the sample is calculated according to formula (4). X=(-V)Xc×0.0243
Wherein:
X is the magnesium content in the sample, in grams per hundred grams (g/100g); X100
is the volume of the standard disodium ethylenediaminetetraacetic acid solution consumed in the titration of calcium ions, in milliliters (mL); Vh
V2 is the volume of the standard disodium ethylenediaminetetraacetic acid solution consumed in the titration of the total amount of calcium and magnesium ions, in milliliters (mL); c is the concentration of the standard disodium ethylenediaminetetraacetic acid solution, in moles per liter (mol/L); m is the mass of the sample, in grams (g);
·(4)
0.0213 is the mass of magnesium equivalent to 1mL of the standard disodium ethylenediaminetetraacetic acid solution [c(CHN.O.Na?·2H.0)=0.010mo1/L], in grams (g).
The calculation result shall retain two significant figures.
4.5.1.6 Precision
Under repeatability conditions, the absolute difference in the volume of two parallel titrations of the standard titrant shall not exceed 0.10mL. 4.5.2 Oscillographic polarography
4.5.2.1 Principle
The magnesium-chrome black T complex has a sharp and well-symmetrical complex adsorption wave at 1.03V (VS·SCE) in the ethylenediamine-potassium hydroxide catalytic system. The greatest supporting electrolyte is ethylenediamine (20%)-chrome black T (5×0.00010mol/L)-potassium hydroxide (0.050mol/L). In this base solution, the wave height is linearly related to the magnesium concentration between 0.10uμg/ml and 4.0μg/mL. The peak current of magnesium in the sample is quantitatively compared with the peak current of the standard series.
4.5.2.2 Reagents
All test water is deionized water.
4.5.2.2.1 Ethylenediamine (20%): Take 20mL ethylenediamine (monohydrate) and dilute to 100mL with water. 4.5.2.2.2 Eriochrome Black T Solution (5×0.00010mol/L): Weigh 0.2307g Eriochrome Black T and dissolve it with triethanolamine solution (5%) to 100ml. Store in refrigerator. It is effective within three days. When using, dilute this solution 10 times with triethanolamine solution (5%). 4.5.2.2.3 Potassium Hydroxide Solution (0.050mol/L): Weigh 2.8g potassium hydroxide, dissolve it with water and dilute to 100mL. 4.5.2.2.4 Magnesium standard solution: Accurately weigh 0.5000g of magnesium metal, add 9mL of hydrochloric acid (1+1) to dissolve, then add hydrochloric acid (1+99) to make up to 500ml. 1ml of this solution is equivalent to 1.0mg of magnesium. When using, dilute this solution with water to the standard working solution, and each milliliter is equivalent to 10.0μg of magnesium.
4.5.2.3 Instruments
4.5.2.3.1 Oscillographic polarograph.
4.5.2.3.2 25ml test tube.
4.5.2.3.3 10μl~100μl microsyringe or pipette. 4.5.2.3.4 Glassware IIIL: All glassware III are soaked in nitric acid (10%) overnight, and finally rinsed with water, and dried in a dust-free and smoke-free environment for use.
4.5.2.4 Sample treatment
GB/T5009.42—2003
Collect the commercially available salt sample (if it is in granular state, first grind it into powder in a glass mortar) and place it in a clean porcelain dish and heat it in a drying oven at 100℃±5℃ for 4h, cool it to room temperature, store it in a wide-mouth plastic bottle, cover it and set it aside. 4.5.2.5 Analysis steps
4.5.2.5.1 Weigh about 0.500g of salt, dissolve it in water and make it 50mL, draw 0.01mL~2.0mL of this sample solution (equivalent to 0.10μg4μg magnesium) into a 25mL test tube, dilute it with water to 5.0mL for testing. 4.5.2.5.2 Pipette 0, 0.010, 0.025, 0.050, 0, 10, 0.20, 0, 30, 0.40 mL of magnesium standard solution (4.5.2.2.4) (equivalent to 0, 0.10, 0.25, 0.50, 1.0, 2.0, 3.0, 4.0 μg magnesium) into a 25 mL test tube, add water to 5.0 mL and wait for testing. 4.5.2.5.3 In the sample tube and standard push tube, add 1.0mL ethylenediamine (20%), 1.0mL chrome black T solution (5×10-*mol/L) and 0.5mL potassium hydroxide solution (0.50mol/L) in sequence, add water to 10mL, shake well, at the origin potential of -0.7V, three electrodes, cathode polarization, adjust the current magnification appropriately to perform a derivative scan measurement, record the peak current value of the sample and magnesium standard at -1.03V, and calculate the result by direct comparison method. 4.5.2.6 Calculation of results
The magnesium content in the sample is calculated according to formula (5). (h,-h.) ×C, ×V, ×100
（hh)xV.Xmx1000
Wherein:
X—magnesium content in the sample, in grams per hundred grams (g/100g):-peak current value in the sample, in microamperes (μA); hi
h. Peak current value of reagent blank, in microamperes (pA): h,—peak current value of magnesium standard, in microamperes (uA); C, standard mass of magnesium, in micrograms (μg); V—volume of sample solution, in milliliters (mL); V.-volume of sample solution used for determination, in milliliters (mL); m
mass of sample, in grams (g).
