In general, the detection of F and other halogens is challenging through conventional techniques. In this paper, various approaches for the qualitative and quantitative analysis of F using the laser-induced breakdown spectroscopy (LIBS) technique were demonstrated. In LIBS, fluorine detection can be realized by means of atomic lines and molecular bands. For the purposes of our experiment, two sets of pellets with various contents of CaF2, CaCO3 and cellulose were analyzed using a lab-based LIBS system under a He atmosphere. The fluorine atomic line at 685.60 nm was correlated with CaF signals proving their close relationship. Consequently, the limits of detection were determined for both analytical signals. Moreover, conditions necessary for the quantification of F via CaF band signals were estimated. The dependence of the CaF signal on the varying ratio of Ca and F contents was investigated. Finally, a chip of a real CaF2 crystal was prepared and its surface was mapped with Raman and LIBS systems. The obtained elemental and molecular maps showed good numerical correlations. Thus, the yielded results validated the possibility to substitute the fluorine atomic line by non-conventional CaF molecular bands in the qualitative and quantitative LIBS analysis of fluorine.

Multivariate data analysis (MVDA) is getting popular across the spectroscopic community. To assess accurate results, the obtained data should be preprocessed prior to utilization of any MVDA algorithm. The process of data normalization or “internal standardization” is widely used across a broad range of applications. In this manuscript we investigate the utilization of Laser-Induced Breakdown Spectroscopy (LIBS) coupled with MVDA. However, many articles regarding the use of MVDA on data from LIBS do not provide any information about the data pretreatment. This work describes the impact of LIBS data normalization approaches on MVDA classification accuracy. Also, the impact of classical data preprocessing (mean centering and scaling) exploiting the prior utilization of MVDA was studied. This issue was investigated exploiting simple soft independent modelling of class analogies algorithm. The findings were generalized for three sample matrices (steel, Al alloys, and sedimentary ores). Furthermore, the selection of an appropriate normalization algorithm is not trivial since the spectrum of each sample matrix is composed of a different number of elements and corresponding elemental lines.

MACHINE REGRESSION-MODEL; CONVEX-OPTIMIZATION; COEFFICIENTS; LIBS

In quantitative laser-induced breakdown spectroscopy analysis, spectral signals are usually represented by the linear combination of characteristic peaks with useful spectral information and unwanted noise components. All of the existing regression analysis methods are related to a spectral data matrix, which is composed of certified samples with different spectral intensity. Therefore, spectral data matrix processing is critical for quantitative LIBS analysis. A prevalent assumption when constructing a matrix approximation is that the partially observed matrix is of low-rank. Moreover, the low-rank structure always reflects the useful information and is regarded as a powerful data preprocessing method. In this paper, a novel and quantitative LIBS analysis method based on a sparse low-rank matrix approximation via convex optimization is proposed. Based on the sparsity of the spectral signals, we present a convex objective function consisting of a data-fidelity term and two parameterized penalty terms. To improve the accuracy of the quantitative analysis, a new non-convex and non-separable penalty based on the Moreau envelope is proposed. Then, the alternating direction method of multipliers algorithm was utilized to solve the optimization problem. The proposed method was applied to the quantitative analysis of 23 high alloy steel samples. Both of the performances of the Partial Least Squares and Support Vector Machine regression models are improved by using the low-rank matrix approximation scheme, which proves the effectiveness of the proposed method.

SPECTRAL-LINE; EMISSION-LINES; INDUCED FLUORESCENCE; RESONANCE LINES; INDUCED PLASMAS; COEFFICIENTS; PRESSURE; ALUMINUM; CALIBRATION; LIBS

Reducing self-absorption is one of the most important steps in achieving accurate analyses in laser-induced breakdown spectroscopy . In this work, LIBSassisted with laser-stimulated absorption was used to reduce self-absorption effects in LIBS. A wavelength-tunable laser was used to resonantly excite cold atoms and reduce their amount in laser-induced plasmas, and thus fewer cold atoms at the plasma periphery re-absorb light from the plasma center. Accordingly, the self-absorption effect was reduced. Copper and chromium elements in steels were taken as examples to evaluate and compare the self-absorption effects in LIBS and LSA-LIBS. The results of calculated self-absorption coefficients supported the effectiveness in reducing self-absorption and improving analytical linearity using LSA-LIBS.

INDUCED BREAKDOWN SPECTROSCOPY; SUPPORT VECTOR MACHINES; PARTIAL LEAST-SQUARES; DISCRIMINANT-ANALYSIS; SUBSET-SELECTION; LASER; CLASSIFICATION; SAMPLES; IDENTIFICATION; ALGORITHM

In recent years, LIBS quantitative analysis based on multivariate regression has received considerable attention, and variable selection is critical for improving accuracy of multivariate regression analysis of LIBS. In the present study, sequential backward selection combined with random forest was proposed to improve detection accuracy of sulfur and phosphorus in steel. First, LIBS spectrum line of S and P was identified by the NIST database. Second, input variables for RF calibration model were selected and optimized by SBS, and RF model parameters and m) were optimized by out-of-bag estimation. Finally, optimized input variables and model parameters were employed to build an SBS-RF calibration model for quantitative analysis of P and S in steel. Results showed that the SBS-RF model provided good predictions for S and P compared with those provided by the univariate method, PLS model and traditional RF model. Thus, LIBS coupled with SBS-RF is an effective method for quality supervision and control of steel products.

