Assessment of LIBS for Spectrochemical Analysis: A Review

Abstract

This review assesses the applications of laser-induced breakdown spectroscopy (LIBS) for the analysis of a variety of samples, including biomaterials (teeth, nail, hair, gallstones, and kidney stones, etc.), food materials (fruits and vegetables, milk, salt, nutritional supplements, etc.), medicinal plants, industrial waste, liquid samples, etc. In addition, for the first time the identification of cholesterol and pigment stones was performed on the basis of atomic lines of different elements and molecular bands of C₂ molecules present in the LIBS spectra of gallstones. Chemometric techniques such as principal component analysis (PCA) was also applied to LIBS data for rapid identification/classification of different gallstone samples. LIBS analysis of toxic/heavy elements present in vegetables (spinach, tomato) and rice is also presented in this review. It was observed that vegetables grown near industrial areas are rich in several toxic metals like Pb and Cr. The wastewater samples from different industries were also analyzed by recording their spectra using a liquid jet. These results clearly demonstrate the ability of LIBS technique as an instant monitoring device to detect heavy metals present in liquid samples. Finally, this review shows that LIBS is a versatile analytical technique with unlimited applications.     

Biomedical and environmental applicationsof laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is an emerging analytical technique with numerous advantages such as rapidity, multi-elemental analysis, minimal sample preparation, minimal destruction, low cost and versatility of being applied to a wide range of materials. In this paper, we report the preliminary observations we obtained using LIBS for clinical and environmental samples. Elemental analysis has been done qualitatively in human teeth samples which show encouraging results. It has also been demonstrated in this paper that LIBS can be very well utilized in field applications such as plastic waste sorting and recycling.     

Analytical Assessments of Gallstones and Urinary Stones: A Comprehensive Review of the Development from Laser to LIBS

Abstract

Laser-induced breakdown spectroscopy (LIBS) is a sensitive optical technique capable of fast multi-elemental analysis of various kinds of materials (solid, liquids, and gases) and its applications are growing rapidly and continue to extend to include a broad variety of biological materials. Its application is suited particularly for urinary stones and gallstones bulk analysis and microanalysis because investigation of the spatial distribution of matrix and trace elements can help to explain their emergence and growth. Therefore, we review the application of LIBS for the analysis of different kinds of gallstones and urinary stones. In brief, we also describe the history, fundamentals, advantages, and disadvantages of LIBS and its potential for spectrochemical analysis of gallstones and kidney stones. We also emphasize the applications of different kinds of lasers in urology, particularly the laser ablation of gallstones and urinary stones and its recent progress. We also summarize and compare the analytical figures of merits of analytical techniques that are commonly used to characterize and/or analyze stones.     

激光诱导击穿光谱在疾病诊断中的应用前景

微量元素与人体健康密切相关。比如,金属元素的稳态可能会影响细胞的代谢功能,进而诱发某些疾病的产生。激光诱导击穿光谱（LIBS）,是一种可用于分子复杂的生物材料或临床标本的无因子分析技术,具有从单个激光脉冲和少量材料（纳克级数）中获得元素信号的能力。综述了2015年以来LIBS技术在疾病诊断方面的相关研究,包括几种常见疾病（结石、脱发、眼病,等）和恶性肿瘤（皮肤癌、肝癌、胃癌、乳腺癌、卵巢癌、宫颈癌,等）。研究的样品涵盖块状组织、结石、组织切片、血清、血浆、全血等生物材料。这些生物样品包含或积累了可以检测、定量和成像的金属物质和金属化合物。LIBS能够以百万分之几的灵敏度和微观分辨率对样品中内源性和外源性化学元素进行微分析、定位分析以及定量分析。最后,对LIBS技术的医学发展趋势进行了展望。希望简单的评述能够吸引更多的科学家关注LIBS技术在疾病诊断领域的应用,进而促进LIBS技术的日趋完善,为疾病诊断和治疗发挥更大的作用。     

