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Articolo in rivista, 2020, ENG, 10.1016/j.sab.2019.105731

Nanoparticle enhanced laser ablation inductively coupled plasma mass spectrometry

Mangone, A. and Mastrorocco, F. and Giannossa, L.C. and Comparelli, R. and Dell'Aglio, M. and De Giacomo, A.

Dipartimento di Chimica, Universit? Aldo Moro, via Orabona 4, Bari, 70126, Italy; CNR-IPCF, c/o Dipartimento di Chimica, Universit? Aldo Moro, Via Orabona, 4, Bari, 70126, Italy; CNR-NANOTEC, c/o Dipartimento di Chimica, Universit? Aldo Moro, Via Orabona, 4, Bari, 70126, Italy

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 provide a general idea of the perspectives of NELA-ICPMS in-vestigating the effect of NPs during ablation and subsequent transportin the ICP torch, in order to extend knowledge on the causes of theenhancement of the signal of some trace elements in a standard sample

Spectrochimica Acta 163