Nanoparticle enhanced laser ablation inductively coupled plasma mass spectrometry

aser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) is a powerful and well-established analytical technique, withhigh sensitivity and fast response, extensively applied to investigateinorganic elements in solid specimen [1-3]. Little or no sample pre-paration is required and analyses can be performed on a large range ofmaterials: conducting, non-conducting, opaque and transparent. Thesample mass size required is in the order of sub-micrograms, whichessentially keeps the item aspect unaltered. It can be applied to dif-ferent analysis approaches: from bulk analysis and depth profiling toelemental/isotope mapping.All these advantages make the technique both extremely versatileandflexible, so it is currently applied in various scientificfields, such asbiology, metallurgy, archeology, material science, geology, etc.Nevertheless, LA-ICPMS cannot be considered as a direct all-purposetechnique to be applied any solid item due to some issues: the aerosolsample composition is not always perfectly representative, transportefficiency is problematic and there may be a possible incomplete de-composition of particles that reach the ICP.Studies to improve LA-ICPMS instrumentation and quantificationstrategies are still ongoing. The biggest challenge regards elementalfractionation, which is related to abundances of detected ions, fre-quently not stoichiometrically corresponding to the composition of thepristine sample [1-5]. In the aerosol, differing sizes and geometry ofparticles ablated from different matrices represent another importantissue to be investigated and is related to the laser-sample interactionwhich affects sample transport efficiency from the ablation cell to theplasma and the subsequent atomization of particles in the ICP.Various efforts have been carried out to control these issues[1, 6-20]. Most studies have investigated the effect of instrumentalparameters on aerosol formation. In particular, the influence of bothlaser wavelength and pulse duration on the formation of a homo-geneous aerosol have been extensively monitored.Recently, the use of metallic nanoparticles (NPs) has been proposedto improve the efficiency of energy transfer from the ns-laser pulse tothe sample in Laser Induced Breakdown Spectroscopy (LIBS), namelyNELIBS [21]. In these works, an improvement of the LOD up to 2 ordersof magnitude has been found. LIBS and LA-ICPMS are clearly two dif-ferent analytical approaches, as thefirst is based on the direct ob-servation of the laser induced plasma, while the latter also involves thetransportation of the aerosol to the ICP torch, its atomization and io-nization. In any case, both techniques are based on the same sampleoperation, i.e. the laser ablation, so the use of NPs deposited on thesurface can improve, although in a different extent, LA-ICPMS too.Recently, the feasibility of enhancing the LA-ICPMS signal of major andminor elements in Al alloy and brass by Ag and Au NPs was proven [22]but many questions remain unanswered. In this paper a detailed char-acterization of the processes occurring during NELA-ICPMS (Nano-particle-Enhanced LA-ICPMS) is proposed, in order to improve itsgeneral performance. Inside this framework, the effects of NP size andtype(i.e. Au, Ag, Pt), with specific SPR (Surface Plasmon Resonance),on the signal enhancement of a large variety of trace elements, both inconductive and dielectric matrices, were tested. The obtained resultsopen the way to several fundamental issues concerning both NPs' en-hanced photoablation and the consequent effect of NPs on particleformation and the subsequent stages (transport, ionization, atomiza-tion).Although further studies are still required to obtain a completeunderstanding of the effect of the use of NPs in LA-ICPMS, this paperaims to