ARTIFICIAL NEURAL-NETWORK; ICP-MS; LASER; LIBS; PLASMA; MATRIX; MODEL

Laser-induced breakdown spectroscopy can be used for measuring the concentrations or ratios of various trace elements in solid samples. A laser pulse with a 532 nm wavelength, 5 ns pulse duration, 100 mm beam spot diameter, and 30 mJ single pulse energy is used for ablating the United States Geological Survey series of geological standard samples. The concentrations of iron in different geological samples are obtained using artificial neural networks. In addition, the influence of matrix effects on the measurement error is analyzed. Experimental results reveal that the relative errors of BCR-1G, BHVO-2G, BIR-1G, GSD-1G, and GSE-1G between the measured concentrations and the certified concentrations are 1.86%, 5.73%, 0.27%, 3.86%, and 2.63%, respectively, which indicate that the LIBS method using back propagation artificial neural networks can effectively determine the iron concentrations of USGS geological standard samples. The matrix effects of standard samples are analyzed, which shows that the matrix effects of GSD-1G and GSE-1G are more different than others. As a result, some significant measurement errors in concentration determination resulted from different matrix effects.

INDUCED BREAKDOWN SPECTROSCOPY; LASER-INDUCED FLUORESCENCE; SOLID-PHASE EXTRACTION; ICP-MS; QUANTITATIVE-ANALYSIS; LIQUID SAMPLES; METAL ANALYSIS; ULTRASONIC NEBULIZATION; ATOMIC FLUORESCENCE; AQUEOUS-SOLUTION

To realize ultrasensitive detection of trace amounts of lead in water, laser-induced breakdown spectroscopy combined with laser-induced fluorescence was investigated. A wood-slice substrate was selected: as a water absorber to convert liquid-sample analysis to solid-sample analysis; to eliminate the influence of a water matrix to spectral analysis in the plasma during direct analysis of water samples. The wood slice after treatment was ablated by a Q-switched Nd:YAG laser to produce plasma. Then, the lead atoms in the plasma were re-excited by a second tunable dye laser resonantly. The LIF signal of lead was detected to improve its sensitivity to spectral analysis significantly. Under the assistance of this matrix-converting method, the calibration curve of lead in water samples was created and the limit of detection was found to be 0.32 ppb, two orders of magnitude better than that obtained by analyzing water samples directly using the same LIBS-LIF technique. This sample-pretreatment procedure was rapid and easy to handle. Upon combination with LIBS-LIF, ultrasensitive detection of trace amounts of toxic metal elements in water could be realized. This approach could be applied in water-quality control and monitoring of environmental pollution.

INDUCED BREAKDOWN SPECTROSCOPY; ELEMENTAL ANALYSIS; SPECTRUM STANDARDIZATION; UNBURNED CARBON; FLY-ASH; SAMPLES; SPECTROMETRY; PELLETS; MODEL; PLANT

Quantitative analysis of elements by laser-induced breakdown spectroscopy (LIBS) is significantly affected by matrix effects in coal. Coal powder was mixed with the KBr binder and pressed into pellets to reduce matrix effects. Four groups of mixed-pressed pellet samples were prepared from nine different coal types and different percentages of the KBr binder (KBr accounts for 0 wt%, 30 wt%, 60 wt%, and 90 wt%, respectively). To optimize the percentages of the KBr binder in the mixed-pressed pellets, the influence of KBr binder on laser-induced plasma was investigated in detail. The results indicate that the plasma excitation temperature decreases with increase of the KBr binder concentration. The difference of the excitation temperature between the nine different coal samples was minimal when KBr accounts for 60 wt% in the mixed-pressed pellets. The relative standard deviation of the excitation temperature is 4.26%. The matrix changes from coal to KBr when the percentages of KBr are higher than 60 wt%, which was confirmed by scanning electron microscopy images of the ablated crater. Finally, Si and K were individually chosen as the internal calibration element to construct the calibration curves of carbon. Better results were obtained when Si I 288.16 nm was used as the internal standard. The correlation coefficients R-2 of the four groups of mixed-pressed pellet samples are 0.835, 0.893, 0.983, and 0.903, respectively. Hence, the appropriate percentage of binders needs to be carefully confirmed to reduce matrix effects in quantitative analysis of coal by LIBS.

SPECTRUM STANDARDIZATION; QUANTITATIVE-ANALYSIS; LIBS; NORMALIZATION; SIGNAL; MODEL

The uncertainty of collected spectral data is one of the most important issues for the application of laser-induced breakdown spectroscopy (LIBS) quantitative analysis. The fluctuation of the target surface simultaneously affects both the focus depth of the laser beam and the relative collection position, either of which may lead to severe fluctuation of the spectral signal. Thus, in this study, for detecting and reducing the fluctuation, an imaging system was deployed to monitor the plasma, and a mathematical model was also built based on both spectral signal and positional information. An ICCD camera was used to record the image of the plasma so as to detect the plasma and acquire positional information. Furthermore, the relationship between plasma position and specific spectral line intensity was obtained by the fitting function. Five aluminium alloy samples were employed to validate the reliability of the proposed method. As a result, the average RSDs of the samples (with a position fluctuation range of about 2 mm) in different spectral lines (Si 288.15 nm, Fe 273.95 nm, Cu 324.75 nm, Mn 259.37 nm and Mg 280.27 nm) were reduced from 34.57%, 38.86%, 31.05%, 39.74%, and 36.91% (without normalization) to 4.63%, 6.84%, 5.64%, 7.64%, and 4.83% (with the combination method presented in this paper), respectively; the determination coefficients (R-2) reached 0.996, 0.999, 0.989, 0.999, and 0.9999, respectively. These results prove that the proposed method can both improve measurement reliability and guarantee measurement accuracy.

