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This paper reports the use of an advanced statistical algorithm for the recognition and classification of a set of 30 archaeological metallic objects from the Museum of Malaga. In-situ laser-induced breakdown spectrometry (LIBS) analysis was performed using a portable analyzer. The coordinate-obtaining method provided the statistical weights of each element in the sample. A comparative study between the coordinate-obtaining method and the linear correlation method is also discussed in order to corroborate the applicability of the proposed approach to the field of cultural heritage. The possibility of fast identification based on the simultaneous comparison of all the spectra in the reference LIBS library while allowing the analysis of heterogeneous materials is the main advantage of the method. In addition, statistical analysis (Euclidean distance analysis and binary diagrams) suggested that differentiating between archaeological sites is feasible.

Combined nano- and microsecond laser pulses are used for ablation and elemental depth profiling of metal targets down to as deep as 2 mm without any sample treatment. Combination of nanosecond and microsecond pulses allows producing few-mm craters together with inducing plasma close to the bottom of a crater. Laser plasma spectra at different crater depths are used to measure the elemental depth profile of the target. Using a wear-resistant coating (nickel alloy reinforced by tungsten carbide particles) as an example, we demonstrate for the first time that individual tungsten particles can be identified at a depth of up to 2 mm in the coating by the intensity of the tungsten line in the laser-induced plasma spectrum and thus the coating quality can be estimated within few seconds without any sample treatment. [ABSTRACT FROM AUTHOR]

We demonstrate the possibility of the quantitative multielement analysis of a composite wear-resistant coating (tungsten carbide particles in chromium–nickel matrix) during its synthesis by coaxial laser cladding. The developed probe for the laser-induced breakdown spectrometry (LIBS) was used for the online analysis of the concentration of carbon, tungsten, and nickel in the process of applying a wear-resistant coating. The results of online LIBS measurements agreed closely with the results of the offline analyses using conventional methods such as X-ray fluorescence spectrometry, X-ray spectral electron probe microanalysis, and the combustion infrared absorption method using a LECO gas analyzer. [ABSTRACT FROM AUTHOR]

A method was proposed for the determination of Cr in a thin surface nanolayer deposited on top of a micrometrical Zn-based anticorrosive coating of steel sheets using laser-induced breakdown spectrometry (LIBS). Optimization of the LIBS parameters was performed with respect to the statistical parameters of regression, these being the coefficient of determination ( R ), akaike information criterion and mean-squared prediction error. These were calculated for curves describing the relationship between the Cr surface concentration and the intensity of LIBS signal. The most critical parameter of analysis appears to be the focal spot diameter. When its value was 200 μm and corresponding energy density (fluence) had value of 413.8 J/cm, the intensity-concentration relationship revealed a negative slope. This phenomenon was caused by the difference in total ablated volume for samples with a different content of Cr in the surface layer. This phenomenon was not observed for higher values of the focal spot diameter (400 and 500 μm) and lower values of fluence (103.5 and 66.2 J/cm). A range of calibration obtained under optimal conditions (focal spot diameter of 400 μm; single pulse mode, laser pulse energy of 130 mJ) was 11-21 mg/m and the limit of detection was 0.7 mg/m. The recovery values calculated from the results of the proposed LIBS method and the standard ED XRF method ranged from 99.2 to 101%. [ABSTRACT FROM AUTHOR]

We consider collinear and orthogonal beam-convergence configurations in double-pulse laser-induced breakdown spectrometry (LIBS, also known as laser-spark emission spectrometry) for chlorine determination in plants and concrete from the Cl I 837.59 nm line. We have observed that the signal-to-noise ratio is not much lower for the orthogonal configuration due to spatial instability in the second breakdown. At the same time, suppression of interfering molecular bands in this configuration lets us improve the sensitivity of LIBS for chlorine determination in plant material. [ABSTRACT FROM AUTHOR]

In the recycling of polymer e-waste, there is a pressing need for rapid measurement technologies for the simple identification and classification of these materials. The goal of this work was to instantly identify e-waste polymers by laser-induced breakdown spectrometry (LIBS). The studied polymers were acrylonitrile-butadiene-styrene (ABS), polystyrene (PS), polyethylene (PE), polycarbonate (PC), polypropylene (PP), and polyamide (PA). Emission lines were selected for C (247), H (656), N (742 + 744 + 747), and O (777), as well as the molecular band of C2 (516), and the ratios of the emission lines and molecular band were utilized. Classification models, k-nearest neighbors (KNN) and soft independent modeling of class analogy (SIMCA), were used to rank the polymers. Both constructed models gave satisfactory results for the validation samples, with average accuracies of 98% for KNN and 92% for SIMCA. These results prove the predictive analytical capabilities of the LIBS technique for plastic identification and classification. [ABSTRACT FROM AUTHOR]