激光诱导击穿光谱与拉曼光谱技术在危险物检测中的研究进展

炸药、生物及化学危险物检测在反恐和公共安全领域具有重要应用价值,也是目前亟需解决的问题。激光诱导击穿光谱技术利用高能激光脉冲诱导材料产生等离子体,通过探测等离子体辐射光谱从而分析其组成成分。拉曼光谱技术是基于非弹性光散射的一种光谱检测方法,可以反映分子的振动信息。由于它们都具有快速和非接触遥测的优点,成为最有发展潜力和应用前景的危险物检测技术。介绍了激光诱导击穿光谱、拉曼光谱以及二者联合探测技术在危险物检测中的国内外发展现状,并对各自的优缺点进行了分析。激光诱导击穿光谱信号强、实时性好,但重复性差、基底效应影响显著,在判别组成元素相同而分子结构不同的危险物和干扰物时面临巨大挑战。拉曼光谱能够提供被测物的分子信息,适合于鉴别有机危险物,但信号弱、受荧光干扰大、检测低浓度样品及分析混合物的能力弱,外场使用时受周围杂散光以及环境变化的影响大。将这两种光谱探测技术相融合,发挥各自的优点,可以有效地提高探测危险物的准确度。但两种光谱联合探测系统结构和数据处理复杂,成本高,还有许多技术难点亟需解决。文章最后,对危险物激光诱导击穿光谱和拉曼光谱研究的前景进行了展望。     

Quantitative analysis of ITO film by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is an effective method for nondestructive rapid element analysis in a wide range of media in situ. We use the LIBS technique for quantitative analysis of indium tin oxide (ITO) films, which are transparent conducting materials widely used in industry. The plasma is generated by focusing a Nd:YAG laser pulse with a duration of 10 ns and a wavelength of 1064 nm onto the ITO-sample surface. We perform test experiments to define optimum values of the laser-pulse energy and the time delay between the laser pulse and the beginning of the LIBS spectra acquisition. Next, by the calibration-free Boltzmann plot method, we assess the plasma temperature and finally calculate the content of In and Sn in the test ITO specimen, and this agrees well with real concentration values.     

Determination of Chloride Content in Different Types of Cement Using Laser-Induced Breakdown Spectroscopy

The characterization and accurate determination of the chloride content in cement/concrete is very important for the assessment of the durability and safety of a concrete structure. The available analytical techniques are relatively expensive and time consuming. In this study, a laser-induced breakdown spectroscopy (LIBS) system was used for determination of elemental composition in three different types of cement samples. The plasma was generated by focusing a pulsed Nd: YAG laser at 1064 nm on the cement samples. The concentrations of different elements of significance for structural stability in cement samples were determined. The evaluation of the potential and the capabilities of LIBS as a rapid tool for characterization of cement samples is discussed. The optimum LIBS setup and experimental conditions to detect and measure chloride in building materials are reported. The LIBS results were compared with the results obtained using a standard analytical technique such as inductively coupled plasma emission spectroscopy (ICP–ES). The limits of detection were determined, and calibration curves were measured. The results of this investigation indicate the reliability of LIBS to characterize different cement samples and to assess the chloride content in these cements.     

激光诱导击穿光谱分析钢中酸不溶铝含量

激光诱导击穿光谱(LIBS)具有分析速度快、非接触测量、表面微区分析以及易于实现在线实时监控分析等优点。通过LIBS对块状钢铁样品表面进行扫描分析,实现了钢中酸不溶铝含量的定量表征。铝的异常信号采用Nalimov迭代法剔除,以剩余信号强度的平均值加三倍标准偏差作为阈值强度,高于阈值强度的信号认为由酸不溶铝产生,反之由酸溶铝产生。在用含量校准曲线获得钢中总铝的含量后,分别根据酸不溶铝信号总强度或信号总个数与总铝信号之比,计算钢中酸不溶铝的含量。几种钢铁标准样品及实际生产板坯样品中酸不溶铝含量的对比分析结果表明,根据铝信号总强度获得的分析结果与传统湿法分析结果吻合得更好,可用于快速定量表征钢中酸不溶铝的含量。     

An improved approach for hydrogen analysis in metal samples using single laser-induced gas plasma and target plasma at helium atmospheric pressure

We report in this paper the results of an experimental study on hydrogen analysis of solid samples in high pressure helium ambient gas employing the basic scheme of laser induced breakdown spectroscopy (LIBS). It is shown that the metastable excited state of helium atom can be utilized to induce delayed excitation of the ablated hydrogen atoms, and thereby avoid the Stark broadening effect as well as overcoming the undesirable mismatch effect, which are responsible for inefficient excitation respectively. It is further demonstrated that for samples of high boiling-point materials such as zircaloy, successful hydrogen analysis can be achieved by a newly introduced double excitation technique employing single laser realized in a modified configuration of the conventional LIBS method. PACS 51-52     

