Some standard content:
Chemical Industry Standard of the People's Republic of China
HG2321—92
Potassium dihydrogen phosphate
Published on June 1, 1992
Ministry of Chemical Industry of the People's Republic of China
Implemented on September 1, 1992
Chemical Industry Standard of the People's Republic of China
1 Subject Content and Scope of Application
HG2321—92
This standard specifies the technical requirements, test methods, inspection rules, and packaging, marking, storage and transportation of potassium dihydrogen phosphate for industrial and agricultural use. This standard applies to potassium dihydrogen phosphate for industrial and agricultural use. This product: used in medicine, buffer, culture agent, etc. in industry; used as fertilizer in agriculture.
Molecular formula: KH2PO
Relative molecular mass: 136.09 (according to the 1989 international relative atomic mass) Reference standards
Preparation of standard solutions for titration analysis (volume analysis) of chemical reagents Preparation of standard solutions for determination of impurities in chemical reagents Preparation of preparations and products used in test methods for chemical reagents GB610.1
GB1250
GB3049
GB3050
GB768 6
GB8569
3 Technical requirements
Chemical reagents General method for determination of arsenic (arsenic spot method) Method for expressing and determining limit values General method for determination of iron content in chemical products O-phenanthroline spectrophotometry General method for determination of chloride content in inorganic chemical products Potentiometric titration General method for determination of arsenic content in chemical products Packaging of solid chemical fertilizers
3.1 Appearance: Potassium dihydrogen phosphate is a white product or powder, and potassium dihydrogen phosphate for agricultural use is allowed to have a slight color. 3.2 Potassium dihydrogen phosphate should meet the requirements of Table 1. Table 1
Potassium dihydrogen phosphate (KH2PO4 on dry basis) content ≥ moisture
Water insoluble matter content
Chloride (CI) content
Technical indicators of potassium dihydrogen phosphate
First-class product
Qualified product
Approved by the Ministry of Chemical Industry of the People's Republic of China on June 1, 19920.5
% (m/m)
Qualified product
Implemented on September 1, 1992
Iron (Fe) content
Arsenic (As) content
Heavy metal (Pb) content
Potassium oxide (K20 on dry basis) content
4Test methods
HG2321—92
Continued Table 1
First-class products
Qualified products
%(m/m)
Qualified products
The reagents and water used in the test methods of this standard refer to analytical reagents and distilled water or water of equivalent purity unless otherwise specified.
The standard solutions, preparations and products prepared in the test methods are prepared and calibrated in accordance with the provisions of GB601, GB602 and GB603 unless otherwise specified.
For the determination of impurity content in this standard, the factory can prepare a unified sample solution for the determination of impurity content according to the amount specified in the standard. 4.1 Determination of potassium dihydrogen phosphate (KH2PO4) content Phosphomolybdic acid quinoline gravimetric method (arbitration method) 4.1.1 Principle
In an acidic medium, orthophosphate ions in a phosphorus-containing solution and quinoline phosphomolybdic acid reagent generate a yellow precipitate of quinoline phosphomolybdic acid, which is filtered, washed, dried and weighed. The amount of the precipitate is converted to potassium dihydrogen phosphate content. 4.1.2 Reagents and solutions
