Nondestructive Determination of Cu Residue in Orange Peel by Laser Induced Breakdown Spectroscopy

Laser induced breakdown spectroscopy(LIBS) is an emerging tool with rapid,nondestructive,green characteristics in qualitative or quantitative analyses of composition in materials.But LIBS has its shortcomings in detect limit and sensitivity.In this work,heavy metal Cu in Gannan Navel Orange,which is one of famous fruits from Jiangxi of China,was analyzed.In view of LIBS's limit,it is difficult to determinate heavy metals in natural fruits.In this work,nine orange samples were pretreated in 50-500 μg/mL Cu solution,respectively.Another one orange sample was chosen as a control group without any pollution treatment.Previous researchers observed that the content of heavy metals is much higher in peel than in pulp.So,the content in pulp can be reflected by detecting peel.The real concentrations of Cu in peels were acquired by atomic absorption spectrophotometer(AAS).A calibration model of Cu I 324.7 and Cu Ⅰ 327.4was constructed between LIBS intensity and AAS concentration by six samples.The correlation coefficient of the two models is also 0.95.All of the samples were used to verify the accuracy of the model.The results show that the relative error(RE) between predicted and real concentration is less than 6.5%,and Cu Ⅰ 324.7 line has smaller RE than Cu Ⅰ 327.4.The analysis demonstrated that different characteristic lines decided different accuracy.The results prove the feasibility of detecting heavy metals in fruits by LIBS.But the results are limited in treated samples.The next work will focus on direct analysis of heavy metals in natural fruits without any pretreatment.This work is helpful to explore the distribution of heavy metals between pulp and peel.     

A strategy to significantly improve the classification accuracy of LIBS data:application for the determination of heavy metals in Tegillarca granosa

Tegillarca granosa, as a popular seafood among consumers, is easily susceptible to pollution from heavy metals. Thus, it is essential to develop a rapid detection method for Tegillarca granosa. For this issue, five categories of Tegillarca granosa samples consisting of a healthy group; Zn, Pb, and Cd polluted groups; and a mixed pollution group of all three metals were used to detect heavy metal pollution by combining laser-induced breakdown spectrometry(LIBS) and the newly proposed linear regression classification-sum of rank difference(LRC-SRD)algorithm. As the comparison models, least regression classification(LRC), support vector machine(SVM), and k-nearest neighbor(KNN) and linear discriminant analysis were also utilized. Satisfactory accuracy(0.93) was obtained by LRC-SRD model and which performs better than other models. This demonstrated that LIBS coupled with LRC-SRD is an efficient framework for Tegillarca granosa heavy metal detection and provides an alternative to replace traditional methods.     

Online calibration of laser-induced breakdown spectroscopy for detection of heavy metals in water

In order to reduce the fluctuation of LIBS detection spectrum of liquid sample, the full-spectrum sum method and the internal standardization method is adopted, using an equal-RSD normalization algorithm to calibrate the detection spectrum. Experiment result shows that the full-spectrum sum method reduced the RSD of parallel samples of Cd and Cr to 9.4％ and 11.06％ from 28.32％ and 31.93％ respectively, yielded better overall calibration than the singleelement internal standardization approach, thereby suggesting that the former method is convenient and effective for online calibration of LIBS for detection of aqueous heavy metals.     

Simultaneous Determination of Trace Lead and Chromium in Water Using Laser-Induced Breakdown Spectroscopy and Paper Substrate

Toxic metals such as lead and chromium in aqueous solutions have been analyzed simultaneously by laser-induced breakdown spectroscopy(LIBS), in which the ordinary printing paper is used as a liquid absorber which was immerged into Pb(NO3)2and Cr(NO3)3aqueous solution to enrich the heavy metals. This method overcomes the drawbacks of splashing and low sensitivity in ordinary LIBS analysis of water, in which a laser beam is directly focused on a liquid surface. A good signal intensity and reproducibility has been demonstrated. The Pb 405.78 nm and Cr 427.48 nm spectral lines are used as the analytical lines. The variation of line intensity with immersion time was investigated. The calibration curve for quantitative measurement of Pb and Cr in water was established, and the detection limits are 0.033 mg/L and 0.026 mg/L respectively,which is about 2-3 orders of magnitude better than that in the ordinary LIBS analysis of heavy metal in solution.     

