Quantitative elemental analysis of steel using calibration-free laser-induced breakdown spectroscopy

We report the quantitative elemental analysis of a steel sample using calibration-free laser-induced breakdown spectroscopy (CF-LIBS). A Q-switched Nd:YAG laser (532 nm wavelength) is used to produce a plasma by focusing it onto a steel sample in air at atmospheric pressure. The time-resolved spectra from atomic and ionic emission lines of the steel elements are recorded by an echelle grating spectrograph coupled with a gated intensified CCD camera and are used for the plasma characterization and quantitative analysis of the sample. The time delay at which the plasma is in local thermodynamic equilibrium as well as optically thin, necessary for elemental analysis, is deduced. An algorithm for the CF-LIBS relating the experimentally measured spectral intensity values with the basic physics of the plasma is developed and used for the determination of Fe, Cr, Ni, Mg, and Si concentrations in the steel sample. The analytical results obtained from the CF-LIBS technique agree well with the certified values of the elements in the sample, with relative uncertainties of less than 5%.     

Emission following laser-induced breakdown spectroscopy of organic compounds in ambient air

Laser-induced breakdown spectroscopy (LIBS) was applied to nitroaromatic (NC) and polycyclic aromatic hydrocarbon (PAH) samples in ambient air to characterize their resultant emission. Compounds covering various surface, were ablated by use of the second (532-nm) or the fourth (266-nm) harmonic of a nanosecond pulsed Nd:YAG laser. The emission consisted of spectral features related mostly to CNand C2 molecular fragments and to C, H, N, and O atomic fragments. The transitions of the molecular fragments correspond to the CN (B 2sigma+ - X 2sigma+) violet system and the C2 (d 3IIg - a 3IIu) Swan system; the intensity of the former is higher in NCs than in PAHs. The intensity ratios between C2 and CN and between O and N correlate to the molecular structure, suggesting the possibility of distinguishing one chemical class from another and in optimum cases even identifing specific compounds by use of LIBS.     

Quantitative hydrogen analysis of zircaloy-4 using low-pressure laser plasma technique

It is found in this work that variation of laser power density in low-pressure plasma spectrochemical analysis of hydrogen affects sensitively the hydrogen emission intensity from the unwanted and yet ubiquitous presence of ambient water. A special experimental setup has been devised to allow the simple condition of focusing/defocusing the laser beam on the sample surface. When applied to zircaloy-4 samples prepared with various hydrogen impurity concentrations using low-pressure helium surrounding gas, good-quality hydrogen emission lines of very high signal to background ratios were obtained with high reproducibility under weakly focused or largely defocused laser irradiation. These measurements resulted in a linear calibration line with nonzero intercept representing the residual contribution from the recalcitrant water molecules. It was further shown that this can be evaluated and taken into account by means of the measured intensity ratio between the oxygen and zirconium emission lines. We have demonstrated the applicability of this experimental approach for quantitative determination of hydrogen impurity concentrations in the samples considered.     

Quantitative carbon measurement in anthracite using laser-induced breakdown spectroscopy with binder

Quantitative carbon measurement in anthracites remains difficult with laser-induced breakdown spectroscopy (LIBS) due to its relatively high measurement uncertainty. To improve the measurement repeatability, binders to bind the anthracite powder together were utilized for LIBS measurement. Results showed that the optimized binder Na(2)SiO(3)·9H(2)O, with Si from the binder as the internal calibration element, can yield the overall best measurement precision and accuracy. Using 15 anthracites for calibration and 7 anthracites for validation and with optimized percentage of Na(2)SiO(3)·9H(2)O as binder, the average value of the measurement's relative standard deviation (RSD), R(2), and root mean square error of prediction (RMSEP) were 12.1%, 0.76, and 6.25%, respectively, proving the applicability of binder for carbon measurement in anthracites.     

Helium detection in gas mixtures by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been evaluated as a tool for monitoring trace levels of helium in gas mixtures consisting mostly of hydrogen. Calibration data for helium in hydrogen was investigated at different helium concentration levels. At high concentrations of helium (>7.25%), the LIBS signal is quenched due to Penning ionization. The hydrogen alpha line (656.28 nm) was observed to broaden as the concentration of helium impurities in the hydrogen gas mixture increased. The helium line at 587.56 nm was selected as the analyte line for helium impurity detection. The effects of laser energy, the delay time between the laser pulse and data acquisition, and the gas pressure on the LIBS signal of helium were investigated to determine the optimum conditions for helium detection. The LIBS signal from the helium line at 587.56 nm shows good linear correlation with helium concentration for He concentrations below 1%. Thus, LIBS can be reliably used to detect the low levels of helium. The limit of detection for helium was found to be 78 ppm.     

