Quantitative elemental determination in water and oil by laser induced breakdown spectroscopy

Improving the Laser-Induced Breakdown Spectroscopy for Highly Efficient Trace Measurement of Hazardous Components in Waste Oils

Improper disposal of waste oils containing hazardous components damages the environment and the ecosystem, posing a significant threat to human life and health. Here, we present a method of discharge-assisted laser-induced breakdown spectroscopy combined with filter paper sampling (DA-LIBS-FPS) to detect hazardous components and trace the source of polluting elements. DA-LIBS-FPS significantly enhances spectral intensity by 1-2 orders of magnitude due to the discharge energy deposition into the laser-induced plasma and the highly efficient laser-sample interaction on the filter paper, when compared to single-pulse LIBS with silica wafer sampling (SP-LIBS-SWS). Additionally, the signal-to-noise ratio and the signal-to-background ratio are both significantly increased. Resultantly, indiscernible lines, such as CN and Cr I, are well distinguished. In contrast with DA-LIBS combined with silica wafer sampling (DA-LIBS-SWS), the spectral signal fluctuations in DA-LIBS-FPS are reduced by up to 33%, because of the homogeneous distribution of the oil layer on the filter paper in FPS. Further examination indicates that the limit of detection for Ba is reduced from a several parts per million level in SP-LIBS-SWS to a dozens of parts per billion level in DA-LIBS-FPS, i.e., nearly 2 orders of magnitude enhancement in analysis sensitivity. This improvement is attributed to the extended plasma lifespan in DA-LIBS and the increasing electron density and plasma temperature in FPS. DA-LIBS-FPS provides a low-cost, handy, rapid, and highly sensitive avenue to analyze the hazardous components in waste oils with great potential in environmental and ecological monitoring.

Metal micro/nanostructure enhanced laser-induced breakdown spectroscopy

This study used a femtosecond laser to ablate a Cu sample, forming a micro/nanostructural layer on the surface. And the effect of this structural layer on nanosecond laser-induced breakdown spectroscopy (LIBS) was discussed. Firstly, the effect of the micro/nanostructural layer on the intensity of laser-induced Cu plasma spectra was investigated. The micro/nanostructure could significantly enhance the spectral intensity of the Cu plasma by 82.5 times at 13.3 mJ laser energy. Secondly, the Cu plasma temperature and electron density were calculated. The micro/nanostructures could significantly increase Cu plasma temperature and electron density. Finally, the effect of micro/nanostructure surface on the spectral intensities of Pb and Cr elements in water was investigated for LIBS analysis. It was found that the detection limit of Pb and Cr trace metal elements in water was 1.85 ng/mL and 0.51 ng/mL at a lower laser energy (13.3 mJ), which was significantly better than other LIBS methods reported so far. The results show that the micro/nanostructure enhanced LIBS is a more sensitive method for detecting trace metal elements in the water.

Sensing with Femtosecond Laser Filamentation

Femtosecond laser filamentation is a unique nonlinear optical phenomenon when high-power ultrafast laser propagation in all transparent optical media. During filamentation in the atmosphere, the ultrastrong field of 10¹³-10¹⁴ W/cm² with a large distance ranging from meter to kilometers can effectively ionize, break, and excite the molecules and fragments, resulting in characteristic fingerprint emissions, which provide a great opportunity for investigating strong-field molecules interaction in complicated environments, especially remote sensing. Additionally, the ultrastrong intensity inside the filament can damage almost all the detectors and ignite various intricate higher order nonlinear optical effects. These extreme physical conditions and complicated phenomena make the sensing and controlling of filamentation challenging. This paper mainly focuses on recent research advances in sensing with femtosecond laser filamentation, including fundamental physics, sensing and manipulating methods, typical filament-based sensing techniques and application scenarios, opportunities, and challenges toward the filament-based remote sensing under different complicated conditions.

Review of Element Analysis of Industrial Materials by In-Line Laser—Induced Breakdown Spectroscopy (LIBS)

Laser-induced breakdown spectroscopy (LIBS) is a rapidly developing technique for chemical materials analysis. LIBS is applied for fundamental investigations, e.g., the laser plasma matter interaction, for element, molecule, and isotope analysis, and for various technical applications, e.g., minimal destructive materials inspection, the monitoring of production processes, and remote analysis of materials in hostile environment. In this review, we focus on the element analysis of industrial materials and the in-line chemical sensing in industrial production. After a brief introduction we discuss the optical emission of chemical elements in laser-induced plasma and the capability of LIBS for multi-element detection. An overview of the various classes of industrial materials analyzed by LIBS is given. This includes so-called Technology materials that are essential for the functionality of modern high-tech devices (smartphones, computers, cars, etc.). The LIBS technique enables unique applications for rapid element analysis under harsh conditions where other techniques are not available. We present several examples of LIBS-based sensors that are applied in-line and at-line of industrial production processes.

