Characterization of laser-induced plasma in a vacuum using laser ablation mass spectrometry and laser-induced breakdown spectrometry

An analytical system for simultaneously monitoring laser-ablation mass spectra and laser-induced breakdown spectra for solid sample has been developed. The performance of the developed system is evaluated by measuring characteristics of laser-induced plasma such as lifetime of ions inside the plasma and laser power dependence of mass resolution for solid samples. Adopted samples are gadolinium plate, gadolinium coated on stainless steel plate, and one of the NIST standard samples, C-1248 (Ni–Cu alloy). The threshold laser energy in obtaining mass spectrum was dependent on the type of sample characteristics in the order of a few MW/cm², while a few hundred MW/cm² was necessary in order to observe emission signal. When laser energy was increased enough to produce emission signal, mass resolution of the time-of-flight mass spectrum was severely deteriorated. The lifetime of the continuum ion signal was estimated 200 and 250 ns for Gd plate and C-1248, respectively, by monitoring emission signals, while the lifetime of ions near sample surface was estimated as 400 ns and 430 ns for Gd plate and C-1248, respectively. The deterioration of mass resolution can be understood as originating from the space charge effect in high plasma density in a given space and different velocity distribution of ions inside the plasma, while longer lifetime of ions near sample surface can be understood as originating from speed of ion ejection near the sample surface. The details of the characteristics of laser-induced plasma are discussed and optimum experimental conditions for simultaneous monitoring are suggested.     

Discrimination of bacteria from Jamaican bauxite soils using laser-induced breakdown spectroscopy

Soil bacteria are sensitive to ecological change and can be assessed to gauge anthropogenic influences and ecosystem health. In recent years, there has been a significant increase in the focus on new technologies that can be applied to the evaluation of soil quality. Laser-induced breakdown spectroscopy (LIBS) is a promising technique that has been used for the investigation and characterization of explosives, solids, liquids, gases, biological and environmental samples. In this study, bacteria from un-mined and a chronosequence of reclaimed bauxite soils were isolated on Luria–Bertani agar media. Polymerase chain reaction amplification of the bacterial 16S rDNA, sequencing, and phylogenetic analysis were applied to each isolated soil bacteria from the sample sites resulting in the identification and classification of the organisms. Femtosecond LIBS performed on the isolated bacteria showed atomic and ionic emission lines in the spectrum containing inorganic elements such as sodium (Na), magnesium (Mg), potassium (K), zinc (Zn), and calcium (Ca). Principal component analysis and partial least squares regression analysis were performed on the acquired bacterial spectra demonstrating that LIBS has the potential to differentiate and discriminate among bacteria in the un-mined and reclaimed chronosequence of bauxite soils.     

Application of laser-induced breakdown spectrometry in urban health

The use of laser-induced breakdown spectrometry (LIBS) for elemental determination and detection in urban health is reviewed. It highlights the unique use of LIBS in fiber-based optics, in process control, and for field instrumentation. Selected applications confirm that LIBS could be the technique of choice for many applications in urban health.     

Qualitative and quantitative investigation of chromium-polluted soils by laser-induced breakdown spectroscopy combined with neural networks analysis

Laser-induced breakdown spectroscopy (LIBS) has been applied to the analysis of three chromium-doped soils. Two chemometric techniques, principal components analysis (PCA) and neural networks analysis (NNA), were used to discriminate the soils on the basis of their LIBS spectra. An excellent rate of correct classification was achieved and a better ability of neural networks to cope with real-world, noisy spectra was demonstrated. Neural networks were then used for measuring chromium concentration in one of the soils. We performed a detailed optimization of the inputs of the network so as to improve its predictive performances and we studied the effect of the presence of matrix-specific information in the inputs examined. Finally the inputs of the network—the spectral intensities—were replaced by the line areas. This provided the best results with a prediction accuracy and precision of about 5% in the determination of chromium concentration and a significant reduction of the data, too. Awarded a poster prize on the occasion of the Euro-Mediterranean Symposium on Laser-induced Breakdown Spectroscopy (EMSLIBS 2005), Aachen, Germany, 6–9 September 2005.     

