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Three laser wavelengths (1064, 532, and 266 nm) were employed for laser ablation at varied laser pulse energies to study the effect of irradiance and wavelength upon analytical results for laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Two important results were observed and are reported here: (1) the intensity of the MS signal came to a local minimum when the laser focal point was on the sample surface, and (2) elemental fractionation based upon laser wavelength and laser pulse energy was observed. For the waste glass simulant studied, ablation with 1064-nm (IR) and 532-nm (green) radiation produced elemental fractionation that relates to the melting point of the elemental oxide, whereas with 266-nm (UV) ablation the response was independent of the elemental oxide melting point. At high laser powers, ablation at 266 nm produced an elemental bias based upon the mass of the elements. These observations suggest the use of ultraviolet radiation at low pulse energies to obtain improved analytical results.

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At Los Alamos National Laboratory (LANL), Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is routinely used to analyze a wide variety of plutonium samples for inorganic analytes. Approximately 75% of the elements of the periodic table can easily be determined by ICP-MS analysis. Techniques that use atomic emission for element detection and quantification encounter a large number of spectral interferences when analyzing plutonium samples due to the numerous emission lines of plutonium. Mass spectrometric techniques do not have that problem. In ICP-MS the main effect plutonium has on the elemental determinations is a signal suppression. With matrix dilution and signal normalization that problem is mitigated. This report describes the ICP-MS method used in the analysis of plutonium samples and the resulting detection limits.

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