Portable analyzer for continuous monitoring of sulfur dioxide in gas stream based on amperometric detection and stabilized gravity-driven flow

The construction, optimization and application are described for a portable gas analyzer which gives real-time measurement of sulfur dioxide in a gas stream. The SO₂ is absorbed from the analyte gas stream into a gravity-driven carrier solution flowing through a diffusion scrubber (DS), in the form of a bundle of polymeric hollow fibers. The sulfite ions in the carrier solution are detected by anodic amperometry at a novel carbon nanotube (CNT) electrode polarized at 0.35 V vs Ag/AgCl reference electrode. A novel compact design is the result of integrating the DS with the amperometric detector and yields a light weight portable analyzer (900 g) with a small footprint. The optimized analyzer has favorable performance characteristics such as (i) good sensitivity (LOD = 4 ppm, S/N = 3), (ii) wide linear dynamic range up to 5000 ppm, (iii) reasonably fast response time (t_95%, 4.1 min), (iv) excellent signal stability and repeatability (RSD = 1.3%), and (v) continuous standalone operation for 6 h. The interfering effect of H₂S is avoided by removing H₂S using a prior guard column. The analyzer can successfully monitor the removal of SO₂ from SO₂-N₂ gas mixtures and in determining sulfite in foodstuffs.