Laser-induced plasma on a metal surface for ionization of organic compounds at atmospheric pressure

Laser-induced plasma generated by exposing a metal target to pulsed laser radiation with a power density of ∼70 GW cm−2 is used to ionize organic compounds in gases at atmospheric pressure. The estimation of the plasma temperature based on the analysis of the plasma emission spectra has shown that in the first few nanoseconds the temperature exceeds 5.5 × 104 K. The vacuum ultraviolet radiation of that plasma provides ionization of any organic compounds and water molecules. The main ionization channels of the studied compounds are proton transfer reactions, addition reactions with the formation of [M + NH4]+ and [M + H3O]+ ions and photoionization. Hydrocarbons are ionized by pre-oxidation and subsequent ionization of oxygenated molecules. The optimal surrounding gas for the analysis is pure argon, since the ionization efficiency of organic compounds in argon is up to a hundred times higher than that in atmospheric air and pure nitrogen.