Characterization of cinematographic films by Laser Induced Breakdown Spectroscopy

The emulsion-coated transparent plastic-base film has been the main carrier for production and preservation of motion picture contents since the 19th century. The knowledge of the composition of black and white silver gelatine cinematographic films is of great importance for the characterization of the photographic process and for identifying the optimum conditions for conservation. A cinematographic film is a multi-component system that consists of a layer of photographic emulsion overcoating a polymeric support (plasticized cellulose triacetate) and a protective transparent cross-linked gelatine layer coating the emulsion. In the present work, Laser Induced Breakdown Spectroscopy (LIBS) is used to characterize the composition of the materials of cinematographic films. LIB spectra of film samples and of different individual film components, polymeric support and reference gelatines, were acquired in vacuum by excitation at 266 nm (Q-switched Nd:YAG laser, 6 ns, 10 Hz). In the cinematographic film, silver lines from the light-sensitive silver halide salts of the photographic emulsion are accompanied by iron, lead, chrome and phosphorus lines. Iron and lead are constituents of film developers, chrome is included in the composition of the hardening agents and phosphorus has its origin in the plasticizer used in the polymeric support. By applying successive pulses on the same spot of the film sample, it was possible to observe through stratigraphic analysis the different layers composition. Additionally, the results obtained reveal the analytical capacity of LIBS for the study and classification of the different gelatine types and qualities used for the protecting layer and the photographic emulsion.     

Quantitative Analysis of Metallic Elements in Tobacco and Tobacco Ash by Calibration Free Laser-Induced Breakdown Spectroscopy

Cigarette smoking may be a substantial source of intake of some hazardous elements to the human health. In this work calibration-free laser-induced breakdown spectroscopy technique was employed to investigate the trace metallic elements (Fe, Ca, Al, Cu, K, Li, Mg, Mn, Na, Sr, Ti, and Zn) concentration in tobacco and tobacco ash. Moreover, variation of metallic elements mass concentration between tobacco and tobacco ash has been observed.     

Laser Induced Surface Morphology of Molybdenum Correlated with Breakdown Spectroscopy

Surface modifications of laser irradiated molybdenum have been correlated with plasma parameters. Nd:YAG laser (1064 nm, 10 ns) was employed at various laser irradiances ranging from 6 to 50 GW/cm² under argon environment. The ablation efficiency has been investigated by measuring the crater depth using surface profilometry analysis. Scanning electron microscope (SEM) analysis reveals the formation of coarse grains along with cracked boundaries, cavities and cones at the central ablated areas. Whereas, uplifted re-solidified material, cavities, ridges, droplets and cones were observed at boundary regions. Laser Induced Breakdown Spectroscopy (LIBS) analysis has been performed to evaluate electron temperature and number density of molybdenum plasma. Electron temperature and electron density varies from 6670 to 9305 K and 0.62 × 10¹⁸ to 0.72 × 10¹⁸ cm^?3 respectively. Both the parameters showed similar trend in variation with laser irradiance i.e. an initial increase from 13 to 19 GW/cm² followed by a decrease from 19 to 25 GW/cm² and then a saturation from 25 to 50 GW/cm². The initial increasing trend is attributed to the enhanced excited vapor content of the ablated material, confinement effects of the surrounding argon and absorption of laser energy into the molybdenum vapor plasma during the trailing part of laser pulse leading to ignition of laser supported combustion (LSW) waves. The decreasing trend is attributed to the shielding effect and saturation is explainable on the basis of the formation of a self-regulating regime. Surface modifications of laser irradiated molybdenum were correlated with the plasma parameters.     

Detection of Nutrition and Toxic Elements in Dry Milk Powders Available in Pakistan Using Laser Induced Breakdown Spectroscopy

Plasma Chemistry and Plasma Processing - In this work, qualitative as well as the quantitative study of nutritional and trace toxic metals in various dry milk powders (local and branded) available...     