4.1.2.1 Nitric acid (GB626) 1+1 solution.
4.1.2.2 Preparation of quinoline phosphomolybdic acid reagent:
Solution A: Dissolve 70g of sodium molybdate in a 400mL beaker with 100mL of water. Solution B: Dissolve 60g of citric acid in a 1000mL beaker with 100mL of water, and then add 85mL of nitric acid. Solution C: Add solution A to solution B and mix well. Solution D: Mix 35mL nitric acid and 100mL water in a 400mL beaker, and add 5mL quinoline. Solution E: Add solution D to solution C, mix, let stand for 24 hours, filter with filter paper, add 280mL acetone to the filtrate, and dilute with water to 1000mL. The solution is stored in a polyethylene bottle in a dark place, away from light and heat. 4.1.3 Instruments
Usually used laboratory instruments and
4.1.3.1 Glass filter: filter plate number 4; 4.1.3.2 Drying oven: can control the temperature at 180±2℃. 4.1.4 Analysis steps
4.1.4.1 Preparation of sample solution:
Weigh 1g of sample that has been dried at 105-110℃ for 2h, accurately to 0.0002g, place in a 50mL beaker, dissolve with water, transfer to a 250mL volumetric flask, dilute to scale, and mix. 4.1.4.2 Determination:
Put 10.0mL of sample solution in a 500mL beaker, add 10mL of nitric acid (1+1) solution, dilute to 100mL with water, heat to near boiling, add 50mL of quinoline molybdate reagent, cover with blood, keep warm on a hot plate for 1min or in a near-boiling water bath until precipitation and stratification, take out and cool to room temperature, rotating the beaker 3-4 times during the cooling process. Filter with a glass filter that has been dried to constant weight at 180±2℃ in advance. Filter the upper clear liquid first, then wash the precipitate 1 to 2 times by pouring method (use 25mL water each time), transfer the precipitate to the filter, and continue washing with water, using a total of 125 to 150mL of water. Place the filter and precipitate 2
HG2321-92
in a drying oven at 180±2℃, dry for 45 minutes after the temperature reaches, transfer to a desiccator, cool to room temperature, and weigh. 4.1.4.3 Blank test:
At the same time as the determination, perform a blank test according to the same operating steps, with the same reagents and dosage, but without the sample. Take the arithmetic mean of the parallel determination results as the blank test value.
4.1.5 Expression of analytical results
The content of potassium dihydrogen phosphate (KH2PO4) X1, expressed as the mass percentage of potassium dihydrogen phosphate, is calculated according to formula (1): X; (mm) X0. 061 5 × 100
m×250
Wherein: m1——mass of quinoline phosphate precipitate, g; m2
——mass of quinoline phosphomolybdic acid precipitate measured in the blank test, g;
0.0615——coefficient for converting the mass of quinoline phosphomolybdic acid precipitate into the mass of potassium dihydrogen phosphate. 4.1.6 Allowable difference
Take the arithmetic mean of the parallel determination results as the determination result: the absolute difference of the parallel determination results shall not exceed 0.30%; the absolute difference of the determination results of different laboratories shall not exceed 0.60%. 4.2 Determination of potassium dihydrogen phosphate (KH,PO) content - volumetric method 4.2.1 Principle
Potassium dihydrogen phosphate aqueous solution is titrated with sodium hydroxide standard titration solution in the presence of thymol blue indicator solution until the solution changes from yellow-green to blue, and the potassium dihydrogen phosphate content is calculated. 4.2.2 Reagents and solutions
4.2.2.1 Sodium chloride (GB1266);
4.2.2.2 Potassium hydrogen phthalate (GB1257): reference reagent; 4.2.2.3 Sodium hydroxide (GB629) standard titration solution: c(NaOH)=1.000mol/L solution, prepared and calibrated according to GB601; 4.2.2.4 Thymol blue (GB629) indicator solution: 1.0g/L, dissolve 1.0g thymol blue in 22mL 0.1mol/L sodium hydroxide solution, and dilute to 1000mL with 50% ethanol solution. 4.2.3 Instruments
Usually used laboratory instruments.
4.2.4 Analysis steps
4.2.4.1 Determination:
Weigh 3g of sample that has been dried at 105~110℃ for 2h, accurate to 0.001g, place in a 250mL conical flask, add 80mL of water to dissolve, add 5g of sodium chloride, 8~10 drops (about 3mL) of thymol blue indicator (or use an acidometer), and titrate with sodium hydroxide standard titration solution until blue or pH value 9.1 is the end point.
4.2.4.2 Blank test:
At the same time as the determination, perform a blank test according to the same operating steps, the same reagents and amounts, but without the sample. Take the arithmetic mean of the parallel determination results as the blank test value.
4.2.5 Expression of analytical results
The content of potassium dihydrogen phosphate (KH2PO4) X2, expressed as the mass percentage of potassium dihydrogen phosphate, is calculated according to formula (2): c(V_ V) X 0.136 1 >
Wherein: c——concentration of sodium hydroxide standard titration solution, mol/L; volume of sodium hydroxide standard titration solution consumed in the determination, mL; V
V1——volume of sodium hydroxide standard titration solution consumed in the blank test, mL; m——mass of the sample, g;
HG2321-92
0.1361——mass of potassium dihydrogen phosphate equivalent to 1.00mL sodium hydroxide standard titration solution [c(Na0H)=1.000mol/L], expressed in grams.
