Automated measurement system for H₂O₂ in the atmosphere by diffusion scrubber sampling and HPLC analysis of Ti(IV)-PAR-H₂O₂ complex

An automated selective measurement system for monitoring hydrogen peroxide (H₂O₂) in the atmosphere was developed (using a diffusion scrubber coupled to a high performance liquid chromatograph) due to the importance of H₂O₂ in understanding tropospheric chemistry and its harmful effects on vegetation. H₂O₂ in the atmosphere was effectively collected by a diffusion scrubber, which consisted of a hydrophobic porous polytetrafluoroethylene (PTFE) tube positioned concentrically within a Pyrex glass tube. Titanium(IV)-4-(2-pyridylazo)resorcinol (Ti(IV)-PAR) solution acidified at pH 2.2 was used as the scrubbing solution for the diffusion scrubber. After the collection of the air sample by the diffusion scrubber, the pH value of the Ti(IV)-PAR scrubbing solution was adjusted to pH 11.9 to form a stable complex of Ti(IV)-PAR-H₂O₂. An aliquot of the sample solution was injected into a high performance liquid chromatograph equipped with a semi-micro-reversed-phase column and a spectrophotometric detector set at 508 nm for separating and determining the Ti(IV)-PAR-H₂O₂ complex. The automated measurement could be performed at 60 min intervals. The collection efficiency of H₂O₂ was higher than 98% at an air flow rate of 1.0 1 min^-1. The detection limit (3σ of the blank value) of H₂O₂ was 9 parts per trillion by volume (pptv) for an air sampling volume of 55 1. The interference from coexisting O₃ or SO₂ in the atmosphere was negligible during the collection of H₂O₂ by the diffusion scrubber. The developed automated measurement system was suitable for monitoring H₂O₂ in the atmosphere.