Sulphur dioxide is a typical air pollutant among sulphur-containing compounds, which originates from the combustion of fuels such as coal and petroleum, smelting of sulphur-containing ores, and emissions of sulphuric acid and other chemical product production waste gases. It is estimated that 1/3 of the earth's sulfur dioxide is emitted through the combustion of fossil fuels. Sulfur dioxide enters the airways through respiration and produces irritation and corrosive effects on local tissues, especially when it coexists with aerosols such as soot, which can aggravate the damage to the mucous membranes of the respiratory tract. Sulfur dioxide is also usually the main substance that constitutes acid rain.
Operation method
Absorption in formaldehyde buffer - Spectrophotometric method with pararosaniline hydrochloride
Principle
Absorb sulfur dioxide in the gas sample with formaldehyde buffer to generate hydroxysulfonic acid addition compound, then add sodium hydroxide solution to make the addition compound decompose and release SO2, SO2 then reacts with hydrochloric acid pararosaniline to generate violet-red complex, and then quantitatively determined by spectrophotometric method. The method has the advantages of high sensitivity, high accuracy and good stability of sample collection, but the operating conditions require strict requirements. The main interferences are nitrogen oxides, ozone, heavy metals, etc. The addition of amine sulfamate can eliminate the interference of nitrogen oxides, and the addition of phosphoric acid and sodium tetraacetate can eliminate the interference of heavy metals.
Materials and Instruments
Air Move I. Instrumentation Caveat 1. The calculation of sulfur dioxide concentration requires the retention of 3 decimal places. 2. correctly grasp the color development temperature and time of this standard, especially at 25 ~ 30 ° C under the condition of strict control of the reaction conditions is the key. 3. when the Mn2+content in air is more than 1 ug/10mL or Cr6+ in the air is greater than 1 ug/10mL or Crgreater than 0.3 ug/10mL will be interfered with, then increase the amount of alkali can eliminate the effect. 4. the purpose of adding EDTA-2Na solution when preparing sulfur dioxide solution is to stabilize the sulfite, because SO32-oxidized by dissolved oxygen in water by reagents and water trace Fe3+The oxidation of SO 3 2- by dissolved oxygen in water is accelerated by the reagent and trace Fe 3+ in water, and EDTA complexes Fe3+, the catalytic effect decreases, and SOand the catalytic effect decreases, SO32-concentration is more stable. 5. PRA impurity interferes with the color development, the color developer PRA solution to join the way to invert the addition, that is, the A tube group poured into the PRA has been added to the B tube group, otherwise the precision is poor, but if the use of adjustable quantitative liquidizer, according to the provisions of the absorption of the PRA solution directly under pressure squeezed into the sample solution, the alkaline samples in the instantaneous transformation of the color reaction of the suitability of a strong acidic solution determination is also possible.It is also possible to do so. 6. Cr6+can make the purple-red complex discoloration, negative interference, so try to avoid the use of chromic acid wash solution to wash the utensils, if already washed with (1 + 1) hydrochloric acid soak for 1 hour, wash with water sufficiently to remove Cr6+.If it has been washed, it should be soaked in (1+1) hydrochloric acid for 1 hour and washed well with water to remove Cr 6+. 7. In order to make the color development time of the solution in each colorimetric tube close to the time, when adding PRA, every 3 copies of the solution, a 3-minute interval, and so on. 8. When calibrating sodium thiosulfate solution, the indicator should not be added too early, otherwise it will cause experimental error and make the result low. Common Problems I. Introduction Sulfur dioxide is a typical atmospheric pollutant among sulfur-containing compounds, which originates from the combustion of fuels such as coal and petroleum, the smelting of sulfur-containing ores, and the emission of waste gases from the production of chemical products such as sulfuric acid. It is estimated that 1/3 of the earth's sulfur dioxide is emitted through the combustion of fossil fuels. Sulfur dioxide enters the airways through respiration and has an irritating and corrosive effect on local tissues. For more product details, please visit Aladdin Scientific website.
Sodium hydroxide Cyclohexylenediaminetetraacetic acid (CDTA) Methanol Potassium hydrogen phthalate Aminosulfonic acid Iodine Potassium iodide Starch Potassium iodate Sodium thiosulfate Sodium carbonate anhydrous Sodium sulfite Glacial acetic acid Disodium ethanedioate tetraacetic acid Hydrochloric acid Formaldehyde Hydrochloric acid Paraben Concentrated phosphoric acid.
Spectrophotometer Porous glass plate absorber tube Plugged cuvette Water bath Air sampler
(1) Spectrophotometer;
(2) Multi-well glass plate absorber tubes, 10 mL for short-term sampling and 50 mL for 24-h sampling;
(3) 10 mL stoppered cuvette;
(4) Water bath
(5) Air samplers
II. Pharmaceuticals
Sodium hydroxide, cyclohexylenediaminetetraacetic acid (CDTA), methanol, potassium hydrogen phthalate, sulfamic acid, iodine, potassium iodide, starch, potassium iodate, sodium thiosulphate, anhydrous sodium carbonate, sodium sulphite, glacial acetic acid, disodium ethanediyl tetraacetic acid (EDTA-2Na), hydrochloric acid, formaldehyde, paraben, and 85% phosphoric acid in concentrate.
