Analysis of Laser-Produced Aerosols by Inductively Coupled Plasma Mass Spectrometry: Transport Phenomena and Elemental Fractionation
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文摘
The transport phenomena of laser-produced aerosolsprior to analysis by inductively coupled plasma massspectrometry (ICPMS) were examined. Aerosol particleswere visualized over the cross section of a transport tubeattached to the outlet of a conventional ablation cell bylight scattering using a pulsed laser source. Experimentswere carried out under laminar or turbulent in-cell flowconditions applying throughputs of up to 2.0 L/min andreveal the nature of aerosol transportation to stronglydepend on both flow rate and carrier gas chosen. Forinstance, laser ablation (LA) using laminar in-cell flow andhelium as aerosol carrier resulted in stationary butinhomogeneous dispersion patterns. In addition, aerosolsappear to be separated into two coexisting phases consisting of (i) dispersed particles that accumulate at theboundary layer of several vortex channel flows randomlyarranged along the tube axis and (ii) larger fragmentsmoving inside. The occurrence of these fragments wasfound to affect the accuracy of Si-, Zn-, and Cd-specificICPMS analyses of aerosols released by LA of silicate glass(SRM NIST610). Accuracy drifts of more than 10% wereobserved for helium flow rates of >1 L/min, most probably, due to preferential evaporation and diffusion lossesof volatile constituents inside the ICP. The utilization ofturbulent in-cell flow made the vortex channels collapseand resulted in an almost complete aerosol homogenization. In contrast, LA using argon as aerosol carriergenerally yielded a higher degree of dispersion, which wasnearly independent of the flow conditions applied. Toillustrate the differences among laminar and turbulent in-cell flow, furthermore, the velocity field inside the ablationcell was simulated by computational fluid dynamics.