Evaluation of laser induced breakdown spectroscopy for multielemental determination in soils under sewage sludge application

Laser induced breakdown spectroscopy (LIBS) is an atomic emission spectroscopy technique for simple, direct and clean analysis, with great application potential in environmental sustainability studies. In a single LIBS spectrum it is possible to obtain qualitative information on the sample composition. However, quantitative analysis requires a reliable model for analytical calibration. Multilayer perceptron (MLP), an artificial neural network, is a multivariate technique that is capable of learning to recognize features from examples. Therefore MLP can be used as a calibration model for analytical determinations. Accordingly, the present study proposes to evaluate the traditional linear fit and MLP models for LIBS calibration, in order to attain a quantitative multielemental method for contaminant determination in soil under sewage sludge application. Two sets of samples, both composed of two kinds of soils were used for calibration and validation, respectively. The analyte concentrations in these samples, used as reference, were determined by a reference analytical method using inductively coupled plasma optical emission spectrometry (ICP OES). The LIBS-MLP was compared to a LIBS-linear fit method. The values determined by LIBS-MLP showed lower prediction errors, correlation above 98% with values determined by ICP OES, higher accuracy and precision, lower limits of detection and great application potential in the analysis of different kinds of soils.     

Femtosecond and nanosecond laser induced breakdown spectroscopic studies of NTO,HMX, and RDX

We present our results from the laser induced breakdown spectroscopic studies of 5-Nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO), Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and 1,3,5-Trinitroperhydro-1,3,5-triazine (RDX) investigated using nanosecond and femtosecond pulses. The presence of C, CN peaks in the spectra, signatures of high energy materials, was confirmed and persistence of emissions has been measured. Some of the Nitrogen peaks in fs LIBS spectra were found to be lower in magnitude (after normalization with N 868.60 nm peak) compared to the ns LIBS spectra. The presence of an additional CN peak in the fs spectra was identified for all samples. The ratio of CN peaks (388.28 nm, 387.08 nm, 386.16 nm) to C peak (247.82 nm), recorded with similar fluences, was discovered to be stronger in the fs case. Some of the possible mechanisms ensuing from our studies towards discrimination of such materials are outlined.     

Comparison of laser induced breakdown spectroscopy and spark induced breakdown spectroscopy for determination of mercury in soils

Mercury is a toxic element found throughout the environment. Elevated concentrations of mercury in soils are quite hazardous to plants growing in these soils and also the runoff of soils to nearby water bodies contaminates the water, endangering the flora and fauna of that region. This makes continuous monitoring of mercury very essential. This work compares two potential spectroscopic methods (laser induced breakdown spectroscopy (LIBS) and spark induced breakdown spectroscopy (SIBS)) at their optimum experimental conditions for mercury monitoring. For LIBS, pellets were prepared from soil samples of known concentration for generating a calibration curve while for SIBS, soil samples of known concentration were used in the powder form. The limits of detection (LODs) of Hg in soil were calculated from the Hg calibration curves. The LOD for mercury in soil calculated using LIBS and SIBS is 483 ppm and 20 ppm, respectively. The detection range for LIBS and SIBS is discussed.     

Evaluation of laser induced breakdown spectroscopy for cadmium determination in soils

Cadmium is known to be a toxic agent that accumulates in the living organisms and present high toxicity potential over lifetime. Efforts towards the development of methods for microanalysis of environmental samples, including the determination of this element by graphite furnace atomic absorption spectrometry (GFAAS), inductively coupled plasma optical emission spectrometry (ICP OES), and inductively coupled plasma-mass spectrometry (ICP-MS) techniques, have been increasing. Laser induced breakdown spectroscopy (LIBS) is an emerging technique dedicated to microanalysis and there is a lack of information dealing with the determination of cadmium. The aim of this work is to demonstrate the feasibility of LIBS for cadmium detection in soils. The experimental setup was designed using a laser Q-switched (Nd:YAG, 10 Hz, λ = 1064 nm) and the emission signals were collimated by lenses into an optical fiber coupled to a high-resolution intensified charge-coupled device (ICCD)-echelle spectrometer. Samples were cryogenically ground and thereafter pelletized before LIBS analysis. Best results were achieved by exploring a test portion (i.e. sampling spots) with larger surface area, which contributes to diminish the uncertainty due to element specific microheterogeneity. Calibration curves for cadmium determination were achieved using certified reference materials. The metrological figures of merit indicate that LIBS can be recommended for screening of cadmium contamination in soils.     