4.2.6 Allowable difference
Take the arithmetic mean of the parallel determination results as the determination result. The absolute difference of the parallel determination results shall not exceed 0.30%; the absolute difference of the determination results of different laboratories shall not exceed 0.40%. 4.3 Determination of moisture content Drying loss method
4.3.1 Summary of the method
Dry the sample at 105-110℃ for 2h, and calculate the moisture content from the weight loss. 4.3.2 Instruments
Usually used laboratory instruments and
4.3.2.1 Weighing bottle: a flat bottle with a ground cover, 50mm in diameter and 30mm in height; 4.3.2.2 Drying oven: capable of controlling the temperature at 105-110℃. 4.3.3 Analysis steps
Weigh 10g of the sample to an accuracy of 0.001g, place it in a weighing bottle that has been dried to constant weight at 105-110℃ in advance, flatten the sample, place it in a drying oven at 105-110℃, dry it for 2h, take it out and place it in a desiccator to cool to room temperature, and weigh it. 4.3.4 Expression of analysis results
Water content X:, expressed as the mass percentage of water, calculated according to formula (3): Xs=\=㎡ ×100
Where: mi—mass of the sample after drying, g; m—mass of the sample, g.
4.3.5 Allowable difference
The arithmetic mean of the parallel determination results is taken as the determination result; the absolute difference of the parallel determination results shall not exceed 0.20%; the absolute difference of the determination results of different laboratories shall not exceed 0.30%. 4.4 Determination of pH value Potentiometric method
4.4.1 Summary of method
Use an acidometer with a glass electrode and a calomel electrode to determine the pH value of a solution with a concentration of 3g/L of potassium dihydrogen phosphate. 4.4.2 Reagents and solutions
4.4.2.1 The reagents used are all standard reagents or reagents of superior purity or above. The water used refers to distilled water without carbon dioxide. 4.4.2.2 Potassium dihydrogen phosphate (Cc (KH2PO) = 0.025 mol/L) and disodium hydrogen phosphate (Lc (Na2HPO4) = 0.025 mol/L) buffer solution: Weigh 3.40g potassium dihydrogen phosphate and dissolve it in about 400mL water; weigh 3.55g disodium hydrogen phosphate and dissolve it in about 400mL water; transfer these two solutions to a 1000mL volumetric flask, dilute with water to the scale, and mix well. This solution is stored in a sealed container. The pH value of this buffer solution is 6.86 at 25°C. Potassium dihydrogen phosphate and disodium hydrogen phosphate need to be dried at 120±10°C for 2h. 4.4.2.3 Potassium hydrogen phthalate [c(CHg0,K) = 0.05mol/) buffer solution: Weigh 10.21g of potassium hydrogen phthalate dried at 110℃ for 1h, dissolve it in water and transfer it to a 1000mL volumetric flask, dilute it to the mark with water and mix it. This solution is stored in a sealed container. The concentration of this solution c(CgH,cOzHCOzK) is 0.05mol/L, and the pH value is 4.01 at 25℃. 4.4.3 Instruments
Usually laboratory instruments and acidometers with glass electrodes and calomel electrodes have a sensitivity of 0.1pH units. 4.4.4 Analysis steps
4.4.4.1 Preparation of sample solution:
Weigh 3g of sample, accurate to 0.01g, place it in a suitable beaker, add water to 100mL to dissolve it and set aside for use. 4.4.4.2 Calibration of acidometer:
Use buffer solution (4.4.2.2 and 4.4.2.3) to calibrate the acidometer according to the instruction manual of the acidometer. 4
4.4.4.3 Determination:
HG2321—92
Insert the two electrodes of the acidometer into the sample solution and measure under the same conditions as during calibration. 4.4.5 Expression of analytical results
The pH value of potassium dihydrogen phosphate solution is expressed in pH. 4.5 Determination of water-insoluble matter content Gravimetric method
4.5.1 Summary of method
Dissolve the sample in water, filter it through a glass filter, wash it, dry it, weigh it, and calculate the water-insoluble matter content. 4.5.2 Instruments
Usually used laboratory instruments and
4.5.2.1 Glass filter: filter plate No. 4; 4.5.2.2 Drying oven: can control the temperature at 105~110℃. 4.5.3 Analysis steps
Weigh 10g of sample, accurate to 0.001g, put it in a 400mL beaker, add 100mL of 80℃ distilled water to dissolve, filter it while hot through a glass filter that has been weighed at 105~110℃ in advance, wash the beaker and glass filter with water 68 times, and dry the filter and water-insoluble matter in a drying oven at 105~110℃ to constant weight.