Lead of detection in rhododendron leaves using laser-induced breakdown spectroscopy assisted by laser-induced fluorescence

Laser-induced breakdown spectroscopy assisted by laser-induced fluorescence (LIBS-LIF) was applied to determine lead (Pb) in rhododendron leaves. Rhododendron leaves are essential types of herbal materials. Rapid detection of lead in rhododendron leaves is urgent for drug monitoring. In this paper, the powder method and solid-liquid-solid transformation (SLST) method were employed as sample preparation. The results showed that the signal of the Pb I 405.78 nm line was substantially enhanced. For samples A, B and C, the LoD values of 0.054 mg/kg, 0.059 mg/kg, 0.062 mg/kg were achieved with R² values of 0.997, 0.996, 0.997 via the SLST approach, whose sensitivity and accuracy was slightly higher compared to the powder method. The RMSECV values of both methods were minimal, ranging from 0.538 to 2.117 mg/kg. Lead content detected by LIBS-LIF in the three samples was between 1.5 and 2.8 mg/kg. The results of lead were validated by inductively coupled plasma optical emission spectrometry (ICP-OES). This research provided us with new technology for the rapid and accurate determination of Pb element in rhododendron leaves.

Heavy Metals Detection in Zeolites Using the LIBS Method

In this study, a possibility of laser-induced breakdown spectroscopy (LIBS) for the analysis of zeolites containing copper, chromium, cobalt, cadmium, and lead in the concentration range of 0.05–0.5 wt.% is discussed. For the LIBS analysis, microporous ammonium form of Y zeolite with the silicon to aluminum molar ratio of 2.49 was selected. Zeolites, in the form of pressed pellets, were prepared by volume impregnation from the water solution using Co(CH3COO)2.4H2O, CuSO4.5H20, K2Cr2O7, PbNO3, and CdCl2 to form a sample with different amounts of heavy metals—Co, Cu, Cr, Pb, and Cd. Several spectral lines of the mentioned elements were selected to be fitted to obtain integral line intensity. To prevent the influence of the self-absorption effect, non-resonant spectral lines were selected for the calibration curves construction in most cases. The calibration curves of all elements are observed to be linear with high regression coefficients. On the other hand, the limits of detection (LOD) were calculated according to the 3σ/S formula using the most intensive spectral lines of individual elements, which are 14.4 ppm for copper, 18.5 ppm for cobalt, 16.4 ppm for chromium, 190.7 ppm for cadmium, and 62.6 ppm for lead.

Laser-Induced Breakdown Spectroscopic (LIBS) Analysis of Trace Heavy Metals Enriched by Al2O3 Nanoparticles

We demonstrated a unique method for the detection of heavy metals, such as Ni, Cr, and Cd, at trace level in aqueous solutions by laser induced breakdown spectroscopy (LIBS) enriched by aluminum oxide (Al₂O₃) nanoparticles (NP) adsorption. Al₂O₃ NPs were used for the sample phase transformation and heavy metals pre-concentration because of its excellent adsorption capacity and sparse spectral lines. The influence of laser wavelength and laser irradiance on the signal intensity was investigated. With 45 mL solutions used for enrichment and adsorption, limits of detection obtained for Ni, Cr, and Cd were 9.61, 8.49, and 71.6 μg/L under 532 nm laser ablation, and 22.5, 20.4, and 83.8 μg/L under 1064 nm laser ablation, respectively. The relative standard deviations of all elements were about 12% or 13%. Moreover, Al₂O₃ NPs adsorption enrichment of target elements was verified and the detection sensitivity was improved by increasing the amount of sample solutions.

Rapid qualitative and quantitative analysis of elemental composition of Cu(In, Ga)Se2 thin films using laser-induced breakdown spectroscopy

The composition of Cu, In, Ga, and Se constituting the Cu(In,Ga)Se₂ (CIGS) layer is important for the performance of the thin film. Laser-induced breakdown spectroscopy (LIBS) is very useful in quantitative analysis of elemental composition. In this paper, detection parameters of LIBS were optimized, and the CIGS thin films deposited at different sputtering powers were detected. LIBS results showed that the intensity ratio (Ga/(ln+Ga)) of the analytical spectral line of CIGS film increased initially then reduced with an increase of the sputtering power, and the evolution was consistent with optical bandgaps calculated from the transmission spectra. The intensity ratios of Ga/(ln+Ga) and Cu/(ln+Ga) detected were very highly correlated corresponding to the value obtained from energy dispersive x-ray spectroscopy. All results indicate that it is available and feasible of LIBS to fabricate high-performance CIGS thin film using the one-step radio frequency magnetron sputtering method.

Potential use of surface-assisted LIBS for determination of strontium in wines

Laser-induced breakdown spectroscopy (LIBS) is a well-established technique for elemental analysis and has been widely used for qualitative and quantitative analysis of different solid samples. LIBS is also well-known for not requiring sample preparation, but the analysis of liquids is actually a great challenge. In the present work, a novel approach of elemental analysis of liquids with an organic matrix has been performed, to the best of our knowledge, making a liquid-to-solid matrix conversion by drying wine samples on aluminum and silicon wafers, which have demonstrated an increase in the analytical performance of LIBS. A red wine from Slovakia (not blended with any other variety or wine from other regions or adulterants) was prepared according to the procedure consisting of drying 2 ml of wine dropped on a solid wafer having a flat surface area of about 25  cm². Surface-assisted LIBS in combination with the conversion of liquid into solid avoids the difficulties and limitations of working with liquid samples by LIBS, improving the limit of detection (LOD), repeatability, and sensitivity. The quantification of strontium (Sr) has been realized by addition of the known concentration of SrCl₂·6H₂O in wine before the drying process. Sr is an important element among those usually used as markers for identification of the soils on which the vines grow. Two ionic (407.771 nm and 421.552 nm) and two neutral (460.733 nm and 481.188 nm) Sr lines were used to plot the calibration curves in order to study the LODs and the matrix effects for the analysis of Sr in the tested wines and for different wafer materials. This direct surface-assisted LIBS measuring method has been successfully applied for the determination of Sr in a red wine sample from Slovakia, and the obtained results with two kinds of substrates (Al and Si) were compared. Finally, a validation sample has been employed to test the accuracy of the established calibration curves.