Quantitative analysis of deuterium in zircaloy using double-pulse laser-induced breakdown spectrometry (LIBS) and helium gas plasma without a sample chamber

A crucial safety measure to be strictly observed in the operation of heavy-water nuclear power plants is the mandatory regular inspection of the concentration of deuterium penetrated into the zircaloy fuel vessels. The existing standard method requires a tedious, destructive, and costly sample preparation process involving the removal of the remaining fuel in the vessel and melting away part of the zircaloy pipe. An alternative method of orthogonal dual-pulse laser-induced breakdown spectrometry (LIBS) is proposed by employing flowing atmospheric helium gas without the use of a sample chamber. The special setup of ps and ns laser systems, operated for the separate ablation of the sample target and the generation of helium gas plasma, respectively, with properly controlled relative timing, has succeeded in producing the desired sharp D I 656.10 nm emission line with effective suppression of the interfering H I 656.28 nm emission by operating the ps ablation laser at very low output energy of 26 mJ and 1 μs ahead of the helium plasma generation. Under this optimal experimental condition, a linear calibration line is attained with practically zero intercept and a 20 μg/g detection limit for D analysis of zircaloy sample while creating a crater only 10 μm in diameter. Therefore, this method promises its potential application for the practical, in situ, and virtually nondestructive quantitative microarea analysis of D, thereby supporting the more-efficient operation and maintenance of heavy-water nuclear power plants. Furthermore, it will also meet the anticipated needs of future nuclear fusion power plants, as well as other important fields of application in the foreseeable future.     

Quantitative analysis of toxic metals lead and cadmium in water jet by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been applied to the analysis of toxic metals Pb and Cd in Pb(NO3)2 and Cd(NO3)2.4H2O aqueous solutions, respectively. The plasma is generated by focusing a nanosecond Nd:YAG (λ=1064?nm) laser on the surface of liquid in the homemade liquid jet configuration. With an assumption of local thermodynamic equilibrium (LTE), calibration curves of Pb and Cd were obtained at different delay times between 1 to 5?μs. The temporal behavior of limit of detections (LOD) was investigated and it is shown that the minimum LODs for Pb and Cd are 4 and 68 parts in 10(6) (ppm), respectively. In order to demonstrate the correctness of the LTE assumption, plasma parameters including plasma temperature and electron density are evaluated, and it is shown that the LTE condition is satisfied at all delay times.     

Parametric study of pellets for elemental analysis with laser-induced breakdown spectroscopy

The effect of various parameters on the accuracy of the laser-induced breakdown spectroscopy (LIBS) data taken from pellet samples has been investigated. The dependence of the standard deviation of the LIBS data on the amount and nature of the binder used, pressure used to press the powder into a pellet, and the position of the focal spot on the pellet has been investigated. Pellets made from industrially important materials such as silica, alumina, and lime with polyvinyl alcohol, sucrose, and starch as binders have been studied. The results thus obtained are tested by preparation of the calibration curves for Si, Fe, and B in the pellets made from the powder glass batch used as a surrogate for the batch employed for the vitrification of radioactive waste.     

Absolute analysis of particulate materials by laser-induced breakdown spectroscopy

We have developed a new data acquisition approach followed by a suitable data analysis for Laser-induced breakdown spectroscopy. It provides absolute concentrations of elements in particulate materials (e.g., industrial dusts and soils). In contrast to the known calibration procedures (based on the ratio of spectral lines), which are applicable only when one component is constant, this approach requires no constant constituent and results in absolute (rather than relative) concentrations. Thus, the major drawback of this analytical method, namely, the signals' instability (especially when particulate materials are concerned) is partially solved. Unlike the commonly used integrated data acquisition, we use a sequence of signals from single breakdown events. We compensate for pulse to pulse fluctuations in an intrinsic way, and the final results do not depend on the presence of any constant component. Extended linear calibration curves are obtained, and limits of detection are improved by 1 order of magnitude relative to previous methods applied to the same samples (e.g., detection limit of 10(-12) g of Zn in aerosol samples). The proposed compensation for pulse variations is based on the assumption that they can be described as a multiplicative effect for both the spectral peaks and a component of the baseline. In other words, we assume that the same fluctuation pattern observed in the spectral peaks is present in the baseline as well. This assumption is shown to hold and is utilized in the proposed method. In addition, a proper data-filtering process, which eliminates ill-conditioned spectra, is shown to partially compensate for problems due to the nature of analysis of particulate materials.     

