Abstract: In this tutorial review paper, we illustrate how computer modeling can contribute to a better insight in inductively coupled plasma-mass spectrometry (ICP-MS). We start with a brief overview on previous efforts, studying the fundamentals of the ICP and ICP-MS, with main focus on previous modeling activities. Subsequently, we explain in detail the model that we developed in previous years, and we show typical calculation results, illustrating the plasma characteristics, gas flow patterns and the sample transport, evaporation and ionization. We also present the effect of various experimental parameters, such as operating conditions, geometrical aspects and sample characteristics, to illustrate how modeling can help to elucidate the optimal conditions for improved analytical performance.

Abstract: Redox processes activated by environmental factors have been identified as the main cause of the chromatic alterations of a number of artists' pigments, including the yellow pigment orpiment (As2S3). Although a general comprehension of the mechanisms has been provided through characterization of degradation compounds of As2S3, experimental evidences to prove how other paint components and how different environmental agents influence the formation pathways of specific secondary compounds are still lacking. Thus, it becomes fundamental to develop a methodological strategy which enable achieving a discrimination among the causes affecting the chemical stability of more heterogenous As2S3-based paints and defining the mechanism through which the alteration establishes and evolves, with the ultimate goal of optimizing the preventive conservation measures of unique masterpieces. In this paper, we propose a comprehensive multi-material and multi-method approach based on the combination of synchrotron radiation X-ray micro-analytical techniques (i.e., X-ray diffraction, X-ray fluorescence and X-ray absorption near edge structure spectroscopy at S K-/Ag L-3-/As K-edges) and vibrational micro-spectroscopy methods to unveil the causes and mechanism of darkening of “fake-gilded” decorations in tempera paintings, originally consisting of an unusual mixture of As2S3 and metallic silver (Ag-0). Such degradation process is a not yet understood phenomenon threatening a series of Old Master paintings, including those by the Italian painters Cimabue and Pietro Lorenzetti. The high specificity, sensitivity and lateral resolution of the employed analytical methods allowed providing first-time evidence for the presence of black acanthite (alpha-Ag2S), mimetite [Pb-5(AsO4)(3)Cl] and syngenite [K2Ca(SO4)(2)center dot H2O] as degradation products of the “fake-gilded” decorations in the Maesta by Cimabue (Church of Santa Maria dei Servi, Bologna, Italy). Furthermore, the study of the painting combined with that of tempera paint mock-ups permitted to explore and define the environmental agents and internal factors causing the darkening, by proving that: (i) Ag-0 and moisture are key-factors for triggering the transformation of As2S3 to alpha-Ag2S and As-oxides; (ii) S2--ions arising from the degradation of As2S3 are the main responsible for the formation of alpha-Ag2S; (iii) light exposure strengthens the tendency of the paint components towards alteration. Based on our findings, we finally propose a degradation mechanism of As2S3/Ag-0-based tempera paints.

Abstract: The laser ablation-induced plasma was used as a composition-con trolled source for ion implantation in Si crystals. Then, laser ablation in combination with inductively coupled plasma mass spectrometry was used for the elemental depth profiling of the implanted samples. Monte Carlo simulations permitted us to conclude that a depth resolution of tens of nm would be necessary to define the shape of the implantation profiles, as is obtained using XPS and RBS, whereas a hundred nm depth resolution is sufficient to determine the total implanted dose. The detection power of LA-ICP-MS would routinely allow rapid analytical control on the trace level implanted dose. Nevertheless, this technique is limited in terms of depth profiling resolution due to pulse mixing and signal tailing induced during the aerosol transport. Raw signal processing procedures were developed for the minimization of shapeline dispersion, deconvolution of pulse mixing and more appropriate assessment of the implanted profiles. Shapeline dispersion could be corrected for by determining the signal waning constant and implementing this information for a non-affine alibi transformation of the LA-ICP-MS signal traces. Pulse mixing deconvolution was attained with an algorithm that considered accumulated signal intensity due to pulse-on-pulse stacking, i.e., the latest pulse on top of all antecedent individual pulses' exponential tails proportionally.