Quantitative, colorimetric paper probe for hydrogen sulfide gas

Abstract Hydrogen sulfide (H 2 S) is a regulated industrial hazard, as it is a chemical asphyxiant with acute toxicity. The characteristic rotten egg smell of hydrogen sulfide is not a suitable indicator for the presence of the gas, as the olfactory system is often overwhelmed and desensitized to the gas. A new probe utilizing the copper(II) complex of 1-(2-pyridylazo)-2-naphthol (Cu-PAN) on a moist, porous, paper-like substrate has been developed to replace commercial lead acetate-based test papers for the detection of hydrogen sulfide gas at low concentrations. The reaction between H 2 S gas and the copper complex produces a distinct color change from purple to yellow/orange. The color change is observable to the naked eye for concentrations as low as 30 ppb H 2 S in a small, 1.35-L of gas, a typical volume of human breath. In comparison, the commercial Pb(II)(acetate) 2 test papers require large volumes of 5 ppm H 2 S gas. Incorporation of a base in the current probe aids in trapping weakly acidic H 2 S. The moist probe enhances the kinetics of the reaction between H 2 S gas and the base/Cu-PAN. These features increase the sensitivity of the probe, making it potentially suitable for both human breath tests and industrial H 2 S monitoring. The utilization of a handheld colorimeter allows for quantitative analysis of gaseous H 2 S, with a limit of detection (LoD) of 16 ppb and a limit of quantification (LoQ) of 53 ppb. The probe, offering rapid detection, is easy to prepare, inexpensive, disposable, and a green alternative to the commonly used lead acetate test papers.