Single-pollen analysis by laser-induced breakdown spectroscopy and Raman microscopy

The application of laser-induced breakdown spectroscopy to the analysis of single biological microparticles (bioaerosols) is described, exemplified here for a range of pollens. Spectra were recorded by exposure of the pollen to a single laser pulse from a Nd:YAG laser (lambda = 1064 nm, Ep approximately 30 mJ). The intensities of the single-pulse laser-induced breakdown spectra fluctuated dramatically, but an internal signal calibration procedure was applied that referenced elemental line intensities to the carbon matrix of the sample (represented by molecular bands of CN and C2). This procedure allowed us to determine relative element concentration distributions for the different types of pollen. These pollens exhibited some distinct concentration variations, for both major and minor (trace) elements in the biomatrix, through which ultimately individual pollens might be identified and classified. The same pollen samples were also analyzed by Raman microscopy, which provided molecular compositional data (even with spatial resolution). These data allowed us to distinguish between biological and nonbiological specimens and to obtain additional classification information for the various pollen families, complementing the laser-induced breakdown spectroscopy measurement data.     

激光诱导击穿光谱法快速定量检测皮革中的铅和铬

建立了激光诱导击穿光谱(laser-induced breakdown spectroscopy,LIBS)结合自由定标法快速定量分析皮革中重金属元素Pb和Cr的方法.采用由调Q脉冲Nd:YAG激光器、中阶梯光栅光谱仪、ICCD检测器和旋转样品台等组成的激光诱导击穿光谱系统,采集了3类皮革样品的激光诱导击穿光谱.选取Pb和Cr的特征谱线,优化激光能量、延时时间和焦深参数,结合自由定标法建立了样品中Pb和Cr的玻尔兹曼曲线,计算获得3类皮革样品中Pb和Cr的含量.Pb含量分析相对标准偏差在3.22%~7.66%之间,Cr含量分析相对标准偏差在12.19%~14.00%之间.t检验表明,两种元素测量值与实际值无显著差异.     

Approach to detection in laser-induced breakdown spectroscopy

Gated detection with intensified detectors, e.g., ICCDs, is today the accepted approach for detection of plasma emission in laser-induced breakdown spectroscopy (LIBS). However, these systems are more cost-intensive and less robust than nonintensified CCDs. The objective of this paper is to compare, both theoretically and experimentally, the performance of an intensified (ICCD) and nonintensified (CCD) detectors for detection of plasma emission in LIBS. The CCD is used in combination with a mechanical chopper, which blocks the early continuum radiation from the plasma. The detectors are attached sequentially to an echelle spectrometer under the same experimental conditions. The laser plasma is induced on a series of steel samples under atmospheric conditions. Our results indicate that there is no substantial difference in the performance of the CCD and ICCD. Signal-to-noise ratios and limits of detection achieved with the CCD for Si, Ni, Cr, Mo, Cu, and V in steel are comparable or even better than those obtained with the ICCD. This result is further confirmed by simulation of the plasma emission signal and the corresponding response of the detectors in the limit of quantum (photon) noise.     

Slag analysis with laser-induced breakdown spectrometry

Laser-induced breakdown spectrometry (LIBS) has been applied for multi-elemental analysis of slag samples from a steel plant. In order to avoid the time-consuming step of sample preparation, the liquid slag material can be filled in special probes. After cooling of the liquid slag and solidification, the samples can be analyzed with LIBS. Chemical analysis of slag is an essential input parameter used for numerical simulations to control liquid steel processing. The relative variation range of element concentrations in slag samples from steel production can amount to up to 30%. A multivariate calibration model is used to take into account matrix effects caused by these varying concentrations. By optimizing the measuring parameters as well as the calibration models, an agreement between the standard X-ray fluorescence (XRF) analysis and LIBS analysis in terms of the coefficient of determination r2 of 0.99 for the main analytes CaO, SiO2, and Fetot of converter slag samples was achieved. The average repeatability of the LIBS measurement for these elements in terms of the relative standard deviation of the determined concentration is improved to less than 1.0%. With these results, the basis is established for future on-line applications of LIBS in the steel-making industry for slag analysis.     

Effect of laser-induced crater depth in laser-induced breakdown spectroscopy emission features

The influence of crater depth on plasma properties and laser-induced breakdown spectroscopy (LIBS) emission has been evaluated. Laser-induced plasmas were generated at the surface and at the bottom of different craters in a copper sample. Plasmas produced at the sample surface and at the bottom of the craters were spatially and temporally resolved. LIBS emission, temperature, and electronic number density of the plasmas were evaluated. It is shown that the confinement effect produced by the craters enhances the LIBS signal from the laser-induced plasmas.     

