Laser time-of flight mass analysis of PAHs on single diesel particulates

Spatially resolved laser desorption/laser ionization time-of-flight (L2ToF) mass spectrometry has been employed for the detection of PAHs in individual micrometer-sized diesel particulates from the NIST Diesel Particulate Matter (SRM1650) Standard Reference Material. Pulsed laser desorption was carried out on isolated 20-mu m-diameter particulates using a tightly focused (1-2 mu m) Nd:YAG laser beam. Neutral PAHs entrapped in the plume were ionized with a second time delayed 266-nm pulse. Scanning electron microscopy demonstrated that 2-5-mu m-diameter holes could be drilled through the particulates. The mass spectra were dominated by parent ions of PAHs known to be present in the certified sample. The limit of detection, per component, was estimated to be <20 mu g g(-1) in the diesel soot. In addition, the L2ToF analysis revealed the presence of other PAHs or derivatives not certified by NIST.