LIBS Detection of Heavy Metal Elements in Liquid Solutions by Using Wood Pellet as Sample Matrix

Laser-induced breakdown spectroscopy （LIBS） has been applied to the analysis of heavy metals in liquid samples. A new approach was presented to lower the limit of detection （LOD） and minimize the sample matrix effects, in which dried wood pellets absorbed the given amounts of Cr standard solutions and then were baked because they have stronger and rapid absorption properties for liquid samples as well as simple elemental compositions. In this work, we have taken a typical heavy metal Cr element as an example, and investigated the spectral feasibility of Cr solutions and dried wood pellets before and after absorbing Cr solutions at the same experimental conditions. The results were demonstrated to successfully produce a superior analytical response for heavy metal elements by using wood pellet as sample matrix according to the obtained LOD of 0.07 ppm for Cr element in solutions.     

Quantitative Analysis of Heavy Metals in Water Based on LIBS with an Automatic Device for Sample Preparation

Heavy metals in water can be deposited on graphite flakes,which can be used as an enrichment method for laser-induced breakdown spectroscopy(LIBS) and is studied in this paper.The graphite samples were prepared with an automatic device,which was composed of a loading and unloading module,a quantitatively adding solution module,a rapid heating and drying module and a precise rotating module.The experimental results showed that the sample preparation methods had no significant effect on sample distribution and the LIBS signal accumulated in 20 pulses was stable and repeatable.With an increasing amount of the sample solution on the graphite flake,the peak intensity at Cu Ⅰ 324.75 nm accorded with the exponential function with a correlation coefficient of 0.9963 and the background intensity remained unchanged.The limit of detection(LOD) was calculated through linear fitting of the peak intensity versus the concentration.The LOD decreased rapidly with an increasing amount of sample solution until the amount exceeded 20 mL and the correlation coefficient of exponential function fitting was 0.991.The LOD of Pb,Ni,Cd,Cr and Zn after evaporating different amounts of sample solution on the graphite flakes was measured and the variation tendency of their LOD with sample solution amounts was similar to the tendency for Cu.The experimental data and conclusions could provide a reference for automatic sample preparation and heavy metal in situ detection.     

Identification of heavy metal-contaminated Tegillarca granosa using laser-induced breakdown spectroscopy and linear regression for classification

Tegillarca granosa (T. granosa) is susceptible to heavy metals, which may pose a threat to consumer health. Thus, healthy and polluted T. granosa should be distinguished quickly. This study aimed to rapidly identify heavy metal pollution by using laser-induced breakdown spectroscopy (LIBS) coupled with linear regression classification (LRC). Five types of T. granosa were studied, namely, Cd-, Zn-, Pb-contaminated, mixed contaminated, and control samples. Threshold method was applied to extract the significant variables from LIBS spectra. Then, LRC was used to classify the different types of T. granosa. Other classification models and feature selection methods were used for comparison. LRC was the best model, achieving an accuracy of 90.67%. Results indicated that LIBS combined with LRC is effective and feasible for T. granosa heavy metal detection.     

Heavy Metal Detection in Soils by Laser Induced Breakdown Spectroscopy Using Hemispherical Spatial Confinement

Spatial confinement has great potential for Laser Induced Breakdown Spectroscopy(LIBS) instruments after it has been proven that it has the ability to enhance the LIBS signal strength and repeatability.In order to achieve in-situ measurement of heavy metals in farmland soils by LIBS,a hemispherical spatial confinement device is designed and used to collect plasma spectra,in which the optical fibers directly collect the breakdown spectroscopy of the soil samples.This device could effectively increase the stability of the spectrum intensity of soil.It also has other advantages,such as ease of installation,and its small and compact size.The relationship between the spectrum intensity and the laser pulse energy is studied for this device.It is found that the breakdown threshold is 160 cm~(-2),and when the laser fluence increases to 250 J/cm~2,the spectrum intensity reaches its maximum.Four different kinds of laser pulse energy were set up and in each case the limits of detection of Cd,Cu,Ni,Pb and Zn were calculated.The results show that when the laser pulse fluence was 2.12 GW/cm~2,we obtained the smallest limits of detection of these heavy metals,which are all under 10 mg/kg.This device can satisfy the needs of heavy metal in-situ detection,and in the next step it will be integrated into a portable LIBS instrument.     