Laser Induced Breakdown Spectroscopy machine for online ash analyses in coal

Presently, online coal ash content monitoring is performed by PGNAA (Prompt Gamma Neutron Activation Analyses) machines. Laser Detect Systems has developed an online mineral analysis system using Laser Induced Breakdown Spectroscopy (LIBS). The main advantages of the system are that it is without a radioactive source, compact (1.5 m × 0.8 m × 1.3 m), comparatively light (250 kg) and easy to install. The main disadvantage is that a LIBS system analyzes surface chemistry of the mineral exclusively and not the volume. To prove the LIBS machine analytical ability for coal ash content evaluation, a trial was arranged at Optimum Colliery (South Africa). The LIBS machine was installed in line with a PGNAA machine and laboratory data served as a referee in the final assessment for analytical accuracy. The trial was carried out over a four month period. This paper presents the successful trial results achieved for accurate (at least +/− 0.5% mean absolute error) online coal ash content monitoring.     

Analysis of heavy metals in liquids using Laser Induced Breakdown Spectroscopy by liquid-to-solid matrix conversion

Laser Induced Breakdown Spectroscopy has been applied to the analysis of heavy metals in liquid samples, an issue of major importance for environmental monitoring. In this work, a new approach was developed in which liquid solutions were converted into solid pellets of calcium hydroxide by mixing with CaO. Therefore, liquid sample analysis is replaced by solid matrix analysis, overcoming the well-known difficulties and drawbacks of the analysis of liquid samples, and providing additional advantages with respect to other experimental setups. The plasma was produced in air at atmospheric pressure, by a pulsed Nd:YAG laser. Analytical results were achieved for Cr, Pb, Cd and Zn through calibration curves and limits of detection.     

Study of phase transformation in iron oxides using Laser Induced Breakdown Spectroscopy

Synthetic magnetite (Fe₃O₄) was heated in air at 200–500 °C for different time periods to study its phase transformation to maghemite (γ-Fe₂O₃) and hematite (α-Fe₂O₃). Laser Induced Breakdown Spectroscopy (LIBS) was used to take the spectra of these samples which were then compared to the spectra of standard iron oxide powders using linear correlation. The linear correlation procedure used showed probabilities of identification close to unity. Complementary techniques to LIBS, Fourier Transform Infrared (FTIR) spectroscopy and X-ray Diffraction (XRD) analysis were also used to characterize iron oxides. By taking advantage of the time gated detector capability of LIBS, the identification of iron oxide phases was found to be in good agreement with FTIR and XRD analysis. This study demonstrates that LIBS can be successfully applied to the characterization of the oxidation states of multivalent oxides of elements like Fe, Cr, Pb, and others.     

Wavelength dependence on the elemental analysis of glass by Laser Induced Breakdown Spectroscopy

Laser Induced Breakdown Spectroscopy (LIBS) is presented as a tool for the elemental analysis of glass in forensic applications. Two harmonics of the Nd:YAG laser at 266 nm and 532 nm were used as the irradiation source for the analysis of several glass standards and soda–lime glass samples of interest to forensic scientists. Both lasers were kept at a constant energy of 20 mJ and focused using a 150 mm focal length lens. A series of experiments were also conducted to determine the importance of wavelength on lens-to-sample distance (LTSD) at each wavelength. It was determined that the optimal LTSD was found at ~ 1–2 mm focused into the surface for both wavelengths yet the crater depth resulting from the irradiation at 266 nm was significantly deeper (112 µm) than that from the 532 nm laser (41 µm). In addition, the analytical performance of LIBS on 5 NIST glasses and 6 automobile glasses at both wavelengths is reported. Good correlation for the quantitative analysis results for the trace and minor elements Sr, Ba and Al are reported along with the calibration curves, in most cases R² > 0.95, using absolute intensities at various emission lines. Although 266 nm resulted in more mass removal, the 532 nm produced greater emission intensities. A slightly higher plasma density was determined for irradiation by 532 nm using the Stark broadening technique in comparison to the 266 nm irradiation.     