Detection of heavy metals in Arabian crude oil residue using laser induced breakdown spectroscopy

Laser induced breakdown spectroscopy (LIBS) was applied for the elemental analysis of Arabian crude oil residue samples. The spectra due to trace elements such as Ca, Fe, Mg, Cu, Zn, Na, Ni, K and Mo were recorded using this technique. The dependence of time delay and laser beam energy on the elemental spectra was also investigated. Prior to quantitative analysis, the LIBS system was calibrated using standard samples containing these trace elements. The results achieved through this method were compared with conventional technique like inductively coupled plasma.     

Evaluation of laser induced breakdown spectroscopy for the determination of macronutrients in plant materials

Laser induced breakdown spectroscopy (LIBS) has become an analytical tool for the direct analysis of a large variety of materials in order to provide qualitative and/or quantitative information. However, there is a lack of information for LIBS analysis of agricultural and environmental samples. In this work a LIBS system has been evaluated for the determination of macronutrients (P, K, Ca, Mg) in pellets of vegetal reference materials. An experimental setup was designed by using a Nd:YAG laser operating at 1064 nm and an Echelle spectrometer with ICCD detector. The plasma temperature was estimated by Boltzmann plots and instrumental parameters such as delay time, lens-to-sample distance and pulse energy were evaluated. Certified reference materials as well as reference materials were used for analytical calibrations of P, K, Ca, and Mg. Most results of the direct analysis of plant samples by LIBS were in reasonable agreement with those obtained by ICP OES after wet acid decomposition.     

Evaluation of laser induced breakdown spectroscopy for the determination of micronutrients in plant materials

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.     

Spark discharge assisted laser induced breakdown spectroscopy

Laser induced breakdown spectroscopy is combined with a spark discharge to operate in a laser triggered spark discharge mode. This spark discharge laser induced breakdown spectroscopy (SD-LIBS) is evaluated for Al and Cu targets in air under atmospheric pressure. Significant enhancement in the measured line intensities and the signal-to-background ratios, which depend on the spark discharge voltage and the laser fluence, is observed in spark discharge laser induced breakdown spectroscopy when compared to laser induced breakdown spectroscopy alone for similar laser conditions. The measured line intensities increase with the applied voltage for both targets, and the ratio of the measured line intensity using spark discharge laser induced breakdown spectroscopy to that using laser induced breakdown spectroscopy is found to increase as the laser fluence is decreased. For Al II 358.56, such intensity enhancement ratio increases from 50 to 400 as the laser fluence is decreased from 48 to 4 J/cm² at an applied voltage of 3.5 kV. Thus, spark discharge laser induced breakdown spectroscopy allows for using laser pulses with relatively low energy to ablate the studied material, causing less ablation, and hence less damage to its surface. Moreover, applying spark discharge laser induced breakdown spectroscopy gives up to 6-fold enhancement in the S / B ratio, compared to those obtained with laser induced breakdown spectroscopy for the investigated spectral emission lines.     

Analysis of fresco by laser induced breakdown spectroscopy

The laser-based techniques have been shown to be a very powerful tool for artworks characterization and are used in the field of cultural heritage for the offered advantages of minimum invasiveness, in situ applicability and high sensitivity. Laser induced breakdown spectroscopy, in particular, has been applied in this field to many different kinds of ancient materials with successful results. In this work, a fragment of a Roman wall painting from the archaeological area of Pompeii has been investigated by LIBS. The sample elemental composition resulting from LIBS measurements suggested the presence of certain pigments. The ratio of the intensities of different lines related to some characteristic elements is proposed as an indicator for pigment recognition.     

