Cationization by Alkali Ion Attachment in Laser Desorption Mass Spectrometry

Abstract

The formation of quasimolecular ions by alkali ion attachment in laser desorption mass spectrometry has been investigated by using a CW CO2 laser. For molecules such as sucrose the desorption of preformed ions could be excluded. Evidence is presented for the ionization by alkali ion attachment in the gas phase. Quasimolecular ions of organic salts were found to result from cationization reactions in the gas phase and from surface reactions. Very fast cation exchange reactions have been discovered for salts and acids impinging on alkali ion emitting surfaces.

Intermolecular proton transfer reactions in the laser mass spectrometry of organic acids

“…Recently, Hillenkamp proposed four possible ion formation mechanisms for laser mass spectrometry: (1) thermal evaporation of ions from the solid; (2) thermal evaporation of neutral molecules from the solid, followed by ionization in the gas phase; (3) "true" laser desorption; and (4) ion formation in a laser-generated plasma (15). The two thermal processes have been confirmed for nonlaser radiative heating of organic salts (16,17) and cationization of thermally evaporated neutrals (17)(18)(19). The detection of similar species in laser mass spectrometry implies that such thermal processes may occur in LMS (20).…”

Infrared Desorption of Neutral Molecules Embedded in Transparent Matrices

“…A CW C 0 2 laser, if focussed onto a sample for a sufficient time, produces ions, but the delay time between the start of laser irradiation and the emission of ions is on the order of hundreds of milliseconds [9]. High-powered pulsed C 0 2 [10] and Nd-YAG (1.06 pm) [11][12][13] lasers have also been used to pro duce ions from organic surfaces.…”

“…The production of ions by IR radiation was shown to be caused by adduct ion formation. Ions, such as Na + , leave the sur face and combine in the gas phase with desorbed neu tral molecules via ion-dipole interactions [9,14], Several interesting studies have also been done on IR and thermal desorption of neutrals using postionization techniques. Allison et al [15] and Röllgen et al [16] showed that the emitted neutrals could be ionized in the gas phase by using an intersecting Reprint requests to Dr. J. Grotemeyer, Institut für Physi kalische und Theoretische Chemie, Technische Universität München, Lichtenbergstraße 4, D-8046 Garching, BRD.…”

Influence of the wavelength in high-irradiance ultraviolet laser desorption mass spectrometry of organic molecules

“…In particular, the extremely wide range of laser parameters (continuous wave (CW) to picosecond pulses, irradiances from 10°to 1012 W/cm2, far-UV to IR wavelengths) as well as the varying size of the laser spot and different ion source geometries complicates the interpretation of the available data with regard to the general desorption processes. Whereas at least parts of the results of laser desorption (LD) initiated by IR lasers can qualitatively be described by applying thermal models (2)(3)(4)(5)(6), only general theoretical approaches exist for LD with pulses of 10 ns or less of visible or UV radiation (7) as used in a laser micro mass analyzer (LAMMA).…”