Influence of wavelength on fractionation in laser ablation ICP-MS

As laser ablation becomes more ubiquitous for direct solid sampling with inductively coupled plasma mass spectrometry (ICP-MS), the need to understand and mitigate fractionation (non-stoichiometric generation of vapor species) becomes critical. The influence of laser-beam wavelength on fractionation is not well established; in general, it is believed that fractionation is reduced as the wavelength becomes shorter. This manuscript presents an investigation of fractionation during ablation of NIST glasses and calcite using three UV wavelengths (157 nm, 213 nm and 266 nm). Fractionation can be observed for all wavelengths, depending in each case on the laser-beam irradiance and the number of laser pulses at each sample-surface location. The transparency of the sample influences the amount of sample ablated (removed) at each wavelength, and the extent of fractionation. Pb/Ca and Pb/U ratios are used as examples to demonstrate the degree of fractionation at the different wavelengths.