Simultaneous Determination of SO3(g) and SO2(g) in a Flowing Gas

A method for assaying a flowing gas mixture for SO 2(g) and SO 3(g) is described. The proof-of-concept for this method presented here uses the quantitative reaction of SO 3(g) with CaC 2 O 4(s) at 325 °C to produce CO 2(g) . The gas mixture is passed first through a plug of CaC 2 O 4 and then through a series of two optical cells. SO 2(g) is measured directly at one cell by UV spectrometry, and SO 3(g) is measured indirectly as CO 2(g) at the second cell by IR spectrometry. Good correlation coefficients were found for both analytes. Potential interference by SO 2 on the IR response of CO 2 can be neglected within a 1% error margin except when the ratio CO 2 /SO 2 is very small. A summary of key analytical methods for the analysis of sulfur oxides is given.