Laser Spectroscopic Sensors for the Development of Anthropomorphic Robot Sensitivity

The development of underwater robotics sensitivity, which is based on the sensors of laser spectroscopy methods, have been discussed. The ways to improve Laser Induced Fluorescence (LIF) and Laser Induced Breakdown Spectroscopy (LIBS) methods were investigated in order to develop and create laser sensitivity for underwater robotics. A brief overview is done in the article, where LIF and LIBS spectroscopy in underwater robotics are used as spectroscopy sensors in order to investigate underwater environments by means of underwater vehicles. Limit of Detection (LoD) of oil and oil product solutions in the seawater have been detected by means of nanosecond and femtosecond spectroscopy LIF. All results, which had been received by laser pulses of different duration, were compared. The same experiments have been provided in order to measure concentrations of elements in the seawater and solutions by the LIBS method. It was discovered that the LoD of a group of elements was reduced when the femtosecond LIBS was used. Anthropomorphic complexes were under discussion in order to adopt laser spectroscopy sensors for underwater environments. The submersible module, which was constructed to investigate and examine laser spectroscopy sensors, has been described.

Laser-induced-breakdown-spectroscopy-based detection of metal particles released into the air during combustion of solid propellants

Numerous metals and metal compounds are often added to propellants and explosives to tailor their properties such as heat release rate and specific impulse. When these materials combust, these metals can be released into the air, causing adverse health effects such as pulmonary and cardiovascular disease, particulate-matter-induced allergies, and cancer. Hence, robust, field-deployable methods are needed to detect and quantify these suspended metallic particles in air, identify their sources, and develop mitigation strategies. Laser-induced breakdown spectroscopy (LIBS) is a technique for elemental detection, commonly used on solids and liquids. In this study, we explored nanosecond-duration LIBS for detecting airborne metals during reactions of solid propellant strands, resulting from additives of aluminum (Al), copper, lead, lead stearate, and mercury chloride. Using the second harmonic of a 10-ns-duration 10-Hz, Nd:YAG laser, plasma was generated in the gas-phase exhaust plume of burning propellant strands containing the target metals. Under the current experimental conditions, the ns-LIBS scheme was capable of detecting Al at concentrations of 5%, 10%, and 16% by weight in the propellant strand. As the weight percentage increased, the LIBS signal was detected by more laser shots, up to a point where the system transition from being nonhomogeneous to a more-uniform distribution of particles. Further measurements and increased understanding of the reacting flow field are necessary to quantify the effects of other metal additives besides Al.

Qualitative and quantitative analysis of an additive element in metal oxide nanometer film using laser induced breakdown spectroscopy

The photoelectric performance of metal ion-doped TiO₂ film will be improved with the changing of the compositions and concentrations of additive elements. In this work, the TiO₂ films doped with different Sn concentrations were obtained with the hydrothermal method. Qualitative and quantitative analysis of the Sn element in TiO₂ film was achieved with laser induced breakdown spectroscopy (LIBS) with the calibration curves plotted accordingly. The photoelectric characteristics of TiO₂ films doped with different Sn content were observed with UV visible absorption spectra and J-V curves. All results showed that Sn doping could improve the optical absorption to be red-shifted and advance the photoelectric properties of the TiO₂ films. We had obtained that when the concentration of Sn doping in TiO₂ films was 11.89  mmol/L, which was calculated by the LIBS calibration curves, the current density of the film was the largest, which indicated the best photoelectric performance. It indicated that LIBS was a potential and feasible measured method, which was applied to qualitative and quantitative analysis of the additive element in metal oxide nanometer film.

Sample Preparation for Repeated Measurements on a Single Liquid Droplet Using Laser-Induced Breakdown Spectroscopy

We studied changes in laser-induced breakdown spectroscopy (LIBS) signal intensity with the thickness of a liquid layer placed on a solid substrate, where an easily evaporating methanol sample was used. For a certain optimal liquid film thickness we obtained a manifold increase of the LIBS signal from methanol. Progressive liquid film thinning leads to a reduction and a successive disappearance of laser-induced splashes; the latter condition drastically reduces the sample consumption and allows measurements to be repeated many times on a single liquid droplet. In following, we developed two methods for actively controlled deformation, i.e., thinning of a liquid droplet (volume ∼10 µl) prior to its sampling by LIBS. Control of the droplet's height was achieved on a Si-SiO₂ wafer substrate by electro-wetting in the case of water solutions or by target rotation in the case of viscous liquids. The chosen substrate also has the advantages of low cost, easy manipulation, and very high purity, thus minimizing interference with analytes. Through the droplet deformation, in a single-pulse excitation at moderate laser energy (70 mJ), we clearly detected Fe and Mn in peanut oil, which represent trace elements in edible oils (∼ 1 part per billion), according to results published in the literature.

