DESIGN, OPERATION AND ROLE OF THE LASER-ABLATION MICROPROBE COUPLED WITH AN INDUCTIVELY-COUPLED PLASMA - MASS-SPECTROMETER (LAM-ICP-MS) IN THE EARTH-SCIENCES

The coupling of a laser-ablation microprobe (LAM) to an Inductively Co upled Plasma - Mass Spectrometer (ICP-MS) has a relatively simple and inexpensive multi-element, high-sensitivity trace-element microbeam an alytical system with ideally suited to research in the Earth Sciences. The LAM should be designed to allow for flexibility in sampling wide variety of materials of various physical sizes and shapes, at variable , but small-scale, spatial resolution. The data and processing protoco ls of the LAM-ICP-MS system must allow the use of time-resolved analyt ical data for routine work. Raw analytical data must be acquired and s tored for processing on a time scale appropriate to the rare of laser ling and the scale of chemical variation in the sample (normally, inte grated data for each mass, at least each second, during le ablation). Robust calibrations, with reference materials (NIST trace-element glas ses) and suitable internal standards in both the sample and reference material, allow quantification of the concentrations of many petrogene tically trace elements. Relative fractionation of elements does occur during the analysis, and understanding of these is required before the full potential of LAM-ICP-MS can be realized. Despite this current li mitation, the method now capable of unique applications in mineralogic al acid geological research. Of particular importance is its ability t o not only the chemical concentration of trace elements at ppm to ppb levels in minerals, but also the nature of their Time-resolved analysi s of the analytical data allows distinction between trace elements inc orporated in the host crystal-structure and those located in other pha ses (inclusions, etc,).