Evaluation of self-absorption of manganese emission lines in Laser Induced Breakdown Spectroscopy measurements

This paper is part of a more general study aimed to the determination of the best experimental procedures for reliable quantitative measurements of Fe–Mn alloys by LIBS. In this work, attention is pointed on the self-absorption processes, whose effect deeply influences the LIBS measurements, reflecting in non-linear calibration curves. The effect of self-absorption on the line intensity can be quantified by defining a self-absorption coefficient, that measures the deviation of the line intensity from the linear extrapolation of the curve of growth in the optically thin regime. The authors demonstrated in a previous paper that self-absorption coefficients could be calculated once the electron density of the plasma is known and the Stark coefficients of the lines are available. However, when the Stark coefficients of the lines of interest are not known, a different approach is needed. In this work a new method for evaluation of self-absorption coefficients in LIBS measurements is presented, which does not require the knowledge of Stark coefficients. In order to understand the basic principles and setting out the theoretical tools that will be used for the analysis of the alloys, a preliminary study was done on pure Mn; LIBS spectra were acquired in different experimental conditions, at different laser energies and different delays after the laser irradiation of the sample. Moreover, collinear double pulse measurements were also performed. Analytical relations were derived and experimental procedures devised for evaluation of the self-absorption coefficients of several Mn lines, which are important for characterization and control of the experimental conditions in which the analysis is performed.     

激光诱导击穿光谱(LIBS)技术在低碳钢铁冶金行业的应用

激光诱导击穿光谱技术(Laser induced breakdown spectroscopy,简称LIBS)是一种基于激光等离子体的发射光谱技术,具有样品制备简单,分析迅速,多元素同时分析,现场在线和远程分析等独特优势,已在钢铁冶金领域取得了越来越广泛的应用与发展。综述了近年来LIBS技术在钢铁冶金领域的应用研究进展,从冶金生产的全流程进行介绍,包括矿石、熔融钢水/铁水、钢铁产品及炉渣和废气分析。同时,还总结了LIBS技术在钢铁冶金领域应用的优点和缺点,并对该技术的应用前景及未来发展方向进行展望。     

Comparison of Single Pulse and Double Simultaneous Pulse Laser Induced Breakdown Spectroscopy

A simple and cost-effective variant of laser induced breakdown spectroscopy is presented that involves a double simultaneous pulse configuration employing a single laser source. Its performance is compared with conventional single pulse configuration. Double simultaneous pulses were accomplished by splitting a Nd:YAG laser (1064 nm, 6 ns, 360 mJ) beam into two components that were focused on the sample surface to produce two concurrent breakdowns. Experiment was repeated for single pulse and double simultaneous pulses under different ambient pressures. The performance was evaluated on the basis of self-absorption, signal-to-noise ratio (SNR), and relative standard deviation (RSD) of the Mg II doublet (280.2704 nm, 279.553 nm). Optically thin emission lines of better profiles with higher signal-to-noise ratio resulted from double simultaneous pulses. The lowest relative standard deviations obtained by single pulse and double simultaneous pulse configurations were 18.89% and 12.01%, respectively. In fact, double simultaneous pulses have performed better than single pulse in all respects within the studied regime.     

A Comparative Study of Calibration Free Methods for the Elemental Analysis by Laser Induced Breakdown Spectroscopy

We have used two calibration free laser induced breakdown spectroscopy (CF-LIBS) methods for the quantitative analysis of Pb–Sn alloys with different compositions. The first method is based on Boltzmann plots where the elemental concentration is determined from the intercept along the y-axis whereas the second method is the electron density conservation method, in which elemental compositions are determined by comparing the experimentally measured number density with the theoretical results obtained by CF-LIBS. The neutral spectral lines of lead and tin have been used for the estimation of plasma temperature by the Boltzmann plot method whereas the Saha–Boltzmann equation has been used to calculate the electron number density. By comparing the results of both CF-LIBS methods, it is concluded that the CF-LIBS (electron number density conservation) method is more appropriate than the CF-LIBS (Boltzmann plot method) for the quantitative elemental analysis.     

