Abstract: A method and device for volatilizing and thereafter ionizing quantitatable femtomole and smaller amounts of molecules of nonvolatile solid oranic materials is disclosed. The method and device employ a laser pulse to desorb the organic material from a support upon which it is physisorbed. The support and the laser are related to provide a rate of heating of the support surface of at least 10.sup.6 .degree. K./sec with the support withstanding this heating rate without volatilization. Glass and similar inorganic oxidic substrates are preferred. The molecules so generated can be ionized, preferably with the use of resonance-enhanced muiltiphoton ionization. The ions so formed are characterized by a heavy predominance of ions corresponding to the molecules so as to permit their sensitive and unambiguous resolution by mass spectrometry.