Laser Ablation Mass Removal versus lncident Power Density during Solid Sampling for lnductively Coupled Plasma Atomic Emission Spectroscopy

Abstract

For laser ablation solid sampling, the quantity of material ablated (removed) influences the sensitivi1y of chemical analysis. The mass removal rate depends strongly on the laser power density, which is the main controDable parameter for a given material and wavelength parameter using laser solid samplingfor inductively coupled plasma atomic emission spectroscopy (ICP-AES). For a wide variety of materials, a decrease in the rate of change, or roll-off, in mass removed is observed with increasing incident laser power density. The roll-off results from a change in the efticiency of material removed by the laser beam, primarily due to shielding of the target from the incident laser energy by a laser-vapor plume interaction. Several analytical technologies were employed to studythe quantity of mass removed versus laser power density. Data for mass ablation behavior versus laser power density are reported using ICP-AES, atomic emission from a Iaser-induced plasma near the sample surface, acoustic stress power in the target, and measurements of crater volumes •. This research demonstrates that the change in ICP-AES intensity with laser power density is dueto changes in the mass removal. The roll-off in mass ablation is not due to a change in particle size distn"bution of the ablated species, fractionation of the sample, or a change in transport efticiency to the ICP torch. Accurate tracking of the ICP-AES with the laser ablation process justifies the use of internal and external standardization.