Characteristics of solid aerosols produced by optical catapulting studied by laser-induced breakdown spectroscopy

Optical catapulting (OC) constitutes an effective method to transport small amounts of different materials in the form of a solid aerosol. In this report, laser-induced breakdown spectroscopy (LIBS) is used for the analysis of those aerosols produced by OC. For this purpose, materials were catapulted using a Q-switch Nd:YAG laser. A second Q-switch Nd:YAG laser was used for LIBS analysis of the ejected particles. Data processing of aerosols was conducted using conditional data analysis. Also, the standard deviation method was used for the qualitative identification of the ejected particles. Two modes of interaction in OC (OC with focused or defocused pulses) have been evaluated and discussed. LIBS demonstrates that the distribution (spreading) of the ejected particles along the propagation axis increased as a function of the interpulse delay time. The mass density and the thickness of the target also play an important role in OC-LIBS.     

Role of Purging Gases in the Analysis of Polycarbonate With Laser-Induced Breakdown Spectroscopy

Polycarbonate is a strong, durable, and high-transparent material. It is being used extensively in electronics applications, eyewear lenses, exterior automotive components, construction industry, and manufacturing of containers. Laser-induced breakdown spectroscopy (LIBS) is a well-known and widely-used technique in quantitative and qualitative analysis of materials. The analysis is based on the spectra obtained in the LIBS process. We investigate the LIBS spectrum of polycarbonate (C₁₂H₁₈O₇)_n polymer in the presence of air, helium, argon, neon, and mixed-gas atmospheres using a Spectrolaser-7000 system. We investigate the peak intensities of hydrocarbon fragments like C₂, C, and CN in He, Ar, and Ne atmospheres. Moreover, we observe the CN molecular lines in the LIBS spectrum of polycarbonate in air only. We show that, in the He and Ne atmospheres, the peak intensity of the hydrogen (656 nm) line increases 1.85 and 4.5 times, and the peak intensity of the carbon (247 nm) line increases 1.46 and 2.6 times, respectively, as compared to that in air. These results are very useful and will help in the analysis and detection of polymers and bio-samples, which are mostly comprised of carbon and hydrogen.     

多次放电的激光诱导击穿光谱信号增强

激光诱导击穿光谱技术(LIBS)是一种广泛应用于科学和工程方面的元素分析技术。LIBS测量一些微量元素时存在探测极限高的不足,因此增强LIBS信号强度,降低元素探测极限,对扩展其应用范围有着重要的意义。为了实现LIBS光谱信号的增强,提出多次放电增强激光诱导击穿光谱方法,并以固体铝合金材料为例进行了光谱信号强度增强的研究。实验发现,激光作用在铝合金材料上烧蚀样品产生等离子体并溅射到样品上方高压放电电极所在区域,该区域在等离子体产生之后50 μs之内均可以诱导高压电极放电。因此采用高频脉冲电源可以实现一次LIBS产生的等离子体诱导电极多次放电。多次放电会对等离子体进行多次激发,同时多次放电对等离子的加热作用会延缓等离子体冷却速率从而延长等离子体的持续时间,两者共同作用可以增强LIBS光谱信号强度,进而降低LIBS对微量元素的探测极限。使用频率为100 kHz的高频直流脉冲电源,利用数字延迟脉冲发生器同步激光与高压电源,在激光过后3.6 μs触发高压放电,一次LIBS产生的等离子体可以诱导电极5次放电,即对等离子体进行5次激发和加热。利用光谱仪对5次放电等离子体光谱进行积分测量。实验结果表明：使用多次放电增强之后,等离子体持续时间得到大幅延长,光谱信号强度得到大幅增强,其中,Mg Ⅱ (~279 nm)的信号强度可以增强约48倍,Al Ⅱ (~358 nm)的信号强度可以增强约72倍,微量元素Mn Ⅰ (~403 nm)的信号强度增强约6.3倍,微量元素Cu Ⅰ (~403 nm) 的信号强度增强约8.3倍。Mn Ⅰ (~403 nm)和Cu Ⅰ (~403 nm) 的探测极限分别降低为LIBS单次放电的1/6和1/8。多次放电增强激光诱导击穿光谱方法很好地增强了LIBS的光谱信号强度,降低了对微量元素的探测极限,扩展了LIBS技术的应用范围。该方法有潜力应用到贵重物品、稀有材料及文物的鉴定之中。     