QUANTITATIVE-ANALYSIS; CARBON CONTENT; LIBS; TEMPERATURE; TRANSFORM; PLASMAS; LINES

To minimize the impact of spectral interference on laser-induced breakdown spectroscopy (LIBS) quantitative analyses, an algorithm based on wavelet transform was developed for simultaneous correction of spectral interference and continuum background. The root-mean-square error of calibration (RMSEC) of the univariate regression model for the element of interest was applied to determine the wavelet function, decomposition level, and scaling factor alpha. When the interference-free analytical lines of the elements of interest cannot be directly obtained from the measured spectra, they can be extracted from the spectra with the developed method for quantitative analysis. This method was applied for LIBS analyses of chromium (Cr), silicon (Si), titanium (Ti), and manganese (Mn) with continuum backgrounds and spectral interference in low alloy steel samples. The root-mean-square errors of cross-validation (RMSECV) of elements Cr, Si, Ti, and Mn were 0.0295, 0.0140, 0.0183, and 0.0558 wt%, respectively. The results demonstrated that the developed algorithm contributed to accuracy improvement for LIBS quantitative analyses with the presence of spectral interference.

LASER-INDUCED BREAKDOWN; PLASMA-MASS SPECTROMETRY; RESOLUTION CONTINUUM SOURCE; PARTICLE ICP-MS; RAY-FLUORESCENCE SPECTROMETRY; MULTI-ANALYTICAL APPROACH; OPTICAL-EMISSION SPECTROSCOPY; LI-ION BATTERIES; ELECTRON-PARAMAGNETIC-RESONANCE; ELEMENTAL IMPURITIES ANALYSIS

This ASU review focuses on developments in applications of atomic spectrometry to the characterisation of metals, chemicals and materials. It is difficult to identify research trends solely from an annual review of the literature, but a certain perspective can be obtained from examining the developments described in recent years in this ASU review series. It is, for example, evident that there has been a decline in truly novel applications for the analysis of chemicals, perhaps indicative of the fact that, for most sample types, there is now an abundance of methods available in the literature. Those papers that have appeared in the year under review have either focused on specific problems not yet fully addressed (e.g. determination of Si in gasoline) or on incremental development of well-established approaches to sample preparation or measurement. Nevertheless, there has been a very noticeable increase in activity in relation to publication of methods for the characterisation of pharmaceuticals. This is directly linked to changes in the US Pharmacopeia requirements for registration of pharmaceuticals for human use that require assessments to be made for trace element content. Laser-induced breakdown spectrometry is becoming widely employed for applications involving the characterisation of a wide variety of metals, materials and other solid sample types. Efforts are being made to overcome the perceived weaknesses of the technique, such as lack of sensitivity, elemental fractionation, accuracy and/or precision. Advances have been made, for example, using dual-pulse lasers to improve sensitivity, or by employing chemometrics methods with full spectrum data to improve the robustness of calibration. Many of these reported LIBS developments draw from, and have relevance for, applications involving LA-ICP-MS, which continues to be a popular means of generating highly sensitive lateral and depth profiling and bulk compositional information for a wide range of materials and solids. The use of field portable instrumentation for in situ analysis continues grow, with LIBS and XRF techniques amongst those most frequently cited. The development of such instrumentation has had a substantial impact in the examination of cultural heritage artefacts, especially in relation to paintings, wall murals and other objects of unique historical value. The latter area of application has also seen continued use of combinations of surface (SIMS, XPS, SEM-EDS, PIXE, GD and laserablation methods) and bulk (ICP-OES, ICP-MS, AAS, XRF) analysis techniques to reveal details of objects that would not otherwise be identified (for example preparatory sketches hidden under original works of art or materials provenance). This trend towards using a multi-technique based approach has also been apparent in the characterisation of multi-layer or heterogeneous organic and inorganic materials and metals. Finally, methods for the analysis of nanoparticles and nanostructures have been reported, based primarily on single particle (SP)-ICP-MS and flow field flow fractionation (A4F). The investigation of methods of drift correction, the use of flow injection and isotope dilution methodologies in combination with SP-ICP-MS are indicative of the further development of this field.

INDUCED BREAKDOWN SPECTROSCOPY; INDUCED ALUMINUM PLASMA; FEMTOSECOND LASER; ISOTOPIC SPECTROMETRY; TEMPORAL EVOLUTION; EMISSION-SPECTRA; ABLATION; ALO; DYNAMICS; CARBON

Measurements with Laser Ablation Molecular Isotopic Spectrometry (LAMIS) are usually performed in atmosphere for rapid isotope analysis, and an understanding of molecule formation via plasma-air chemical reactions is important for quantitative analysis by LAMIS. In this work, the expansion of a plasma plume from ablation of pure aluminum in air is studied with time-and space-resolved monochromatic imaging and emission spectroscopy. The distributions of neutral Al and O atoms and AlO radicals formed through plasma chemical reactions are characterized. The emission spectra of the AlO bands of a B-2 Sigma(+)-X-2 Sigma(+) system are recorded and the rotational-vibrational temperature was obtained through fitting experimental spectra. Inter-molecular vibrational band interference is well reconstructed, and self-absorption of bandheads, especially for the (0-0) band, is corrected. Interpretation of the spatial-temporal evolutions of plasma species and plasma temperature provides insights into the formation mechanism of AlO radicals in laser-induced plasma.

ECHELLE SPECTROMETER; ELEMENTAL ANALYSIS; INDUCED PLASMA; LIBS LIMIT; ALLOYS; SALT; AIR

Laser-induced breakdown spectroscopy (LIBS) was applied to inspect trace substances on aluminum alloy surfaces. Silicone oil, which is often used as a release agent, was employed as the adhered substance. Nanosecond laser pulses at UV wavelengths (KrF laser, lambda = 248 nm) were employed for the LIBS measurements. Although the absorption of silicone oil at 248 nm was negligible, the Si emission of surface-adhered silicone oil was detected. The intensity ratio of the Si emission at 288 nm to the Al emission at 309 nm increased with increasing surface concentrations in the range 1-35 mu g cm(-2), and a linear dependence on the silicone oil surface concentration was observed at low surface concentrations (<5.0 mu g cm(-2)). The limit of detection was evaluated to be 1.18 mu g cm(-2).

