Improvement of spatial resolution of elemental imaging using laser ablation-ICP-mass spectrometry.

Laser ablation-ICP-mass spectrometer (LA-ICPMS) now becomes one of the most principal analytical technique for mapping analysis for major to trace elements in rocks, minerals, functional materials, or biological tissue samples. In this study, imaging analysis was conducted with coupling of small volume cell and off-set laser ablation protocol to improve the spatial resolution. Combination of newly designed small volume cell and in-torch gas mixing protocols provides faster washout time of the signals (about 0.8 s for reducing 238U being one part in a hundred, 1% level). This is very important to improve the spatial resolution in a direction of laser scanning. Moreover, combination of small distances between the laser-line scan (laser pitch distance) and preferential and total ablation of only biological tissue samples placed on glass substrate results in laser ablation of smaller areas than the size of laser ablation pit (shaving ablation). With the shaving ablation, laser-line scanning with narrower-band width (e.g., 2 µm) can be achieved even by the laser beam of 8 µm diameter. To demonstrate the practical usage of the present technique, imaging analysis of Gd-ethylenediamine tetra-methylene phosphonic acid-doped mouse bone was conducted. Preferential distribution of Gd at the edge of the apatite cell was more clearly identified by the present technique. Combination of the shorter washout system setup and the shaving ablation protocol enables us to improve the spatial resolution of the elemental imaging obtained with the LA-ICPMS technique.