Experimental and theoretical comparison of single-pulse and double-pulse laser induced breakdown spectroscopy on metallic samples

In this paper, single pulse (SP)- and double pulse (DP)- Laser Induced Breakdown Spectroscopy (LIBS) on metallic titanium, aluminum-based alloy and copper-based alloy have been studied by spectrally resolved imaging to find out the fundamental difference in terms of fluid-dynamic and chemical aspects. To better clarify the different nature of SP- and DP-Laser Induced Plasma (LIP) a qualitative theoretical model including both fluid-dynamics and chemical processes has been applied for the interpretation of the experimental results. Moreover, an attempt to quantify the mechanisms inducing the DP-LIBS enhancement has been made. By the analysis of spectrally resolved imaging data, the temporal and spatial maps of the emission signal and of the corresponding DP-LIBS enhancement have been built in order to improve the analytical information conveyed. Finally, it has been pointed out the important effect of the different environment where SP- and DP-LIPs expand, as well as its relevance to the understanding of the basic questions underlying the comparison between SP- and DP-LIBS.     

Particulate formation induced by infrared laser dielectric breakdown

Laser induced dielectric breakdown has been utilized to initiate, sustain and study a number of chemical reactions. A 1 joule per line TEA CO₂ laser has been used as the source to induce dielectric breakdown. Product analysis was carried out by mass spectrometry and infrared spectroscopy. The reaction and method are discussed in terms of efficiency, selectivity and scope.     

Experimental determination of conformational isomerization energy thresholds in serotonin

Stimulated emission pumping-population transfer (SEP-PT) and hole-filling (SEP-HF) spectroscopies were used to determine the energy thresholds to isomerization between thirteen reactant-product conformer pairs in the biomolecule serotonin (SERO). Serotonin is a close structural analog of tryptamine (TRA), differing in having a hydroxyl group in the 5 position of the indole ring. A previous spectroscopic study (LeGreve; et al. J. Am. Chem. Soc. 2007, 129 (13), 4028) identified eight conformational isomers of SERO, whose interconversion involves motion of the 3-ethylamine side chain, the 5-OH group, or both. In the cases in which only an ethylamine side chain reorientation occurred, the barriers were found to be similar to, but systematically somewhat smaller than, those in TRA, which has been studied by similar methods (Dian; et al. Science 2004, 303 (5661), 1169; Clarkson; et al. J. Chem. Phys. 2005, 122 (21), Art. No. 214311). In most cases, the experimental thresholds are well reproduced by calculated transition states separating the conformational wells; however, tunneling effects may artificially reduce the thresholds observed for isomerization of SERO(A,Gpy(out)) and SERO(B,Gpy(up)) into SERO(C,Gph(out)). The A --> A' isomerization involving only the OH rotation from anti to syn was found to be 721-761 cm-1, in accordance with the calculated classical barrier. For isomerizations in which the ethylamine side chain reorients as does the OH group, the barriers to isomerization were consistent with sequential rather than concerted motion of both groups. Finally, some evidence for mode-specific effects in the product quantum yields near threshold is presented.     

Effect of laser pulse energies in laser induced breakdown spectroscopy in double-pulse configuration

In this paper, the effect of laser pulse energy on double-pulse laser induced breakdown spectroscopy signal is studied. In particular, the energy of the first pulse has been changed, while the second pulse energy is held fixed. A systematic study of the laser induced breakdown spectroscopy signal dependence on the interpulse delay is performed, and the results are compared with the ones obtained with a single laser pulse of energy corresponding to the sum of the two pulses. At the same time, the crater formed at the target surface is studied by video-confocal microscopy, and the variation in crater dimensions is correlated to the enhancement of the laser induced breakdown spectroscopy signal. The results obtained are consistent with the interpretation of the double-pulse laser induced breakdown spectroscopy signal enhancement in terms of the changes in ambient gas pressure produced by the shock wave induced by the first laser pulse.     