INDUCED BREAKDOWN SPECTROSCOPY; TRANSFORM; IDENTIFICATION; CALIBRATION; SIGNALS; ALLOYS

Laser-induced breakdown spectroscopy (LIBS) is becoming a rapid and easy technique for quantitative elemental analysis. However, the implementation of accurate quantitative LIBS analysis is always subject to noise interference. In this work, in order to improve LIBS analysis performance for trace elements in aluminium alloys, a modified trade-off soft and hard threshold method is proposed based on the wavelet theory, where optimal parameters are deduced to eliminate noise interference. By using the modified algorithm combined with an Al I line at 308.215 nm as an internal standard, the statistical parameters including the determination coefficient (R-2), the root mean square error (RMSE) and the relative standard deviation (RSD) of magnesium (Mg), manganese (Mn) and cuprum (Cu) in aluminium alloys are all significantly improved. The most significant improvement of R-2 is 0.066 for Cu. The maximum RMSE reduction value is 0.583 for Mg, and the mean value of RMSE reduction is 0.261 for all three trace elements. And after de-noising, the value of RSD gets smaller for each trace element. Such results indicate that the optimized algorithm is valid for the effective improvement of the accuracy of quantitative LIBS analysis in the trace element determination of aluminium alloys.

INDUCED BREAKDOWN SPECTROSCOPY; MOLECULAR ISOTOPIC SPECTROMETRY; LASER-INDUCED PLASMA; SECONDARY EXCITATION SOURCE; PRESSURE GLOW-DISCHARGE; OPTICAL-EMISSION; STEEL ANALYSIS; LINE LISTS; BANDS; QUANTIFICATION

Enhancement of the emission intensity by a secondary electric pulse following a laser ablation pulse was investigated in application to the chemical analysis by Laser-Induced Breakdown Spectroscopy (LIBS) and Laser Ablation Molecular Isotopic Spectrometry (LAMIS). A stable reheating pulsed discharge presumably sustained in a diffuse glow regime at atmospheric pressure was demonstrated as a rational approach to increase the sensitivity of the optical emission analysis over the conventional single-pulse laser ablation techniques. The enhancement in the emission intensity was illustrated by several examples of both atomic (Ca, Na) and molecular (OH, AlO, CaF) emission in LIBS and LAMIS, respectively. Especially large emission enhancement was realized for isotopologues (OH)-O-16, (OH)-O-18 and (OD)-O-16 at the transition A(2)Sigma(+)/X-2 Pi(i) (1-0) with clearly resolved lines of their rotational branches. An increase in rotational temperature from 3370 to 4560 K was measured subsequently to the reheating of plasma by a pulsed electric discharge. Such reheating can be especially useful for the minimally destructive analysis, chemical mapping and depth profiling by LIBS. Enhancement in the emission intensity of CaF can be used for further reduction of the detection limits in fluorine determination. A brief review of the earlier publications on the cross-excitation by an electric pulse after laser ablation is provided and a comparison is made to the similar reheating of the ablation plasma in double-pulse LIBS.

INDUCED PLASMA SPECTROSCOPY; HEAVY-METAL AEROSOLS; X-RAY-FLUORESCENCE; PARTICULATE MATTER; ELEMENTAL COMPOSITION; NANOMATERIALS; WORKPLACES; APPRAISAL; RELEASE; COBALT

Exposure assessment is a key step in the evaluation of the risk induced by the handling of engineered nanomaterials. It is a very complex task, because several properties of nanoparticles are assumed to have an effect on their hazards. For exposure monitoring at the workplace, real-time onsite measurements are commonly implemented to measure the particles size and number density, whereas the sampled material is subsequently analysed by electron microscopy. A complementary approach would consist in doing onsite chemical analysis of the filter samples, in order to routinely monitor a potential chronic exposure. Laser-induced breakdown spectroscopy (LIBS) has distinctive advantages for this purpose. Therefore, this work aims at evaluating the performances of LIBS to assess the exposure to airborne carbon nanotubes (CNTs) at the workplace. As carbon is a ubiquitous element in the environment, our strategy was to target metal impurities in CNTs, aluminum and iron in our case. Then, we proceeded in three steps. First, we optimized the choice of the filter type to get the lowest detection limit for both elements. Secondly, this filter was used to quantitatively measure deposited CNTs. Eventually, we conducted an onsite measurement campaign in an industrial CNT production plant to evaluate the exposure in a real situation. We demonstrated that we could reach a detection limit for CNTs compliant with the current NIOSH recommendation of 1 mu g m(-3), and that the detected CNTs during the onsite campaign in areas accessible to workers were at an extremely low concentration, several orders of magnitude lower than this recommendation.

INDUCED BREAKDOWN SPECTROSCOPY; SPECTRUM STANDARDIZATION METHOD; PARTIAL LEAST-SQUARES; MICROCHIP LASER; CARBON ANALYSIS; MN; SPECTROMETRY; CONFINEMENT; IMPROVEMENT; REGRESSION

Laser-induced breakdown spectroscopy (LIBS) was named a future superstar. Nevertheless, in the last couple of years, several commercial instruments of LIBS and its different variants have become available on a limited scale due to the confinement of quantitative analysis. In this paper, quantitative analysis of various steel samples using a specially designed handheld mu-LIBS instrument and dominant factor based partial-least squares (PLS) regression with spectral standardization is presented. Average absolute measurement errors of 0.019, 0.039, 0.013 and 0.001% for the elements of Si, Cr, Mn and Ni, respectively, were achieved. The average relative standard deviation (RSD) for these elements was less than 5%. A linear calibration response was obtained for C which is difficult to achieve using traditional PLS and for Cu whose concentration in the samples is very low. The results are better than the results of previous LIBS studies using mu J lasers or portable handheld devices, comparable to those obtained using conventional benchtop LIBS systems and better than those of commercial handheld XRF instruments. The present work presents the best results for steel analysis using portable LIBS systems so far and shows the feasibility of the technology for real industrial applications.

