COMPARISONS OF INFRARED AND ULTRAVIOLET-LASER PROBE MICROANALYSIS INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY IN MINERAL ANALYSIS

The application of an infrared and an ultraviolet laser probe microana lysis ablation system, coupled to an inductively coupled plasma mass s pectrometer is described for the analysis of olivine, garnet, phlogopi te, magnetite, apatite, calcite, quartz and feldspar. These minerals r epresent a range of composition, absorption characteristics and physic al properties (for example cleavage) and were prepared both as cut blo cks and thin sections, The analytical performance of the two laser pro be systems is compared for each mineral type in terms of lateral and v ertical resolution, duration of ablation, and the importance of minera l orientation. Lower limits of detection are presented for the two las er systems, Lateral resolution in the ultraviolet system is a function of laser power and can be varied from less than 5 to >70 mu m. For th e infrared system, laser power is essentially fixed and lateral resolu tion is a function of mineral type and sample preparation, Mineral ori entation is an important factor in analysis using the infrared system but for the ultraviolet system this is of no significance, For the ult raviolet laser system, lower limits of detection are dependent on the amount of material ablated which is a function of laser power density and range from hundreds to thousands of ppm at low power to sub-ppm le vels at high power, The removal of material by the ultraviolet laser p robe system is facilitated by the strong absorption in the ultraviolet region of the electromagnetic spectrum that all the minerals in this study possess, The ultraviolet laserprobe system provides a superior a nalytical performance for mineral microanalysis when compared with the infrared system.