The calculation result shall retain two significant figures.
4.5.2.7 Precision
The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 10% of the arithmetic mean. 4.6 Lock
4.6.1 Principle
Barium ions react with sulfate to form barium sulfate, which is turbid. Turbidimetry is used for limit determination. 4.6.2 Reagents
4.6.2.1 Dilute sulfuric acid: Measure 5.7 mL of sulfuric acid, pour it into 50 mL of water, and then dilute it to 100 mL with water. ·(5)
4.6.2.2 Barium standard solution: Accurately weigh 1.7887 g of barium chloride (BaCl22H20), dissolve it in water, transfer it to a 100 mL volumetric flask, add water to the mark, and mix. This solution is equivalent to 10.0 mg per milliliter. 4.6.2.3 Lock standard solution: Pipette 1.0 mL of barium standard solution, place it in a 100 mL volumetric flask, and dilute it to the mark with water. This solution is equivalent to 0.10 mg per milliliter.
4.6.3 Analysis steps
Weigh 50.00g of sample, add water to dissolve to 500mL, filter, discard the primary filtrate, measure 50mL of filtrate into a 50mL colorimetric tube, take another 1mL of lock standard solution (equivalent to 0.10mg) and place it in a 50mL colorimetric tube, add water to the scale, and mix. Add 2mL of dilute sulfuric acid to each of the two tubes, shake, and leave for 2h. The sample tube should not be more turbid than the standard tube, that is, <20mg/kg. 339
CB/T5009.42--2003
4.7.1 Colorimetric method
4.7.1.1 Principle
Some natural substances containing hydroxyl groups have good adsorption and exchange properties for some elemental ions. In the presence of fluoride, hydroxyl groups and fluoride ions exchange with each other. This reaction can be used to separate and enrich trace fluoride, and then fluorine and lanthanum (III) and alizarin aminocarboxylic acid complexing agent are used to generate a blue ternary complex in an acidic solution. 4.7.1.2 Reagents
4.7.1.2.1 Dilute hydrochloric acid: Take 23.4mL of hydrochloric acid and dilute it to 100mL with water. 4.7.1.2.2 Fluoride lock solution (100g/L). 4.7.1.2.3 Magnesium hydroxide suspension: Take 15.6g magnesium sulfate (MgSO·7H,O), place it in a 2000mL conical flask, add 100mL water, dissolve it, slowly add 1350mL sodium hydroxide solution (4g/L) under constant stirring, heat the suspension and keep it at 60℃～70℃ for 10min～15min, cool it to room temperature, and after the suspension settles, use siphon method to discard the upper solution. Wash the suspension with water repeatedly until the washing liquid is no longer turbid when adding dilute hydrochloric acid and barium chloride solution. Transfer the suspension to a 500mL volumetric flask, dilute it to the scale with water, mix it thoroughly before use, and the suspension keeps the adsorption performance unchanged for two months. 4.7.1.2.4 Buffer solution (pH4.7): Weigh 30g anhydrous sodium acetate, dissolve it in 400mL water, add 22mL glacial acetic acid, then slowly add glacial acetic acid to adjust the pH to 4.7, and then dilute it to 500mL with water. 4.7.1.2.5 Lanthanum nitrate solution (0.0010 mol/L): Same as 3.7 in GB/T5009.18--2003. 4.7.1.2.6 Alizarin aminocarboxylic acid complexing agent solution (0.0010 mol/L): Same as 3.5 in GB/T5009.18-2003. 4.7.1.2.7 Acetone.
4.7. 1.2.8
4.7.1.2.9
Fluorine standard solution: Same as 3.12 in GB/T5009.18-2003. Fluorine standard solution: Before use, take 1.0 mL of fluorine standard solution (4.7.1.2.8), put it in a 100 mL volumetric flask, and dilute it to the mark with water. Each mL of this solution is equivalent to 10.0 ug of fluorine. 4.7.1.2.10 Nitric acid (1+31): Measure 5 mL of nitric acid and dilute it to 160 mL with water. 4.7.1.3 Instrument
Centrifuge.