INDEPENDENT COMPONENT ANALYSIS; SUPPORT VECTOR MACHINES; NEURAL-NETWORK WNN; QUANTITATIVE-ANALYSIS; RANDOM FOREST; FLY-ASH; WAVELET-TRANSFORM; UNBURNED CARBON; SIGNAL; MODEL

The classification and identification of coal ash contributes to recycling and reuse of metallurgical waste. This work explores the combination of the laser-induced breakdown spectroscopy (LIBS) technique and independent component analysis-wavelet neural network (ICA-WNN) for the classification analysis of coal ash. A series of coal ash samples were compressed into pellets and prepared for LIBS measurements. At first, principal component analysis (PCA) was used to identify and remove abnormal spectra in order to optimize the training set for the WNN model. And then, ICA was employed to select and optimize input variables for the WNN model. The classification of coal ash was carried out by using the WNN model with optimized model parameters (the number of hidden neurons (NHN), the number of iterations (NI), the learning rate (LR) and the momentum) and input variables optimized by ICA. Under the optimized WNN model parameters, the coal ash samples for test sets were identified and classified by using WNN and artificial neural network (ANN) models, and the WNN model shows a better classification performance. It was confirmed that the LIBS technique coupled with the WNN method is a promising approach to achieve the online analysis and process control of the coal industry.

IN-SITU; LIBS; STEELS; CLASSIFICATION; EXPLORATION; ELEMENTS; SPECTRA; SAMPLES; SOIL; MN

Stand-off laser-induced breakdown spectroscopy (ST-LIBS) has attracted increasing attention as a valuable method for the remote analysis of materials. In this work, a multi-collector (MC) system combining low cost small lenses imitating the structure and shape of an artificial optical compound eye (AOCE) is presented to enhance the spectral intensity of ST-LIBS. The volume of the MC system is one eighteenth smaller than that of a telescope system and the number of collectors can be flexibly changed according to the requirements. The mechanisms of spectral enhancement are also discussed. In order to illustrate the performance of the MC system, the spectral intensities and the limits of detection (LoDs) of Mn and Cr elements acquired by the telescope system and the MC system were compared at a distance of 2 meters. The results showed that the spectral intensity acquired from the MC system was enhanced by 2.2 times, and the LoDs of Mn and Cr were decreased to 294 mu g g(-1) and 49 mu g g(-1). These results indicate that the MC system has great potential in providing a portable, flexible and effective collection method for remote detection.

SINGLE-PULSE; CAVITATION BUBBLE; ABLATION; CERAMICS; WATER; NANOPARTICLES; LIQUID; DYNAMICS; SPECTRA; METALS

The goal of this study was to investigate whether a secondary plasma can be formed on a non-metallic target under water and to give insight into the related processes. The material of choice here was alumina, since its physical, thermal and mechanical properties are substantially different from those of pure Al, only for which secondary plasma formation was recently demonstrated. To achieve this, plasma and bubble formation on alumina under water after single pulse laser excitation were studied using fast photography, shadowgraphy, Schlieren and LIBS techniques. The results show that the secondary plasma caused by backward heating of the target and successive slow target evaporation into the growing vapour bubble also occurs for alumina. The secondary plasma formed on alumina involves only a narrow interaction region on the target resulting in an almost spherical plume shape. In contrast, on thermally conductive and easily melting/evaporating aluminium, the secondary plasma is intense, with a large volume which is flattened on the target surface. Inside the expanded bubble above the alumina target, glowing particles were not observed. Due to less efficient secondary plasma formation on alumina compared to aluminium, its optical emission only slightly increases at a delay of 400 ns from the laser pulse but emission persists during three bubble cycles with a total duration of about 650 ms. The LIBS spectra related to the secondary plasma are almost free from any continuum component and show narrow emission lines from low excited states. Here we discuss the observed differences in the plasma's spatial, temporal and spectral evolution on the two considered target materials. The obtained results indicate that under water a secondary plasma might be formed on very different materials and that its detection produces a good quality LIBS signal from single pulse excitation using a commercial nanosecond laser source.

FEMTOSECOND DOUBLE-PULSE; OPTICAL-EMISSION; PLASMA; ENHANCEMENT; SILICON

The spatial confinement effect in laser-induced plasma with different distances between the target surface and focal point is investigated by optical emission spectroscopy. A Nd: YAG laser is used to produce plasma from a silicon sample in air atmosphere. When the appropriate distance is selected, the duration of spectral emission enhancement is much longer, and the enhancement effect is much stronger. The phenomenon is attributed to the aspect ratio of the lateral to axial direction of the plasma plume. The plasma plume of a large aspect ratio will interact with the reflected shockwave in a long range of delay time, leading to high particle density. This provided a better understanding about the effect of the distance between the target surface and focal point, leading to better conditions for spatially confined laser-induced breakdown spectroscopy.