III. Reagents
1. 5 mol/L NaOH solution.
2. 0.005 mol/L Cyclohexylenediaminetetraacetic acid disodium salt (CDTA-2Na) solution: weigh 1.82 g of CDTA, add 1.5 mol/l of NaOH solution 6.5 mL diluted to 100 mL with water.
3. Formaldehyde buffer absorption storage solution: absorb 36%~38% methanol solution 5.5 mL, CDTA-2Na solution (reagent 2) 20.00 mL, weigh 2.04 g potassium hydrogen phthalate, dissolved in a small amount of water, the above three solutions are combined, and then diluted to 100 mL with water, stored in the refrigerator, can be stored for one year.
4. Formaldehyde buffer absorbing solution: dilute the formaldehyde buffer absorbing solution 100 times with water, and prepare it when it is used.
5. 6.0 g/L sodium sulfamate solution: weigh 0.60 g of sulfamic acid ( H2NSO3H ), place in a 100 mL volumetric flask, add 4.0 mL of NaOH solution (Reagent 1), dilute to the mark with water, shake well, seal and store, available for 10 days.
6. Iodine storage solution: weigh 12.7 g of iodine ( I2 ) in a beaker, add 40.0 g of potassium iodide and 25 mL of water, stir until completely dissolved, transfer to a 1,000 mL volumetric flask, dilute to the mark, shake well, and store in a brown bottle.
7. Iodine solution: Take 250 mL of iodine reservoir solution, dilute to 500 mL with water and store in a brown bottle.
8. 0.5 g/100 mL of starch solution: weigh 0.5 g of soluble starch, use a small amount of water to make a paste, slowly into 100 mL of boiling water, continue to boil until the solution is clarified, cooled and stored in a reagent bottle. Prepare when ready to use.
9. Potassium iodate standard solution ( CKIO3=0.1000 mol/L: weigh 3.5667 g of superior pure potassium iodate dried at 110°C for 2 h, dissolve in water and transfer to a 1 000 mL volumetric flask, dilute to the mark with water and shake well.
10. 1.2 mol/l HCl solution.
11. Sodium thiosulfate standard storage solution (C ≈ 0.1 mol/L): weigh 25.0 sodium thiosulfate ( NaS2O3-5H2O ) dissolved in 1 000 mL of freshly boiled and cooled distilled water, add 0.2 g of anhydrous sodium carbonate, stored in a brown bottle, placed in a week to calibrate its concentration, if the solution is turbid, it must be filtered. Calibrate with standard solution of potassium iodate (reagent 9). Calibration of standard solution of sodium thiosulfate: take 3 portions of 10.00 mL of standard solution of potassium iodate (reagent 9), respectively, placed in 250 mL iodine measuring flask, add 70 mL of freshly boiled and cooled distilled water, add 1.0 g of potassium iodide solid, and shake until completely dissolved. Add 10.00 mL of 1.2 mol/l HCl solution, immediately cover the bottle, shake well, placed in a dark place for 5 min, with sodium thiosulfate standard solution (reagent 10), titration to a light yellow color, add 2 mL of starch solution, continue to titrate until the blue color is just faded until the concentration of sodium thiosulfate standard solution is calculated according to the following formula.
C( NaS2O3 ) = 0.1000 x 10.00/VFormula:V - Volume of sodium thiosulfate solution consumed for titration, mL;C - concentration of sodium thiosulfate solution, mol/l.
12. Sodium thiosulfate standard use solution: dilute the standard sodium thiosulfate storage solution 10 times with freshly boiled and cooled water.
13. 0.05 g/mL EDTA-2Na solution: weigh 0.25 g of EDTA-2Na in 500 mL of freshly boiled and cooled distilled water, and make up when ready for use.
14. Sulfur dioxide standard solution (320-400 ug/mL): weigh 0.2000 g of sodium sulfite ( Na2SO3 ), dissolve in 200 mL of EDTA-2Na solution, shake slowly to prevent oxygenation, and let stand for 2-3 hours to calibrate the concentration of this solution.
Sulfur dioxide standard solution calibration: Absorb three 20.00 mL of sulfur dioxide standard solution (reagent 14), were placed in a 250 mL iodine measuring flask, add 50 mL of freshly boiled and cooled distilled water, add 20.00 mL of iodine solution (reagent 7) and 1 mL of glacial acetic acid, cover the stopper and shake well, placed in a dark place for 5 min, and then titrate with the calibrated sodium thiosulphate standard solution to a light yellow color. When adding 2 mL of starch solution, continue titration of the blue color just disappeared as the end point, record the volume of sodium thiosulfate solution consumption V (mL). Another three copies of EDTA-2Na solution 20 mL, with the same method for the blank test, record the blank test consumption of sodium thiosulfate solution consumption volume V0 (mL). The difference in the volume of sodium thiosulfate solution consumed in parallel test should not be greater than 0.04 mL, take the average value, and calculate the concentration of standard solution of sulfur dioxide according to the following formula.
