Laser Microprobe Mass Spectrometry

The use of lasers as an ionization source for solid samples is nearly as old as the laser itself. The first papers in this field were published in 1963 [1]. Since then there has been a growing interest as well as a proliferation of publications on this subject, to the extent that a recent bibliography listed nearly 1000 references [2]. The reasons for this increase in popularity are twofold. First, commercial instruments that use lasers as a microprobe have become available in the last five years. Second, the laser is one of a class of “soft” ionization sources that have become popular in organic mass spectrometry for the analysis of nonvolatile and thermally labile materials. The laser is unique as a means of ionizing solids because the ionization mechanism can be altered by simply changing the power density in the focal spot.