Flow injection determination of gaseous sulfur dioxide with gas permeation denuder-based online sampling and preconcentration

A simple and novel flow injection method for the determination of gaseous SO2 is described based on gas permeation denuder (GPD) online sampling and preconcentration. The GPD is easily prepared with poly(vinylidene) difluoride microporous membrane as gas permeable material and two Perspex blocks with smooth and flat interface and rectangular engraved channels of mirror image. The sample gas is on one side of the membrane and phosphate buffer of pH 7.0 as the absorbing solution is on the other side. Gaseous SO2 permeates partially through the gas permeable membrane and dissolves in the absorbing solution. After preconcentration for 5.0 or 8.0 min, the solution is injected into the flow of 5.0×10–4 mol L–1 5,5'-dithiobis(2,2'-dinitrobenzoic acid) (DTNB) in 0.025 mol L–1 phosphate buffer. The resulting product formed between DTNB and absorbed SO2 is spectrophotometrically monitored at 410 nm with a charge coupled device (CCD) fiber optic spectrometer. The calibration graphs for preconcentration of 5.0 and 8.0 min are linear up to 4.0 and 3.2 mg m–3 with detection limits of 50 and 35 µg m–3, respectively. The corresponding analysis speeds are 8.5 and 6 samples h–1. The method is selective and just suffer from interference of hydrogen sulfide at higher than 1% of SO2 level (in m/V) with an error >+10%. The assay just uses cheap and common membrane and reagents and shows potential application in the monitoring of atmospheric SO2.