ABSTRACT
The characterization of the aerosol (size, composition, and concentration) generated by Laser Ablation is of great interest due to its impact on the analytical performances when coupled to Inductively Coupled Plasma Mass Spectrometry (ICPMS). The capabilities of High Resolution ICPMS as a direct tool to characterize nanoparticles produced by femtosecond Laser Ablation of pure copper are presented. An analytical protocol, similar to the "single particle ICPMS" technique used to characterize the size distribution of nanoparticles in solution, was developed in order to observe the signals of individual particles produced by a single ablation shot. A Visual Basic for Applications (VBA) data processing was developed to count and sort the particles as a function of their size and thus determine the particle size distribution. To check the reliability of the method, the results were compared to a more conventional technique, namely, Electrical Low Pressure Impaction (ELPI) for 4000 shots. Detection limit for the particles produced by the laser ablation of a copper foil is of a few attograms corresponding to a nanoparticle of 14 nm. The direct online determination of particle size by ICPMS gave similar results than ELPI for copper particles ejected during the ablation shot by shot at a fixed spot, from 1 to 100 shots. Particles larger than 159 nm represented less than 1% of the aerosol whose distribution was centered on 25-51 nm.
ABSTRACT
The isotope drift encountered on short transient signals measured by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) is related to differences in detector time responses. Faraday to Faraday and Faraday to ion counter time lags were determined and corrected using VBA data processing based on the synchronization of the isotope signals. The coefficient of determination of the linear fit between the two isotopes was selected as the best criterion to obtain accurate detector time lag. The procedure was applied to the analysis by laser ablation-MC-ICPMS of micrometer sized uranium particles (1-3.5 µm). Linear regression slope (LRS) (one isotope plotted over the other), point-by-point, and integration methods were tested to calculate the (235)U/(238)U and (234)U/(238)U ratios. Relative internal precisions of 0.86 to 1.7% and 1.2 to 2.4% were obtained for (235)U/(238)U and (234)U/(238)U, respectively, using LRS calculation, time lag, and mass bias corrections. A relative external precision of 2.1% was obtained for (235)U/(238)U ratios with good accuracy (relative difference with respect to the reference value below 1%).
