Copper-ion assisted photochemical vapor generation of bromide and bromate

Abstract

Significant enhancements in the photochemical vapor generation (PVG) efficiencies of both Br⁻ and BrO₃⁻ species from a 2% acetic acid medium occur in the presence of 10 mg L⁻¹ Cu²⁺. Rapid and near quantitative synthesis of CH₃Br from both Br⁻ and BrO₃⁻ is achieved using a 19 W flow-through photochemical reactor exposing the sample to intense 185 and 254 nm radiation. Additionally, for the first time, efficient PVG of Br⁻ was achieved using a simple 15 W germicidal 254 nm lamp irradiating a sample flowing in a PTFE coil wrapped around this source. Evidence is presented for a H₃C˙ radical-Br˙ atom transfer reaction from a copper bromide complex to account for the high PVG efficiency wherein Cu²⁺ serves as a photocatalyst in both PVG systems. Experimental conditions were optimized for the ICP-MS detection of Br at m/z 79 and 81. Sample flow rates of 3 and 2 mL min⁻¹, yielding irradiation times of 14 and 60 s in the flow-through and germicidal photoreactors, respectively, provided ⁷⁹Br limits of detection of 0.01 and 0.04 ng mL⁻¹ and precision of measurement of 2.5 and 4% (RSD) at 1 ng mL⁻¹, respectively. PVG efficiencies for Br⁻ were determined to be 92 ± 5 and 94 ± 5% for the flow-through and germicidal systems, respectively, whereas 76 ± 5% was estimated for BrO₃⁻ using the flow-through lamp.