Remote open-path laser-induced breakdown spectroscopy for the analysis of manganese in steel samples at high temperature

A remote open-path laser-induced breakdown spectroscopy(LIBS) system was designed and studied in the present work for the purpose of combining the LIBS technique with the steel production line. In this system, the relatively simple configuration and optics were employed to measure the steel samples at a remote distance and a hot sample temperature. The system has obtained a robustness for the deviation of the sample position because of the open-path and alloptical structure. The measurement was carried out at different sample temperatures by placing the samples in a muffle furnace with a window in the front door. The results show that the intensity of the spectral lines increased as the sample temperature increased. The influence of the sample temperature on the quantitative analysis of manganese in the steel samples was investigated by measuring ten standard steel samples at different temperatures. Three samples were selected as the test sample for the simulation measurement. The results show that, at the sample temperature of 500 ℃, the average relative error of prediction is 3.1% and the average relative standard deviation is 7.7%, respectively.     

Development of a fiber-coupled laser-induced breakdown spectroscopy instrument for analysis of underwater debris in a nuclear reactor core

To inspect the post-accident nuclear core reactor of the TEPCO Fukushima Daiichi nuclear power plant (F1-NPP), a transportable fiber-coupled laser-induced breakdown spectroscopy (LIBS) instrument has been developed. The developed LIBS instrument was designed to analyze underwater samples in a high-radiation field by single-pulse breakdown with gas flow or double-pulse breakdown. To check the feasibility of the assembled fiber-coupled LIBS instrument for the analysis of debris material (mixture of the fuel core, fuel cladding, construction material and so on) in the F1-NPP, we investigated the influence of the radiation dose on the optical transmittance of the laser delivery fiber, compared data quality among various LIBS techniques for an underwater sample and studied the feasibility of the fiber-coupled LIBS system in an analysis of the underwater sample of the simulated debris in F1-NPP. In a feasible study conducted by using simulated debris, which was a mixture of CeO₂ (surrogate of UO₂), ZrO₂ and Fe, we selected atomic lines suitable for the analysis of materials, and prepared calibration curves for the component elements. The feasible study has guaranteed that the developed fiber-coupled LIBS system is applicable for analyzing the debris materials in the F1-NPP.     

Signal processing for real-time identification of similar metals by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy(LIBS) is regarded as a promising technique for realtime sorting of scrap metals due to its capability of fast multi-elemental and in-air analysis. This work reports a method for signal processing which ensures high accuracy and high speed during similar metal sorting by LIBS. Similar metals such as aluminum alloys or stainless steel are characterized by nearly the same constituent elements with slight variations in elemental concentration depending on metal type. In the proposed method, the original data matrix is substantially reduced for fast processing by selecting new input variables(spectral lines) using the information for the constituent elements of similar metals. Specifically, principal component analysis(PCA) of full-spectra LIBS data was performed and then, based on the loading plots, the input variables of greater significance were selected in the order of higher weights for each constituent element. The results for the classification test with aluminum alloy, copper alloy,stainless steel and cast steel showed that the classification accuracy of the proposed method was nearly the same as that of full-spectra PCA, but the computation time was reduced by a factor of 20 or more. The results demonstrated that incorporating the information for constituent elements can significantly accelerate classification speed without loss of accuracy.     

