Research Product

Negative chemical ionization (NCI) mass spectra of 9 ortho-fused, 8 ortho and peri-fushed, and 13 methylated polynuclear aromatic hydrocarbons (PAHs) were obtained using iosbutane as the reagent gas. The isobytane-mediated NCI (NCI-IB) spectra of all 30 PAHs were characterized by a small number of abundant, large-mass ions, suitable for qualitative or quantitative detection. In general, initial processes of resonance electron capture or anion arrangement account for the principal ions formed by the unsubstituted PAHs, whereas dissociative capture resulting in loss of a hydorgen atom produces the most abundant ion in the NCI-IB mass spectrum of the alkylated PAHs. For most of the compounds studied, NCI-IB mass spectra produced in a hot (235) ion source were better suited for high-sensitivity measurements than the corresponding spectra produced in a cooler (125) source. NCI mass spectra do not provide information concurring isomeric structures, e.g., it would not be possible to distinguish benz(a)pyrene from benz(e)pyrene; however, the spectra reported indicate substantial potential for use of NIC mass spectrometry in screening environmental extracts for contamination with PAHs and their derivatives.