GB/T 5831-1986 Determination of trace oxygen in gases - Colorimetric method
Some standard content:
National Standard of the People's Republic of China
Determination of trace oxygen in the gases-Cokorimett ic method
UDC 661.91/.99
GB 5881-86
This standard is applicable to the determination of oxygen in hydrogen, nitrogen, chlorine, ammonia, chlorine, nitrogen, xenon, methane and any other gas that does not react with monovalent copper ammine ions or ammonia. The determination range is 0.5~1000pPm. 1 Principle of the method
1.1 The oxygen in the gas reacts quantitatively with the colorless monovalent copper hydrogen complex ion to generate the blue divalent copper ammine complex ion, and the reaction formula is: [Cu? (NH,>)3 Clg+2NH,OH+2NH,C+↓O2—2 [Cu (NH,),) CI2+3H,0According to the reaction equation, 1ml0.05N copper sulfate solution is equivalent to 0.300ml oxygen at 20℃ and 760mmHg. The calculation method is as follows:
0.05×11.2×1000×293= 0.300 (ml)1000
1.2 According to the distinguishability of the color scale and the reasonable color scale difference, a series of standard color scales are prepared using different amounts of 0.05N copper sulfate solution. The amount of oxygen (V,) corresponding to each standard color scale is calculated according to formula (1): y1 = 0.300 × V
Where: V2 is the amount of 0.05N copper sulfate solution added to each standard color scale solution, ml. The amount of oxygen (V,) corresponding to each milliliter of standard color scale solution is calculated according to formula (2): V3 = 0.300 × V2/V
·(2))
Where: V—the volume of the standard color scale solution, ml. 1.3 In a closed analyzer, the oxygen in the sample gas reacts quantitatively with a certain amount of monovalent colorless copper ammonia solution, and the generated divalent copper ammonia solution is visually compared with the standard color scale. The ratio of the volume of oxygen corresponding to the standard color scale selected for color comparison to the volume of the sample gas is the concentration of oxygen in the sample gas. 2 Instrumentation
2.1 Apparatus
The recommended apparatus is shown in Figure A1 of Appendix A (reference). The device consists of an analyzer, a series of standard colorimetric tubes, a liquid storage bottle, an air suction bottle, etc.
When other measuring devices (such as reduction columns) are used, they must be in accordance with the provisions of this standard. 2.2 Analyzer
The analyzer and its processing reference dimensions are shown in Figure A2 of Appendix A (reference part). The analyzer is made of hard glass with a glass wall thickness of 1 to 2 mm. The sphere diameter of the analyzer determines the volume of the analyzer, and the volume of the analyzer (the closed volume after closing pistons 1, 5, and 6) is determined by the oxygen concentration in the sample gas: when the oxygen concentration in the sample gas is lower than 5ppm, the volume of the analyzer is not less than 3000ml; when the oxygen concentration in the sample gas is lower than 100ppm, the volume of the analyzer is not less than 1500ml; when the oxygen concentration in the sample gas is lower than 1000%Pm, the volume of the analyzer is about 500ml. Issued by the National Bureau of Standards on January 27, 1986
Implemented on November 1, 1986
The volume of the analyzer is determined by weighing water to one decimal place. Its volume (V,) is calculated by formula (3): V,=(G2-G)/0t
Where: G—mass of the analyzer,
G 2——total mass of the analyzer and water, g Pu is the density of water when the water temperature is ℃.
The volume between the piston 5, 6 of the analyzer and the liquid volume mark is 25.00ml. 2.3 Colorimetric tube
The colorimetric tube and its processing reference dimensions are shown in Figure A3 of Appendix A (reference) (A or B). (3)
The colorimetric tube is made of hard colorless glass. The length, diameter, wall thickness, glass quality, light transmission performance, etc. of each colorimetric tube must be exactly the same as the colorimetric tube on the analytical instrument.
