Trace detection of environmental contaminants by laser photofragmentation/fragment detection spectrometry

Trace concentrations of NO₂, other nitro-compounds, R-NO₂, and brominated species are detected by one color, laser-induced photofragmentation/fragment detection spectrometry. Laser radiation near 226 nm is used to both photolyze the nitrocompound and to facilitate the detection of the characteristic NO fragment by 1+1 resonance-enhanced multiphoton ionization (REMPI) via its A²Σ⁺-X²II (0,0) transitions. Similarly, laser radiation at 260.63 nm is used to fragment the target brominated compound and excite the characteristic Br atom photofragment via its two-photon 4p⁴5p⁴D_3/2^o ←4p^{5 2}P_3/2^o transition. Detection of Br is accomplished by 2+1 REMPI, and by laser-induced fluorescence and stimulated emission via the 4p⁴5p ⁴ D_3/2^o→4p⁴5s ⁴P _5/2,3/2 transitions at 844 and 751.5 nm. The analytical merits of the technique are evaluated and discussed, and the limits of detection for various compounds reported