基于激光诱导击穿光谱技术的土壤泥浆中Pb元素检测

激光诱导击穿光谱(LIBS)作为一种新兴的元素分析技术,具有实时在线、非接触、多元素同时探测等渚多优点.将LIBS技术引入土壤泥浆重金属污染的检测分析,力图发展一种针对泥浆重金属污染监测的原位传感技术.实验选择Pb作为探测元素,Mn为内标元素;采用重复频率10 Hz的Nd:YAG调Q激光器的二倍频(532 nm)输出作为激发光源,OCD收集信号,对实验室配制的不同浓度Pb泥浆样品的LIBS信号进行了探测分析.获得了各种浓度下Pb泥浆样品在Pb 405.78 nm和Mn 403.07 nm处的原子线强度比IPb/IMn及其随浓度变化的规律.结果显示IPb/IMn与样品的含铅浓度有着很好的线性关系,线性拟合相关系数R2达到0.994 9.初步证实了采用内标法对土壤泥浆中重金属Pb进行LIBS检测分析的可行性.文章还对泥浆重金属LIBS检测的影响因素进行了讨论.     

Challenges and opportunities in quantitative analyses of lead,cadmium, and hexavalent chromium in plant materials by laser-induced breakdown spectroscopy: A review

Bearing the merits of rapid, minimally destructive, and simultaneous multi-element analyses, laser-induced breakdown spectroscopy (LIBS) shows its unique advantages in quantitative analyses of lead, cadmium, and hexavalent chromium in plant materials. However, the greatest challenge LIBS must confront is calibration. Various methods for calibration are proposed and put into effect; nevertheless, limits of detection acquired by LIBS are not acceptable when they are compared with the maximum residue limits drawn up by governments, and LIBS's performances in quantitative analyses are to be improved. This review summarizes recent studies of analyzing lead, cadmium, and hexavalent chromium in plant materials quantitatively by LIBS; weighs the strengths and weaknesses of their calibration methods; and recommends the combination of matrix-matched standards based on spiked sample materials and internal standard as well as chemometrics in complicated situations for calibration in LIBS. Selecting the emission line of the analyte, sample enrichment and signal enhancement are measures that this review puts forward to improve the performances of LIBS in calibration. These quantitative analyses of lead, cadmium, and hexavalent chromium in plant materials by LIBS provide an opportunity to be utilized in mapping distributions and remediation for soil and water, as well as supervision for agricultural products safety and pollution treatments.     

Effects of experimental parameters on elemental analysis of coal by laser-induced breakdown spectroscopy

The purpose of this work is to improve the precision of the elemental analysis of coal using laser-induced breakdown spectroscopy (LIBS). The LIBS technique has the ability to allow simultaneous elemental analysis and on-line determination, so it could be used in the elemental analysis of coal. Organic components such as C, H, O, N and inorganic components such as Ca, Mg, Fe, Al, Si, Ti, Na, and K of coal have been identified. The precision of the LIBS technique depends strongly on the experimental conditions, and the choice of experimental parameters should be aimed at optimizing the repeatability of the measurements. The dependences of the relative standard deviation (RSD) of the LIBS measurements on the experimental parameters including the sample preparation parameters, lens-to-sample distance, sample operation mode, and ambient gas have been investigated. The results indicate that the precision of LIBS measurements for the coal sample can be improved by using the optimum experimental parameters.     

Calibration-free laser-induced breakdown spectroscopy for quantitative elemental analysis of materials

The application of calibration-free laser-induced breakdown spectroscopy (CF-LIBS) for quantitative analysis of materials, illustrated by CF-LIBS applied to a brass sample of known composition, is presented in this paper. The LIBS plasma is produced by a 355?nm pulsed Nd:YAG laser with a pulse duration of 6?ns focussed onto a brass sample in air at atmospheric pressure. The time-resolved atomic and ionic emission lines of Cu and Zn from the LIBS spectra recorded by an Echelle spectrograph coupled with a gated intensified charge coupled detector are used for the plasma characterization and the quantitative analysis of the sample. The time delay where the plasma is optically thin and is also in local thermodynamic equilibrium (LTE), necessary for the elemental analysis of samples from the LIBS spectra, is deduced. An algorithm relating the experimentally measured spectral intensity values with the basic physics of the plasma is developed. Using the algorithm, the Zn and Cu concentrations in the brass sample are determined. The analytical results obtained from the CF-LIBS technique agree well with the certified values of the elements in the sample, with an accuracy error <1%.     