4.5.4 Expression of analysis results
The content of water-insoluble matter X, expressed as the mass percentage of water-insoluble matter, is calculated according to formula (4): Xx=mi=m2×100
Wherein: m1—the mass of water-insoluble matter plus glass filter, g, m2——the mass of glass filter, g;
m—the mass of sample, g.
4.5.5 Allowable difference
The arithmetic mean of the parallel determination results is taken as the determination result: the absolute difference of the parallel determination results shall not exceed 0.05%; the absolute difference of the determination results of different laboratories shall not exceed 0.10%. 4.6 Determination of chloride content Potentiometric titration method (arbitration method) 4.6.1 Principle
Same as Chapter 2 of GB3050.
4.6.2 Reagents and solutions
Same as Chapter 4 of GB3050.
4.6.3 Instruments
Same as GB3050.
4.6.4 Analysis steps
4.6.4.1 Calibration of silver nitrate standard titration solution: Accurately pipette 5.0mL 0.01mol/L potassium chloride standard solution into a 100mL beaker, add 5mL nitric acid solution (1+1), dilute to 50mL with water, put in an iron core stirring rod, place the beaker on an electromagnetic stirrer, and control the solution temperature below 20℃. Insert the silver electrode and calomel electrode into the solution, connect the line between the electrode and the potentiometer, and calibrate the instrument zero point. Use a microburette to add 4mL 0.01mol silver nitrate standard titration solution, and continue to add silver nitrate standard titration solution in batches, 0.10mL each time. After the potential value stabilizes, record the volume of the silver nitrate standard titration solution and the corresponding potential value, and calculate the continuous increment of the potential value (E1) and the difference of the secondary △E1 (△E2 positive or negative value). The silver nitrate standard titration solution required to titrate to the endpoint gives the silver nitrate standard titration solution consumed to give the maximum E1 value. Then take 10.0mL of 0.01mol/L potassium chloride standard solution for titration. Except that the amount of silver nitrate standard titration solution added at the beginning is changed from 4mL to 9mL, the other operations are the same as the titration of 5.0mL potassium chloride standard solution. The volume (V) of the silver nitrate standard titration solution consumed to the endpoint is calculated according to formula (5): 5
HG2321-92
V=Vo+VB
Wherein, V. —The volume of the silver nitrate standard titration solution before the maximum △E, mL; V1 —The volume of the silver nitrate standard titration solution equivalent to the last (end point) added part, 0.10mL; 5——AE, the last positive value;
—The sum of the absolute values of the last positive value and the first negative value of △E. For an example of the test record format, see Appendix C in GB3050. The concentration of the silver nitrate standard titration solution (mol/L) is calculated according to formula (6): 5
Wherein: cr-
concentration of potassium chloride standard solution, mol/L; - equivalent to the volume of 10mL potassium chloride standard solution, mL; V
Vs-equivalent to the volume of 5mL potassium chloride standard solution, mL, 5-the difference between the volumes of two potassium chloride standard solutions, mL. 4.6.4.2 Determination:
(5)
(6)
Weigh about 1g of sample (chlorine content not exceeding 1.5mg), accurate to 0.0002g, dissolve it in 50mL water in a 100mL beaker, add 5mL nitric acid solution (1+1), put in an iron core stirring rod, and operate according to "Put the beaker on the electromagnetic stirrer..." in 4.6.4.1" to "consumed silver nitrate standard titration solution". 4.6.4.3 Blank test:
At the same time as the determination, a blank test is performed according to the same operating steps, the same reagents and amounts, but without the sample. The arithmetic mean of the parallel determination results is taken as the blank test value.
The volume of the silver nitrate standard titration solution consumed in the blank test, V6 (mL), is calculated according to formula (7): Ve-2V:-V2
Where: V and V: —
Same as described in 4.6.4.1.
4.6.5 Expression of analytical results
The chloride content X6, expressed as the mass percentage of chlorine (Cl), is calculated according to formula (8): X -V): × 0. 035 45 × 100bzxz.net
c(V,-V)X3.545
Wherein: o-
-concentration of standard silver nitrate titration solution, mol/L; -volume of standard silver nitrate titration solution consumed in the determination, mL; -volume of standard silver nitrate titration solution consumed in the blank test, mL; mass of the sample, 8;
(8)
0.03545-the mass of chlorine equivalent to 1.00mL standard silver nitrate titration solution [c(AgNOs)=1.000mol/L], expressed in grams.