4.7.1.4 Analysis steps
Weigh 5.00 g of sample into a 50 mL centrifuge tube and dissolve it in water to 20 mL. Pipette 0, 1.0, 2.0, 3.0, 4.0, 5.0 mL of fluorine standard solution (4.7.1.2.9) (equivalent to 0, 102030, 40, 50 μg fluorine) into 50 mL centrifuge tubes respectively, and then add water to 20 mL each. Add 20 mL of magnesium hydroxide suspension into each of the sample and standard tubes, stir thoroughly, heat in a boiling water bath for 10 min, and let cool. Centrifuge at 2000r/min for 5min, carefully pour out the supernatant, add 40mL of water, mix and centrifuge again, repeat 2 to 3 times, and finally pour out the supernatant. Add 20mL of nitric acid (1 in 31) to each tube, and heat and shake in a water bath to completely dissolve the precipitate. Transfer the solution in each tube to a 50mL colorimetric tube, wash the centrifuge tube with water several times, combine the washing solution in the colorimetric tube, add water to the scale, mix, and then add 3ml of alizarin aminocarboxylic acid complex solution (0.0010mol/L) 3mL buffer (pH4.7), 8mL of acetone, and 3mL of nitric acid solution (0.0010mol/L) to each tube, mix, and place for 10min. Use a 1cm colorimetric cup to adjust the zero point with a zero tube, measure the absorbance at a wavelength of 580nm, draw a standard curve, and compare the quantification.
4.7.1.5 Calculation of results
The fluorine content in the sample shall be calculated according to formula (6). Where:
X=m×1000
m2×1000
X is the fluorine content in the sample, in milligrams per kilogram (mg/kg); m
is the mass of the sample for determination, in micrograms (ug); and the mass of the sample, in grams (g).
The calculation result shall be rounded to two significant figures.
·(6)
4.7.1.6 Precision
GB/T5009.42—2003
The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 10% of the arithmetic mean. 4.7.2 Fluoride electrode method
4.7.2.1 Principle, reagents, instruments
Ionic strength buffer: Weigh 62.0g of anhydrous sodium acetate, 0.3g of sodium citrate, and 15mL of glacial acetic acid, dissolve and dilute to 1L. Others are the same as Chapters 10, 11, and 12 of GB/T5009.18-2003, but require that each milliliter of the fluorine standard solution is equivalent to 50.0pg of fluorine. 4.7.2.2 Analysis steps
Weigh about 100g of the sample, put it in a mortar and grind it appropriately (particle size is about 0.5mm) for later use. Weigh 2.00g of the ground sample, put it in a 25mL small beaker, add 10mL of water and 10mL of ionic strength buffer, put it on a magnetic stirrer, immerse the electrode in the solution to be tested, stir for 30min, and read the millivolt number in a static state as El. Add 0.2mL of fluorine standard solution (1mL is equivalent to 0.050mg of fluorine), stir for 10 minutes, and measure the millivolt number as E2. At this time, E, is less than E, and the solution temperature during the measurement is recorded.
4.7.2.3 Calculation of results
4.7.2.3.1 The fluorine content in the sample is calculated according to formula (7). X=mix1000
7m2×1000
Where:
X—fluorine content in the sample, in milligrams per kilogram (mg/kg); m
—the mass of fluorine in the sample for measurement, in micrograms (rg); the mass of the sample, in grams (g).
4.7.2.3.2 The mass of fluorine in the sample for measurement is calculated according to formula (8). mi
In the formula:
The mass of the added fluorine is known to be 10μg;
The difference between the two millivolts, that is, E1-E2,
- represents the slope, which is 59.16mV at 25℃. The calculation result retains two significant figures.
4.7.2.4 Precision
(logAE
The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 10% of the arithmetic mean. 4.8 Lead
According to GB/T5009.12.
According to GB/T5009.11 Operation.
Operate according to the second method in GB/T5009.14.
4.11 Potassium ferrocyanide (ferrous sulfate method) 4.11.1 Principle
(7)
(8)
Potassium ferrocyanide reacts with ferrous sulfate to form a blue complex salt under acidic conditions, which can be quantitatively compared with the standard. The minimum detection concentration is 1.0 mg/kg.