Fast analysis of wood preservers using laser induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is used for the investigation of wood preservers in timber and in furniture. Both experiments in laboratory and practical applications in recycling facilities and on a building site prove the new possibilities for the fast detection of harmful agents in wood. A commercial system was developed for mobile laser-plasma-analysis as well as for industrial use in sorting plants. The universal measuring principle in combination with an Echelle optics permits real simultaneous multi-element-analysis in the range of 200–780 nm with a resolution of a few picometers. It enables the user to detect main and trace elements in wood within a few seconds, nearly independent of the matrix, knowing that different kinds of wood show an equal elemental composition. Sample preparation is not required. The quantitative analysis of inorganic wood preservers (containing, e.g. Cu, Cr, B, As, Pb, Hg) has been performed exactly using carbon as reference element. It can be shown that the detection limits for heavy metals in wood are in the ppm-range. Additional information is given concerning the quantitative analysis. Statistical data, e.g. the standard deviation (S.D.), were determined and calibration curves were used for each particular element. A comparison between ICP-AES and LIBS is given using depth profile correction factors regarding the different penetration depths with respect to the different volumes in wood analyzed by both analytical methods.     

Recognition of archeological materials underwater by laser induced breakdown spectroscopy

The detection of different materials immersed in seawater has been studied by means of Laser Induced Breakdown Spectroscopy. The plasma emission was produced by a Q-Switched Nd:YAG laser operated at 1064 nm in a dual pulse mode. Different classes of materials potentially found in the undersea archaeological parks, such as iron, copper-based alloys, precious alloys, marble and wood have been examined. Data acquisition and processing were optimized for better signal control and in order to improve the detection threshold. In all the examined cases but wood, qualitative analysis was successful and allowed for the material recognition. The spectral features necessary to clearly distinguish marble materials from calcareous rocks have been also established. It was found that these characteristic spectral intervals could be also used for the recognition of sedimentary layers deposited on the underwater findings. Quantitative chemical analysis was also performed on submerged bronze samples, after generating calibration curves with standards of similar matrix composition.     

Preliminary evaluation of laser induced breakdown spectroscopy for slurry samples

Laser-induced breakdown spectroscopy (LIBS) was applied to the analysis of simulant slurry samples used in the vitrification process of liquid radioactive wastes. A spectroscopic analysis was performed by two different detection systems: Czerny-Turner spectrometer coupled with intensified diode array detector (IDAD) and an Echelle spectrometer with intensified charge coupled device (ICCD). For the Czerny-Turner detection system, the normalized intensity method, which is the normalization of the atomic emission intensity by the released whole plasma emission area intensity, was employed to improve the reproducibility of LIBS signals. The Echelle detection system showed a high efficiency in simultaneous multi-element detection and determination of the physical quantities of the simulant.     

Investigation of polarization effects for nanosecond laser-induced breakdown spectroscopy

