5:15 PM - 6:30 PM
[SCG47-P05] Effect of Laser Parameters on LA-ICP-MS Analysis
LA-ICP-MS consists of a combination of three processes: (1) laser ablation for sample aerosol generation, (2) aerosol transport, and (3) aerosol ionization in an ICP torch. The accuracy and precision of the analysis depend on the optimization of each stage of those LA-ICP-MS processes and the condition of the sample, such as particle size and preparation method especially for powder samples. In this study, the effect of laser parameters at the laser ablation stage, which is easier to adjust and change than other stages, is examined. The effects by the choice of laser spot sizes, fluences and repetition rates were investigated on the analysis of single crystal and powder sample pellets. The analysis was performed using LA-ICP-MS combined with an Agilent 7500s and a YAG laser system with a wavelength of 213 nm in Kanazawa University. We also compared the results with those obtained with a Excimer laser system (wavelengths of 193 nm) previously used at Kanazawa University to investigate the effect of laser wavelength. When compressed pellets were used as a preparation method for LA-ICP-MS analysis of powder samples, pellet breakage was observed after three analyses with laser settings that had high impact on the pellets, such as wide spot size and high repetition rate. Therefore, we investigated whether resin tablets, which possess the strength to allow multiple analyses could be used as an alternative method of powder sample preparation for LA-ICP-MS analysis. Each elemental signal obtained from the LA-ICP-MS analysis was calibrated and converted to concentration using external and internal standards. Single crystal samples, Durango apatite and 3F zircon, and powder samples, BCR-2 and JA-2, were analyzed. Silica gel powder samples doped with known amount of uranium were also analyzed. Seven laser settings were prepared with spot sizes in the range of 15~30 μm, repetition rate in 3~8 Hz, and fluence in 4~12 J/cm² for single crystal samples. For powdered sample pellets, four settings were applied with constant fluence of 6~8 J/cm², spot size in the range of 100~200 μm, and repetition rate of 5 and 10 Hz. For single crystal samples, a wide spot size and a high repetition rate lead to relatively high accuracy and precision for a laser setting with a fluence of about 8 J/cm². For powder sample pellets, the use of appropriate internal and external standards, a spot size of about 175 μm lead to high quality analysis. A repetition rate must be chosen considering the strength of the pellet. Successful tablet formation depends on the grain size distribution of a powder sample. The contamination from the resin in the signal intensity was small enough for analyses of resin tablet. The accuracy was improved when similarly formed tablet was used as an external standard.