The extraction of sulphate from the alkaline impregnated
filters is described in Section 3.6. For the Thorin method the extract has a
too high pH to permit a direct analysis and the solution has to be treated with
a cation resin before analysis.
The procedure after the extraction from the filter (Section
3.6) for Dionex systems and Waters systems are described in Section 4.1.
This method can be used for the determination of sulphur dioxide in ambient air after the sulphur dioxide has been absorbed on a potassium hydroxide impregnated filter (see Section 3.6). The concentration range is 0.1 to 8 mg SO2 per litre leaching solution.
Sulphur dioxide is absorbed on a potassium hydroxide impregnated filter as sulphite. During the sampling period and storage the sulphite will be partly oxidized to sulphate. The filters are extracted with water, and hydrogen peroxide is added to oxidize the remaining sulphite to sulphate. Before analysis by the Thorin method (see Section 3.6.3), the extracted solution has to be treated with a cation exchange resin to remove the potassium and to neutralize the solution.
Same as listed in Section 4.2.1 In addition 100-150 ml polyethylene beakers or 30 ml centrifuge tubes are needed for the extraction.
Same as listed in Section 4.2.1. In addition: Hydrogen peroxide (H2O2), 30%. Traces of sulphate can be removed from the ion exchange resin by washing with 0.1 M sodium hydroxide, 0.1 M hydrochloric acid and distilled water before use.
Same as listed in Section 4.2.1.
Proceed as described in Section 4.2.1.
The concentration of sulphur dioxide in the air expressed as microgram of sulphur per cubic metre, is given by:
a = concentration
of sulphur in milligrams per litre in the leaching solution, read from the
calibration curve.
v1 = the
volume, in litres, of the leaching solution.
v2 = the
volume, in cubic metres, of the air sample.
Healy, C. and Atkins, D.H.F. (1975) The determination of atmospheric sulphur dioxide after collection on impregnated filter paper. Harwell, U.K. Atomic Energy Authority (AERE-R 7956).