Extraction-spectrophotometric determination of sulphur dioxide

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Abstract
A sensitive spectrophotometric method for the determination of trace amounts of sulphur dioxide, after fixation in buffered formaldehyde solution, is described. The method is based on the reaction between iodate and sulphur dioxide in the presence of an excess of chloride ions. The resulting ICI4 - species forms an ion pair with pyronine-G, which is then extracted into benzene. The colour system obeys Beer's law in the range 0–4 µg of sulphur dioxide. The coefficient of variation is 4.3% for 10 determinations of 2 µg of sulphur dioxide. The effect of interfering gases is discussed. The method has been applied to the determination of sulphur dioxide in ambient air in the vicinity of a coal-fired power station and the results have been compared with the widely used pararosaniline method.

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