AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Comprehensive Real-time Characterization of Particles Produced by Laser Ablation for Analysis by Inductively Coupled Plasma Mass Spectrometry
KAITLYN J. SUSKI, David Bell, Lizabeth Alexander, Matt Newburn, David Koppenaal, Dan Imre, Alla Zelenyuk, Pacific Northwest National Laboratory
Abstract Number: 521 Working Group: Instrumentation and Methods
Abstract Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a powerful technique used for trace element analysis of solid samples. While quantitative analysis can be achieved for select masses with careful use of standards, the complex relationship between properties of LA-generated particles, their transport, and often incomplete evaporation and ionization in the ICP-MS prevents this technique from being fully quantitative over a wider range of masses and conditions. Previous studies have identified shorter laser wavelengths and pulse widths as being superior at producing particles that yield more quantitative results; however, a full understanding of how laser settings affect particle properties and how particle properties relate to ICP-MS signal is lacking.
We will present the results of a recent study that employed multidimensional particle characterization to investigate the effect of LA conditions (laser power, repetition rate, flow rate, scan rate, and spot size) on properties of particles generated by LA of a NIST standard reference material glass sample and their elemental composition as measured with the ICP-MS.
We characterize number concentrations, mobility and vacuum aerodynamic diameter distributions, mass, composition, and effective density of individual particles as a function of LA conditions. For the fractal particles generated by LA, these measurements yield fractal dimension, average diameter of primary spherules, number of spherules, void fraction, and dynamic shape factors as a function of particle mass or size.
Preliminary results indicate that an increase in laser power results in significantly higher particle number concentration. However, particle size distributions are highly variable, especially for high repetition rates, which effects ICP-MS results. All particles are fractal and comprised of agglomerated primary spherules with average diameters between 12 and 17 nm, depending on LA conditions. Particle effective density decreases with increasing mobility diameter/mass, but even for the smallest particles density is significantly lower than particle material density due to large particle void fractions. We find that particles with mobility diameters of 30 nm have ~25% voids, whereas 300 nm particles that are comprised of more than 1000 primary spherules have ~90% voids.
The ultimate goal of this work is to develop an understanding of the effects of particle mass, shape, and morphology on particle “critical” size and ICP-MS quantification.