Evaluation of Laser Ablation in Liquid (LAL) technique as a new sampling technique for elemental and isotopic analysis using ICP-mass spectrometry

Laser ablation in liquid (LAL) is widely used for the micro fabrications or production of nano-particles of various materials. In this study, we have evaluated the analytical capability of the LAL as a new sampling technique for elemental and isotopic analysis of solid samples. The solid sample was set into the deionized water, and the laser ablation was carried out within the water using a Ti:S femtosecond laser operating at fundamental wavelength (780 nm). The laser-induced sample particles were directly trapped and collected in the ambient water with high efficiency. We have investigated the possible elemental and isotopic fractionation during the LAL sampling. Five isotopic ratios (Pb-208/U-238, U-238/Th-232, Pb-208/Pb-206, Fe-56/Fe-54 and Fe-57/Fe-54) were measured on the resulting sample particles obtained with various ablation conditions (fluence and repetition rate) using ICP-mass spectrometry (ICP-MS). Series of experiments revealed that either with the higher fluence (>200 J cm(-2)) or with higher repetition rate (>250 Hz), the resulting Pb-208/U-238 ratios varied significantly (>1%) from those obtained with source materials (hence, NIST SRM 610). For the U-238/Th-232, Pb-208/Pb-206, Fe-56/Fe-54 and Fe-57/Fe-54 ratios, the measured values did not vary measurably (<0.5%) under the LAL conditions employed here. The data obtained here demonstrate clearly that the LAL technique can be applied for the elemental and isotopic analyses with the careful optimization of laser ablation conditions.