Investigation of the Matrix Effect on the Accuracy of Quantitative Analysis of Trace Metals in Liquids Using Laser-Induced Breakdown Spectroscopy with Solid Substrates

The detection limit of trace metals in liquids has been improved greatly by laser-induced breakdown spectroscopy (LIBS) using solid substrate. A paper substrate and a metallic substrate were used as a solid substrate for the detection of trace metals in aqueous solutions and viscous liquids (lubricating oils) respectively. The matrix effect on quantitative analysis of trace metals in two types of liquids was investigated. For trace metals in aqueous solutions using paper substrate, the calibration curves established for pure solutions and mixed solutions samples presented large variation on both the slope and the intercept for the Cu, Cd, and Cr. The matrix effects among the different elements in mixed solutions were observed. However, good agreement was obtained between the measured and known values in real wastewater. For trace metals in lubricating oils, the matrix effect between the different oils is relatively small and reasonably negligible under the conditions of our experiment. A universal calibration curve can be established for trace metals in different types of oils. The two approaches are verified that it is possible to develop a feasible and sensitive method with accuracy results for rapid detection of trace metals in industrial wastewater and viscous liquids by laser-induced breakdown spectroscopy.

Laser-induced breakdown spectroscopy of liquid solutions: a comparative study on the forms of liquid surface and liquid aerosol

Liquid surface and liquid aerosol as the traditional liquid forms for laser-induced breakdown spectroscopy (LIBS) and inductively coupled plasma (ICP), respectively, have been used to analyze chromium (Cr) and cadmium (Cd) elements using LIBS in a liquid solution. The spectral differences, the effects of laser energy and laser frequency, the accumulated number of laser pulses, gate delay time, and the quantitative analyses for a liquid surface and a liquid aerosol were compared. The results showed that the liquid surface demonstrated a lower plasma threshold, higher optical emission intensity, and higher single-to-noise ratio. Moreover, the relative standard deviations (RSDs) of the intensities of the liquid aerosol are better than those of the liquid surface. Furthermore, the results of the quantitative analyses of Cr I 357.86 nm and Cd I 361.05 nm of the liquid surface are close to those of the liquid aerosol. The limit of detections of Cr and Cd of the liquid surface were 2.764 and 86.869  μg/mL, which were close to those of liquid aerosol, 2.847  μg/mL of Cr and 97.635  μg/mL of Cd. For both the liquid surface and liquid aerosol, the coefficient of determination R² of the calibration curve for Cr and Cd were above 0.99, and the average RSDs of Cr and Cd of the liquid surface were 0.027 and 0.054, which were similar to the 0.020 of Cr and 0.042 of Cd of the liquid aerosol. These results suggest that both the liquid surface and aerosol have similar detection abilities for water quality monitoring.

Sensitive determinations of Cu, Pb, Cd, and Cr elements in aqueous solutions using chemical replacement combined with surface-enhanced laser-induced breakdown spectroscopy

In this study, chemical replacement combined with surface-enhanced laser-induced breakdown spectroscopy (CR-SENLIBS) was for the first time applied to improve the detection sensitivities of trace heavy metal elements in aqueous solutions. Utilizing chemical replacement effect, heavy metal ions in aqueous solution were enriched on the magnesium alloy surface as a solid replacement layer through reacting with the high chemical activity metallic magnesium (Mg) within 1 minute. Unitary and mixed solutions with Cu, Pb, Cd, and Cr elements were prepared to construct calibration curves, respectively. The CR-SENLIBS showed a much better detection sensitivity and accuracy for both unitary and mixed solutions. The coefficients of determination R² of the calibration curves were above 0.96, and the LoDs were of the same order of magnitude, i.e., in the range of 0.016-0.386 μg/mL for the unitary solution, and in the range of 0.025-0.420 μg/mL for the mixed solution. These results show that CR-SENLIBS is a feasible method for improving the detection sensitivity of trace element in liquid sample, which definitely provides a way for wider application of LIBS in water quality monitoring.

Optimization of liquid jet system for laser-induced breakdown spectroscopy analysis

A complex optimization of geometrical and temporal parameters of a jet system (developed in Laser-induced breakdown spectroscopy (LIBS) laboratory of Brno University of Technology) for direct elemental analysis of samples in a liquid state of matter using LIBS was carried out. First, the peristaltic pump was synchronized with the flashlamp of the ablation laser, which reduced variation of the ablated sample amount. Also, the fluctuation of the laser ray angle incident on the jet surface was diminished. Such synchronization reduced signal standard deviations and thus increased repeatability of the measurements. Then, laser energy and distance of the focusing lens from the sample were optimized. The gate delay time and the gate width were optimized for single pulse (SP) experiments; the gate delay time and the inter-pulse delay were optimized for the use of double pulse (DP) variant. Results were assessed according to the highest signal to noise ratios and the lowest relative standard deviations of the signal. The sensitivity of the single pulse and the double pulse LIBS for the detection of heavy metals traces, copper (Cu i at 324.754 nm) and lead (Pb i at 405.781 nm), in aqueous solution of copper (ii) sulfate and lead (ii) acetate, was estimated in terms of limits of detection (LODs). As a result, sensitivity improvement of DP LIBS system was observed, the LOD of Cu obtained with DP was calculated 40% lower than LOD gained from SP technique.