红外光谱法在线测量高浓度重水

为了准确、快速、安全定量工艺系统中的高浓度重水,采用离线式傅里叶变换红外光谱仪,以空光路状态下的单光束谱为背景光谱,得到不同浓度标准重水样品的红外吸收光谱,对3410cm^-1处重水浓度与吸光度进行线性拟合,建立红外光谱法测量高浓度重水的工作曲线。在此基础上,设计重水在线测量方案,实现高浓度重水在线测量。结果表明,测量浓度为99.85%的重水时,相对标准偏差优于0.01%。重水浓度范围为99.06%~99.98%时,线性相关系数R²=0.999 9。该测量方法准确、快速、无损样品、无放射性辐照等,可拓展到其他浓度段重水在线测量。     

Ultrasonic Nebulizer Assisted LIBS: a Promising Metal Elements Detection Method for Aqueous Sample Analysis

A newly developed approach for trace metal elements detection for aqueous samples analysis is presented in this paper. The idea of this approach is to improve ablation efficiency by transforming the liquid sample into a dense cloud of droplets using an ultrasonic nebulizer. The resulting droplets are then subjected to analysis by laser induced breakdown spectroscopy (LIBS). A purpose-built ultrasonic nebulizer assisted LIBS (UN-LIBS) system has been applied to the analysis of aqueous samples at trace levels of concentration. Experimental investigations of solution samples were carried out with various dissolved trace metal elements (Mn, Zn, Cu, Pb, Fe, Mg and Na) using this approach. The characteristics of UN-LIBS signal of the elements were investigated regarding the lifetime and S/B ratio and the calibration curves for trace metal elements analyses. The obtained LODs are comparable or much better than the LODS of the reported signal enhancement approaches when the laser pulse energy was as low as 30 mJ. The good linearity of calibration curves and the low LODs shows the potential ability of this method for metal elements analysis application. The density of the electrons was calculated by measuring the Stark width of the line of Hα. The possible mechanism of the LIBS signal enhancement of this approach was briefly discussed.     

Development of an Automated LIBS Analytical Test System Integrated with Component Control and Spectrum Analysis Capabilities

The present paper proposes an automated Laser-Induced Breakdown Spectroscopy(LIBS) analytical test system,which consists of a LIBS measurement and control platform based on a modular design concept,and a LIBS qualitative spectrum analysis software and is developed in C#.The platform provides flexible interfacing and automated control;it is compatible with different manufacturer component models and is constructed in modularized form for easy expandability.During peak identification,a more robust peak identification method with improved stability in peak identification has been achieved by applying additional smoothing on the slope obtained by calculation before peak identification.For the purpose of element identification,an improved main lines analysis method,which detects all elements on the spectral peak to avoid omission of certain elements without strong spectral lines,is applied to element identification in the tested LIBS samples.This method also increases the identification speed.In this paper,actual applications have been carried out.According to tests,the analytical test system is compatible with components of various models made by different manufacturers.It can automatically control components to get experimental data and conduct filtering,peak identification and qualitative analysis,etc.on spectral data.     

A Hydrogel's Formation Device for Quick Analysis of Liquid Samples Using Laser-Induced Breakdown Spectroscopy

The laser-induced breakdown spectroscopy technique has irreplaceable advantages in the field of detection due to its multi-phase specimen detection ability.The development of the LIBS technique for liquid analysis is obstructed by its inherent drawbacks like the surface ripples and extinction of emitted intensity,which make it unpractical.In this work,an in-situ hydrogel formation sampling device was designed and used the hydrogel as the detection phase of LIBS for Cu,Cr and Al in an aqueous solution.With the measured amount of resin placed in the device,the formed hydrogel could be obtained within 20 s after putting the device into water solution.The formed hydrogel could be directly analyzed by LIBS and reflect the elemental information of the water sample.The prominent performance made this hydrogel's formation device especially suitable for quick in-situ environmental liquid analysis using LIBS.     

Quantitative analysis of uranium in electrorecovery salt of pyroprocessing using laser-induced breakdown spectroscopy

The amounts of nuclear materials in the Li Cl-KCl salt in pyroprocessing have to be analyzed to prevent the diversion of the nuclear material. An alternative method to the chemical analysis has been pursued, and laser-induced breakdown spectroscopy(LIBS) is one candidate. In the present work, an in situ and quantitative analysis method of electro-recovery(ER) salt was proposed and demonstrated by using LIBS combined with dipstick sampling. Two types of simulated salt samples were prepared: ER salt sample and salt obtained from the dipstick sampling, and pulsed neodymium-doped yttrium aluminum garnet(Nd:YAG) laser with a wavelength of 532 nm was focused on the salt to generate plasma. The plasma emission was measured by using an Echelle spectrometer with a resolution of 0.01 nm in conjunction with an Intensified Charge-Coupled Detector camera. The U and other rare earth peaks in the spectra were identified. The best Limit of Detection and Root Mean Square Error of Calibration of U were 38 ppm and 0.0203 wt%,respectively. Our work shows that the U in the pyroprocessing ER salt can be monitored with LIBS.     