Spatial distribution profiles of magnesium and strontium in speleothems using laser-induced breakdown spectrometry

Laser-induced breakdown spectrometry (LIBS) has been applied to spatially locate several atomic species in speleothems taken from the Nerja’s Cave (Málaga, Spain). Spatial distribution profiles of Mg at 285.21 nm and Sr at 407.77 nm were obtained while the laser was rastered through different paths along the sample. These elements were selected due to their importance as palaeoclimatic indicators. The 532 nm output of a Nd:YAG laser was used to irradiate the samples and generate the plasma that was spectrally analyzed and detected by using an intensified CCD detector. The signals were normalized to the Ca line to minimize pulse-to-pulse fluctuations in the laser source. Several studies were carried out to check for the point-to-point heterogeneity of the natural speleothem.     

Spatial distribution profiles of magnesium and strontium in speleothems using laser-induced breakdown spectrometry

Laser-induced breakdown spectrometry (LIBS) has been applied to spatially locate several atomic species in speleothems taken from the Nerja’s Cave (Málaga, Spain). Spatial distribution profiles of Mg at 285.21 nm and Sr at 407.77 nm were obtained while the laser was rastered through different paths along the sample. These elements were selected due to their importance as palaeoclimatic indicators. The 532 nm output of a Nd:YAG laser was used to irradiate the samples and generate the plasma that was spectrally analyzed and detected by using an intensified CCD detector. The signals were normalized to the Ca line to minimize pulse-to-pulse fluctuations in the laser source. Several studies were carried out to check for the point-to-point heterogeneity of the natural speleothem. Received: 1 August 1997 / Revised: 23 October 1997 / Accepted: 30 October 1997     

Determination of trace metals in water using x-ray fluorescence spectrometry

A simple, rapid and accurate method for water analysis is proposed. The analytical procedure for the determination of Fe, Mn, Zn, Cu, Cd, As, Pb and Se in water in concentrations as low as a few ppM involves precipitation with a carrier of the metals by diethyldithiocarbamate (DDTC) or 1-(2-pyridylazo)-2-naphthol (PAN) and filitration through a Millipore filter. The precipitates collected on the filter disc are examined by X-ray fluorescence analysis. PAN is excellent for the determination of several metal ions at the ppM level, and DDTC can be used with tartrate as a masking agent if water samples contain large amounts of iron(III).     

Speciation of heavy metals in polluted soils by sequential extraction and ICP spectrometry

Heavy metals were leached from various polluted soils by selective extraction reagents (water, BaCl2, acetate buffer + EDTA, HNO3) in order to establish the distribution of the chemical species of Cd, Zn, Cu and Pb. The leachates were directly injected into a plasma spectrometer in order to analyse immediately the extraction solution. This continuous on-line analysis gives qualitative information about the chemical behaviour of each element in function of the type of soil. It permits also to modify the extraction procedure for each sample studied by adjusting the volume of the extraction solution, the time of extraction, or by choosing another extraction reagent more adapted to the sample. The sum of the respective fraction is in rather good agreement with the total analysis of the soil.     

Determination of phosphorus in steel by the combined technique of laser induced breakdown spectrometry with laser induced fluorescence spectrometry

Laser induced breakdown spectrometry (LIBS) combined with laser induced fluorescence spectrometry (LIFS) has been applied for detection of trace-level phosphorus in steel. The plasma induced by irradiation of Nd:YAG laser pulse for ablation was illuminated by the 3rd harmonic of Ti:Sapphire laser tuned to one of the resonant lines for phosphorus in the wavelength region of 253–256 nm. An excitation line for phosphorus was selected to give the highest signal-to-noise ratio. Fluorescence signals, P213.62 and P214.91 nm, were observed with high selectivity at the contents as low as several tens µg g^− 1. Fluorescence intensities were in a good linear correlation with the contents. Fluorescence intensity ratio of a collisionally assisted line (213.62 nm) to a direct transition line (214.91 nm) was discussed in terms of the analytical conditions and experimental results were compared with a calculation based on rate equations. Since the fluorescence signal light in the wavelength range longer than 200 nm can be transmitted relatively easily, even through fiber optics of moderate length, LIBS/LIFS would be a versatile technique in on-site applications for the monitoring of phosphorus contents in steel.     

