COMPARISON OF THE REPRODUCIBILITY OF NEGATIVE-ION CHEMICAL IONIZATION MASS-SPECTRA OBTAINED BY DIFFERENT REAGENT GASES ON 2 COMMERCIAL QUADRUPOLE INSTRUMENTS

The reproducibility of negative ion chemical ionization (NICI) mass spectra on two commercial quadrupole instruments (Finnigan 4021/4500 and Hewlett-Packard 5985B) using different reagent gases is investigated. Both instruments gave relatively similar CH4 NICI mass spectra for polychlorinated test compounds in the higher mass range. High abundances of Cl and HCl2 anions were characteristic for the Finnigan system. The presence of rhenium oxide ions from the filament in the background spectra is dependent on both the construction of the ion source and the use of a carbon-containing reagent gas. Use of N2, C2H4, and CH4 as reagent gas is discussed and the results are compared with earlier finding. The OH- NICI mass spectra of isomeric aza arenes recorded on both instruments showed a high degree of similarity and allowed the differentiation of isomers.