GB/T 15262-94 Determination of sulfur dioxide in ambient air—Methanol absorption-pararosaniline spectrophotometric method
1. Introduction
Sulfur dioxide (SO2) is a colorless, odorless gas, which is mainly from industrial and domestic combustion sources. It is one of the major causes of air pollution and considered as important factor for the formation of acid rain.
SO2 is emitted into the atmosphere, rapidly react with other components such as oxygen and water, to form sulfuric acid (H2SO4) aerosol, which may be hazardous to human health and the environment.
2. Principle
This method is based on the principle that SO2 reacts with para-rosaniline in the presence of methanol to produce a yellow compound which is red under alkaline conditions. The portion remaining red is measured by a spectrophotometer and concentration of SO2 is calculated.
3. Reagents
3.1 Methanol
Methanol: from the street, or industrial grade meets the requirement.
3.2 Para-rosaniline hydrochloride
Para-rosaniline hydrochloride: commercial product of analytical grade reagent, meets the requirement.
3.3 Sodium hydroxide
Sodium hydroxide: high purity, meets the requirement.
4. Apparatus
4.1 Spectrophotometer
Spectrophotometer: The wavelength of absorbance for the solution of para-rosaniline and methanol is 445nm. Make sure that the spectrophotometer sensitive remain the same during the time of use, and ensure that the output of the photodetector is linear over the concentration range of interest.
4.2 Colorimetric visualization system
Colorimetric visualization system: Must be included of automated sample introduction system, gas collection bag, and automatic continuous aspirating pump.
5. Procedure
5.1 Sample collection
5.1.1 About 1L gas sample is collected and stored in a damp cloth bag.
5.1.2 Weigh the bag and record its weight (W1).
5.2 Whole air sample is transferred into a 2L flasking and break the bag in the flask.
5.3 Add 0.3M naOH to the flask and swirled gently to completely dissolve the collected gas into water.
5.4 Place the lid of flasking on to the flask and invert it several times.
5.5 Let stand for 1h and then assess the density of gas-water mixture.
5.6 Add sufficient quantity of acetate buffer to maintain the pH at 8.6 ± 0.2.
5.7 Measure the absorbance of formed solution at 445nm.
6. Calculation
Assuming absorbance is A, mass of the bag is W1, concentration of para-rosaniline hydrochloride is C, and volume of gas sample is V.
The concentration of SO2 in the sample is calculated as follows:
C = A W1/ (C V)
7. Conclusion
This method is applicable to the determination of sulfur dioxide in ambient air. The method provides a simple, rapid, and precise procedure for the determination of sulfur dioxide in air. The results obtained by this method are reliable and accurate.
