Crossed beam LC/MS using laser vaporization for samples of environmental interest
A new approach to combined liquid chromatography/mass spectrometry (LC/MS) is described which uses laser vaporization of the liquid chromatograph (LC) effluent and molecular beam techniques to transport and ionize the sample. A key feature of this approach is that samples eluting from the LC are vaporized, ionized, and mass analyzed with minimal contact with solid surfaces. The purpose of this investigation is to evaluate the performance and demonstrate the utility of an instrument based on this approach. The present status of LC/MS interfaces is discussed and the need for a practical LC/MS interface system is established. The instrumentation involved in this work is described. Theoretical discussions of laser vaporization and of the mechanism for transporting the solute into the ionization region of the mass spectrometer are presented. Performance of the crossed-beam equipment as an analytical tool is discussed in terms of sensitivity, detectabi1ity , linearity, repeatability, peak shape integrity, resolution integrity, flow and temperature sensitivity, transmission efficiency and ease of operation and maintenance. Mass spectra are presented which were obtained from laser vaporization of the LC effluent under both reversed phase and ion exchange conditions. Both positive and negative ion chemical ionization mass spectra and positive ion electron impact mass spectra are presented. The performance of the LC/MS system is evaluated by considering the instrumental design goals and performance characteristics. Applications of the crossed-beam system for the analysis of samples of environmental interest such as polynuclear aromatics, chlorinated and al kyl-phenols, amines, components of nucleic acidsâ€”bases, nucleosides, and nucleotidesâ€”and some herbicides are given. Several actual environmental samples were also analyzed. These samples include a LC/MS analysis of a New Orleans drinking water concentrate and a LC/MS analysis of an aerated lagoon effluent concentrate. Thus, the utility of the LC/MS system is demonstrated by citing prepared and actual samples of environmental interest.