CHEMICAL CHARACTERIZATION OF SINGLE PARTICLES BY LASER ABLATION DESORPTION IN A QUADRUPOLE ION-TRAP MASS-SPECTROMETER/

Particles are introduced into the center of the space surrounded by th e hyperbolic electrode surfaces of a quadrupole ion trap mass spectrom eter. Ions are desorbed or ablated from the surfaces of the particles with laser pulses from a Nd:YAG laser as the particles fall through th e trap. The ions are trapped and subsequently mass analyzed using the mass-selective instability mode of operation of the ion trap. Desorpti on experiments were performed with similar to 100 mu m silicon carbide particles with an average of a few nanograms of adsorbed trimethylphe nylammonium chloride, tetraphenylphosphonium bromide, or 2,4,6-trinitr otoluene per particle. A conservative detection limit of 0.7 fm per pa rticle was determined for tetraphenylphosphonium bromide. Ablation exp eriments were performed with similar to 50 mu m nickel particles for i sotope ratio measurements with good agreement between accepted and ave rage experimental values.