LA-ICP-MS; INDIVIDUAL PARTICLES; ANALYTICAL-CHEMISTRY; FEMTOSECOND; GLASS; NANOSECOND; IONIZATION

Laser ablation - inductively coupled plasma -mass spectrometry (LA-ICP-MS) in tandem with laser induced breakdown spectroscopy (LIBS) was employed to chemically map and characterize uranium particles. The uranium particles were doped in various concentrations (0.01, 0.1, 1.0, and 2.0%) to a 50 : 50 Ni : Fe mixture. There was an excellent correlation in regards to concentration and the LA-ICP-MS measurements. In addition, the isotopic composition of the uranium particles was determined within 10% measurement uncertainty. LIBS measurements also showed strong agreement in the particle mapping when compared to the LA-ICP-MS analysis. Moreover, the total analysis time for a 5 x 5 mm area was only 50 minutes. These data suggest that the tandem LA-ICP-MS/LIBS technique can provide rapid and valuable information for nuclear material safeguards and actinide material characterization.

INDUCED BREAKDOWN SPECTROSCOPY; LASER-INDUCED FLUORESCENCE; EXCITED ATOMIC FLUORESCENCE; ELEMENTAL ANALYSIS; ABLATION; LIBS; SPECTROMETRY; MECHANISM; METALS; WASTE

Coupling laser-induced fluorescence to laser ablation can reduce detection limits relative to LIBS. The wing of the broadband similar to 193.3 nm emission from unmodified argon fluoride lasers can excite arsenic fluorescence via its 193.76 nm ground state transition for a simple fluorescence scheme. We present argon fluoride-excited laser-ablation laser-excited atomic fluorescence (LA-LEAF) measurements in steel and copper under argon and helium atmospheres. Because the ArF laser saturates the absorption transition and the steel samples show substantial nonspecific iron fluorescence, it is necessary to optimize the laser energy in addition to interpulse delay. LODs are slightly lower under helium (1.0 ppm in steel, 0.15 ppm in copper). These detection limits represent a modest improvement over previous LODs with LIBS, but suggest potential for improvement with line narrowing of the ArF laser.

BIVALVE SHELLS; SR/CA; HETEROGENEITY; PALEOCLIMATE; EDULIS; BA/CA; LIBS

Records of past environmental conditions in shell carbonate are usually derived from compositional analysis (i.e. trace elements, stable oxygen, carbon, and nitrogen isotopes) performed along the direction of the shell's growth and thus through time. However, compositional variations within isochronous parts of the shell can distort the environmental record and are difficult to assess without extensively mapping the whole shell. Here we apply Laser Induced BreakdownSpectroscopy (LIBS) to efficiently map the elemental change throughout the growth increments of three mollusc shells (Conomurex fasciatus, Ostrea edulis, Anomalocardia flexuosa). We employ an automated LIBS setup to map the Mg/Ca composition of whole shell sections with over 2000 data points per hour. By assessing the spatial variability of Mg/Ca intensity ratios this method has the potential to mitigate distorted results while increasing the resolution of derived palaeoenvironmental information.

WATER-BASED LIQUIDS; METALLIC TRACES; LIBS EMISSION; ENHANCEMENT; IMPROVEMENT; CONFINEMENT; SENSITIVITY; PULSE; LONG

Laser-induced breakdown spectroscopy (LIBS) can benefit from sustaining laser generated plasma with microwaves to enhance elemental detection sensitivity. To achieve efficient microwave coupling, critical factors, such as the electromagnetic environment and reflection coefficient of the coupling device, need to be considered to quantitatively predict the electric-field strength in the plasma location. 3D full-wave electromagnetic simulations were used to design near-field microwave applicators suitable to maximize microwave coupling into the short-lived laser-induced plasmas. The simulations pointed out to four effective and practical designs containing varieties of isolation techniques. The four developed microwave applicators were then used to improve the detection of copper present in a mineral ore solid sample, using LIBS and imaging techniques simultaneously. It was found that, with 1.2 kW microwave power, an applicator design with a 30 mm diameter ground plane can significantly boost the signal of copper line 324.754 nm with a factor of 849, which is, to the authors' best knowledge, the highest reported value. Furthermore, an outstanding signal to noise ratio of 166 was recorded in a solid sample containing a certified 3.38 mg g(-1) copper concentration.

INDUCED BREAKDOWN SPECTROSCOPY; SELF-ABSORPTION; EMISSION-LINES

The temporal evolution of doublet lines intensity ratio, plasma temperature (T) and electron density (N-e) of different radial parts of aluminum plasma as well as the relationship between optically thin condition and plasma characteristics are investigated. With respect to doublet lines intensity ratio, the optimal delay time (t(ot)) when the plasma is optically thin is determined by comparing the experimental intensity ratio of doublet Al(I) lines with the theoretical value. The optimal integration time, fiber collection angle, and delay time corresponding to the optically thin condition are 400 ns, 45 degrees, and 500 ns, respectively, in which case the linearity of the calibration curve reaches 0.98, enabling more accurate composition measurements. The maximum temperature values are reached within 300 ns at 10 degrees, 30 degrees, 45 degrees, and 80 degrees, but after 900 ns at 55 degrees, 60 degrees, and 70 degrees. Combined with the morphologic image of the plasma, we infer that the time at which a radial part of plasma reaches the highest temperature is related to the extent of its expansion. It is generally understood that the faster the radial part of plasma expands, the sooner the temperature reaches its maximum. The radial part of plasma may not be optically thin when the corresponding temperature reaches its maximum. If the highest temperature is obtained earlier, the optically thin condition is likely to appear in the descending stage of the temporal evolution curve of temperature. Otherwise, it may appear in the ascending stage. There seems to be no simple positive correlation between electron density and optically thin condition.