4.11.2 Reagents
4.11.2.1 Ferrous sulfate solution (80 g/L). 4.11.2.2 Dilute sulfuric acid: Measure 5.7 mL of sulfuric acid and pour it into 50 mL of water. After cooling, add water to 100 mL. 341
GB/T5009.42—2003
4.11.2.3 Potassium ferrocyanide standard solution: Accurately weigh 0.1000g potassium ferrocyanide, soak in a small amount of water, transfer to a 100mL volumetric flask, and dilute to scale with water. Each milliliter of this solution is equivalent to 1.0mg potassium ferrocyanide. 4.11.2.4 Potassium ferrocyanide standard working solution: Pipette 10.0mL potassium ferrocyanide standard solution, cover in a 100mL volumetric flask, and dilute to scale with water. Each milliliter of this solution is equivalent to 0.10mg potassium ferrocyanide. 4.11.3 Instrument
Spectrophotometer.
4.11.4 Analysis steps
Weigh 10.00g of sample and dissolve it in water. Transfer it to a 50mL volumetric flask, add water to the mark, mix, filter, discard the initial filtrate, and then pipette 25.0mL of filtrate into a colorimetric tube.
Pipette 0, 0.1, 0.2, 0.30.4mL of potassium ferrocyanide working solution (equivalent to 0, 10.0, 20.0, 30.0, 40.0μg potassium ferrocyanide), place them in 25mL colorimetric tubes, and add water to 25mL each. Add 2mL of ferrous sulfate solution (80g/L) and 1mL of dilute sulfuric acid to the sample tube and the standard tube respectively, and mix them well. After 20 minutes, use a 3cm colorimetric cup and adjust the zero point with a zero tube, measure the absorbance at a wavelength of 670nm, draw a standard curve, and find out the content of the sample from the curve, or compare it with the standard color column by visual inspection.
4.11.5 Calculation of results
The content of potassium ferrocyanide in the sample shall be calculated according to formula (9). X
Wherein:
m,×1000
mx1000×1000
X is the content of potassium ferrocyanide in the sample, in grams per kilogram (g/kg); m is the mass of potassium ferrocyanide in the sample solution for determination, in micrograms (ug); mz is the mass of the sample, in grams (g).
The calculation result shall be rounded to two significant figures.
4.11.6 Precision
The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 10% of the arithmetic mean. 4.12 Iodine (iodized salt)
4.12.1 Qualitative
4.12.1.1 Reagents
(9)
Mixed reagent: 4 drops of sulfuric acid (1+3): 8 drops of sodium nitrite solution (5g/L): 20mL of starch solution (5g/L). Mix before use. 4.12.1.2 Analysis steps
Take about 2g of sample, place it on a white porcelain plate, and drop (2-3) drops of mixed reagent on the sample. If it turns blue-purple, it indicates the presence of iodide. 4.12.2 Qualitative analysis with potassium iodate
4.12.2.1 Principle
Potassium iodate is an oxidant. Under acidic conditions, it is easily reduced by sodium thiosulfate to generate iodine. It turns blue when it comes into contact with starch. This qualitative reaction can be established by controlling the concentration of sodium thiosulfate.
4.12.2.2 Reagents
Preparation of color developing solution: 10mL starch solution (5g/L), 12 drops of sodium thiosulfate (NaS.O,·5HzO) (10g/L); 5~10 drops of sulfuric acid (5+13). Prepare immediately before use.
4.12.2.3 Analysis steps
Weigh several grams of sample, add 1 drop of color developing solution, light blue to blue is a positive reaction, negative is no reaction (this reaction is specific). Determination range: 30μg potassium iodate (i.e. 18μg iodine) per gram of salt, light blue immediately, 50μg is blue, the more iodine, the darker the blue. 342
4.12.3 Quantification
4.12.3.1 Principle
GB/T5009.42—2003
The iodide in the sample is oxidized to potassium iodate with saturated bromine water under acidic conditions, and then the potassium iodide is oxidized in acidic conditions to release iodine. Starch is used as an indicator and titrated with sodium thiosulfate standard solution to calculate the content. 4.12.3.2 Reagents
4.12.3.2.1 Phosphoric acid.
4.12.3.2.2 Potassium iodide solution (50g/L): Prepare immediately before use. 4.12.3.2.3 Saturated bromine water.
4.12.3.2.4 Starch indicator solution: Weigh 0.5g of soluble starch, add a small amount of water and stir well, pour into 50mL boiling water, boil, and prepare immediately before use.
4.12.3.2.5
Sodium thiosulfate standard solution [c (Na2S, O3) = 0.100mol/L, accurately diluted 50 times before use, the concentration is 0.0020mol/L.