Dehydrated Carbon Coupled with Laser-Induced Breakdown Spectrometry (LIBS) for the Determination of Heavy Metals in Solutions

In this article, a novel and alternative method of laser-induced breakdown spectroscopy (LIBS) analysis for liquid sample is proposed, which involves the removal of metal ions from a liquid to a solid substrate using a cost-efficient adsorbent, dehydrated carbon, obtained using a dehydration reaction. Using this new technique, researchers can detect trace metal ions in solutions qualitatively and quantitatively, and the drawbacks of performing liquid analysis using LIBS can be avoided because the analysis is performed on a solid surface. To achieve better performance using this technique, we considered parameters potentially influencing both adsorption performance and LIBS analysis. The calibration curves were evaluated, and the limits of detection obtained for Cu(2+), Pb(2+), and Cr(3+) were 0.77, 0.065, and 0.46 mg/L, respectively, which are better than those in the previous studies. In addition, compared to other absorbents, the adsorbent used in this technique is much cheaper in cost, easier to obtain, and has fewer or no other elements other than C, H, and O that could result in spectral interference during analysis. We also used the recommended method to analyze spiked samples, obtaining satisfactory results. Thus, this new technique is helpful and promising for use in wastewater analysis and management.

Laser-induced breakdown spectroscopy application in environmental monitoring of water quality: a review

Water quality monitoring is a critical part of environmental management and protection, and to be able to qualitatively and quantitatively determine contamination and impurity levels in water is especially important. Compared to the currently available water quality monitoring methods and techniques, laser-induced breakdown spectroscopy (LIBS) has several advantages, including no need for sample pre-preparation, fast and easy operation, and chemical free during the process. Therefore, it is of great importance to understand the fundamentals of aqueous LIBS analysis and effectively apply this technique to environmental monitoring. This article reviews the research conducted on LIBS analysis for liquid samples, and the article content includes LIBS theory, history and applications, quantitative analysis of metallic species in liquids, LIBS signal enhancement methods and data processing, characteristics of plasma generated by laser in water, and the factors affecting accuracy of analysis results. Although there have been many research works focusing on aqueous LIBS analysis, detection limit and stability of this technique still need to be improved to satisfy the requirements of environmental monitoring standard. In addition, determination of nonmetallic species in liquid by LIBS is equally important and needs immediate attention from the community. This comprehensive review will assist the readers to better understand the aqueous LIBS technique and help to identify current research needs for environmental monitoring of water quality.

Accuracy improvement of quantitative analysis in laser-induced breakdown spectroscopy using modified wavelet transform

A modified algorithm of background removal based on wavelet transform was developed for spectrum correction in laser-induced breakdown spectroscopy (LIBS). The optimal type of wavelet function, decomposition level and scaling factor γ were determined by the root-mean-square error of calibration (RMSEC) of the univariate regression model of the analysis element, which is considered as the optimization criteria. After background removal by this modified algorithm with RMSEC, the root-mean-square error of cross-validation (RMSECV) and the average relative error (ARE) criteria, the accuracy of quantitative analysis on chromium (Cr), vanadium (V), cuprum (Cu), and manganese (Mn) in the low alloy steel was all improved significantly. The results demonstrated that the algorithm developed is an effective pretreatment method in LIBS to significantly improve the accuracy in the quantitative analysis.

Quantitative determination of manganese in aqueous solutions and seawater by laser-induced breakdown spectroscopy (LIBS) using paper substrates

The detection of manganese (Mn) in industrial wastewater and seawater plays an important role in pollution monitoring and the investigation of geochemical and biological processes in the ocean. An approach has been introduced in this work to improve the detection sensitivity of Mn in liquids by laser-induced breakdown spectroscopy with a filter paper as solid substrate. The calibration curves of Mn in aqueous solutions were obtained with the detection of a Czerny-Turner spectrometer and an echelle spectrometer, respectively. The results showed that the Czerny-Turner spectrometer equipped with an intensified charge-coupled device (ICCD) had a more sensitive detection of Mn in aqueous solution with this approach. The limit of detection (LOD) for Mn was down to 0.11 mg/L with laser pulse energy of 90 mJ. With the same approach, the compact echelle spectrometer equipped with an ICCD was used to verify the feasibility for rapid onsite detection. The calibration curves for Mn in simulated industrial wastewater and seawater were constructed to calculate relevant LODs. The LODs of Mn were 2.78 mg/L in mixed solutions and 2.73 mg/L in seawater by calculation. Both the calibration curves and LODs were affected slightly by the matrix effect in the experiment. In order to assess the accuracy, a mixed solution including Mn, Cr, Cd, and Cu with known concentrations was determined, and good agreement between the measured and real values were achieved. It demonstrated that this approach has significant potential for rapid onsite detection of Mn and other metal elements in industrial wastewater and seawater.

