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 microanalysis ablation system, coupled to an inductively coupled plasma mass spectrometer is described for the analysis of olivine, garnet, phlogopite, magnetite, apatite, calcite, quartz and feldspar. These minerals represent a range of composition, absorption characteristics and physical properties (for example cleavage) and were prepared both as cut blocks and thin sections. The analytical performance of the two laser probe systems is compared for each mineral type in terms of lateral and vertical resolution, duration of ablation, and the importance of mineral orientation. Lower limits of detection are presented for the two laser systems. Lateral resolution in the ultraviolet system is a function of laser power and can be varied from less than 5 to >70 μm. For the infrared system, laser power is essentially fixed and lateral resolution is a function of mineral type and sample preparation. Mineral orientation is an important factor in analysis using the infrared system but for the ultraviolet system this is of no significance. For the ultraviolet 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 levels at high power. The removal of material by the ultraviolet laser probe 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 analytical performance for mineral microanalysis when compared with the infrared system.