INDUCED PLASMA SPECTROSCOPY; ATOMIC EMISSION-SPECTROMETRY; VACUUM-ULTRAVIOLET; SULFUR; STEEL; NANOPARTICLES; CALIBRATION; SAMPLES; RATIOS; SYSTEM

This work introduces a new approach to perform LIBS elemental imaging in the vacuum ultraviolet (VUV) wavelength range by using an argon purged probe coupled to a compact spectrometer. In spite of several important elements for geological and industrial applications such as S, P, As, B, C, or Zn presenting strong lines in the VUV range, the need for using specific optics and working under oxygen-free conditions has limited the extension of LIBS systems available for such a range. Herein, we present an adaptation of our LIBS imaging instrumentation to access the VUV while operating under ambient conditions. The proposed detection system is based on an optical probe directly coupled to a Maya2000Pro compact spectrometer (Ocean Optics), all purged with argon. The technical design along with a detailed evaluation of the VUV probe is addressed. The possibility of using this VUV probe for LIBS imaging is also investigated by studying a Canadian mine core sample with special emphasis on the detection of sulfur. In addition to sulfur, more than 15 elements including P, As, C, Ca, Si, Mo, B, and Zn have also been detected. Elemental images covering sample surfaces in the range of cm(2) with a micrometric spatial resolution (10 mu m) are presented. A detection limit of 0.2 wt% for sulfur is demonstrated in a single shot configuration. These results open new perspectives for both conventional LIBS and LIBS-based imaging in various application fields.

INDUCED BREAKDOWN SPECTROSCOPY; LASER-INDUCED PLASMA; HIGH-PRESSURE BANDS; EXPLOSIVE RESIDUES; CULTURAL-HERITAGE; OPTICAL-EMISSION; ABLATION PLASMAS; SOLID-SURFACES; DYNAMICS; CARBON

In the present work, six novel high energy materials (HEMs) were investigated by femtosecond and nanosecond LIBS techniques with an intention to comprehend the influence of different functional groups as well as their positions on the LIBS emission. The examined HEMS are functional and structural isomers of triazole-substituted nitroarene derivatives and have methyl (CH3), methoxy (OCH3), and amino (NH2) groups in ortho and para positions. CN and C-2 molecular bands along with atomic lines of C, H, N and O were identified in the ns and fs LIBS spectra. As expected, the molecular signatures in the earlier times of plasma expansion were observed to be prominent in femtosecond LIBS spectra. The various formation pathways for CN and C-2 as well as the correlation of emission intensities with C-C, C=C, C-N, and C=N bonds and % O are investigated using the fs and ns LIBS data recorded in air and argon atmospheres. The influence of functional groups and their position on CN and C-2 emissions is elucidated through the CN/C-2 ratio. Furthermore, the detonation parameters of these materials namely oxygen balance, velocity of detonation, detonation pressure and chemical energy of detonation were found to correlate well with the (CN + C-2)/(C + H + N + O) ratio. Such correlation studies are expected to support the understanding and improve the discrimination procedures for such hazardous materials.

II SPECTRAL-LINES; ATOMIC TRANSITION-PROBABILITIES; STARK-BROADENING PARAMETERS; CALIBRATION-FREE; INDUCEDPLASMA; QUANTITATIVE-ANALYSIS; CRITICAL COMPILATION; SELF-ABSORPTION; WIDTHS; SHIFTS

We report a validation experiment of the C sigma-LIBS method, proposed recently by our group for quantitative laser-induced breakdown spectroscopy. This method is applied to determine eight elements (Si, Al, Ca, Mg, Fe, Ti, Mn, and V) in rocks prepared as fused glass samples, having a wide range of certified concentrations. The characterization stage of the method is performed using only two standard fused glass samples prepared from mixtures of pure compounds (SiO2, Al2O3, Fe2O3 and CaCO3). The average precision obtained is 3.4% for concentrations higher than 0.1 wt%. This validation suggests that the accuracy and precision of this technique, if combined with fused glass sample preparation under favourable conditions, may become as good as those produced by certification laboratories.

INDUCED BREAKDOWN SPECTROSCOPY; MOLECULAR-EMISSION; LASER; AIR; SPECTROMETRY; CHLORINE

The determination of fluorine in solid samples using Laser Induced Breakdown Spectroscopy (LIBS) is a challenging task due to the low excitation efficiency of this element. Recently, the use of molecular CaF bands was demonstrated to improve the analytical capabilities of LIBS fluorine detection in Ca-containing samples. In this work, a novel approach has been developed to extend this methodology for fluorine quantification in calcium-free samples. In particular, the on-line nebulization of a Ca-containing solution on the surface of a fluorine containing sample has been successfully evaluated to obtain the desired CaF molecular emission. Nebulization parameters have been optimized in order to maximize the molecular emission. A linear relationship between the CaF molecular emission signal and the amount of F in the solid samples has been obtained. The calculated limit of detection for fluorine (about 50 mu g g(-1)) is in the same order of magnitude as that obtained for Ca-containing samples. This novel approach for fluorine quantification opens new ways for the analysis of halogens in solid samples.

SILICON-WAFERS; CRYSTAL-GROWTH; SOLAR-CELL; AEROSOLS; ABLATION; CU(IN,GA)SE-2; TRANSISTORS; CAPACITANCE; THICKNESS; RESIDUES

The current Largest market share and continually growing industry of the semiconductor manufacturing sector in the US demands rapid and cost-effective quality control and characterization of thin film semiconducting materials. To this end, we demonstrate Laser Induced Breakdown Spectroscopy (LIBS) as a facile and effective analytical tool for rapid process-Line characterization of metal-oxide semiconductor (MOS) transistors and capacitors. Specifically, we carry out quantitative LIBS analysis on siLicon oxide (Si02) thin-films of various thicknesses grown by high-temperature moisture-free oxidation on industrial-grade Si wafers. The stoichiometric ratios of oxygen to siLicon ([O]/[Si]) in various SiO2 films are measured by LIBS anaLyses using an internal calibration technique. The results are verified against benchmark anaLyses based on oxide Layer thicknesses and Laser-induced crater profile topographies from eLLipsometry, scanning electron microscopy (SEM), atomic force microscopy (AFM), and profflometry measurements. The stoichiometric ratios of [O]/[Si] calculated from thickness and profflometry measurements are used to compare with our direct LIBS measurements. Our results indicate good agreement between the LIBS and profibmetry calculation results, demonstrating the future capability of LIBS for thin film characterization during their industrial processing.

