Colorimetric determination of sulfur dioxide in air using a droplet collector of malachite green solution

The measurement of sulfur dioxide in air at the parts-per-billion level is described. The experimental arrangement consists of two optical fibers plac ed on opposite sides of a liquid droplet of malachite green solution. After light has been passed through the droplet, the transmitted light is measur ed by a referenced photodetection arrangement. The light used in this absor ption process is from a monochromatic source (lambda(max) 625 nm). This arr angement permits the variation of color in the droplet to be measured. The sulfur dioxide in the sample is collected by the droplet; it reacts with ma lachite green resulting in a colorless dye. The decoloration of the solutio n is proportional to the concentration of sulfur dioxide sampled. The signa l depends on the sample flow rate. The present technique is simple, inexpen sive, and permits a fast and near real time measurement while consuming ver y little reagent, (C) 1999 Academic Press.