Speciation of Arsenic Oxides Using Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Positive and negative ion mass spectra of arsenic trioxide (As₂O₃) and arsenic pentaoxide (As₂O₅) have been obtained by single-step laser desorption/ionization time-of-flight mass spectrometry. Pulsed UV radiation at 266 nm was used for the simultaneous desorption and ionization of the solid sample. High-mass cluster ions that are unique to the oxidation state of each oxide sample appear in the negative ion mass spectra. The As₂O₃ produces As₃O₅ ^-, while the As₂O₅ yields As₃O₈ ^-. The formation of unique negative cluster ions presents the capability for arsenic oxidation state speciation by laser desorption/ ionization mass spectrometry. The ability of time-of-flight mass spectrometry to examine the relative amounts of each arsenic oxide present in a series of mixtures is discussed. Application of our speciation technique to a model incinerator sample is demonstrated.