A comparative study of pressure-dependent emission characteristics in different gas plasmas induced by nanosecond and picosecond neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers

An experimental study has been performed on the pressure-dependent plasma emission intensities in Ar, He, and N2 surrounding gases with the plasma induced by either nanosecond (ns) or picosecond (ps) yttrium aluminum garnet laser. The study focused on emission lines of light elements such as H, C, O, and a moderately heavy element of Ca from an agate target. The result shows widely different pressure effects among the different emission lines, which further vary with the surrounding gases used and also with the different ablation laser employed. It was found that most of the maximum emission intensities can be achieved in Ar gas plasma generated by ps laser at low gas pressure of around 5 Torr. This experimental condition is particularly useful for spectrochemical analysis of light elements such as H, C, and O, which are known to suffer from intensity diminution at higher gas pressures. Further measurements of the spatial distribution and time profiles of the emission intensities of H I 656.2 nm and Ca II 396.8 nm reveal the similar role of shock wave excitation for the emission in both ns and ps laser-induced plasmas, while an additional early spike is observed in the plasma generated by the ps laser. The suggested preference of Ar surrounding gas and ps laser was further demonstrated by outperforming the ns laser in their applications to depth profiling of the H emission intensity and offering the prospect for the development of three-dimensional analysis of a light element such as H and C.

Optimization of chemical and instrumental parameters in hydride generation laser-induced breakdown spectrometry for the determination of arsenic, antimony, lead and germanium in aqueous samples

A laser induced breakdown spectrometry hyphenated with on-line continuous flow hydride generation sample introduction system, HG-LIBS, has been used for the determination of arsenic, antimony, lead and germanium in aqueous environments. Optimum chemical and instrumental parameters governing chemical hydride generation, laser plasma formation and detection were investigated for each element under argon and nitrogen atmosphere. Arsenic, antimony and germanium have presented strong enhancement in signal strength under argon atmosphere while lead has shown no sensitivity to ambient gas type. Detection limits of 1.1 mg L(-1), 1.0 mg L(-1), 1.3 mg L(-1) and 0.2 mg L(-1) were obtained for As, Sb, Pb and Ge, respectively. Up to 77 times enhancement in detection limit of Pb were obtained, compared to the result obtained from the direct analysis of liquids by LIBS. Applicability of the technique to real water samples was tested through spiking experiments and recoveries higher than 80% were obtained. Results demonstrate that, HG-LIBS approach is suitable for quantitative analysis of toxic elements and sufficiently fast for real time continuous monitoring in aqueous environments.

Laser-induced breakdown spectroscopy (LIBS) of heavy metal ions at the sub-parts per million level in water

We report a simple sub parts per million (sub-ppm) detection method for heavy metals in water by laser-induced breakdown spectroscopy (LIBS). Filter papers were used as the substrates for both transforming aqueous solutions to solid samples and for pre-concentrating dissolved heavy metal ions. The amount of sample uptake was 1.2 g by soaking a filter paper. This provides limit-of-detection (LOD) values of 2.7 and 0.36 ppm for Pb and Cr, respectively. The LODs could be improved remarkably by pre-concentrating the heavy metal ions. When a 40 g sample solution was evaporated on a filter paper, the LODs of 75 and 18 parts per billion (ppb) were obtained for Pb and Cr, respectively. Moreover, by either increasing the evaporated amount of sample solution or applying an argon gas flow, further improvement of the LODs was found to be very promising. The LIBS spectra of tap water were recorded using the pre-concentration method and are discussed in comparison with the results from inductively coupled plasma atomic emission spectroscopy (ICP-AES). We could observe strong emission lines of Ca, Mg, K, Cu, and Sr in the tap water, of which concentrations were determined to be 6.3, 1.3, 1.1, 0.64, and 0.046 ppm, respectively, by ICP-AES. Our method shows promise as a fast, reliable, water-quality monitoring tool for heavy-metal concentrations as well as for hardness.

Laser-induced breakdown spectroscopy (LIBS), part II: review of instrumental and methodological approaches to material analysis and applications to different fields

The first part of this two-part review focused on the fundamental and diagnostics aspects of laser-induced plasmas, only touching briefly upon concepts such as sensitivity and detection limits and largely omitting any discussion of the vast panorama of the practical applications of the technique. Clearly a true LIBS community has emerged, which promises to quicken the pace of LIBS developments, applications, and implementations. With this second part, a more applied flavor is taken, and its intended goal is summarizing the current state-of-the-art of analytical LIBS, providing a contemporary snapshot of LIBS applications, and highlighting new directions in laser-induced breakdown spectroscopy, such as novel approaches, instrumental developments, and advanced use of chemometric tools. More specifically, we discuss instrumental and analytical approaches (e.g., double- and multi-pulse LIBS to improve the sensitivity), calibration-free approaches, hyphenated approaches in which techniques such as Raman and fluorescence are coupled with LIBS to increase sensitivity and information power, resonantly enhanced LIBS approaches, signal processing and optimization (e.g., signal-to-noise analysis), and finally applications. An attempt is made to provide an updated view of the role played by LIBS in the various fields, with emphasis on applications considered to be unique. We finally try to assess where LIBS is going as an analytical field, where in our opinion it should go, and what should still be done for consolidating the technique as a mature method of chemical analysis.

Highly sensitive analysis of boron and lithium in aqueous solution using dual-pulse laser-induced breakdown spectroscopy

We have applied a dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) to sensitively detect concentrations of boron and lithium in aqueous solution. Sequential laser pulses from two separate Q-switched Nd:YAG lasers at 532 nm wavelength have been employed to generate laser-induced plasma on a water jet. For achieving sensitive elemental detection, the optimal timing between two laser pulses was investigated. The optimum time delay between two laser pulses for the B atomic emission lines was found to be less than 3 μs and approximately 10 μs for the Li atomic emission line. Under these optimized conditions, the detection limit was attained in the range of 0.8 ppm for boron and 0.8 ppb for lithium. In particular, the sensitivity for detecting boron by excitation of laminar liquid jet was found to be excellent by nearly 2 orders of magnitude compared with 80 ppm reported in the literature. These sensitivities of laser-induced breakdown spectroscopy are very practical for the online elemental analysis of boric acid and lithium hydroxide serving as neutron absorber and pH controller in the primary coolant water of pressurized water reactors, respectively.