4.6.6 Allowable difference
The arithmetic mean of the parallel determination results is taken as the determination result; the absolute difference of the parallel determination results shall not exceed 0.01%. 4.7 Determination of chloride content Visual turbidimetry 4.7.1 Principle
In an acidic medium, the chloride in the sample reacts with silver nitrate to form insoluble silver chloride. When the chloride ion content is low, the silver chloride is suspended for a certain period of time, making the solution turbid. The chloride content in the sample is determined by comparing it with the standard turbidity of silver chloride. Editor's note: The original version is 1.5×10°mg, and this version is changed to 1.5mg. 6
4.7.2 Reagents and solutions
4.7.2.1 Nitric acid (GB626) solution: 5mol/L; HG2321-92
4.7.2.2 Silver nitrate (GB670) solution: 0.1mol/L; 4.7.2.3 Potassium chloride (GB646) (superior purity) standard solution: 0.01mg/mL Chlorine solution: Accurately weigh 0.4206g potassium chloride that has been dried at 130℃ for 1h to the nearest 0.0002g, dissolve it in a small amount of water, transfer it to a 1000mL volumetric flask, dilute it to the mark, and mix it. Pipette 25.0mL of the above potassium chloride solution, inject it into a 500mL volumetric flask, dilute it to the mark with water, and mix it. 4.7.3 Instruments
Usually laboratory instruments and
4.7.3.1 25mL colorimetric tube;
4.7.3.2 2.0 and 10.0mL pipettes.
4.7.4 Analysis steps
4.7.4.1 Preparation of standard turbidity:
Take 2.0mL of chlorine standard solution and inject it into a 25mL colorimetric tube, add 2.0mL of nitric acid solution (4.7.2.1) and 1mL of silver nitrate solution (4.7.2.2), dilute with water to the scale, and mix well. 4.7.4.2 Determination:
Weigh 0.1g of sample, accurate to 0.0002g, place it in a beaker, add 50mL of water to dissolve it, add 20mL of nitric acid solution (4.7.2.1) and transfer it to a 100mL volumetric flask, dilute with water to the scale, and mix well. If the solution is turbid, dry filter it. Take 10.0mL of the sample solution, put it into a 25mL colorimetric tube, add 1mL of the silver nitrate standard solution (4.7.2.2), dilute it to the mark with water, and mix it. After standing for 10 minutes, compare the turbidity with the standard.
4.8 Determination of iron content O-phenanthroline spectrophotometry 4.8.1 Principle
Same as Chapter 2 of GB3049.
4.8.2 Reagents and solutions
Same as Chapter 3 of GB3049.
4.8.3 Instruments
Same as Chapter 4 of GB3049.
4.8.4 Analysis steps
4.8.4.1 Preparation of sample solution:
Weigh 5g of sample accurately to 0.001g, dissolve it in water in a 50mL beaker, transfer it to a 50mL volumetric flask, dilute to the mark, and mix well. If the solution is turbid, dry filter it. 4.8.4.2 Reagent blank test:
Same as 5.2 of GB3049.
4.8.4.3 Drawing of standard curve:
Put 0, 10.0, 20.0, 30.0, and 40.0mL of iron standard solution (equivalent to iron content of 100, 200, 300, and 400μg) in 5 100mL volumetric flasks respectively. The following steps are carried out according to GB3049, starting from 5.3.2 "Color development" until "Drawing a standard curve". 4.8.4.4 Determination:
Take 20.0mL of the test solution (4.8.4.1) and place it in a 100mL beaker. The following operations are carried out according to 5.4.1 of GB3049, starting from "If necessary, add water to .....". Using water as a reference, measure the absorbance of the test solution and the reagent blank solution. 4.8.5 Expression of analysis results
The iron content Xe, expressed as the mass percentage of iron (Fe), is calculated according to formula (9): Xg = mi X10-8
HG2321—92
Where: mi——iron content in the test solution obtained from the standard curve, mg; m——mass of the sample, g.