Dual-pulse Laser Induced Breakdown Spectroscopy for analysis of gaseous and aerosol systems: Plasma-analyte interactions

Dual-pulse LIBS has been previously investigated to a large extent on solid and liquid phase analytes, where it has been demonstrated to significantly enhance atomic emission signal intensity, and more importantly, to enhance the analyte peak-to-base and signal-to-noise ratios. This study focuses on the effects of an orthogonal dual-pulse laser configuration on the atomic emission response for both purely gaseous and calcium-based aerosol samples. The gaseous sample consisted of purified (i.e. aerosol free) air, from which nitrogen and oxygen spectral emission lines were analyzed. Measurements for the gaseous system resulted in no notable improvements with the dual-pulse configuration as compared to the single-pulse LIBS. Experiments were also conducted in purified air seeded with calcium-rich particles, which revealed a marked improvement in calcium atomic emission peak-to-base (∼ 2-fold increase) and signal-to-noise ratios (∼ 4-fold increase) with the dual-pulse configuration. In addition to increased analyte response, dual-pulse LIBS yielded an enhanced single-particle sampling rate when compared to conventional LIBS. Transmission measurements with respect to the plasma-creating laser pulse were recorded for both single and dual-pulse methods over a range of temporal delays. In consideration of the spectroscopic and transmission data, the plasma-analyte interactions realized with a dual-pulse methodology are explained in terms of the interaction with the initially expanding plasma shock wave, which differs between gaseous and particulate phase analytes, as reported in a recent study [V. Hohreiter, D.W. Hahn, Calibration effects for laser-induced breakdown spectroscopy of gaseous sample streams: analyte response of gas-phase species versus solid-phase species, Anal. Chem. 77 (2005) 1118–1124].     

Laser Induced Breakdown Spectroscopy methodology for the analysis of copper-based-alloys used in ancient artworks

In this paper Laser Induced Breakdown Spectroscopy has been applied for determining the elemental composition of a set of ancient bronze artworks coming from archaeological site of Minervino Murge — Southern of Italy (dated around VII b.C.). Before carrying on the analysis of the archaeological samples, the characterization of the analytical technique has been accomplished by investigating the trueness of the typical assumptions adopted in LIBS, such as Local Thermodynamic Equilibrium, congruent ablation and plasma homogeneity. With this purpose, two different laser pulse durations, 7 ns and 350 fs, have been used. We have focused our attention on LIBS analysis of bronze standards by considering and discussing the bases of both methodology and analytical approach to be followed for the analysis of ancient copper-based-alloy samples. Unexpectedly, regardless from the laser pulse duration, the LIBS technique has shown, by considering an adequate approach on the emitting plasma features, that its peculiarities are anyway preserved so that a fast analysis of ancient copper-based-alloys can be achieved. After verifying the suitability of the methodology, it has been possible to fulfill the typical assumptions considered for the LIBS calibration curves method and use it for ancient bronze artworks analysis.     

Phosphate ore beneficiation via determination of phosphorus-to-silica ratios by Laser Induced Breakdown Spectroscopy

We report development and application of an in-situ applicable method to determine phosphate ore rock quality based on Laser-Induced Breakdown Spectroscopy (LIBS). This is an economically viable method for real-time evaluation of ore phosphate rocks in order to separate high-silica pebbles prior to deep beneficiation. This is achieved by monitoring relative emission line intensities from key probe elements via single laser ablation shots: the ratio of the phosphorous to silica line intensities (P/Si ratio) provides a simple and reliable indicator of ore rock quality. This is a unique LIBS application where no other current analytical spectroscopic method (ICP or XRF) can be applied. Method development is discussed, and results with actual ore samples are presented.     

便携式激光诱导击穿光谱仪测定土壤中重金属

土壤重金属污染对农作物生长和人体健康都有严重危害,现场快速检测对土壤重金属污染调查、应急监测具有重要意义。采用自主研发的土壤重金属激光诱导击穿光谱现场快速检测仪对矿区周边土壤进行现场检测分析,以835个不同基质土壤的光谱数据建立定标数据库,通过支持向量机建立回归模型对土壤重金属元素含量进行定量反演。现场检测获取的全波段光谱波动在15%以内,Cd、Cr、Cu、Ni、Pb和Zn等6种元素光谱强度相对标准偏差平均值为6.31%。将检测结果与实验室电感耦合等离子体质谱法分析对比,6种元素的皮尔逊相关系数r在0.850 1～0.982 9,检测结果80%以上处于±30%相对误差区间分布。对比结果表明自主研发的土壤重金属激光诱导击穿光谱现场检测仪可以满足现场快速检测需求。     