Monitoring and assessment of toxic metals in Gulf War oil spill contaminated soil using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was applied for the detection of toxic metals in oil spill contaminated soil (OSCS). The OSCS samples were collected from Khursania Saudi Arabia along the coast of Persian Gulf exposed to oil spills in 1991 Gulf war. Environmentally important elements like Aluminum Magnesium, Calcium, Chromium, Titanium, Strontium, Iron, Barium, Sodium, potassium, Zirconium and Vanadium from the contaminated soil have been detected. Optimal experimental conditions for analysis were investigated. The LIBS system was calibrated using standard samples containing these trace elements. The results obtained using Laser-Induced Breakdown Spectroscopy (LIBS) were compared with the results obtained using Inductively Coupled Plasma Emission Spectroscopy (ICP). The concentrations of some elements (Ba and Cr) were found higher than permissible safe limits. Health risks associated with exposure to such toxic elements are also discussed.

Laser-induced breakdown spectroscopy of bulk aqueous solutions at oceanic pressures: evaluation of key measurement parameters

The development of in situ chemical sensors is critical for present-day expeditionary oceanography and the new mode of ocean observing systems that we are entering. New sensors take a significant amount of time to develop; therefore, validation of techniques in the laboratory for use in the ocean environment is necessary. Laser-induced breakdown spectroscopy (LIBS) is a promising in situ technique for oceanography. Laboratory investigations on the feasibility of using LIBS to detect analytes in bulk liquids at oceanic pressures were carried out. LIBS was successfully used to detect dissolved Na, Mn, Ca, K, and Li at pressures up to 2.76 x 10(7) Pa. The effects of pressure, laser-pulse energy, interpulse delay, gate delay, temperature, and NaCl concentration on the LIBS signal were examined. An optimal range of laser-pulse energies was found to exist for analyte detection in bulk aqueous solutions at both low and high pressures. No pressure effect was seen on the emission intensity for Ca and Na, and an increase in emission intensity with increased pressure was seen for Mn. Using the dual-pulse technique for several analytes, a very short interpulse delay resulted in the greatest emission intensity. The presence of NaCl enhanced the emission intensity for Ca, but had no effect on peak intensity of Mn or K. Overall, increased pressure, the addition of NaCl to a solution, and temperature did not inhibit detection of analytes in solution and sometimes even enhanced the ability to detect the analytes. The results suggest that LIBS is a viable chemical sensing method for in situ analyte detection in high-pressure environments such as the deep ocean.

Laser-induced breakdown spectroscopy in analysis of Al3+ liquid droplets: On-line preconcentration by use of flow-injection manifold

Laser-induced breakdown spectroscopy (LIBS), combined with a flow-injection system, is demonstrated to analyze liquid droplets of aluminum salt, as generated with an electrospray ionization device. The spray needle also serves as the anode, through which the analyte solution is spread toward the other metal base as the cathode. Along the passage of the FI manifold, the Al-sample loading speed is controlled at 0.15 mL min(-1), restricted to the small diameter of the spray needle, and the loading volume amounts to 0.1 mL. The metal ion is retained in a cation-exchange resin microcolumn immobilized with Chromotrope 2B chelating agent, followed by elution with a 0.5 M HCl solution into LIBS. Upon laser irradiation at the preconcentrated liquid droplets, the time-resolved laser-induced breakdown (LIB) emission and plasma-induced current signals are acquired concurrently on a single-shot basis. The area under the LIB/current distribution increases in linear proportion as the concentration of the sample solution increases. The detection limit thus obtained can reach 1.5 mg L(-1), about an order of magnitude lower than those achieved previously using single-laser ablation without involvement of preconcentration. The linear dynamic range is more than two orders of magnitude.

Comparisons between LIBS and ICP/OES

In the framework of the development of new techniques, the ability of laser-induced breakdown spectroscopy (LIBS) to analyse remotely complex aqueous solutions was investigated. The jet configuration with a collimated gas stream was chosen because it appeared to be the most promising method for the LIBS probe, particularly in terms of sensitivity and repeatability. For emission collection, the echelle spectrometer offers a simultaneously recorded wavelength range from the UV to the near IR and is interesting for multielemental analysis for LIBS and also for inductively coupled plasma (ICP) optical emission spectroscopy (OES). The importance of parameters influencing the quantitative results of LIBS such as multispecies analysis, sheath gas, use of an internal standard and temporal parameters for analysis is described. LIBS quantitative data have been directly compared with results from the more standard ICP/OES technique.