The spectral and temporal polarization dependencies of nanosecond laser-induced plasmas are explored for analysis of gaseous and solid samples using various experimental configurations. Plasma emission measurements were resolved into vertical and horizontal polarization components, and the ratio of the two polarization-resolved measurements was calculated for each sample and configuration. For the solid target, measurements were recorded with the sample oriented both normal to the incident laser beam as well as at oblique angles of incidence. The results for the breakdown of a pure, nitrogen gaseous sample revealed no degree of polarization in either the continuum or atomic emission, with the ratios of the horizontally-to-vertically resolved plasma emission showing values equal to unity when resolved both temporally and spectrally. The analysis of both copper and steel solid samples also showed no polarization dependency in the spectral and temporal data when the laser was incidentally normal to the sample surface. For oblique angles of incidence, some polarization (< 10%) was observed within the first tens of nanoseconds of plasma lifetime. The polarization was manifested as a slight reduction in the horizontal component of plasma emission, but significantly, the observed polarization was found to be spectrally flat, with no difference observed between continuum and atomic emission features. The small polarization effect was found to diminish with plasma residence time, effectively vanishing by about 1 μs following breakdown. The transient polarization is hypothesized to arise from reflection effects (i.e. Fresnel reflectivity) between the plasma light and the solid target surface present with oblique angles of incidence for reflected light, with temporal effects due to the dynamic nature of the plasma development and plasma–surface interactions. Overall, no evidence was found to support any inherent anisotropy or polarization specific to the plasma continuum or the atomic emission for the transitions studied.     

Double pulse laser ablation and laser induced breakdown spectroscopy: A modeling investigation

A numerical model, describing laser–solid interaction (i.e., metal target heating, melting and vaporization), vapor plume expansion, plasma formation and laser–plasma interaction, is applied to describe the effects of double pulse (DP) laser ablation and laser induced breakdown spectroscopy (LIBS). Because the model is limited to plume expansion times in the order of (a few) 100 ns in order to produce realistic results, the interpulse delay times are varied between 10 and 100 ns, and the results are compared to the behavior of a single pulse (SP) with the same total energy. It is found that the surface temperature at the maximum is a bit lower in the DP configuration, because of the lower irradiance of one laser pulse, but it remains high during a longer time, because it rises again upon the second laser pulse. Consequently, the target remains for a longer time in the molten state, which suggests that laser ablation in the DP configuration might be more efficient, through the mechanism of splashing of the molten target. The total laser absorption in the plasma is also calculated to be clearly lower in the DP configuration, so that more laser energy can reach the target and give rise to laser ablation. Finally, it is observed that the plume expansion dynamics is characterized by two separate waves, the first one originating from the first laser pulse, and the second (higher) one as a result of the second laser pulse. Initially, the plasma temperature and electron density are somewhat lower than in the SP case, due to the lower energy of one laser pulse. However, they rise again upon the second laser pulse, and after 200 ns, they are therefore somewhat higher than in the SP case. This is especially true for the longer interpulse delay times, and it is expected that these trends will be continued for longer delay times in the μs-range, which are most typically used in DP LIBS, resulting in more intense emission intensities.     

Compositional characterization of encrustation on marble with laser induced breakdown spectroscopy

This study deals with the analysis of encrustation on marble by laser induced breakdown spectroscopy (LIBS), with the aim to obtain quick in-situ information on the in-depth profiling of the encrustation before advancing to conservation treatments. The encrustation examined is formed on exposed marble: (a) as products of the interaction between the stone surface and atmospheric pollutants (dendritic black and thin black encrustation, of approximately 300 and 200 μm thicknesses, respectively); (b) from deposition of soil–dust on marble surfaces (soil–dust crust, 300 μm thick); and (c) from treatments conducted in the past for aesthetic and/or protective purposes (patina samples, 300 μm thick). The crusts examined are multilayer encrustations on un-weathered marble, as revealed by studying cross sections with optical microscopy and scanning electron microscopy coupled with energy dispersive X-ray analysis. The elemental LIBS profiles of black encrustation based on relative spectral line intensity values show that the Fe, Si, Al and Ti content relative to Ca content decrease significantly with depth, expressing, thus, contamination decreasing within the alteration layers, since these elements originate from atmospheric pollution and deposition. In the cases of soil–dust encrustation and patina samples Si I and Al I emissions identified throughout the analyzed crust, indicate deposition of soil–dust and remnants of previous treatments, respectively. Therefore, LIBS, a micro-destructive technique can be used as an autonomous in-situ diagnostic technique to obtain in-depth elemental profiling of encrustation even in cases of highly in-homogeneous layered crusts, such those of un-weathered Pentelic marble.