Analysis of Ca in BaCl2 matrix using laser-induced breakdown spectroscopy

The simplicity of the sample preparation and the use of an internal standardization method for the quantitative analysis of Ca has been investigated. The experimental set-up allowed the measurement of the intensity of ionic emission lines from Ca(II) and Ba(II), as a function of the composition in the matrix sample. The intensity ratios of the emission of Ca(II) to three different lines of Ba(II) were measured as a function of the distance (time) from the ablation point. With this information, the best experimental conditions for the analysis were determined. The method was then applied to the quantitative analysis of Ca in soils and baby food and the results compared with those obtained with conventional chemical and atomic absorption analysis.     

Determination of poisonous metals in wastewater collected from paint manufacturing plant using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) system was developed for determination of toxic metals in wastewater collected from local paint manufacturing plant. The plasma was generated by focusing a pulsed Nd:YAG laser at 1064 nm on the solid residue from wastewater collected from paint industry. The concentration of different elements of environmental significance like, lead, copper, chromium, calcium, sulphur, magnesium, zinc, titanium, strontium, nickel, silicone, iron, aluminum, barium, sodium, potassium and zirconium, in paint wastewater were 6, 3, 4, 301, 72, 200, 20, 42, 4, 1, 35, 120, 133, 119, 173, 28 and 12 mg kg⁻¹, respectively. The evaluation of potential and capabilities of LIBS as a rapid tool for paint industry effluent characterization is discussed in detail. Optimal experimental conditions were evaluated for improving the sensitivity of our LIBS system through parametric dependence study. The laser-induced breakdown spectroscopy (LIBS) results were compared with the results obtained using standard analytical technique such as inductively coupled plasma emission spectroscopy (ICP). The relative accuracy of our LIBS system for various elements as compared with ICP method is in the range of 0.03-0.6 at 2.5% error confidence. Limits of detection (LOD) of our LIBS system were also estimated for the above mentioned elements.     

Analysis of plutonium oxide surrogate residue using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy was used to determine the elemental composition of a CeO₂ composite powder for process control verification during lanthanide borosilicate glass fabrication. Cerium oxide is used as a surrogate for plutonium oxide, which along with other canister contents will be combined with frit to make glass. Laser-induced breakdown spectroscopy data for the composition of the CeO₂ batch containing concentrations of Ce, Cr, Si, Fe, Ta, Ni, Zn, Al Mg, Gd, and W were quantitatively determined from laser-induced breakdown spectroscopy spectra of both pellet and powder samples. The results of both forms were compared and it was determined that the pellet data gave slightly better precision than the powder sample.     

单波长激发-能量色散X射线荧光光谱法检测蔬菜中多种重金属元素

为实现蔬菜中多种元素的快速检测,利用单波长激发-能量色散X射线荧光光谱仪（MW-EDXRF）,建立了蔬菜中As、Pb、Cd、Cr、Ni、Cu、Zn、Rb、Mn等元素的快速检测方法。对XRF的激发时间、载样量、样品压片等条件进行了优化,结果显示当累积激发时间达到600 s、载样量为2 g、样品压片15 Mpa保持60 s时,可以实现XRF最优检测性能。在最优条件下,As、Pb、Cd、Cr、Ni、Cu、Zn、Rb、Mn的检出限（LOD）分别为0.07 mg/kg、0.07 mg/kg、0.07 mg/kg、0.32 mg/kg、0.32mg/kg、1.2 mg/kg、0.4 mg/kg、0.08 mg/kg、0.3 mg/kg;对菠菜、葱、胡萝卜、豆角、番茄、姜、空心菜、莲藕、芹菜、蒜等蔬菜样品测定11次的相对标准偏差（RSD）在3%~10%,表明方法具有良好的精密度;测定5种蔬菜基体标准物质的回收率在93%~119%,与微波消解电感耦合等离子体质谱法（ICP-MS）测定结果对比的线性回归系数（R2）>0.99（Cu的R2=0.9838）,表明方法具有良好的检测准确度。同时,该仪器仅有不到10 kg,不需要样品消解处理,检测时间在10 min左右,非常适合蔬菜多种重金属的现场快速筛查。     

Quantitative analysis of samples at high temperature with remote laser-induced breakdown spectrometry using a room-temperature calibration plot

A method for measurement of composition in samples at high temperature using a calibration curve performed at low temperature is presented. The method uses a transfer function which avoids the need for building a calibration plot at high temperature. The method has shown suitability for high-temperature measurements up to 850 °C in steel slags exhibiting coefficients of correlation of 0.991 and 0.989 for Si / Ca and Mg / Ca ratios, respectively. The accuracy of the method has been assessed by comparing the results with remote LIBS at high temperature to those by XRF at room temperature. As an example of its versatility, the method has been applied to the determination of the basicity index of steel slags at high temperature.     

