The spectral detectability of fluorine in a helium glow discharge

The theoretical basis of the excitation of the fluorine emission spectrum is discussed, and the negative effects of easily excited impurities are demonstrated. Fluorine can be detected by means of its emission spectrum if it is present as a minor impurity in helium. The amount of water vapor and/or organic compounds in the helium must be minimized because these substances produce easily excited fragments in the glow discharge which dissipate the energy needed to excite fluorine atoms. Direct excitation of a diphenyldifluorosilane residue permits detection of about 70 pg of fluorine; if fluorine is volatilized as hydrofluoric acid and injected directly into the glow discharge, a photocurrent peak of 1.8 Ag^-1 of fluorine is obtained.