4.8.6 Allowable difference
The arithmetic mean of the parallel determination results shall be taken as the determination result. The absolute difference of the parallel determination results shall not exceed 0.0003%, and the absolute difference of the determination results of different laboratories shall not exceed 0.0005%. 4.9 Determination of iron content o-phenanthroline visual colorimetric method 4.9.1 Principle
Use ascorbic acid to reduce the trivalent iron ions in the sample solution to divalent iron ions. Under the conditions of H4.5, the divalent iron ion and o-phenanthroline form an orange-red complex, which is compared with the iron standard color. 4.9.2 Reagents and Solutions
The reagents and solutions used are prepared in the same way as in 4.8.2.
4.9.3 Instruments
Usually, laboratory instruments and 25mL colorimetric tubes are used. 4.9.4 Analysis Steps
4.9.4.1 Preparation of Standard Color
Put 3.0mL of 0.010mg/mL iron standard solution in a colorimetric tube, add about 5mL of water, adjust the solution pH to close to 2 with hydrochloric acid solution (use precision pH test paper), add 2.5mL of ascorbic acid, 5 mL buffer solution, 5.0 mL o-phenanthroline solution, dilute to scale with water, and mix.
4.9.4.2 Determination
Weigh 1 g of sample, accurate to 0.0002 g, add 10 mL of water to dissolve it, adjust the solution pH to close to 2 with hydrochloric acid solution (using precision pH test paper), add 2.5 mL of ascorbic acid, 5 mL of buffer solution, 5.0 mL o-phenanthroline solution, dilute to scale with water, and mix. Compare the color presented with the standard color.
Silver diethyldithiocarbamate spectrophotometry (arbitration method) 4.10 Determination of arsenic content
4.10.1 Original
Same as Chapter 2 of GB7686.
4.10.2 Reagents and solutions
Same as Chapter 3 of GB7686.
4.10.3 Instruments and devices
Same as Chapter 4 of GB7686.
4.10.4 Analysis steps
4.10.4.1 Preparation of sample solution
Weigh 0.5g of sample into an arsenic generator, dissolve it with a small amount of water, add 20mL of hydrochloric acid solution (1+1), add water to the volume of about 40mL, add 2mL of potassium iodide solution and 2mL of stannous chloride solution, stir and let stand for 15min. 4.10.4.2 Reagent blank test
Same as Article 5.2 of GB7686.
4.10.4.3 Drawing of standard curve
Pipette 0, 1.0, 2.0, 4.0, 6.0, 8.0, 10.0mL of 2.5μg/mL standard solution into six arsenic generators respectively. The following steps are in accordance with 5.3.1 of GB7686, starting from "·Add the following solutions in sequence" to "Remove the absorber and mix the solution completely". Draw the standard curve with the arsenic content as the horizontal axis and the corresponding absorbance as the vertical axis. 4.10.4.4 Determination
Put 5.0mL of DDTC-Ag pyridine solution into a 15-bulb tube absorber, connect the various parts of the instrument, and let it stand for 15 minutes. Add 5g of arsenic-free metal zinc to the generator of the sample solution, immediately cover the lid and absorber, and react for about 45 minutes. Remove the absorber and mix the absorption solution. Use a spectrophotometer to measure the absorbance at a wavelength of 540nm, using the blank solution as a reference. 8
4.10.5 Expression of analysis results
HG2321-92
The arsenic content X7, expressed as the mass percentage of arsenic (As), is calculated according to formula (10): m×100
Wherein: m1 is the content of arsenic in the sample solution obtained from the standard curve, mg; m
is the mass of the sample.
The result should be expressed to four decimal places.
4.10.6 Allowable difference
(10)
The arithmetic mean of the parallel determination results is taken as the determination result. The absolute difference of the parallel determination results shall not exceed 0.0003%; the absolute difference of the determination results of different laboratories shall not exceed 0.0005%. 4.11 Determination of arsenic content Arsenic spot method
4.11.1 Principle
Same as Chapter 3 of GB610.1-88.
4.11.2 Reagents and solutions
Same as "4 Reagents" in GB610.1-88.
