Development of a Liquid Beam Technique for Characterization of Solute Molecules in Solution.

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High sensitive detection and characterization of solute molecules in solutions were developed. This technique consists of a continuous liquid flow (liquid beam) and multiphoton ionization mass spectrometry. Several aromatic molecules dissolved in methanol, ethanol and water were tested in order to examine the performance of this technique.The liquid beam was prepared by injecting a solution into a vacuum chamber through a 20 mum aperture. The pressure at the chamber was able to be maintained at 10^<-5>-10^<-6> Torr when the beam was injected. A laser beam with a wave length of about 270 nm was allowed to cross the liquid beam, and the photoions produced in the beam were ejected into vacuum as a result of Coulomb explosion. The mass resolution was attained to be about 300 by using pulse acceleration of the photoions.A variety of results were obtained: In the photoionization of an aniline-ethanol solution, for example, the aniline solute molecule is ionized via a resonant two-photon process in the solution and is ejected out of the liquid beam by Coulomb explosion. In addition, the aniline molecules tend to be associated with increasing the aniline concentration. In the case of a surfactant solution, such as an aqueous solution of N-dodencyl pyridinium, hydrocarbons fragmented from the hydrocarbon chain of the surfactant were observed. This result indicates that the surfactant is placed on the liquid surface with its hydrocarbon chain outside. In order to maximize the sensitivity limit, a method of expelling the photoions from the liquid beam will be developed.