Detection of chlorinated hydrocarbons via Laser-atomization/Laser-induced fluorescence

Abstract

Chlorinated hydrocarbons (CHC), photodissociated at 193 nm, are detected with high sensitivity by observing the atomic chlorine fragment via laser-induced fluorescence (LIF). Photofragment emission spectra from CH₃Cl, CH₂Cl₂, CHCl₃, CCl₄, C₂HCl₃, and C₂Cl₄ demonstrate that photofragment fluorescence and chemiluminescence are negligible in the region 700–800 nm where the 3p ⁴4p ⁴ S ⁰ → 3p ⁴4s ⁴ P fluorescence from atomic chlorine is detected. There is also negligible interference for photodissociation in Ar, N₂, and air bath gases. Total CHC can be readily detected in air flows at mixing fractions less than 20 ppb and averaging times less than 1 minute. Techniques for considerable improvement in this detection limit are discussed.