Beryllium is an extremely hazardous substance because of its effects on the human body. Regulatory standards establishing the maximum permissible concentration of Be in soils of farmlands and population centers at 1.08 mg/kg are currently in the approval process. Be in soils could be determined below this level by laser-induced breakdown spectroscopy (LIBS) using UV laser radiation (355 nm). A recording delay of 0.75 μs and an exposure of 1 μs were optimal for the LIBS Be analysis. The Be detection limit in soils under these conditions was 0.07 mg/kg. [ABSTRACT FROM AUTHOR]

In this paper, two analytical methodologies based on the combination of dispersive liquid–liquid microextraction with inductively coupled plasma optical emission spectrometry and laser-induced breakdown spectrometry, respectively, were evaluated for simultaneous preconcentration and detection of Cd, Co, Ni, Pb and Zn. The microextraction procedure was based on the injection of appropriate quantities of 1-undecanol and methanol into the sample solution containing the complexes formed between metal ions and 1-(2-pyridylazo) 2-naphtol (PAN). The main experimental factors affecting the complexation and the extraction of metals (pH, PAN concentration, salt addition and extractant solvent and disperser solvent volume) were optimized using a multivariate analysis consisting of two steps: a Plackett-Burman design followed by a Circumscribed Central Composite Design (CCCD). Under optimum microextraction conditions, the analytical features of the proposed methodologies were assessed. Accuracy was evaluated by analyzing two certified reference materials, yielding results in agreement with the certified values. Both methodologies were applied to the analysis of a number of beverage samples. [ABSTRACT FROM AUTHOR]

The hydrogen beta line has been widely used in determining plasma parameters such as electron density. In conjunction with other Balmer series lines, electron temperature can be inferred. The asymmetric appearance of the hydrogen beta line, due to quadrupole interactions, can be utilized as well for the determination of electron density. Laser-induced optical breakdown is generated in laboratory air, and particularly for electron densities in the range of 0.3 to 1.0 × 10 17 cm − 3 the use of the asymmetry parameter is elaborated for electron density diagnostics. Also included are results of analysis of the hydrogen beta profiles for which the asymmetry indicates an electron density on the order of 2.0 × 10 18 cm − 3 , which is significantly higher than 6.3 to 6.8 × 10 17 cm − 3 maximum that was measured previously from the Stark-broadened hydrogen beta width following laser-induced optical breakdown. [ABSTRACT FROM AUTHOR]

We present Stark broadened atomic titanium lines recorded following laser-induced optical break during ablation of a 99.999% pure titanium sample. The UV lines reveal electron density on the order of 20 to 60 × 10 23 m − 3 , and the electron temperature is estimated to be on the order of 40,000 K some 200 ns after the ablation process. In our study of the modified semi-empirical approach, we conclude that our results favor the standard Gaunt factor without the requirement of introducing an additional effective Gaunt factor, that others appear to use. [ABSTRACT FROM AUTHOR]

Operational conditions have been previously optimized in our laboratory by using a pulse Nd:YAG laser at 1064 nm with a maximum energy of 200 mJ per pulse focused on the surface of an orange. The optimized delay time, repetition rate, and laser energy were 1.28 μs, 2 Hz, and 120 mJ, respectively. LIBS spectra of peels of 40 oranges were collected. For comparison purpose, the samples of orange peels were also digested using a wet acid-assisted procedure and further analyzed by atomic absorption spectroscopy (AAS). A partial least squares (PLS) model was obtained by using 30 calibration samples and 10 prediction samples. The correlation coefficient between the measurements with LIBS and AAS was 0.9096 and 0.991 for the calibration and prediction sets, respectively. This result demonstrated that most results of direct analysis of Cd in Gannan navel oranges by LIBS were in reasonable agreement with those obtained by AAS after wet acid decomposition. Such performance shows that LIBS is a powerful tool for direct analysis of heavy metals in agricultural products without complex sample preparation. [ABSTRACT FROM AUTHOR]

Abstract: The performance of laser-induced breakdown spectrometry (LIBS) for the determination of Ba, Cd, Cr and Pb in toys has been evaluated by using a Nd:YAG laser operating at 1064 nm and an Echelle spectrometer with intensified charge-coupled device detector. Samples were purchased in different cities of São Paulo State market and analyzed directly without sample preparation. Laser-induced breakdown spectrometry experimental conditions (number of pulses, delay time, integration time gate and pulse energy) were optimized by using a Doehlert design. Laser-induced breakdown spectrometry signals correlated reasonably well with inductively coupled plasma optical emission spectrometry (ICP OES) concentrations after microwave-assisted acid digestion of selected samples. Thermal analysis was used for polymer identification and scanning electron microscopy to visualize differences in crater geometry of different polymers employed for toy fabrication. Results indicate that laser-induced breakdown spectrometry can be proposed as a rapid screening method for investigation of potentially toxic elements in toys. The unique application of laser-induced breakdown spectrometry for identification of contaminants in successive layers of ink and polymer is also demonstrated. [Copyright &y& Elsevier]

