Detection of mercuric bromide in a gas phase flow cell by laser photofragment fluorescence spectroscopy

Photofragment fluorescence (PFF) spectroscopy offers real-time monitoring capability with high-analytical sensitivity and selectivity for volatile mercury compounds found in process gas streams, such as incinerator stacks. In this work, low concentrations (6 ppb to 30 ppm) of mercuric bromide (HgBr₂) vapor were introduced into an atmospheric pressure flow cell. The PFF technique used 222 nm laser radiation to photolyze HgBr₂ and excite fluorescence from the resulting Hg atoms at 253.7 nm. The fluorescence intensity was linear with laser fluence over the range of 45180 mJ/cm₂. Extrapolated detection limits by this method below 1 ppb of HgBr₂ in the absence of air are estimated. A linear dynamic detection range up to 0.7 ppm (11 mg/m³) is reported.