4.12.3.3 Analysis steps
Weigh 10.00g of the sample, place it in a 250mL conical flask, add water to dissolve, add 1mL of phosphoric acid and shake well. Add saturated bromine water dropwise until the solution turns light yellow, and shake while dropping until the yellow color does not fade (about 6 drops). Do not add too much bromine water. Place it at room temperature for 15 minutes. During the placement period, if the yellow color fades, add more bromine water until it turns light yellow. Add 4 to 5 glass beads, heat and boil until the yellow color fades, continue to boil for 5 minutes, and cool immediately. Add 2mL potassium iodide solution (50g/L), shake and titrate immediately with sodium thiosulfate standard solution (0.0020mol/L) until light yellow, add 1mL starch indicator (5g/L), and continue titrating until the blue color just disappears. If the salt sample contains too much impurities, first take the salt sample and add 150mL of water to dissolve it, filter it, take 100mL of the filtrate into a 250mL conical flask, and then operate.
4.12.3.4 Calculation of results
The iodine content in the sample is calculated according to formula (10). X=VXcX21.15×1000
Wherein:
X is the iodine content in the sample, in milligrams per kilogram (mg/kg); V is the volume of sodium thiosulfate standard titration solution consumed by the sample for determination, in milliliters (mL); C is the concentration of sodium thiosulfate standard titration solution, in moles per liter (mol/L); m is the mass of the sample, in grams (g); .....( 10 )
21,15 is the mass of iodine equivalent to 1.0mL sodium thiosulfate standard solution Cc(NazS,0)=1.000mol/L), in milligrams (mg).
The calculation result shall retain two significant figures.
4.12.3.5 Precision
The absolute difference in the volume of the standard titration solution for two parallel titrations under repeatability conditions shall not exceed 0.10mL. 4.13 Copper
Operate in accordance with GB/T5009.13.
Operate in accordance with GB/T5009.15.
4.15 Total mercury
Operate in accordance with GB/T5009.17.
4.16 Nitrite
Operate in accordance with GB/T5009.33.0mL of filtrate is placed in a colorimetric tube.
Pipette 0, 0.1, 0.2, 0.30.4mL of potassium ferrocyanide working solution (equivalent to 0, 10.0, 20.0, 30.0, 40.0μg potassium ferrocyanide) and place them in 25mL colorimetric tubes respectively, and add water to 25mL each. Add 2mL of ferrous sulfate solution (80g/L) and 1mL of dilute sulfuric acid to the sample tube and the standard tube respectively, and mix well. After 20 minutes, use a 3cm colorimetric cup and a zero tube to adjust the zero point, measure the absorbance at a wavelength of 670nm, draw a standard curve, and find the content of the sample from the curve, or compare it with the standard color column visually.
4.11.5 Calculation of results
The content of potassium ferrocyanide in the sample is calculated according to formula (9). X
Wherein:
m,×1000
mx1000×1000
X-the content of potassium ferrocyanide in the sample, in grams per kilogram (g/kg); m-the mass of potassium ferrocyanide in the sample solution for determination, in micrograms (ug); mz-the mass of the sample, in grams (g).
The calculation result shall retain two significant figures.
4.11.6 Precision
The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 10% of the arithmetic mean. 4.12 Iodine (iodized salt)
4.12.1 Qualitative
4.12.1.1 Reagents
(9)
Mixed reagent: 4 drops of sulfuric acid (1+3): 8 drops of sodium nitrite solution (5g/L): 20mL of starch solution (5g/L). Mix before use. 4.12.1.2 Analysis steps
Take about 2g of sample, place it on a white porcelain plate, and drop (2-3) drops of mixed reagent on the sample. If it turns blue-purple, it indicates the presence of iodide. 4.12.2 Qualitative analysis with potassium iodate
4.12.2.1 Principle
Potassium iodate is an oxidant. Under acidic conditions, it is easily reduced by sodium thiosulfate to generate iodine. It turns blue when it comes into contact with starch. This qualitative reaction can be established by controlling the concentration of sodium thiosulfate.
4.12.2.2 Reagents
Preparation of color developing solution: 10mL starch solution (5g/L), 12 drops of sodium thiosulfate (NaS.O,·5HzO) (10g/L); 5~10 drops of sulfuric acid (5+13). Prepare immediately before use.
4.12.2.3 Analysis steps
Weigh several grams of sample, add 1 drop of color developing solution, light blue to blue is a positive reaction, negative is no reaction (this reaction is specific). Determination range: 30μg potassium iodate (i.e. 18μg iodine) per gram of salt, light blue immediately, 50μg is blue, the more iodine, the darker the blue. 342
4.12.3 Quantification
4.12.3.1 Principle
GB/T5009.42—2003
The iodide in the sample is oxidized to potassium iodate with saturated bromine water under acidic conditions, and then the potassium iodide is oxidized in acidic conditions to release iodine. Starch is used as an indicator and titrated with sodium thiosulfate standard solution to calculate the content. 4.12.3.2 Reagents
4.12.3.2.1 Phosphoric acid.
4.12.3.2.2 Potassium iodide solution (50g/L): Prepare immediately before use. 4.12.3.2.3 Saturated bromine water.
4.12.3.2.4 Starch indicator solution: Weigh 0.5g of soluble starch, add a small amount of water and stir well, pour into 50mL boiling water, boil, and prepare immediately before use.
