Study on aerosol characteristics and fractionation effects of organic standard materials for bioimaging by means of LA-ICP-MS

A 213 nm Nd: YAG laser ablation system (LA) coupled to a quadrupole ICP-MS was used to ablate thin slices of gelatin and Technovit, both commonly used as standard materials for bioimaging applications. Particle sizes and their distribution within the ablated aerosols were investigated using an optical particle counter inserted in-line between the LA and the ICP-MS, while helium served as carrier gas for material transport. A considerably larger number of particles above 0.3 mm was found for Technovit, while the gelatin aerosol carried mostly particles in the lower nm regime. Increasing the laser fluence during ablation resulted in a larger number of mm sized particles for both materials. Subsequently, fractionation effects during the material transport into the ICP and the ionization within the ICP were analyzed. An increase in the transportation tube length resulted in a signal broadening for shot experiments, but no material loss was observed. A comparison of ionization characteristics of gelatin particles ablated within the LA to wet aerosol particles introduced via nebulization showed similar ionization efficiencies for both aerosols, but the vaporization of gelatin particles required a prolonged time. Additionally, fractionation during the ablation process in gelatin was studied by recording isotope ratios of spiked standards (i.e. Ti and V) for varying laser fluences. The results indicate a strong deviation of up to 20% from the expected 51V/48Ti ratio for laser fluences close to the threshold for ablation.