GB/T 4702.8-1985 Chemical analysis method for metallic chromium - Determination of arsenic content by distillation-molybdenum blue spectrophotometry GB/T4702.8-1985 standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Methods for chemical analysis of chromium metal
The distillation - molybdenum blue spectrophotometric method for the determination of arsenic content This standard is applicable to the determination of arsenic content in chromium metal. Determination range: 0.0005~0.0020%. This standard complies with GB1467-78 "General Principles and General Provisions for Chemical Analysis Methods for Metallurgical Products" 1 Method Summary
UDC 669.26: 543
42: 546.19
GB 4702.8-85
The sample is dissolved in hydrochloric acid, and arsenic is separated in the form of arsenic trichloride by distillation and formed into potassium arsenic acid. Then, in a perchloric acid medium, use sulfuric acid to reduce it to a blue complex, and measure its absorbance at a wavelength of 840nm on a spectrophotometer. 2 Reagents
2.1 Potassium bromide, high-grade pure.
2.2 Hydrazine sulfate, high-grade pure.
Hydrochloric acid (1+2).
Hydrochloric acid (specific gravity 1.19), high-grade pure.
Nitric acid (2+3), high-grade pure.
Perchloric acid (specific gravity 1.51), high-grade pure. Sulfuric acid (1+1), high-grade pure.
2.8 Sodium hydroxide solution (5%).
2.9 Sodium sulfate solution (0.15%).
2.10 Ammonium hydroxide: Weigh 250g of ammonium hydroxide and dissolve it in 1400ml of hot water at 180℃. The solution is filtered through dense filter paper, cooled, and then 300 ml of ethanol is added, stirred and left for 1 hour. Under vacuum conditions, filter with medium filter paper in a suction funnel, wash the precipitate 3 to 4 times with ethanol, and dry it in honey.
2.11 Perfluoric acid-ammonium chloride mixed solution: Weigh 5 g of ammonium chloride (2.10) and dissolve it in 100 ml of hot water, and cool it. In another 1000 ml beaker, add 5010 ml of water and 230 ml of perchloric acid (2.6) and stir. While stirring, slowly pour in the ammonium chloride solution and transfer the solution to a 1000 ml container Put it in a 1000ml volumetric flask, dilute it to the full mark with water, and mix well. 2.12 Chlorine water: When using, prepare it by passing chlorine gas saturated water directly. 2.13 Arsenic standard solution
2.13.1 Weigh 0.1320g arsenic trioxide, dissolve it in 5ml sodium hydroxide solution (2.8), dilute it to 200ml with water, add sulfuric acid (2.7) and all-cored test paper to induce acid reaction. Transfer the solution to a 1000ml volumetric flask, dilute it to the full mark with water, and mix well. This solution contains 0.1mg arsenic in 1 ml.
2.13.2 Transfer 50.00ml of arsenic standard solution (2.13.1) to a 500ml volumetric flask, dilute it to the full mark with water, and mix well. This solution contains 0.1mg arsenic in 1 ml. ml contains 0.01 mg arsenic.
National Bureau of Standards 1985·04-15 Issued
1986-01-01 Implementation
3 Instruments
3.1 Arsenic distillation device (quartz) (see the figure below). 1—Electric furnace 2
Spectrophotometer.
4 Sample
GB4702.8—85
Arsenic distillation device
Flat-bottomed quartz bottle, 3—Rubber race, 4-Separatory funnel; 5-Glass capillary tube (for buffering); 6-Absorber; 7-Test tube receiver; 8-Glass beaker. All samples should pass through a 1.68 mm sieve.
5 Analysis steps
5.1 Sample quantitybZxz.net
Weigh 1.0000 g of sample.
5.2 Empty self-test
Test with the sample empty.
5.3 Determination
GB 4702.8—85
5.3.1 Place the sample (5.1) in a 100ml distillation flask, add 10ml of chlorine water (2.12) to the test tube receiver, place the test tube in a beaker with ice in advance, add 40ml of hydrochloric acid (2.3) to the distillation flask, plug it, connect the test tube receiver, and heat at low temperature until the sample is dissolved.
5.3.2 After the solution has cooled, add 15ml of chlorine water (2.12) from the glass tube to the distillation flask. ) and the distillate in the test tube receiver must not be less than 30ml.
5.3.3 After the distillation flask has cooled, transfer the solution in the distillation flask and the distilled solution in the test tube to a 250ml beaker, rinse all the instruments with a small amount of water, and merge the washing solution into the main solution. 5.3.4 Cover the beaker with Table III, boil the solution for 10min, cool, wash the surface blood and the wall of the beaker with water, evaporate the solution to 10~15ml without boiling, and cool. Transfer to the distillation flask, rinse the beaker with 20ml hydrochloric acid (2.4), add 0.5g potassium bromide (2.1), 0.2g hydrazine sulfate (2.2), and connect the distillation instrument. Add 10ml water to the test tube receiver that has been placed in ice to control the distillation until the volume of the solution in the distillation flask is 3~5ml.
5.3.5 Transfer the distilled solution into a 100ml beaker, wash the test tube wall with 15ml nitric acid (2.5), wash with a small amount of water, cool it down, and transfer the washing solution into the main solution, slowly heat it until the solution evaporates, and place it in an oven at 130±10℃ for 30~40min. 5.3.6 Add 20ml perchloric acid-ammonium lead acid mixed solution (2.11) and 1ml sulfuric acid solution (2.9), cover with a watch glass, and heat it in a boiling water bath for 10~20min. After the solution cools, transfer it to a 50ml volumetric flask, rinse the beaker and watch glass with perchloric acid-ammonium lead acid mixed solution (2.11), and dilute it to the scale with this mixed solution and mix it well. 5.3.7 Transfer part of the solution into a 3cm colorimetric dish, use water as a reference, and measure its absorbance at a wavelength of 840nm on a spectrophotometer. 5.3.8 Subtract the absorbance of the blank test done with the sample and find the corresponding arsenic content from the working curve. 5.4 Drawing of the working curve
Pipette 0.000.50, 1.00, 1.502.00ml of arsenic standard solution (3.13.2) and place them in a group of 50ml beakers respectively, add 15ml of nitric acid solution (2.5), evaporate the solution to dryness, place it in an oven at 130±10℃ and bake for 30~40min, and proceed as in 5.3.6 and 5.3.7. Subtract the absorbance of the reagent blank and draw the working curve with the amount of the tablet as the horizontal axis and the absorbance as the vertical axis. Calculation of the analysis results
Calculate the percentage of arsenic according to the following formula:
As (%):
Wu Zhong: m,
Arsenic content found from the working curve, g; sample amount, g.
Analysis results shall be accurate to the fourth decimal place. 7 Tolerance
The difference between analysis results of laboratories shall not be too small. The following table lists the tolerance. %
0.0004~0.0010
-0.0010~0.0020
Additional remarks:
GB4702.885
This standard is proposed by the Ministry of Metallurgical Industry of the People's Republic of China. This standard is drafted by Hunan Ferroalloy Factory. From the date of implementation of this standard, the former Ministry of Metallurgical Industry Standard YE582-65 "Metallic Chromium Chemical Analysis Method" shall be invalidated. 221
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