Abstract: A microsecond-pulsed glow discharge is used to excite ablate material generated by the ablation laser in Laser-induced Breakdown Spectrometry (LIBS). The coupled system provides a simple means to excite the material ablated by the incident laser pulse by taking advantage of enhanced collisional excitation. In this way, one can effectively reduce laser energies below the excitation and ionization thresholds to those needed solely for ablation of the sample surface, in which the excitation of the material is performed by a high voltage discharge. Given this development, there exists the potential of improving upon depth resolutions in LIBS material characterization. This article presents the results of a comparative depth profile study conducted on various galvanized steels and layered brass standards by LIBS and GD-LIBS; demonstrating the advantages of coupling a pulsed glow discharge with a typical LIBS set-up used in materials analysis. [Copyright &y& Elsevier]

Abstract: Laser induced breakdown spectroscopy (LIBS) has been evaluated for the determination of micronutrients (B, Cu, Fe, Mn and Zn) in pellets of plant materials, using NIST, BCR and GBW biological certified reference materials for analytical calibration. Pellets of approximately 2 mm thick and 15 mm diameter were prepared by transferring 0.5 g of powdered material to a 15 mm die set and applying 8.0 tons cm−2. An experimental setup was designed by using a Nd:YAG laser operating at 1064 nm (200 mJ per pulse, 10 Hz) and an Echelle spectrometer with ICCD detector. Repeatability precision varied from 4 to 30% from measurements obtained in 10 different positions (8 laser shots per test portion) in the same sample pellet. Limits of detection were appropriate for routine analysis of plant materials and were 2.2 mg kg−1 B, 3.0 mg kg−1 Cu, 3.6 mg kg−1 Fe, 1.8 mg kg−1 Mn and 1.2 mg kg−1 Zn. Analysis of different plant samples were carried out by LIBS and results were compared with those obtained by ICP OES after wet acid decomposition. [Copyright &y& Elsevier]

Abstract: This work discusses the capability of laser-induced breakdown spectrometry (LIBS) for characterization and cataloging of metallic objects belonging to the Bronze and Iron Ages. A set of 37 metallic objects from different locations of the South East of Iberian Peninsula has been sorted according to their metal content. Arsenic concentration in metallic objects has been found a key factor for distinguishing between Bronze and Iron Ages objects, allowing the chronocultural sorting of each piece. For this study, a pulsed Q-switched Nd:YAG laser was used to generate a microplasma onto the sample surface. To quantify and catalogue these metallic objects, calibration curves for copper, arsenic, tin, lead and iron were established. The quantitative results demonstrate that the chronological sorting carried out by LIBS matches agreeably with archaeological dating criteria. [Copyright &y& Elsevier]

The use of laser-induced breakdown spectrometry (LIBS) has grown steadily, and it has proven to be a relatively dynamic research activity for performing direct spectrochemical elemental or metal analysis of a variety of materials, solids, liquids, and gases, with none or little sample pretreatment procedures. Significant progress has been made during the last several years on the diverse and versatile applications of LIBS including remote material analysis in nuclear power stations, space exploration, diagnostics of archaeological objects, and metal diffusion in solar cells, etc. This review presents the more recent applications of LIBS based on the development of fiber-optic (FO) technology and portable instrumentation. The characteristics of matrices, object of analysis, laser system used, and analytical performances are tabulated for metallurgical samples, liquid and colloid samples, aerosol and gases, environmental samples, non-metallic solids, advanced materials, and miscellaneous applications. [ABSTRACT FROM AUTHOR]

The novel and—for archaeometrical applications—still rarely used Laser-Induced Breakdown Spectrometry (LIBS) was tested on various standard glasses for its spectrometric performance. LIBS is an almost non-destructive method based on the time-resolved detection of optical emission following direct laser ablation. A frequency-quadrupoled Nd:YAG laser at 266 nm was found to cause a hardly visible crater of c. 200 µm in diameter. The application of an innovative high-resolution Echelle spectrograph allows the fast and simultaneous determination of up to 90 elements in the spectral range from 200 to 780 nm, with a resolution of 10–30 pm under ambient conditions. In principle, LIBS has a high analytical potential for archaeometry; in particular, for the determination of light elements (Li, Be, B and others). Because the measurement parameters (laser energy, delay time and number of pulses) do not independently influence the emission signal, their optimization proved to be complex and is rather a compromise for the range of elements. The effects of sample distance, surface roughness and the accumulation of depth profiles were studied. Problems arose for the determination of sodium and potassium in higher contents due to self-absorption effects. Quantification tests using a silicon line as internal standard yielded a precision range between 3% and 20% relative, but in general no satisfying accuracy for a number of elements. However, these problems might be overcome in the near future by improved spectrometer set-ups and matrix correction approaches. [ABSTRACT FROM AUTHOR]

