The influence of different types of reactant ions on the ionization behavior of polycyclic aromatic hydrocarbons in corona discharge-ion mobility spectrometry.

RATIONALE Some polycyclic aromatic hydrocarbons (PAHs) are considered to be cancer-causing chemicals, and ion mobility spectrometry (IMS) is used for on-site detection of such hazardous chemicals. In IMS, the ionization behavior of analytes is affected by the types of reactant ions (RIs). In the present work, the influence of different types of RIs on the ionization behaviors of PAHs in an ion mobility spectrometer equipped with a corona discharge ionization source was investigated using various RIs. METHODS Selected PAHs were dissolved in anisole, fluorobenzene, chlorobenzene, or bromobenzene. The IMS analysis procedure was as follows: (1) the PAH solution was dropped onto the smear matrix; (2) the smear matrix was immediately inserted into the sample inlet to minimize evaporation of the solvent; and (3) the IMS analysis was performed. The lowest amount studied was 10 ng. Variations of the IMS spectra with time were investigated. RESULTS PAHs were not ionized by RIs of protonated molecules ([M + H]+ ) such as air/moisture and acetone, but they were ionized by charge transfer reactions with RIs of molecular ions (M•+ ) of solvents such as anisole, fluorobenzene, chlorobenzene, and bromobenzene. The PAH ions were detected following a time delay of ~1 - 5 s after the sample introduction and the times at which the maximum intensities for the PAHs were observed were different. The detection limits of PAHs in chlorobenzene were on the whole better than those in other solvents, whereas those in fluorobenzene were worse. The detection limits of pyrene and benzo[a]anthracene were better than those of the other PAHs irrespective of the solvent used. CONCLUSION PAH molecules were ionized by charge transfer reactions with RIs of the solvents, and their ions were detected ~1 - 5 s after sample introduction. The order of the ionization efficiency was: chlorobenzene > anisole > bromobenzene > fluorobenzene.