4.12.3.2.5
Sodium thiosulfate standard solution [c (Na2S, O3) = 0.100mol/L, accurately diluted 50 times before use, the concentration is 0.0020mol/L.
4.12.3.3 Analysis steps
Weigh 10.00g of the sample, place it in a 250mL conical flask, add water to dissolve, add 1mL of phosphoric acid and shake well. Add saturated bromine water dropwise until the solution turns light yellow, and shake while dropping until the yellow color does not fade (about 6 drops). Do not add too much bromine water. Place it at room temperature for 15 minutes. During the placement period, if the yellow color fades, add more bromine water until it turns light yellow. Add 4 to 5 glass beads, heat and boil until the yellow color fades, continue to boil for 5 minutes, and cool immediately. Add 2mL potassium iodide solution (50g/L), shake and titrate immediately with sodium thiosulfate standard solution (0.0020mol/L) until light yellow, add 1mL starch indicator (5g/L), and continue titrating until the blue color just disappears. If the salt sample contains too much impurities, first take the salt sample and add 150mL of water to dissolve it, filter it, take 100mL of the filtrate into a 250mL conical flask, and then operate.
4.12.3.4 Calculation of results
The iodine content in the sample is calculated according to formula (10). X=VXcX21.15×1000
Wherein:
X is the iodine content in the sample, in milligrams per kilogram (mg/kg); V is the volume of sodium thiosulfate standard titration solution consumed by the sample for determination, in milliliters (mL); C is the concentration of sodium thiosulfate standard titration solution, in moles per liter (mol/L); m is the mass of the sample, in grams (g); .....( 10 )
21,15 is the mass of iodine equivalent to 1.0mL sodium thiosulfate standard solution Cc(NazS,0)=1.000mol/L), in milligrams (mg).
The calculation result shall retain two significant figures.
4.12.3.5 Precision
The absolute difference in the volume of the standard titration solution for two parallel titrations under repeatability conditions shall not exceed 0.10mL. 4.13 Copper
Operate in accordance with GB/T5009.13.
Operate in accordance with GB/T5009.15.
4.15 Total mercury
Operate in accordance with GB/T5009.17.
4.16 Nitrite
Operate in accordance with GB/T5009.33.0mL of filtrate is placed in a colorimetric tube.
Pipette 0, 0.1, 0.2, 0.30.4mL of potassium ferrocyanide working solution (equivalent to 0, 10.0, 20.0, 30.0, 40.0μg potassium ferrocyanide) and place them in 25mL colorimetric tubes respectively, and add water to 25mL each. Add 2mL of ferrous sulfate solution (80g/L) and 1mL of dilute sulfuric acid to the sample tube and the standard tube respectively, and mix well. After 20 minutes, use a 3cm colorimetric cup and a zero tube to adjust the zero point, measure the absorbance at a wavelength of 670nm, draw a standard curve, and find the content of the sample from the curve, or compare it with the standard color column visually.
4.11.5 Calculation of results
The content of potassium ferrocyanide in the sample is calculated according to formula (9). X
Wherein:
m,×1000
mx1000×1000
X-the content of potassium ferrocyanide in the sample, in grams per kilogram (g/kg); m-the mass of potassium ferrocyanide in the sample solution for determination, in micrograms (ug); mz-the mass of the sample, in grams (g).
The calculation result shall retain two significant figures.
4.11.6 Precision
The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 10% of the arithmetic mean. 4.12 Iodine (iodized salt)
4.12.1 Qualitative
4.12.1.1 Reagents
(9)
Mixed reagent: 4 drops of sulfuric acid (1+3): 8 drops of sodium nitrite solution (5g/L): 20mL of starch solution (5g/L). Mix before use. 4.12.1.2 Analysis steps
Take about 2g of sample, place it on a white porcelain plate, and drop (2-3) drops of mixed reagent on the sample. If it turns blue-purple, it indicates the presence of iodide. 4.12.2 Qualitative analysis with potassium iodate
4.12.2.1 Principle
Potassium iodate is an oxidant. Under acidic conditions, it is easily reduced by sodium thiosulfate to generate iodine. It turns blue when it comes into contact with starch. This qualitative reaction can be established by controlling the concentration of sodium thiosulfate.