4.11.3 Instruments and devices
Same as "5 Instruments and devices" in GB610.1-88. 4.11.4 Analysis steps
Weigh 0.5g of sample into the wide-mouth bottle of the arsenic analyzer, add water to dissolve and dilute to about 70mL. The following operations shall be carried out according to Chapter 6 of GB610.1, starting from "add 6mL hydrochloric acid". 4.12 Determination of heavy metal content Visual turbidimetry 4.12.1 Principle
In a weakly acidic medium, hydrogen sulfide combines with hydrogen sulfide in the sample solution to form sulfide precipitates. When the metal content is low, a stable dark suspension is formed, which is determined by visual turbidimetry. 4.12.2 Reagents and solutions
4.12.2.1 Glacial acetic acid (GB676)
4.12.2.2 Lead nitrate (HG3-1070); 4.12.2.3 Acetic acid solution: c(CH2gCOOH) = 1 mol/L, take 57.5 mL of glacial acetic acid and dissolve it in water, dilute to 1000 mL; 4.12.2.4 Nitric acid (GB626);
4.12.2.5 Saturated hydrogen sulfide aqueous solution: Pass hydrogen sulfide gas into water without carbon dioxide until it is saturated (this solution is prepared before use);
Lead standard solution: 0 .01mg/mL. Weigh 0.160g lead nitrate, dissolve it in a small amount of water, add 1mL nitric acid, transfer to 4.12.2.6
1000mL volumetric flask, dilute to scale, and mix. Pipette 10.0mL of the above solution, place it in a 100mL volumetric flask, dilute to scale with water, and mix. This is a 0.01mg/mL lead standard solution. 4.12.3 Instruments
Usually laboratory instruments and 50mL colorimetric tubes. 4.12.4 Analysis steps
4.12.4.1 Preparation of sample solution
Weigh 10g sample, accurate to 0.001g, dissolve it in water, transfer to a 500mL volumetric flask, and dilute to scale , mix, and dry filter. 4.12.4.2 Preparation of standard turbidity
Put 2.5mL of lead standard solution in a 50mL colorimetric tube, dilute to 30mL with water, add 5.0mL of sample solution, add 1mL of acetic acid solution and 10mL of newly prepared saturated hydrogen sulfide aqueous solution, dilute to scale with water, mix, and let stand for 10 minutes. The standard turbidity is presented. 4.12.4.3 Determination
HG2321-92
Pull 25.0mL of sample solution into a 50mL colorimetric tube, add another 5.0mL of sample solution, and perform the following operations according to "add 1mL of acetic acid solution and let stand for 10 minutes" in 4.12.4.2. The turbidity presented is compared with the standard. 4.13 Determination of potassium oxide content Potassium tetraphenylborate gravimetric method 4.13.1 Principle
In a weakly alkaline medium, potassium ions in the sample solution are precipitated with sodium tetraphenylborate solution. In order to prevent the interference of ammonium ions and other cations, an appropriate amount of formaldehyde solution and disodium ethylenediaminetetraacetic acid (EDTA) can be added in advance to make the ammonium ions react with formaldehyde to form hexamethylenetetramine, and other cations are complexed with disodium ethylenediaminetetraacetic acid. Filter, dry and weigh the precipitate.
4.13.2 Reagents and solutions
4.13.2.1 Sodium tetraphenylborate (HG3-1164): 15g/L, take 15g of sodium tetraphenylborate and dissolve it in about 960mL of water, add 4mL of sodium hydroxide solution (4.13.2.5) and 20mL of 100g/L magnesium chloride hexahydrate (GB672) solution, stir for 15min, let it stand and filter it with filter paper; the solution is stored in a brown bottle or plastic bottle, generally not more than one month. If turbidity is found, it should be filtered before use. 4.13.2.2 Sodium tetraphenylborate washing solution: dilute one volume of sodium tetraphenylborate (4.3.2.1) with ten volumes of water; 4.13.2.3 Disodium ethylenediaminetetraacetic acid (GB1401) solution: 40g/L; 4.13.2.4 Formaldehyde (GB685) solution: about 30% or 37% (m/m); 4.13.2.5 Sodium hydroxide (GB629) solution: 400g/L; 4.13.2.6 Phenolphthalein (GB10729): 5g/L ethanol solution, 0.5g phenolphthalein dissolved in 95% (V/V) 100mL ethanol. 4.13.3 Instruments
Usually used laboratory instruments and
4.13.3.1 Glass filter: filter plate No. 4; 4.13.3.2 Drying oven: capable of controlling the temperature at 120±5℃; 4.13.4 Analysis steps
4.13.4.1 Preparation of sample solution
Weigh about 1.2g of sample that has been dried at 105110℃ for 2h, accurate to 0.0002g, place it in a 250mL conical flask, add about 150mL water, heat and boil for 30min, cool, transfer quantitatively to a 250mL volumetric flask, dilute to the scale with water, and mix well. 4.13.4.2 Determination
