LA-ICP-MS
Our LA-ICP-MS system provides in-situ, micron-scale, trace element, light element and isotopic analysis in a wide variety of minerals. It complements our electron microprobe. The instrument consists of a Thermo Finnigan Element 2 high-resolution inductively coupled mass spectrometer (ICP-MS) and a Merchantek LUV213 UV laser ablation microprobe. The high-resolution ICP-MS has a double focusing sector field analyzer with reversed Nier-Johnson geometry; the field sequence is the magnetic sector followed by the electrostatic field. The laminated high power magnet provides for fast scanning rates. The analyzer works at three fixed, computer controlled resolution settings (R≈ 300, 4000 and 10,000). High mass resolutions are needed for interference free measurements. For example, to separate B from Na (in tourmaline or micas) a mass resolution of 4000 would be needed. To effectively measure Se an R-value of 10,000 is needed to separate Se from Ar molecular complexes in the plasma. In the case of the lanthanides, and rare elements such as Ta, Nb, Hf and Zr interferences are ubiquitous so the ability to resolve peaks is of great importance in pegmatite studies. The laser sampling system includes a frame grabber, software, transmitted, reflected and flood light options on a video microscope, a sample cell and sample handling and internal gas controls. The laser operates at 213 nm. The 213nm wavelength (Nd:YAG 5th harmonic) offers superior optical coupling to semi transparent and opaque minerals over and above that of the 266 nm laser (Nd:YAG 4th harmonic). While this is still not optimum for transparent minerals like quartz, calcite, feldspar and apatite it is still capable of improved absorption in calcite and 30 micron diameter ablation pits which is adequate for most analyses.
