Spatially Resolved Time-of-Flight Mass Spectrometry of Polycyclic Aromatic Hydrocarbons: Quantification Studies

Deuterated polycyclic aromatic hydrocarbons (PAHs) have been employed as surrogate internal standards for the quantitative analysis of PAHs by laser postionization time-of-flight mass spectrometry. Experiments were performed on intimate mixtures of chrysene and chrysene-d₁₂ which were desorbed from thin films at 266 nm using a tightly focused (1-2 µm) Nd-YAG laser beam. The neutral molecules within the laser-desorbed plume were ionized by a frequency-doubled dye laser at 260 nm. Under soft ionization conditions, the mass spectrum comprised peaks associated with the parent ion envelope with negligible amounts of fragment ions at lower masses. The ratio of the peak areas of the parent ions of chrysene and chrysene-d₁₂ was proportional to their relative molar concentrations in the standard solutions. With the use of chrysene-d₁₂ as an internal standard, the determined concentration of chrysene in an NIST standard was in good agreement with the certified value.