激光诱导击穿光谱检测青菜中镉元素的多变量筛选研究

利用激光诱导击穿光谱(LIBS)技术与常规化学分析方法获取28个浓度梯度含Cd元素的青菜样品的LIBS谱线信息以及Cd含量信息.对获取的光谱信息结合标准归一化处理(SNV)、一阶导数(FD)、二阶导数(SD)、中心化处理(Center)作为偏最小二乘法(PLS)模型的优选方法;再根据4种预处理方法的预测结果选取最佳方法,同时将该方法作为间隔偏最小二乘法(iPLS)与联合区间间隔偏最小二乘法(SiPLS)优选青菜LIBS谱线的最佳波长区间.结果表明:通过SiPLS优选的特征波长区间分别为214.72 ～ 215.82 nm,215.88～ 216.97 nm,225.08 ～ 226.35 nm,并且经过中心化预处理后建立的验证模型效果最好,结果显示交叉验证均方根误差(RMSECV)为1.487,验证均方根误差(RMSEP)为1.094,相关系数(R)为0.9942,平均相对误差(ARE)为11.60％.研究结果表明,所选优化方法适合青菜中重金属Cd元素的LIBS校正模型的建立,且具有较好的预测效果.     

Characterization of Pollution Indices in Soil Surrounding a Power Plant by Laser Induced Breakdown Spectroscopy

The distribution of pollution indices of copper, iron, lead, and nickel in the soil around a gas fired power plant were determined by laser induced breakdown spectroscopy. A Q-switched Nd:YAG laser operating at 90 mJ and 1064 nm was employed to convert the soil into a plasma that was characterized by optical emission spectroscopy. High concentrations of copper, iron, lead, and nickel were measured near the power station. The enrichment factors for lead, copper, nickel, and iron were 0.38–0.64, 0.2–0.65, 0.49–0.73, and 1.02–1.46 with means of 0.48, 0.37, 0.60, and 1.16. Geo-accumulation was observed to be in class 0 (unpolluted) for all metals except for iron, which was in class 0–1. The ecological risk factor was in the low potential range for all metal concentrations. From the center to the outskirts of power station and from surface to deep soil, the soil quality varied from low polluted to unpolluted for heavy metals due to power plant emission, fuel storage, and station remnants.     

Determination of the postmortem interval by Laser Induced Breakdown Spectroscopy using swine skeletal muscles

Skin and muscle samples are useful to discriminate individuals as well as their postmortem interval (PMI) in crime scenes and natural or caused disasters. In this study, a simple and fast method based on Laser Induced Breakdown Spectroscopy (LIBS) has been developed to estimate PMI using swine skeletal muscle samples. Environmental conditions (moisture, temperature, fauna, etc.) having strong influence on the PMI determination were considered. Time-dependent changes in the emission intensity ratio for Mg, Na, Hα and K were observed, as a result of the variations in their concentration due to chemical reactions in tissues and were correlated with PMI. This relationship, which has not been reported previously in the forensic literature, offers a simple and potentially valuable means of estimating the PMI.     

激光诱导击穿光谱结合CARS变量选择方法定量检测倍硫磷含量

利用双脉冲激光诱导击穿光谱(LIBS)技术对溶液中的倍硫磷含量进行定量检测。采用二通道高精度光谱仪采集不同浓度倍硫磷样品在206.28~481.77 nm波段的LIBS光谱,并对光谱进行多元散射校正(MSC)、标准正态变量变换(SNV)及3点平滑预处理,根据偏最小二乘(PLS)建模确定最优的预处理方法。在此基础上,利用竞争性自适应重加权算法(CARS)筛选与倍硫磷相关的重要变量,然后应用PLS回归建立溶液中倍硫磷含量的定量分析模型,并与单变量定量分析模型及未变量选择的PLS定量分析模型进行比较。结果表明,相比单变量定量分析模型及原始光谱PLS定量分析模型,CARS-PLS定量分析模型的性能更优,其模型的校正集和预测集的决定系数及平均相对误差分别为0.969 4、15.537%和0.995 9、5.016%。此外,与原始光谱PLS模型相比,CARS-PLS模型仅使用其中1.9%的波长变量,但预测集平均误差却由9.829%下降为5.016%。由此可见,LIBS技术检测溶液中的倍硫磷含量具有一定的可行性,且CARS方法能简化定量分析模型,提高模型的预测精度。