Analysis of particulates by Raman microprobe†

Abstract

We describe a new technique of local analysis of heterogeneous samples which is analogous to the electron or ion microprobe but is based on molecular spectra of materials to characterize the different components of a microscopic sample and (or) to obtain images giving their surface distribution. The sample is illuminated by a laser beam causing characteristic Raman lines of the different components to be emitted. Using these Raman lines, the components can then be detected, identified and located. For this purpose, the microscopic area of the preparation which is illuminated is analysed by a conventional optical microscope coupled with a tunable band pass filter and a multichannel or monochannel detection system. One main advantage of this technique is the ability to study samples not under vacuum but in air, under a controlled atmosphere or even inside a transparent matrix. Normal Raman spectra can be obtained from particles of 1 μm size and larger, and are the basis for the qualitative identification of molecular constituents. The technique has been applied to molecular microanalysis of matter in the particulate form (i.e., Airborne particles—stack particulates, flyash, asbestos minerals, defects and inclusions in industrial materials,...). It is especially interesting for organic materials which are not detected by other methods. Different examples illustrate this technique.