Calibration-free Research Articles

Laser-induced breakdown spectroscopy of archaeological findings with calibration-free inverse method: Comparison with classical laser-induced breakdown spectroscopy and conventional techniques

A modified version of the calibration-free (CF) method was applied to the analysis of a set of archaeological brooches made of various copper-based alloys and coming from the archaeological site of Egnatia (Apulia, Southern Italy). The developed methodology consists in determining the plasma temperature by reversing the set of equations employed in the usual CF algorithm, and it is thus referred to as “inverse method”. The plasma temperature is determined for one certified standard, by using its known elemental composition as an input data, and then applied to the set of unknown samples to evaluate their composition in a CF mode. The feasibility of such an approach is demonstrated by comparing the results obtained with classical LIBS (drawing calibration lines with a series of matrix-matched certified standards) and with independent measurements performed with a conventional technique (LA-ICP-MS).

Element analysis of complex materials by calibration-free laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a promising method for fast and quantitative element analysis of complex materials. We report on LIBS measurements of multi-component oxide materials and the compositional analysis of materials by a calibration-free (CF) method. This CF-LIBS method relies on modeling of the optical emission of laser-induced plasma assuming local thermodynamic equilibrium. Various materials are investigated and the calculated concentration values (CCF) of oxides CaO, Al2O3, MgO, SiO2, FeO, and MnO are in agreement with nominal concentration values (CN) from reference analysis. The relative error in oxide concentration er=|CCF−CN|/CN decreases with increasing concentration. The quantification is limited to major oxides (CN≥1 wt%). Slag samples from industrial steel production are analyzed on site by means of a mobile measurement system. LIBS measurements are performed at different sample temperatures. The results obtained show that CF-LIBS is applicable to fast compositional analysis of complex materials in harsh environments.

Determination of lead in soil at a historical mining and smelting site using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was used to determine lead (Pb) concentration in soil and tailing samples collected from a historical mining and smelting area. The Pb emission line at 405.781 nm was found to have the strongest intensity and highest linearity with concentration. It was further normalized by the Al emission line (394.401 nm), and a relationship between the peak area ratio (Pb/Al) and Pb concentration was established to determine Pb concentration of unknown samples. The Pb concentration was the highest at the former smelter site and unremediated mine-tailing areas, indicating that severe Pb contamination is still occurring. The Pb concentration decreased with increasing distance from the two major source areas (smelting and mine-tailing sites), although all samples exceeded the 400 mg/kg standard set by the United States Environmental Protection Agency. The limit of detection (LOD) for Pb was found to be 48 mg/kg, and the Pb concentrations determined by LIBS were in reasonable agreement with concentrations obtained by inductively coupled plasma mass spectroscopy (ICP-MS; within 26%). When Pb concentrations were determined by calibration-free (CF)-LIBS, which does not require standard soil samples and dilution, both LIBS and ICP-MS were also in good agreement, suggesting that the CF-LIBS method can be used to determine Pb concentrations in highly contaminated soil samples. In addition to Pb, other metal emission lines from LIBS spectra were used to classify soil samples among the sites using a principal component analysis (PCA) method, showing a distinct difference in metal distribution between sites that are heavily contaminated by two major sources.

Laboratory feasibility study of fusion vessel inner wall chemical analysis by Laser Induced Breakdown Spectroscopy

Laser Induced Breakdown Spectroscopy (LIBS) is nowadays a well established tool for qualitative, semi-quantitative and quantitative analyses of surfaces, with micro-destructive characteristics and capabilities for stratigraphy. LIBS is an appealing technique compared with many other types of elemental analysis thanks to the set up versatility facilitating non-invasive and remote analyses, as well as suitability to diagnostics in harsh environments. In this work, LIBS capabilities were used for the determination of the atomic composition of multilayered samples simulating the tiles of plasma facing components in the next generation fusion machines such as ITER. A new experimental setup was designed and realized in order to optimize the characteristics of an LIBS system working at low pressure and remotely, as it should be for an in situ system to be applied in monitoring the erosion and redeposition phenomena occurring on the inner walls of a fusion device. The effects of time delay and laser fluence on LIBS sensitivity at reduced pressure were examined, looking for operational conditions suitable to analytical applications. The quantitative analysis of some atomic species in the superficial layer has been carried out using a Calibration Free (CF) approach in the time window where Local Thermal Equilibrium (LTE) was assumed for an LIBS analysis.

Determination of gold fineness by laser induced breakdown spectroscopy with the simultaneous use of CW-CO 2 and Q-SW Nd:YAG lasers

In this work, the gold fineness is precisely determined using the dual beam arrangement including simultaneous irradiation of CW-CO 2 and Q-SW Nd:YAG lasers. It was shown that the enhancement of the characteristic emission lines occurs at higher temperatures with minimal surface distortion of the target respect to that of single beam exposure. The accuracy of gold concentration was determined to be as low as 0.7% using calibration-free (CF) method.

激光诱导击穿光谱的可控定标研究

Laser induced breakdown spectroscopy (LIBS) is a potential technique for rapid analysis of samples present in solids, gases and liquids. In the last two decades it was an object of extensive studies. Controlled calibration method used to analysis the LIBS spectra is investigated. Compared with the inner calibration and calibration-free (CF) methods, this new method overcomes

Calibration analysis of bronze samples by nanosecond laser induced breakdown spectroscopy: A theoretical and experimental approach

A theoretical model for nanosecond laser ablation at 1064 nm of quaternary bronze alloys containing Cu, Sn, Zn and Pb was developed. Starting from a known sample composition, the model provides the element concentrations in the laser produced plasma, and therefore the plasma stoichiometry, here studied for different laser energies on the target. For the considered laser excitation, plasma stoichiometry cannot be achieved in the ablation of bronze materials; however, stable element ratios in the plasma occur for a laser fluence above 600 J/cm 2, corresponding to an irradiance of 75 GW/cm 2. The calculated plasma concentrations were then used to simulate calibration plots in the range of element concentrations corresponding to the standards available. Different kinds of internal standardization were theoretically considered and successively applied to the experimental data obtained. Good agreement between experimental results and model predictions was observed, allowing establishing the optimal method for LIBS calibration of bronze alloys. Further validation of the model was attempted by comparing the predicted element concentrations in the plasma with the experimental results obtained by using the Calibration-Free (CF) approach (Corsi et al., Eur.Phys.J. D13, 2001, 373). The results obtained are in excellent agreement between themselves. However, the estimated element concentrations largely differ from those in samples, and the reasons for the discrepancy are discussed.