Resonance fluorescence spectroscopy in laser-induced cavitation bubbles

Laser-induced breakdown spectroscopy (LIBS) in liquids using a double-pulse Q-switched Nd:YAG laser system has provided reliable results that give trace detection limits in water. Resonant laser excitation has been added to enhance detection sensitivity. A primary laser pulse (at 532 nm), transmitted via an optical fiber, induces a cavitation bubble and shockwave at a target immersed in a 10 mg l(-1)-100 mg l(-1) indium (In) water suspension. The low-pressure rear of the shockwave induces bubble expansion and a resulting reduction in cavity pressure as it extends away from the target. Shortly before the maximum diameter is expected, a secondary laser pulse (also at 532 nm) is fed into the bubble in order to reduce quenching processes. The plasma field generated is then resonantly excited by a fiber-guided dye laser beam to increase detection selectivity. The resulting resonance fluorescence emission is optically detected and processed by an intensified optical multichannel analyzer system.

Elemental analysis of urinary calculi by laser induced plasma spectroscopy

Laser induced plasma spectroscopy (LIPS) has been applied to analyse and identify elemental constituents of urinary calculi. Measurements on seven different urinary stone samples were conducted and the concentrations of some key elemental species were estimated. The elements detected with the present system were: Calcium, Magnesium, Sodium, Samarium, Potassium and Lead. Absolute concentrations of the species were derived from pre-calibration of the system for each element. Their concentrations were found to be widely different in different samples. It was observed that the samples containing a significant amount of lead have large proportion of calcium. It has been established that LIPS would allow real time clinic measurements of elemental contents and the concentrations in the biomaterials without sample preparation. The technique has the potential for routine clinic applications in urological disorder diagnosis.

Temporal dependence of the enhancement of material removal in femtosecond-nanosecond dual-pulse laser-induced breakdown spectroscopy

Despite the large neutral atomic and ionic emission enhancements that have been noted in collinear and orthogonal dual-pulse laser-induced breakdown spectroscopy, the source or sources of these significant signal and signal-to-noise ratio improvements have yet to be explained. In the research reported herein, the combination of a femtosecond preablative air spark and a nanosecond ablative pulse yields eightfold and tenfold material removal improvement for brass and aluminum, respectively, but neutral atomic emission is enhanced by only a factor of 3-4. Additionally, temporal correlation between enhancement of material removal and of atomic emission is quite poor, suggesting that the atomic-emission enhancements noted in the femtosecond-nanosecond pulse configuration result in large part from some source other than simple improvement in material removal.

Analysis of water ice and water ice/soil mixtures using laser-induced breakdown spectroscopy: application to Mars polar exploration

Recently, laser-induced breakdown spectroscopy (LIBS) has been developed for the elemental analysis of geological samples for application to space exploration. There is also interest in using the technique for the analysis of water ice and ice/dust mixtures located at the Mars polar regions. The application is a compact instrument for a lander or rover to the Martian poles to interrogate stratified layers of ice and dusts that contain a record of past geologic history, believed to date back several million years. Here we present results of a study of the use of LIBS for the analysis of water ice and ice/dust mixtures in situ and at short stand-off distances (< 6.5 m) using experimental parameters appropriate for a compact instrument. Characteristics of LIBS spectra of water ice, ice/soil mixtures, element detection limits, and the ability to ablate through ice samples to monitor subsurface dust deposits are discussed.

Effects of sample temperature in femtosecond single-pulse laser-induced breakdown spectroscopy

As much as tenfold atomic emission enhancements have been observed in experiments combining nanosecond (ns) and femtosecond (fs) laser pulses in an orthogonal dual-pulse configuration for laser-induced breakdown spectroscopy (ns-fs orthogonal dual-pulse LIBS). In the examination of one of several potential sources of these atomic emission enhancements (sample heating by a ns air spark), minor reductions in atomic emission and as much as 15-fold improvements in mass removal have been observed for fs single-pulse LIBS of heated brass and aluminum samples. These results suggest that, although material removal with a high-powered, ultrashort fs pulse is temperature dependent, sample heating by the ns air spark is not the source of the atomic emission enhancements observed in ns-fs orthogonal dual-pulse LIBS.

Dual-pulse laser-induced breakdown spectroscopy with combinations of femtosecond and nanosecond laser pulses

Nanosecond and femtosecond laser pulses were combined in an orthogonal preablation spark dual-pulse laser-induced breakdown spectroscopy (LIBS) configuration. Even without full optimization of interpulse alignment, ablation focus, large signal, signal-to-noise ratio, and signal-to-background ratio enhancements were observed for both copper and aluminum targets. Despite the preliminary nature of this study, these results have significant implications in the attempt to explain the sources of dual-pulse LIBS enhancements.

Comparative study of two new commercial echelle spectrometers equipped with intensified CCD for analysis of laser-induced breakdown spectroscopy

The purpose of this paper is to provide the reader with comparative information about two new commercial echelle spectrometers equipped with intensified CCD (ICCD) detectors for laser-induced breakdown spectroscopy analysis. We carried out a performance comparison between two commercial ICCD/echelle spectrometers [ESA 3000 (LLA Instruments GmbH, Berlin-Adlershof, Germany) and a Mechelle 7500 (Multichannel Instruments, Stockholm, Sweden)] for the determination of the concentrations of Be, Mg, Si, Mn, Fe, and Cu in the same Al alloy samples adopting the same experimental conditions. The results show that both systems, despite their differences in terms of resolution, have similar performance in terms of sensitivity and precision of measurements for these elements in an Al alloy matrix at least for the range of wavelength 280-400 nm studied in this work.