基于激光诱导击穿光谱的大米Cr元素检测

激光诱导击穿光谱(LIBS)是一种元素快速分析的光学检测技术.在工业化发展进程中,重金属污染时刻威胁着大米等粮食作物生产地的安全性.以四川地区常见的Cr元素污染为例,采用双脉冲LIBS技术对市面上购买的五种地区大米中的Cr元素进行定量分析,并与电感耦合等离子体质谱法(ICP-MS)检测结果进行对比.结果显示LIBS测量误差满足相对误差标准,证明了LIBS方法具有对元素进行快速定量分析的能力,是检测大米重金属元素含量的一种有效手段.     

应用激光诱导击穿光谱对土壤中多元素同时定量分析

土壤元素的丰缺是对土壤养分检测、农业按需种植和科学施肥的依据,是精准农业农情信息感知技术检测的关键点,更为农业生态、高效和优质生产提供理论指导。该研究运用激光诱导击穿光谱(LIBS)技术结合定标曲线法和偏最小二乘回归(PLSR)方法对土壤中的Al,Fe,Mg,Ca,Na和K多种元素同时进行定量分析。利用LIBS检测仪获取了五种标准土壤样品(国家编号： GBW07446,GBW07447,GBW07454,GBW07455和GBW07456)的LIBS数据之后,将每种土壤的多条谱线平均处理来消除试验误差。通过分析所获取的土壤LIBS谱线信息,选取了Al,Fe,Mg,Ca,Na和K元素的特征分析谱线和分析光谱区间,并利用谱线的峰值信息和分析光谱区间内的单个或多个谱峰的积分信息(峰面积)与对应元素浓度拟合并建立定标曲线。结果表明,基于谱峰的峰面积建立的定标曲线的线性关系优于利用峰值信息建立的定标曲线(Fe除外)。同时,针对所选的分析光谱区间和元素的浓度信息,运用PLSR建立定量分析模型,其结果明显要优于定标曲线的分析精度,这也表明LIBS技术结合化学计量学分析在未来光谱化学分析领域有很大应用前景。研究的结果不仅为现代农业的土壤养分空间分布检测和农田精准施肥技术的应用起指导作用,还为田间使用的便携式LIBS土壤检测仪的开发奠定了理论基础。     

Detection of explosives with laser-induced breakdown spectroscopy

Our recent work on the detection of explosives by laser-induced breakdown spectroscopy (LIBS) is reviewed in this paper. We have studied the physical mechanism of laser-induced plasma of an organic explosive, TNT. The LIBS spectra of TNT under single-photon excitation are simulated using MATLAB. The variations of the atomic emission lines intensities of carbon, hydrogen, oxygen, and nitrogen versus the plasma temperature are simulated too. We also investigate the time-resolved LIBS spectra of a common inorganic explosive, black powder, in two kinds of surrounding atmospheres, air and argon, and find that the maximum value of the O atomic emission line SBR of black powder occurs at a gate delay of 596 ns. Another focus of our work is on using chemometic methods such as principle component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) to distinguish the organic explosives from organic materials such as plastics. A PLS-DA model for classification is built. TNT and seven types of plastics are chosen as samples to test the model. The experimental results demonstrate that LIBS coupled with the chemometric techniques has the capacity to discriminate organic explosive from plastics.     

Influence of Laser Wavelength on Laser-induced Breakdown Spectroscopy Applied to Semi-Quantitative Analysis of Trace-Elements in a Plant Sample

Laser-induced breakdown spectroscopy （LIBS） as a powerful analytical technique is applied to analyze trace- elements in fresh plant samples. We investigate the LIBS spectra of fresh holly leaves and observe more than 430 lines emitted from 25 elements and molecules in the region 230-438nm. The influence of laser wavelength on LIBS applied to semi-quantitative analysis of trace-element contents in plant samples is studied. The results show that the UV laser has lower relative standard deviations and better repeatability for semi-quantitative analysis of trace-element contents in plant samples. This work may be helpful for improving the quantitative analysis power of LIBS applied to plant samples.