Inductively Coupled Plasma Mass Spectrometers (ICP-MS)
Two single collector ICPMSs are in use at RSES, an Agilent 7700 and a Varian 820. These instruments excel at determining concentrations of most elements of the periodic table (see jpeg) but the usual purpose of analysis is determining trace element concentrations. The samples passes through a plasma and is “perfectly ionized’, then focused through lenses, through 4 rods which act to separate ions on the basis of mass/charge then to an electron multiplier (see jpg). By changing voltages to the rods, the collected mass can be changed at a rate of a new mass per 0.01 seconds. Broad ranges of elements (isotopes), from Li to U, can be analysed in 1 routine. Precise isotope ratio work is not possible (see MC-ICPMS and SHRIMP sections) with the exception of the U-Th-Pb system.
Laser Ablation ICP-MS
Excimer lasers with 193 nm wavelengths can be used to ablate many solid materials at spot sizes of 20 to 200 microns and samples can be drilled or rastered. The laser ablation chamber is shown in the gallery. Detection limits are in the ppm (parts per million) range generally. Example materials analysed are: minerals, glass, fossils, pottery, bone, teeth, and paint.
Solution work has 2 advantages compared to lasering: 1) sample homogenization and 2) sample purification and element preconcentration such as platinum group element (PGE) and gold analyses. As these occur at very low concentrations in geological materials they must be concentrated before analysis. Preconcentration and isotope spiking allow detection limits of ppb to ppt to be achieved. Examples of solution work include PGE analysis and trace elements in ground water.