Mass spectrometric isotope dilution analysis is used for the first time to determine traces of bromide and chloride in environmental samples. This technique is an absolute method and is used especially for the standardization of other analytical processes. The principle of the isotope dilution technique is explained using Cl, Br and I. Ionization in the mass spectrometer takes place by the formation of negative halide ions on a hot rhenium filament. The examples given are the Cl− analysis of rain and snow as well as the analysis of traces of Br− and Cl− in surface snow taken from varying distances away from a highway. The latter analysis is compared with results using ion selective electrodes. Unlike the concentration of Br−, the Cl− concentration in surface snow continually decreases, the further away the snow is from the highway. Br− analyses of aerosol from the periphery of the town of Regensburg show that a significant portion of the aerosol bromide originates from traffic exhausts.

An analytical procedure for determining traces of chloride in silicate rocks, using mass spectrometric isotope dilution analysis with a 37 Cl-enriched spike, is described. The chlorine isotope ratios are measured with a double-filament thermal ion-source using the production of negative ions from a hot rhenium filament as the ionization method. The samples are decomposed with hydrofluoric acid in a Teflon bomb and chloride is separated from the acidic solution by selective precipitation as AgCl. The relative standard deviation for the chloride determination is 1–4% for chloride contents of 100–200 ppm. This precision is better than any described in the literature for chloride trace analysis. The problem of the blank in chloride trace determination in rock samples is discussed.