Analytical Sciences

Supercritical Fluid Clean-Up of Environmental Samples for the Analysis of Polycyclic Aromatic Hydrocarbons Using Time-of-Flight Secondary Ion Mass Spectrometry

Tetsuo SAKAMOTO,* Azusa YAMAMOTO,** Masanori OWARI,*** and Yoshimasa NIHEI**

*Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
**Faculty of Science and Engineering, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
***Environmental Science Center, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

A novel sample-pretreatment method for time-of-flight secondary ion mass spectrometry (TOF-SIMS) was developed using supercritical fluid extraction (SFE). In SFE, the extraction efficiency of a certain organic matter is controlled by the pressure and temperature of supercritical CO₂. Two-step SFE (1st step at 10 Mpa, 40°C; 2nd step at 30 MPa, 120°C) was applied to diesel exhaust particles containing many kinds of n-alkanes and aromatic species. n-Alkanes and polycyclic aromatic hydrocarbons (PAHs) were extracted in the 1st and 2nd steps, respectively. This selectivity was utilized for the sample preparation of TOF-SIMS analysis. Diesel exhaust particles after the 1st step of extraction were analyzed with TOF-SIMS, aiming at PAHs as analytical targets. The obtained spectrum was simplified, and mass peaks of individual PAHs were easily assigned, because unwanted compounds, like n-alkanes, were selectively removed by SFE. Furthermore, a simple calculation elucidated the outline of the spectrum.

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