Since the development of atomic spectrometry, trace element and isotopic analysis has been mainly based on the monitoring of atomic spectra and monoionic species. However, according to the literature and considering the current instrumental developments, it seems that some of the remaining challenges in this field can be mitigated via the measurement of molecular spectra or of polyatomic ions. This review discusses recent advances in three of the most important atomic techniques (laser-induced breakdown spectrometry, high-resolution continuum source atomic absorption spectrometry and inductively coupled plasma mass spectrometry) and how the monitoring of such molecules or polyatomic ions containing the target analyte enables attaining better selectivity and opens new ways to determine non-metals and to obtain isotopic information. • Elemental analysis benefits from monitoring highly resolved molecular spectra. • New possibilities for isotopic analysis using optical methods are discussed. • Producing and measuring polyatomic species in ICP-MS/MS improves selectivity. • Applications of the most representative atomic techniques are highlighted. [ABSTRACT FROM AUTHOR]

This paper investigated two-dimensional spatial and temporal images of a copper emission line in laser-induced breakdown spectroscopy (LIBS), in order to clarify the excitation/de-excitation processes occurring in a laser-induced plasma. The measurements were carried out under different plasma gases (argon, krypton, helium, and nitrogen), pressure levels (100 - 900 Pa) and delay times (100 - 1000 ns) with the aim of monitoring their effects on the behavior of the copper emission. Depending on the plasma gas type and the pressure level, large differences were found in the plasma shape and temporal intensity evolution of the copper emission profile. Namely, krypton produced the most compact plasma emitting larger intensities, compared to argon and helium, and an increase in the gas pressure made these plasmas to shrink, which could be related principally to the stopping power of the applied gases. Through temporally resolved analysis, the delay profiles could be obtained for each plasma gas, indicating that the helium plasma disappeared more rapidly than the argon and krypton plasmas. It was suggested that the variations in the emission intensity would be determined by interactions between gas particles and highly energetic particles in the plasma breakdown as well as interactions between excited gas particles and copper species during plasma expansion. These insights could prove to be useful in the understanding of the background of LIBS as well as the optimization of its practical applications.

The composition of the surface layer of 13 low-cost jewelry samples with a high Cd content was analyzed using an energy-dispersive X-ray fluorescence spectrometer (ED XRF). The analyzed jewels were obtained in cooperation with the Czech Environmental Inspectorate. The jewels were leached in two types of artificial sweat (acidic and alkaline) for 7 days. Twenty microliters of the resulting solution was subsequently placed on a paper carrier and analyzed by an LIBS (Laser-Induced Breakdown Spectrometry) spectrometer after drying. The Cd content in the jewelry surface layer detected by using ED XRF ranged from 13.4% to 44.6% (weight per weight-w/w). The samples were subsequently leached in artificial alkaline, and the acidic sweat and leachates were analyzed using laser-induced breakdown spectrometry (LIBS). The amount of released Cd into alkaline sweat ranged from 24.0 to 370 µg Cd per week, respectively 3.23-61.7 µg/cm²/week. The amount of released Cd into acidic sweat ranged from 16.4 to 1517 µg Cd per week, respectively 3.53-253 µg/cm²/week. The limit of Cd for dermal exposure is not unequivocally determined in the countries of the EU (European Union) or in the U.S. Based on the US EPA (United States Environmental Protection Agency) approach used to establish the reference dose (RfD) for Cd contained in food and information about the bioavailability of Cd after dermal exposure, we assessed our own value of dermal RfD. The value was compared with the theoretical amount of Cd, which can be absorbed into the organism from jewelry in contact with the skin. The calculation was based on the amount of Cd that was released into acidic and alkaline sweat. The highest amount of Cd was released into acidic sweat, which represents 0.1% of dermal RfD and into alkaline sweat, 0.5% of dermal RfD. These results indicate that the analyzed jewelry contains Cd over the limit for composition of jewelry available within the territory of the EU. The determined amount of Cd in analyzed jewelry does not, however, pose a threat in terms of carcinogenic toxic effects.