Calibration curve and support vector regression methods applied for quantification of cement raw meal using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy(LIBS) is a qualitative and quantitative analytical technique with great potential in the cement industrial analysis. Calibration curve(CC) and support vector regression(SVR) methods coupled with LIBS technology were applied for the quantification of three types of cement raw meal samples to compare their analytical concentration range and the ability to reduce matrix effects, respectively. To reduce the effects of fluctuations of the pulse-to-pulse, the unstable ablation and improve the reproducibility, all of the analysis line intensities were normalized on a per-detector basis. The prediction results of the elements of interest in the three types of samples, Ca, Si, Fe, Al, Mg, Na, K and Ti, were compared with the results of the wet chemical analysis. The average relative error(ARE),relative standard deviation(RSD) and root mean squared error of prediction(RMSEP) were employed to investigate and evaluate the prediction accuracy and stability of the two prediction methods. The maximum average ARE of the CC and SVR methods is 34.62% instead of 6.13%,RSD is 40.89% instead of 7.60% and RMSEP is 1.34% instead of 0.43%. The results show that SVR method can accurately analyze samples within a wider concentration range and reduce the matrix effects, and LIBS coupled with it for a rapid, stable and accurate quantification of different types of cement raw meal samples is promising.     

Development of a Laboratory Cement Quality Analysis Apparatus Based on Laser-Induced Breakdown Spectroscopy

Determination of the chemical composition of cement and ratio values of clinker plays an important role in cement plants as part of the optimal process control and product quality evaluation. In the present paper, a laboratory laser-induced breakdown spectroscopy (LIBS) apparatus mainly comprising a sealed optical module and an analysis chamber has been designed for possible application in cement plants for on-site quality analysis of cement. Emphasis is placed on the structure and operation of the LIBS apparatus, the sealed optical path, the temperature controlled spectrometer, the sample holder, the proper calibration model established for minimizing the matrix effects, and a correction method proposed for overcoming the ‘drift’ obstacle. Good agreement has been found between the laboratory measurement results from the LIBS method and those from the traditional method. The absolute measurement errors presented here for oxides analysis are within 0.5%, while those of ratio values are in the range of 0.02 to 0.05. According to the obtained results, this laboratory LIBS apparatus is capable of performing reliable and accurate, composition and proximate analysis of cement and is suitable for application in cement plants.     

Trace metal distribution studies in river water by PIXE

Proton induced X-ray Emission (PIXE) has been used to measure the trace metals especially heavy metals in Chaliyar river water samples to assess the impact of pollutants from the industrial wastes. Water samples were collected in summer and rainy seasons from three different depths along the course of the river. Measurements were carried out with 2 MeV proton beam using a 3 MV tandem pelletron accelerator at Institute of Physics, Bhubaneswar. Results from the water Samples collected in both the seasons show that the concentrations of certain heavy metals like Hg, Zn and Pb are more than the prescribed limits. This is because of pollution due to industrial wastes, indicating a need for improvement in the industrial waste treatment.     

Microanalysis of Multi-Element in Juncus effusus L. by LIBS Technique

Laser-induced breakdown spectroscopy (LIBS) was used to decipher the unique multi-elemental characteristics of Juncus e?usus L. The spectral fingerprints of Juncus e?usus L. were established based on elemental microanalysis via LIBS. Microanalysis and multimode sam?pling methodologies were designed in this study. The relative standard deviation (RSD) approach was performed to optimize the multi-shot measurements. Taking advantage of the capability with no or minimal sample pre-treatment of LIBS, a thermodynamic chart of four elements (Mg, Ca, Ba, and Na) was created from twelve collection regions. The diagram of elemental distribution on a micro-scale was generated to explore the nature of Juncus e?usus L. by LIBS. The results demon?strated that LIBS is a promising technique for rapid elemental microanalysis of heterogeneous samples.