2.4 Liquid storage bottle
The volume of the liquid storage bottle is 5~10L, which is used to store the copper ammonia reaction solution (prepared according to Chapter 5 of this standard). The height of its placement is suitable for convenient removal of the reaction solution. The reaction solution is taken out through a siphon, and the siphon is inserted about 20mm from the bottom of the liquid storage bottle. The pressure balance tube is inserted about 20mm below the rubber stopper of the liquid storage bottle and is always above the liquid surface of the reaction solution in the liquid storage bottle. 2.5 Inhalation bottle
The inhalation bottle is used to add oxygen-free gas to the liquid storage bottle, and balance the air pressure in the liquid storage bottle through the pressure balance tube so that the reaction solution can be taken out smoothly. For this purpose, the inhalation bottle is filled with oxygen-free gas in advance. When in use, add water to the inhalation bottle through the liquid addition funnel to discharge the oxygen-free gas into the liquid storage bottle. Other methods can be used to add oxygen-free gas to the liquid storage bottle, but it is necessary to ensure that the hydrogen in the reaction liquid is not lost and the reaction liquid is not oxidized. For example, the spare liquid bottle can be used as an air intake bottle. When it is used, add the gas prepared in 5.2 through the liquid adding bucket. 9 Materials, reagents and solutions
3.1 Ammonia water (GB 631-77): analytical grade. 3.2 Ammonium chloride (GB658-77): analytical grade; 3.3 Copper sulfate (GB665-78): analytical grade 3.4 Potassium iodide (GB1272~77): analytical grade, 10% solution: 3.5 Glacial acetic acid (GB676-78): analytical grade 3.6 Soluble starch (HGB3095-59): 0.5% solution: Sodium thiosulfate (GB637-77): analytical grade, 0.05N standard solution: 3.7
8.8 Hydrochloric acid (GB 622-77): analytical grade, 1:1 solution: 3.9 Copper wire, 1~2mm, chemical composition conforms to the provisions of GB 466-82 "Copper Classification" or YB145-71 "Chemical Composition of Pure Copper Processing Products";
3.10 Distilled water or ion exchange water;
Vacuum piston grease or industrial vanishing forest.
4 Preparation of a series of standard color scales
4.10.05N copper sulfate solution (liquid A)
Preparation: Use a balance with a graduation value of 0.Uu001g to accurately weigh 12.4860g of copper sulfate (CuSO, 5H, 0) that has been dried at room temperature in advance, dissolve it in a 1000ml volumetric flask with distilled water, dilute to the scale with water, and mix. Calibration: Use a pipette to draw 25.00ml of copper sulfate solution, place it in a triangular flask, add 2-3ml of glacial acetic acid and 10ml of 10% potassium iodide solution respectively, and the precipitated iodine is titrated with 0.05N sodium thiosulfate standard solution until it is close to the end point (light yellow), then add 5ml of 0.5% starch solution, and continue to titrate to the end point (milky white). Read the number of milliliters of 0.05N sodium thiosulfate standard solution used for titration. Calculate the concentration of copper sulfate solution (N,) by formula (4):
GB 5831--86
Formula; N—-
-concentration of sodium thiosulfate standard solution, N, V, volume of sodium thiosulfate standard solution for titration, ml. The arithmetic mean of two parallel calibrations is the calibration result. The calibration result of the copper sulfate solution concentration must be greater than 0.049N and less than 0.051N, otherwise it must be re-prepared. 4.2 Mixed solution (solution B)
Prepare saturated ammonium chloride solution and hydrogen water in a volume ratio of 1:1. 4.3 Series of standard color scale solutions
Use a 5ml burette to add solution A to 25 25ml volumetric flasks (or colorimetric tubes with 25.00ml lines) according to the amount of solution A given in Appendix B (Supplement), and then dilute to scale with solution B. After mixing evenly, place them in series standard colorimetric tubes No. 1 to 25 and seal them.
