The application of laser-ablation microprobe - inductively coupled plasma-mass spectrometry (LAM-ICP-MS) to in situ trace-element determinations in minerals

A laser ablation microprobe (LAM) sample-introduction system, designed for in situ microsampling of minerals in petrographic sections, has been interfaced to an Inductively Coupled Plasma - Mass Spectrometer ICP-MS). The LAM consists of a Q-switched Nd:YAG laser with power attenuation and steering optics to guide the laser beam through the phototube of a petrographic microscope, where it is focused onto the petrographic section contained in a sample cell. The response of rock-forming minerals to ablation is related to their absorptivity of the 1064 nm wavelength of the laser beam, and their physical properties, particularly cleavage and tenacity. Most minerals can be ablated controllably in unsupported polished wafers, grain mounts and polished blocks, where ablation pits with diameters of 20-40 μm can be achieved routinely. Comparison of LAM- and solution-ICP-MS analyses of titanite, zircon, apatite, uraninite, and garnet separates demonstrates that a simple scheme of calibration employing a spiked NBS silicate glass reference material, using major-element internal standards to correct for differences in ablation yield, drift, and matrix effects, provides good accuracy and precision for a diverse suite of elements. -from Authors