Spectrophotometric determination of sulphur dioxide by reduction of iron(III) and simultaneous chelation of the iron(II) with 2,4,6-tri(2-pyridyl)1,3,5-triazine

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Abstract
Gaseous samples containing sulphur dioxide are scrubbed through solutions containing iron(III), 2,4,6-tri(2-pyridyl)-1,3,5-triazine and propylene carbonate. The amount of violet bis[2,4,6-tri(2-pyridyl)-1,3,5-triazine]-iron(II) complex ion formed is measured spectrophotometrically at 593 nm. Increased sensitivity can be attained by extracting the complex ion into propylene carbonate-chloroform solutions. The flow-rate of the incoming gas stream can be up to 12 l minute–1 for atmospheric-type samples, without significant loss of sulphur dioxide. Temperature effects are minimal and only manganese(II) and hydrogen sulphide are serious interferences. Beer's law is obeyed over the range 3 to 57 µg of sulphur dioxide. The colour forms as the sample is being scrubbed, therefore automation or continuous application of the proposed method, or both, should be feasible. The practice of using gas permeation tubes in developing methods for the determination of gaseous substances is critically examined.

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