Add 25ml solution B to the colorimetric tube No. *0” and seal it. 5 Preparation of reaction
5.1 Wind a 1~2mm diameter energy wire or a spiral with a diameter of about 5mm and a length of about 20~50mm. After degreasing, remove the surface oxide layer with 1:1 hydrochloric acid, rinse with distilled water or deionized water until neutral, fill it into a liquid storage bottle to about four-fifths, and plug it with a rubber stopper with a siphon and a pressure balance tube. 5.2 Weigh 2.5g of copper sulfate (CuSO-5H,0) and dissolve it in 2000ml of liquid B. .3 Add the solution prepared in 5.2 into the liquid storage bottle until the copper wire loop is completely submerged. Let it stand and reduce to colorless. 4 When the reaction solution cannot be reduced to colorless, or the reaction solution is inconsistent with the colorimetric tube "0", it should be freshly prepared. 6 Determination steps
6.1 Sample
Wash the analyzer with distilled water or ion exchange water. Open all pistons of the analyzer, and connect the branch pipe of the gas piston 1 of the analyzer to the metal sampling tube with a high-quality rubber hose. Open the sample gas, adjust the flow rate to 1000~5000ml/min, and use the sample gas 10 times higher than the volume of the analyzer to fully purge the analyzer. .Reduce the sample gas flow rate, close valves 6, 5, and 1 of the analyzer in turn, and remove the analyzer. Quickly turn piston 1 to balance the gas pressure in the analyzer to normal pressure. Read and record the room temperature and atmospheric pressure. 6.2 Take the reaction liquid
Connect the rubber tube at the outlet of the siphon tube of the storage bottle to the branch pipe of the liquid taking piston 5 of the analyzer, open the spring clamp, turn the piston 5 of the analyzer, release part of the reaction liquid until it is completely colorless, and then turn the piston 5 of the analyzer to take the reaction liquid into the analyzer colorimetric tube to the mark. Close piston 5, clamp the spring clamp, and remove the analyzer. 6.3 Zero point colorimetry
Before the reaction, compare the reaction liquid with the standard color scale, that is, zero point colorimetry. Record the standard color scale number and the corresponding oxygen content selected for the zero point colorimetry (obtained from Appendix B). The zero point colorimetry result should be "0" or not higher than "1". 6.4 Reaction Colorimetry
Invert the analyzer, pour the reaction solution into the sphere, and shake vigorously for 3 to 5 minutes. Then return the reaction solution to fill the analyzer colorimetric tube, and select a standard color scale that is the same or similar to the color of the reaction solution in the analyzer colorimetric tube for colorimetric comparison. Record the standard color scale number selected for colorimetric comparison and the corresponding oxygen content (checked from Appendix B). Repeat the above operation until the colorimetric result is consistent. When the colorimetric result is between two standard color scales, record the two standard color scale numbers at the same time, separated by "two". At this time, the corresponding oxygen content is the average value of the corresponding oxygen content of the two standard color scales. For example, when the colorimetric result is between "7" and "8", record "7--8", and the corresponding oxygen content is (0.0210+0.0270)/2=0.0240 (ml). General precautions
GB5831—86
The measurement of trace oxygen in gas must be particularly careful. Only by strictly observing all the precautions can the measurement result be accurate. 7.1 Accuracy of standard color scale
The factors that affect the accuracy of standard color scale are multifaceted, mainly including the reagents, balances, magnetic codes, various volumetric devices, and mature and careful operation. The balances, codes, volumetric flasks, pipettes, burettes, etc. used should comply with the provisions of their identification procedures. The validity period of the standard color scale is generally 6 months. When the color changes due to over-speed or poor sealing of the colorimetric tube, they should be re-prepared.
2 Air tightness and adsorption of the analyzer
All pistons of the analyzer should have good air tightness. The piston oil should be carefully applied and carefully inspected before use. After long-term use of the analyzer, when the inner wall is corroded by ammonia, it will adsorb oxygen, leading to This will cause errors in the analysis results. At this time, according to GB4471-84 Chemical 1 Product Test Method Precision-Determination of Repeatability and Reproducibility of Inter-laboratory Tests, Article 4.3, standard samples should be used to measure whether the analyzer meets the requirements. When it does not meet the requirements, the analyzer must be replaced. 7.3 Nitrogen loss
The volatilization loss of ammonia in the standard color scale and the liquid storage bottle and the reaction liquid in the analyzer will affect the color comparison and must be prevented. For example: the colorimetric tube and the liquid storage bottle must be strictly sealed, the standard color scale should be prepared in the shortest possible time, the temperature of the sample gas should be pre-equilibrated to room temperature during the measurement, and the room temperature should not be higher than 40°C, etc. 7.4 [Interference issues
If there are impurity gases such as carbon dioxide, carbon monoxide, hydrogen sulfide, sulfur dioxide, olefins, alkynes, etc. in the sample gas, it will cause interference to the measurement, but when it exists in trace amounts, it will not affect the measurement and should be confirmed in advance before the measurement. The allowable amount of interfering impurities in the sample gas to be measured is limited to the error of the measurement result not exceeding 10% (not exceeding 20% when the oxygen content is less than 5ppm). Otherwise, the measurement should be carried out after removing the interfering impurities.