Put 25.0mL of the above test solution (4.3.4.1) into a 200mL beaker, add 20mL of EDTA solution (40mL can be added when it contains more cations), add 23 drops of phenol anhydride solution, add sodium hydroxide solution dropwise until the solution turns red, then add 1mL excess, add formaldehyde solution (calculated based on 1mg nitrogen plus about 60mg formaldehyde, that is, 0.15mL of 37% formaldehyde solution). If the red color disappears, adjust the color to red with sodium hydroxide solution, heat and boil in a fume hood for 15min, then cool or cool with running water. If the red color disappears, adjust the color to red with sodium hydroxide solution. Under constant stirring, add the sodium tetraphenylborate solution (4.3.2.1) dropwise into the sample solution, the amount added is 0.5 mL of sodium tetraphenylborate solution for every 1 mg of potassium oxide, and the excess is about 7 mL. Continue stirring for 1 min, let it stand for 15 min, filter the precipitate into a No. 4 glass filter that has been pre-weighed at 120°C by decantation, wash the precipitate and beaker with washing solution 5 to 7 times, each time using about 5 mL, and the total amount does not exceed 40 mL. Finally, wash the precipitate twice with water, each time using 5 mL. Place the glass filter containing the precipitate in a drying oven at 120±5°C, dry for 1.5 hours, then take it out, put it in a desiccator to cool to room temperature, and weigh it.
4.13.4.3 Blank test
At the same time as the determination, perform a blank test according to the same operating steps, the same reagents, and the same amount, but without the sample. Take the arithmetic mean of the parallel determination results as the blank test value.
4.13.5 Expression of analytical results
The content of potassium oxide (in terms of K20) Xs is expressed as the mass percentage of potassium oxide and is calculated according to formula (11): [(m2-m1) - (mm) × 0.1314 × 100X.=
m×250
In the formula, m-
-sample mass, 8;
filter mass, 8;
HG2321-92
[(mz-mi)-(m4-ms)J×131.4
mass of the filter containing the precipitate, g;
mass of the filter used for the blank test, g;
mass of the filter after filtration during the blank test, g; coefficient for converting the mass of potassium tetraphenylborate into the mass of potassium oxide. 4.13.6 Allowable difference
4.13.6.1 The arithmetic mean of the parallel determination results shall be taken as the determination result; the absolute difference of the parallel determination results shall not exceed 0.40%; 4.13.6.2
4.13.6.3 The absolute difference of the determination results of different laboratories shall not exceed 0.80%. Note: When washing the glass filter, if the precipitate is not easy to wash off, it can be further cleaned with acetone. 5 Inspection rules
P.oi.Po
5.1 Potassium dihydrogen phosphate should be inspected by the quality inspection department of the manufacturer, and the manufacturer should ensure that all potassium dihydrogen phosphate shipped out of the factory meets the requirements of this standard. The quality of this standard is determined by the rounded value comparison method in the national standard GB1250. Each batch of potassium dihydrogen phosphate shipped out of the factory should be accompanied by a quality certificate.
5.2 The user has the right to inspect the quality of the potassium dihydrogen phosphate received in accordance with the inspection rules and inspection methods specified in this standard to check whether its indicators meet the requirements of this standard. 5.3 Potassium dihydrogen phosphate is inspected in batches. The manufacturer takes the daily production as a batch, and the user takes the received product as a batch. 5.4 Bags of potassium dihydrogen phosphate should be randomly sampled according to Table 2: Table 2 Sampling quantity of bags of potassium dihydrogen phosphate
Total number of bags
82~101
102~125
126~151
152~181
Number of sampling bags
Total number of bags
If it exceeds 512 bags, the number of sampling bags shall be calculated according to formula (12): Number of sampling bags = 3×√
Where: n-
-the number of potassium dihydrogen phosphate in each batch is the total number of bags.
Total number of bags
182~216
217~254
255~296
297~343
344~394
395~450
451~512
Number of sampling bags
The number of sample bags drawn according to Table 2 (or calculated by formula (12)) shall be placed in a flat position. Insert the sampling needle from the longest diagonal line of each bag to 3/4 of the bag depth, and take a representative sample of not less than 0.1kg. The total amount of each batch of samples shall not be less than 1.0kg. 5.5 Random sampling of small agricultural packages shall be carried out according to Table 3: 11
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