Evaluation of femtosecond laser-induced breakdown spectroscopy for analysis of animal tissues

The aim of this work was to evaluate the performance of femtosecond laser-induced breakdown spectroscopy (fs-LIBS) for the determination of elements in animal tissues. Sample pellets were prepared from certified reference materials, such as liver, kidney, muscle, hepatopancreas, and oyster, after cryogenic grinding assisted homogenization. Individual samples were placed in a two-axis computer-controlled translation stage that moved in the plane orthogonal to a beam originating from a Ti:Sapphire chirped-pulse amplification (CPA) laser system operating at 800 nm and producing a train of 840 microJ and 40 fs pulses at 90 Hz. The plasma emission was coupled into the optical fiber of a high-resolution intensified charge-coupled device (ICCD)-echelle spectrometer. Time-resolved characteristics of the laser-produced plasmas showed that the best results were obtained with delay times between 80 and 120 ns. Data obtained indicate both that it is a matrix-independent sampling process and that fs-LIBS can be used for the determination of Ca, Cu, Fe, K, Mg, Na, and P, but efforts must be made to obtain more appropriate detection limits for Al, Sr, and Zn.     

Detection of uranium in solids by using laser-induced breakdown spectroscopy combined with laser-induced fluorescence

Detection of uranium in solids by using laser-induced breakdown spectroscopy has been investigated in combination with laser-induced fluorescence. An optical parametric oscillator wavelength-tunable laser was used to resonantly excite the uranium atoms and ions within the plasma plumes generated by a Q-switched Nd:YAG laser. Both atomic and ionic lines can be selected to detect their fluorescence lines. A uranium concentration of 462 ppm in a glass sample can be detected by using this technique at an excitation wavelength of 385.96 nm for resonant excitation of U II and a fluorescence line wavelength of 409.0 nm from U II.     

Correlation of limestone beds using laser-induced breakdown spectroscopy and chemometric analysis

Correlation of limestone beds is commonly based on a variety of features, including the age of the bed, the fossil assemblage, internal sedimentary structures, and the relationship to other units in the stratigraphy. This study uses laser-induced breakdown spectroscopy (LIBS) to correlate 16 limestone beds from Kansas, USA, using three multivariate techniques: (1) soft independent modeling of class analogy (SIMCA) classification, (2) a partial least squares regression, 1 variable (PLS-1) model in which the spectra are regressed against a matrix of the indicator variables 1 through 16, and (3) a matching algorithm that consists of a sequence of binary PLS-1 models. Each gravel-sized limestone particle was analyzed by one LIBS shot; ten spectra were averaged into a single spectrum for chemometric analysis. The entire spectrum (198-969 nm wavelength) is used for multivariate analysis; the only preprocessing is averaging. The SIMCA and PLS-1 models fail to discriminate among the beds, which are chemically similar. In contrast, the matching algorithm has a success rate of 95% to 96%, using half of the spectra to train the model and the other half of the spectra to validate it. However, 100% success can be accomplished by accepting the classification of the majority of spectra for a given bed as the correct classification. This study indicates that LIBS can be applied to complex geologic correlation problems and provide rapid, accurate results.     

Application of laser-induced breakdown spectroscopy technique to hair tissue mineral analysis

The concentration of the main minerals present in human hair is measured on several subjects by Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS) and compared with the results obtained through a commercial analytical laboratory. The possibility of using CF-LIBS for mineral analysis in hair is discussed, as well as its feasibility for the fast and inexpensive determination of the occurrence of heavy-metal poisoning in hair.     

Spectroscopic analysis of fire suppressants and refrigerants by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy is evaluated as a means of detecting the fire suppressants CF(3)Br, C(3)F(7)H, and CF(4) and the refrigerant C(2)F(4)H(2). The feasibility of employing laser-induced breakdown spectroscopy for time- and space-resolved measurement of these agents during use, storage, and recharge is discussed. Data are presented that demonstrate the conditions necessary for optimal detection of these chemicals.     

Quantitative measurements of loss on ignition in iron ore using laser-induced breakdown spectroscopy and partial least squares regression analysis

Laser-induced breakdown spectroscopy (LIBS) and partial least squares regression (PLSR) have been applied to perform quantitative measurements of a multiple-species parameter known as loss on ignition (LOI), in a combined set of run-of-mine (ROM) iron ore samples originating from five different iron ore deposits. Global calibration models based on 65 samples and their duplicates from all the deposits with LOI ranging from 0.5 to 10 wt% are shown to be successful for prediction of LOI content in pressed pellets as well as bulk ore samples. A global independent dataset comprising a further 60 samples was used to validate the model resulting in the best validation R(2) of 0.87 and root mean square error of prediction (RMSEP) of 1.1 wt% for bulk samples. A validation R(2) of 0.90 and an RMSEP of 1.0 wt% were demonstrated for pressed pellets. Data preprocessing is shown to improve the quality of the analysis. Spectra normalization options, automatic outlier removal and automatic continuum background correction, which were used to improve the performance of the PLSR method, are discussed in detail.