4.12.2.2 Reagents
Preparation of color developing solution: 10mL starch solution (5g/L), 12 drops of sodium thiosulfate (NaS.O,·5HzO) (10g/L); 5~10 drops of sulfuric acid (5+13). Prepare immediately before use.
4.12.2.3 Analysis steps
Weigh several grams of sample, add 1 drop of color developing solution, light blue to blue is a positive reaction, negative is no reaction (this reaction is specific). Determination range: 30μg potassium iodate (i.e. 18μg iodine) per gram of salt, light blue immediately, 50μg is blue, the more iodine, the darker the blue. 342
4.12.3 Quantification
4.12.3.1 Principle
GB/T5009.42—2003
The iodide in the sample is oxidized to potassium iodate with saturated bromine water under acidic conditions, and then the potassium iodide is oxidized in acidic conditions to release iodine. Starch is used as an indicator and titrated with sodium thiosulfate standard solution to calculate the content. 4.12.3.2 Reagents
4.12.3.2.1 Phosphoric acid.
4.12.3.2.2 Potassium iodide solution (50g/L): Prepare immediately before use. 4.12.3.2.3 Saturated bromine water.
4.12.3.2.4 Starch indicator solution: Weigh 0.5g of soluble starch, add a small amount of water and stir well, pour into 50mL boiling water, boil, and prepare immediately before use.
4.12.3.2.5
Sodium thiosulfate standard solution [c (Na2S, O3) = 0.100mol/L, accurately diluted 50 times before use, the concentration is 0.0020mol/L.
4.12.3.3 Analysis steps
Weigh 10.00g of the sample, place it in a 250mL conical flask, add water to dissolve, add 1mL of phosphoric acid and shake well. Add saturated bromine water dropwise until the solution turns light yellow, and shake while dropping until the yellow color does not fade (about 6 drops). Do not add too much bromine water. Place it at room temperature for 15 minutes. During the placement period, if the yellow color fades, add more bromine water until it turns light yellow. Add 4 to 5 glass beads, heat and boil until the yellow color fades, continue to boil for 5 minutes, and cool immediately. Add 2mL potassium iodide solution (50g/L), shake and titrate immediately with sodium thiosulfate standard solution (0.0020mol/L) until light yellow, add 1mL starch indicator (5g/L), and continue titrating until the blue color just disappears. If the salt sample contains too much impurities, first take the salt sample and add 150mL of water to dissolve it, filter it, take 100mL of the filtrate into a 250mL conical flask, and then operate.
4.12.3.4 Calculation of results
The iodine content in the sample is calculated according to formula (10). X=VXcX21.15×1000
Wherein:
X is the iodine content in the sample, in milligrams per kilogram (mg/kg); V is the volume of sodium thiosulfate standard titration solution consumed by the sample for determination, in milliliters (mL); C is the concentration of sodium thiosulfate standard titration solution, in moles per liter (mol/L); m is the mass of the sample, in grams (g); .....( 10 )
21,15 is the mass of iodine equivalent to 1.0mL sodium thiosulfate standard solution Cc(NazS,0)=1.000mol/L), in milligrams (mg).
The calculation result shall retain two significant figures.
4.12.3.5 Precision
The absolute difference in the volume of the standard titration solution for two parallel titrations under repeatability conditions shall not exceed 0.10mL. 4.13 Copper
Operate in accordance with GB/T5009.13.
Operate in accordance with GB/T5009.15.
4.15 Total mercury
Operate in accordance with GB/T5009.17.
4.16 Nitrite
Operate in accordance with GB/T5009.33.42—2003
The iodide in the sample is oxidized to potassium iodate with saturated bromine water under acidic conditions, and then the potassium iodide is oxidized in acidic conditions to release iodine. Starch is used as an indicator and titrated with sodium thiosulfate standard solution to calculate the content. 4.12.3.2 Reagents
4.12.3.2.1 Phosphoric acid.
4.12.3.2.2 Potassium iodide solution (50g/L): Prepare before use. 4.12.3.2.3 Saturated bromine water.
4.12.3.2.4 Starch indicator solution: Weigh 0.5g soluble starch, add a small amount of water and stir well, pour into 50mL boiling water, boil, and prepare before use.
4.12.3.2.5
Sodium thiosulfate standard solution [c (Na2S, O3) = 0.100mol/L, accurately diluted 50 times before use, the concentration is 0.0020mol/L.
