LIBS quantitative analysis; reduction of matrix effect; internal standard calibration; normalization; correction of self-absorption;PART II; SAMPLES; PARAMETERS

A procedure for matrix effect reduction is proposed to enhance the precision of quantitative analysis of metal alloys using laser-induced breakdownspectroscopy (LIBS). This procedure is based on a number of successive steps in order to correct the signal fluctuations caused by plasma interaction and the matrix effect. The first step is the selection of optimum parameter settings of the detection system, such as laser power, delay time, and focal distance. The second step is the estimation of the absolute or relative values of impurities on the basis of the internal standard calibration. The third step is the analysis of the metal basis of the alloy used as an internal standard, which requires spectrum averaging, whole integral spectrum normalization, and self-absorption correction. Three sets of metal-based alloys (aluminum, steel, and copper) are used in this investigation as reference standards for calibration and validation. Successive improvements of the quality of calibration curves are observed during the proposed procedure.

Portable LIBS; Micro-invasive investigation; Pyrotechnological materials; Late bronze age workshop contexts; Tiryns-Greece;PIGMENT ANALYSIS; PAINTED PLASTER; COPPER; ABLATION; IRON; ENVIRONMENT; INSTRUMENT; ARTWORKS; BRONZES; GLASSES

Laser-Induced Breakdown Spectroscopy (LIBS) was used in the investigation of pyrotechnological materials (metal and ceramic items, glass-based objects, plaster-based materials) from several Late Bronze Age workshop and activity area contexts at Tiryns, Greece. The use of a portable instrument, which could be brought into the study place where all objects were housed, was crucial in order to establish the elemental content or verify the material composition of almost all materials analysed. In almost all cases, the LIBS analyses led to the preliminary identification of the materials investigated. In most cases, the results sufficed to confirm earlier research carried out or was in agreement with similar analyses published in the literature. The analyses demonstrate that the micro-invasive LIBS technique provides useful preliminary elemental characterization of most of the pyrotechnological materials while for some, additional work needs to be conducted for securing conclusive results. Essentially, the portability and compactness of the instrumentation enable its use in any workspace with a solid desk, light and electricity access which makes this technique very attractive for obtaining preliminary elementary results. While the technique remains limited by spot analyses it does open up an immense array of possibilities for routine characterization or speedy screening of different types of artefacts in any storage or museum context. These important methodological and scientific findings are considered prerequisite steps leading towards and aiding in responsible sampling strategies for further analyses. (C) 2017 Elsevier Ltd. All rights reserved.