C( SO2 )=(V0-V)×C( Na2S2O3 )×100/32.02Eq:C ( SO2 ) - mass concentration of sulfur dioxide standard solution, ug/mL;V0 - volume of sodium thiosulfate solution consumed for blank titration, mL;V - volume of sodium thiosulfate solution consumed for titration of standard solution of sulfur dioxide, mL;C ( Na2S2O3 ) - concentration of sodium thiosulfate solution, mol/l;32.02 - molar mass of sulfur dioxide ( 1/2SO2 ), g/mol.
When the accurate concentration of sulfur dioxide calibration, immediately diluted with the absorbent solution to contain 10.00 ug / mL of sulfur dioxide standard solution reservoir solution, the pro-use and then diluted with the absorbent solution to 1.00 ug / mL. Stored in the refrigerator at 5 ℃, 10.00 ug / mL of sulfur dioxide standard solution reservoir can be stabilized 6 months; 1.00 ug / mL of sulfur dioxide standard solutioncan be stabilized for 1 month.
(15) 0.20 g/100 mL of pararosaniline (PRA, or pararosaniline) reservoir solution.
(16) 0.05 g/100 mL Para-rose aniline PRA solution: Take 25.00 mL of the above solution in a 100 mL volumetric flask, add 30 mL of 85% concentrated phosphoric acid, 12 mL of concentrated hydrochloric acid, dilute with water to the mark, and place in a sealed container overnight away from light for use.
IV. Measurement steps
1. Plotting of standard curves
Fourteen 10 mL stoppered colorimetric tubes were divided into two groups, A and B, with 7 tubes in each group, and numbered separately, and the standard solution series were prepared according to Table 1 in Group A. Each tube in Group A was added with 0.5 mL of sodium sulfamate (reagent 5) and 0.5 mL of NaOH (reagent 1), and mixed well; each tube in Group B was added with 1 mL of PRA (reagent 15), and then each tube of the solutions in Group A was quickly and fully numbered into PRA. Then the solution of each tube of group A was rapidly added into the tube B with PRA solution, immediately plugged and mixed well, and put into a constant temperature water bath for color development (the difference between the color development temperature and the room temperature should not be more than 3 ℃), and the temperature and time of color development were selected according to different seasons and environmental conditions in accordance with Table 2. At the wavelength of 577 nm, the absorbance was measured using a 1 cm cuvette with water as the reference solution, and the calibration curve was calculated by the least-squares method.The regression equation was calculated by the least squares method:Y=bx+aWhere: Y - (A - A0) the difference between the absorbance A of the standard solution and the absorbance A0 of the blank;X - sulfur dioxide content, ug;b - slope of the regression equation;a - intercept of the regression equation (generally 0.005 is required).
Table 1 Sulfur dioxide standard solution series
Table 2 Selection of color development temperature and time
2. Measurement of samples
Any turbidity in the sample solution should be removed by centrifugation prior to measurement; the sample should be left for 20 min to allow ozone decomposition.
(1) Measurement of short-time sampling
Move all the sample solution in the absorption tube into a 10 mL colorimeter tube, dilute it to the calibration line with the absorption solution, add 0.5 mL of sodium sulfamate solution (reagent 5), mix it well, and leave it for 10 min to remove the interference of nitrogen oxides, and the following steps are the same as those for the standard curve. If the absorbance of the sample exceeds the upper calibration limit, the sample can be diluted with reagent blank solution and its absorbance measured within a few minutes, but the dilution times shall not be greater than 6.
(2) Measurement of continuous 24-hour sampling
Transfer the sample solution in the absorbent bottle into a 50 mL volumetric flask, wash the absorbent bottle with a small amount of absorbent solution, pour it into the volumetric flask, and then dilute it to the standard line with absorbent solution. Pipette appropriate amount of sample solution (depending on the concentration of 2 to 10 mL) in 10 mL colorimeter, and then diluted to the standard line with absorbent solution, add 0.5 mL of sodium sulfamate solution (reagent 5), mix well, and let it stand for 10 min to remove the interference of nitrogen oxides, and the following steps are the same with the production of the standard curve.
V. Calculation of results
C( SO2 ) = [(A-A0) × Bs/V0] × (Vt/Va)
Style:C ( SO2 ) - content of SO2, mg/m3;A - absorbance of the sample solution;A0 - absorbance of reagent blank solution;Bs - correction factor, i.e. the number of milligrams of SO2 corresponding to a unit of absorbance, ug/A;Vt - total volume of sample solution, mL;Va - total volume of the sample taken during the determination, mL;V0 - volume of the sample converted to standard conditions (0°C, 101.325 KPa), L.