Particle size-related elemental fractionation in laser ablation in liquid inductively coupled plasma mass spectrometry

Abstract

Particles sampled by means of laser ablation in liquid (LAL) can be analyzed by inductively coupled plasma mass spectrometry (ICPMS) after acid digestion or slurry nebulization. The LAL sampling process is simple, and a standard solution can be used for calibration. In this study, we investigated elemental fractionation during LAL by using a standard glass reference material, NIST 610. NIST 610 was placed in an open-top chamber, and ultrapure water was added until the surface of the glass was 3 mm below the water surface. LAL sampling was carried out in line-scanning mode. The LAL-sampled particles were divided into two size classes by filtration through a polycarbonate filter: particles larger than 0.4 μm were collected on the filter, and particles smaller than 0.4 μm passed into the filtrate. Both sizes of particles were digested with acid and analyzed by ICPMS. Volatile elements were enriched in the smaller particles and depleted in the larger particles. That is, elemental fractionation related to the size of the ablated particles was observed during the LAL-sampling process. When the LAL-sampled particles were introduced into the ICP, the large particles did not decompose completely. Volatile elements in the larger particles were vaporized more easily than calcium. Therefore, positive elemental fractionation was observed when the LAL-sampled particles were analyzed by slurry nebulization ICPMS. Comparison between slurry nebulization and acid digestion revealed that particle size-related elemental fractionation in the ICP was larger than that observed during LAL sampling.