MATRIX CONVERSION; QUANTITATIVE-ANALYSIS; AQUEOUS-SOLUTIONS; METAL DETECTION; HEAVY-METALS; SPECTROMETRY; LIBS; MICROEXTRACTION; PLASMA; MEMBRANE

Laser-induced breakdown spectroscopy (LIBS) is a simple, fast, and direct technique for the elemental analysis of various samples. However, the practical application of this method in direct liquid analysis is limited due to its inherent disadvantages including surface ripples and extinction of emitted intensity. Applicable treatments of liquids always involve complicated procedures or additional instruments, which is disadvantageous to its analytical performance. In this study, we proposed a novel method for the LIBS analysis of liquid samples via a hydrogel-based solidification technique. In this new method, aqueous solution is directly poured into sodium polyacrylate resins. Owing to the high hydroscopicity of sodium polyacrylate resins, the resins quickly form a hydrogel and immediately solidify the liquid samples. After this, the LIBS analysis is directly performed. To estimate the analytical performance of this proposed method, calibration curves were established and limits of detection for Al, Cu, and Cr were obtained. The limits of detection (CODs) for the emission lines of Al(I) 308.21 nm, Cu(I) 324.75 nm, and Cr(I) 425.43 nm were 0.460 mu g mL(-1), 4.69 mu g mL(-1), and 4.44 mu g mL(-1), respectively. According to the obtained results, this proposed method demonstrates its better analytical performance in terms of CODs at the ppm level and requires shorter processing time as compared to other analytical methods based on the LIBS technique for liquid sample analysis. Especially, the short pretreatment of samples and simple auxiliary equipment make this hydrogel-based solidification method bring LIBS out of the laboratory for the direct analysis of environmental liquid samples. The feasibility and potential of this novel method have also been discussed for special analytical applications in slurry samples.

INDUCED PLASMA SPECTROMETRY; IN-SITU ANALYSIS; HIGH-TEMPERATURE; ELEMENTAL ANALYSIS; GRADE TRANSITION; MOLECULAR BANDS; REAL-TIME; MOLD; LIBS; SAMPLES

Among the several controlling routines utilized in the steelmaking process, analytical operations during continuous casting are especially demanding due to the extreme environment of steel plants and the crude conditions of the steel surface at the exit of the casting system. This report presents how dual-pulse laser-induced breakdown spectroscopy (LIBS) can be used for the real-time monitoring of continuous casting sequences in a steel plant and the operations needed for detecting the separation between grades of close chemical compositions. Diverse dual-pulse laser conditions have been tested in order to improve the LIBS system performance. Apart from the scale layer formed by the oxidation of steel by the surrounding air, the presence of residues of mould powder on the steel surface tends to complicate the LIBS analysis as elements present in the powder such as manganese interfere with the steel components. LIBS data processing by discriminant function analysis has been demonstrated to be beneficial for the identification of steel transitions. Changes in steel composition as low as 0.20 percentage points Cr in a stainless steel sample containing above 17% of this element are detected by corresponding changes in Wilks' lambda values from 1.0 to 0.75 during the transition. Changes in the concentration of nickel are of minor relevance as its concentration on the steel surface at the time of continuous casting is depleted. For steel concentrations differing to a larger extent, differentiation of steel grades is straight, involving changes in Wilks' lambda values from 1 to below 0.1.

We present a report on the potential use of the Laser-Induced Breakdown Spectroscopy (LIBS) technique for direct investigation of Mg corrosion and related optimization of the table-top LIBS system. Moreover, the preliminary study to prove the capability of this LIBS technique for the estimation of corrosion grade is given. In order to simulate the real corrosive environment, Mg samples were prepared in a constant climate chamber. We show that the corrosive layer on the sample surface significantly affects the properties of laser–matter interactions, i.e. among other parameters causing the matrix effect. Consequently, the properties and persistence of laser-induced plasmas (LIPs) and their composition, generated on such degraded surfaces, essentially differ. Collected radiation of LIP is then analysed and ratios of ionic to atomic Mg spectral lines are correlated with the grade of magnesium corrosion, i.e. content of Mg(OH)2 on the sample surface. The content of Mg(OH)2 is also correlated with plasma temperature as well as with the electron number density of LIP. Additionally, X-ray diffraction (XRD) analysis and optical profilometry were utilized to obtain more comprehensive information about the degradation grade of high purity Mg samples.

In this paper, the effect of particle size on Laser-Induced Breakdown Spectroscopy (LIBS) analysis of mesoporous V–SiO2 catalyst samples was investigated. The measurements were realized on three LIBS devices with different parameters. Concentrations of V in samples used for LIBS experiments previously determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) varied from 1.2 to 4.7 w/w%. Granulometry of silica samples was modified by two grinding methods (conventional vibration mill and cryogenic mill) and three sets of samples with different particle size distributions were obtained. Ground samples were then deposited in the form of a thin layer on the adhesive tape and analysed by LIBS. Curves describing the relationship between the vanadium concentration and the corresponding intensity of LIBS signal (C–I curves) were constructed for all three groups of samples, with different granulometry profiles measured with three different LIBS devices. The C–I curves for samples with narrow particle size distribution showed the highest values of slopes. Detection limits achieved were in the range 0.063–0.012% (w/w). The best LOD values were obtained for samples with the lowest mean particle size.