Laser desorption and ionization of solid polycyclic aromatic hydrocarbons in air with analysis by ion mobility spectrometry

Solid polycyclic aromatic hydrocarbons with 4-7 rings on metal, glass, ceramic, and plastic substrates were desorbed and ionized in air with a quadrupled Nd-YAG laser. Gaseous product ions were analyzed at ambient conditions in air directly using ion mobility spectrometry. Ablation rates for perylene on borosilicate glass were estimated as 0.01 ng/mm/sup 2/ per pulse and standard deviation for peak heights with roughly 1 ..mu..g/mm/sup 2/ was 34%. Substrate interference was avoided by using an unfocused laser beam at 0.5-1 mJ/pulse although gaseous ions also could be generated from substrates with a focused beam at 1 mJ/pulse.