PARAROSANILINE AS A NEW CHROMOGEN FOR THE EXTRACTIVE SPECTROPHOTOMETRIC DETERMINATION OF TRACE AMOUNTS OF HYDROGEN-SULFIDE IN AIR

A sensitive spectrophotometric method for the determination of trace a mounts of hydrogen sulfide (H2S) in air, after fixing in a zinc acetat e-disodium ethylenediaminetetraacetate-sodium hydroxide solution, is d escribed. The reaction of iodate with the fixed H2S in the presence of acid and an excess of chloride leads to the formation of ICl2- ions. The resulting ICl2- species forms an ion par with pararosaniline catio n, and the product is extracted into isopentyl alcohol. The color syst em obeys Beer's law over the range of 0 to 5.0 mug H2S. The molar abso rption coefficient of the color system is 1.8 X 10(4) L mol-1 cm-1. Th e coefficient of variation is 3.3% for 10 determinations at 3.0 mug H2 S. The effect of interfering gases on the determination is discussed. The method was applied to the determination of residual amounts of H2S present in a laboratory fume cupboard, and results were compared to t hose obtained by the widely used methylene blue method. The current me thod can be used to determine residues as low as 0.2 mug H2S.