Interference suppression in HO fluorescence detection

Preliminary results are presented for a sampling method that greatly reduces the interferences relative to hydroxyl (OH) fluorescence. The method involves expansion of the sampled air from 1 atm to lower pressures, and takes advantage of the fact that the OH fluorescence yield is inversely proportional to the total pressure. Rayleigh, particulate, and Raman scattering decrease linearly with the pressure. The results were obtained in laboratory air into which OH concentrations, approximately 10 billion/cu cm, were introduced from a flowing source. Pertinent experiments demonstrate the suppression of interferences and the preservation of hydroxyl fluorescence when air is expanded.