7.5 Representativeness of sampling
The key to making the sample representative is to strictly prevent the sample gas from being contaminated by air. The sampling of compressed gas must use a pressure reducing valve, the dead volume of the pressure reducing valve must be very small, and the sample gas must be fully replaced by the method of increasing and decreasing the pressure at least three times before sampling.
The sample gas delivery pipe between the sampling point and the analyzer must use a metal pipe, and permeable delivery pipes such as rubber pipes and plastic pipes cannot be used.
8 Result processing
8,1 The oxygen concentration in the gas is calculated according to formula (5); C-ty+in...
- oxygen concentration in the gas, ppm
wherein, C
oxygen equivalent to the standard color level selected for colorimetry, ml; - oxygen equivalent to the standard color level selected for zero-point colorimetry, ml: volume of the analyzer, ml!
(5)
K- correction factor for correcting the gas volume to 20℃, 760mmHg, calculated by formula (6) or obtained from Appendix C (Supplement).
K=293
273 +±760
wherein:! — temperature of the sample gas, C: — indoor atmosphere during measurement, nmHg.
（6）
GB5831--86
8.2 When the amount of reaction liquid taken into the analyzer is not 25.00ml, the oxygen concentration in the gas is calculated according to formula (7): C
Where: C—oxygen concentration in the gas, ppm; VI—(standard color scale selected for reaction colorimetry) equivalent oxygen content per milliliter of standard color scale solution, ml; Vi..—(standard color scale selected for zero point colorimetry) equivalent oxygen content per milliliter of standard color scale solution, mlV. ——Amount of reaction liquid taken into the analyzer, m). 7)
8.3 The arithmetic mean of the two determination results shall be the final determination result. The difference between the two determination results shall be less than the allowable difference specified in the first obstacle.
9 Allowable difference
Repeatability: r=1
Reproducibility:
Where: m——Single mean value of the determination result. R=0.90+0.12mbzxz.net
The repeatability and reproducibility shall be in accordance with the provisions of Chapter 4 of GB4471. The allowable error was determined in accordance with GB4471 in 1984 by 8 laboratories participating in 5 levels of experiments. 10 Report
The report shall include the following:
, all information about the sample, such as the name, number, sampling point, sampling date, time, etc. of the sample; b. Analytical results; the conditions for determining the concentration of oxygen in the sample and the details and explanation of any abnormal phenomena observed during the determination; d. The name of the analyst and the date of analysis, etc. 8
GB 5B31—86
Appendix A
Instrument diagram
(reference)
Figure A1 Measuring device
1—oxygen analyzer; 2—rubber tube; 3—spring clamp; 4—siphon; 5, 8—rubber hose; 6—liquid bottle; 7—pressure balance tube; 9—air suction bottle. 10—adding funnel
GB 58818
Figure A2 Oxygen analyzer
1—gas two-way piston:
2-sphere, 3—reduction mark: 1—colorimetric tube, 5—liquid three-way piston,
6-two-way living chamber
200-220
200~220
Figure A3 Colorimetric tube
Color scale number
GB 5881 86
Appendix B
Series standard color scale table
(supplement)
A amount used
when the girl
0,0600
Note: 1 ~1d color scale, the amount of A used is the disk after A solution is diluted 10 times with B solution. The amount of liquid equivalent to each milliliter of standard color scale
.0.9570
0, 8877
0,8791
0-8662
GB5831-86
Gas volume correction factor K value table
(supplement)
0,8987
0-8671
0,9883
0,9852
.0.9271
#,9240
0, 8789
0, 8761
0,9017
GB 5831-86
0,8904
.0.9908
0: 9760
.1.0035
0,9084
0,9404
0,9037
GB5831--B6
.0.9046
1:0155
1,0046
0 ,9678
0,9215
1:0087
0,9994
1,0007
0,9314
35831—86
1,0-093
:0.9798
0,9962
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