4.12.3.3 Analysis steps
Weigh 10.00g of the sample, place it in a 250mL conical flask, add water to dissolve, add 1mL of phosphoric acid and shake well. Add saturated bromine water dropwise until the solution turns light yellow, and shake while dropping until the yellow color does not fade (about 6 drops). Do not add too much bromine water. Place it at room temperature for 15 minutes. During the placement period, if the yellow color fades, add more bromine water until it turns light yellow. Add 4 to 5 glass beads, heat and boil until the yellow color fades, continue to boil for 5 minutes, and cool immediately. Add 2mL potassium iodide solution (50g/L), shake and titrate immediately with sodium thiosulfate standard solution (0.0020mol/L) until light yellow, add 1mL starch indicator (5g/L), and continue titrating until the blue color just disappears. If the salt sample contains too much impurities, first take the salt sample and add 150mL of water to dissolve it, filter it, take 100mL of the filtrate into a 250mL conical flask, and then operate.
4.12.3.4 Calculation of results
The iodine content in the sample is calculated according to formula (10). X=VXcX21.15×1000
Wherein:
X is the iodine content in the sample, in milligrams per kilogram (mg/kg); V is the volume of sodium thiosulfate standard titration solution consumed by the sample for determination, in milliliters (mL); C is the concentration of sodium thiosulfate standard titration solution, in moles per liter (mol/L); m is the mass of the sample, in grams (g); .....( 10 )
21,15 is the mass of iodine equivalent to 1.0mL sodium thiosulfate standard solution Cc(NazS,0)=1.000mol/L), in milligrams (mg).
The calculation result shall retain two significant figures.
4.12.3.5 Precision
The absolute difference in the volume of the standard titration solution for two parallel titrations under repeatability conditions shall not exceed 0.10mL. 4.13 Copper
Operate in accordance with GB/T5009.13.
Operate in accordance with GB/T5009.15.
4.15 Total mercury
Operate in accordance with GB/T5009.17.
4.16 Nitrite
Operate in accordance with GB/T5009.33.42—2003
The iodide in the sample is oxidized to potassium iodate with saturated bromine water under acidic conditions, and then the potassium iodide is oxidized in acidic conditions to release iodine. Starch is used as an indicator and titrated with sodium thiosulfate standard solution to calculate the content. 4.12.3.2 Reagents
4.12.3.2.1 Phosphoric acid.
4.12.3.2.2 Potassium iodide solution (50g/L): Prepare before use. 4.12.3.2.3 Saturated bromine water.
4.12.3.2.4 Starch indicator solution: Weigh 0.5g soluble starch, add a small amount of water and stir well, pour into 50mL boiling water, boil, and prepare before use.
4.12.3.2.5
Sodium thiosulfate standard solution [c (Na2S, O3) = 0.100mol/L, accurately diluted 50 times before use, the concentration is 0.0020mol/L.
4.12.3.3 Analysis steps
Weigh 10.00g of the sample, place it in a 250mL conical flask, add water to dissolve, add 1mL of phosphoric acid and shake well. Add saturated bromine water dropwise until the solution turns light yellow, and shake while dropping until the yellow color does not fade (about 6 drops). Do not add too much bromine water. Place it at room temperature for 15 minutes. During the placement period, if the yellow color fades, add more bromine water until it turns light yellow. Add 4 to 5 glass beads, heat and boil until the yellow color fades, continue to boil for 5 minutes, and cool immediately. Add 2mL potassium iodide solution (50g/L), shake and titrate immediately with sodium thiosulfate standard solution (0.0020mol/L) until light yellow, add 1mL starch indicator (5g/L), and continue titrating until the blue color just disappears. If the salt sample contains too much impurities, first take the salt sample and add 150mL of water to dissolve it, filter it, take 100mL of the filtrate into a 250mL conical flask, and then operate.
4.12.3.4 Calculation of results
The iodine content in the sample is calculated according to formula (10). X=VXcX21.15×1000
Wherein:
X is the iodine content in the sample, in milligrams per kilogram (mg/kg); V is the volume of sodium thiosulfate standard titration solution consumed by the sample for determination, in milliliters (mL); C is the concentration of sodium thiosulfate standard titration solution, in moles per liter (mol/L); m is the mass of the sample, in grams (g); .....( 10 )
21,15 is the mass of iodine equivalent to 1.0mL sodium thiosulfate standard solution Cc(NazS,0)=1.000mol/L), in milligrams (mg).
The calculation result shall retain two significant figures.
4.12.3.5 Precision
The absolute difference in the volume of the standard titration solution for two parallel titrations under repeatability conditions shall not exceed 0.10mL. 4.13 Copper
Operate in accordance with GB/T5009.13.
Operate in accordance with GB/T5009.15.
4.15 Total mercury
Operate in accordance with GB/T5009.17.
4.16 Nitrite
Operate in accordance with GB/T5009.33.
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.