Depth-resolved analysis by laser-induced breakdown spectrometry at reduced pressure

The 581 nm output from a dye laser in a fluence range between 2.86 and 11.47 J cm⁻² was used to ablate pure Zn and Fe foils. The average ablation rate (AAR, μm per shot) was calculated for different experimental variables (buffer gas, pressure, laser fluence and focal conditions). Deposition of previously ablated material in the ablation crater results in large variation of the observed AAR values. This effect was observed in air and argon buffer gases at atmospheric pressure. The situation is largely alleviated at reduced pressure due to free expansion of the ablated material. Under these circumstances the capability of laser-induced plasmas to resolve interfacial structures is improved. The effect on depth-resolved studies was checked with a commercial Zn-coated steel sample. Due to the Gaussian-like energy distribution of the incident laser beam, the material is ablated to produce a conical crater. This fact ensures that the Zn signal remains for a longer time because the ablated region spreads over the edge gradually. At low pressure the emission peaks are better defined and the background becomes flat. However, these conditions produce also the lowest net intensities and some peaks are not detected. An Ar atmosphere produces more intense spectral lines at both pressure levels. Best analytical results were obtained at reduced pressure, with a slight improvement in depth resolution in the presence of Ar. © 1998 John Wiley & Sons, Ltd.     

Applications of laser-induced breakdown spectrometry (LIBS) in surface analysis

The applicability of laser-induced breakdown spectrometry (LIBS) for surface analysis is presented in terms of its lateral and depth resolution. A pulsed N₂ laser at 337.1 nm (3.65 J/cm²) was used to irradiate solar cells employed for photovoltaic energy production. Laser produced plasmas were collected and detected using a charge-coupled device. An experimental device developed in the laboratory permits an exact synchronization of sample positioning using an XY motorized system with laser pulses. Multielement analysis with lateral resolution of up to 30 m is feasible with the present system. Three-dimensional capabilities of the system are used for studies on the distribution of carbon impurities at the surface of the solar cells.     

Applications of laser-induced breakdown spectrometry (LIBS) in surface analysis

The applicability of laser-induced breakdown spectrometry (LIBS) for surface analysis is presented in terms of its lateral and depth resolution. A pulsed N(2) laser at 337.1 nm (3.65 J/cm(2)) was used to irradiate solar cells employed for photovoltaic energy production. Laser produced plasmas were collected and detected using a charge-coupled device. An experimental device developed in the laboratory permits an exact synchronization of sample positioning using an XY motorized system with laser pulses. Multielement analysis with lateral resolution of up to 30 microm is feasible with the present system. Three-dimensional capabilities of the system are used for studies on the distribution of carbon impurities at the surface of the solar cells.     

Depth profiling of coated metallic artifacts adopting laser-induced breakdown spectrometry

Laser-induced breakdown spectroscopy (LIBS) is a relatively novel technique that is being applied to the characterization of interfaces in layered materials as an alternative to other classic surface analytical techniques.     

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.     

Comparison of two laser-induced breakdown spectroscopy techniques for total carbon measurement in soils

The potentials of two advanced laser-induced breakdown spectroscopy (LIBS) techniques which are used to determine the total carbon content in soils have been examined. The first one is the combination of a single-pulse laser ablation with spark excitation of plasma plume triggering the gap between electrodes close to the target surface. The second one is a more conventional double-pulse LIBS. In both modes the calibration graphs have a nonlinear trend in the actual range of carbon contents and present a good R² value (0.97). In the combined laser-spark approach, using low-cost and portable laser instrumentation is possible, as well as inducing a micro-damage on the target surface. Certain regularities in the spectral line intensities of soil nutritious elements have been detected and appear to be connected to the total carbon content and to the soil origin.