LIES; Spatial confinement; Enrichment of graphite; Heavy metal in water;INDUCED BREAKDOWN SPECTROSCOPY; CHROMIUM; CHINA

According to the need of heavy metal pollution detection in waste water. Pure graphite flake is selected as matrix material, the LIBS method of multiple enrichment of samples combined with spatial confinement is adopted to detect the heavy metals contained in the waste water, and spectral stability and limit of detection of Pb, Cu, Cd and Ni are also analyzed. The experiments uses a wavelength of 1 064 nm Nd : YAG Laser, and a optical spectrometer, which the resolution is less than 0. 1 nm to detect the characteristic spectrum of heavy metal elements content in water. The result shows that this method serves to improve sensitivity and spectral stability of heavy metal in waste water while reducing the limit of detection of heavy metals. The intensity of characteristic spectrum are about 2. 5 times better than it under the condition of non-confinement, the spectral stability has also been improved, RSD is reduced from 11.34% to 8.77% compared with non-confinement condition. The calibration curves of four heavy metal elements have been established, the limits of detection of Pb, Cu, Cd and Ni are lower than 1/6 of discharge standard of national industrial waste water, meeting the demand of heavy metal in industrial waste water online monitoring. This method provides a convincing support for discharge control and online monitoring of warning excessive discharge of heavy metal elements in industrial waste water.

Manure; Calcuim; Laser-induced breakdown spectroscopy; Genetic algorithm;ELEMENTAL ANALYSIS; MEAT

In order to enhance the efficiency and safety of manure resource utilization, a rapid quantitative analysis of calcuim (Ca) content in manure is of great significance. In the presented study, the application of laser-induced breakdown spectroscopy (LIES) technique was used to quantitatively analyze Ca content in manure. Genetic algorithm (GA) was also applied to the LIBS to optimize the model. The dominant factors of LIES were set: 80 collection dots with 15% laser energy, 400 mu m spot size, delay time of 1. 0 mu s, and preforming pressure at 20 tons (T). The modeling results showed that the initial linear model constructed from the characteristic wavebands of Ca presented low precision and accuracy, partial least squares (PLS) models with wavebands at 190 similar to 950 nm exhibited the effects with coefficient of determination for the validation set (R-v(2)) and relative prediction deviation (RPD) of 0. 85 and 2. 13, respectively. The PLS model considered 12 variables, which were selected with GA in the waveband at 190 similar to 950 nm, and presented the R-v(2) and RPD of 0. 90 and 3. 04, respectively. They had presented relatively better results by avoiding complicated sample processing. It is pertinent to note that the efficiency of this method increased by a large margin when the variables were selected based on GA analysis. The results showed that LIES combined with GA can be used for quantitative analysis of Ca in manure.

Laser-induced breakdown spectroscopy; Microscope optics; Mn; Quantitative analysis;SPECTROMETRY; SAMPLES; LIBS

Manganese in the low alloy steel was analyzed quantitatively using micro-laser-induced breakdown spectroscopy. The spatial resolution of 20 mu m and the single pulse limit of detection of 0. 10% were obtained. The calibration curve of Mn was established with basic calibration method, with determination coefficient (R-2) of 0. 97. The average relative error of Mn concentration prediction on 7 samples is 12. 91%, and the root-mean-square error of cross-validation (RMSECV) is 0. 11%. The R2 reaches 0. 99 when using internal calibration method, as well as the average relative error of Mn concentration prediction on 7 samples and RMSECV were decreased to 7. 25% and 0. 07%, respectively. These results show that MicroLIBS technique is an effective approach for material surfaces quantitative microanalysis.

COD; LIBS; Prediction model; Measurement;WASTE-WATER

Using spectroscopy sensing technology to measure water COD is the trend of development of modern environmental monitoring. Compared to the traditional chemical analysis is has the benefits of online continuous detection of environmental water samples for real-time monitoring of water COD. This paper collected real water samples, using laser-induced breakdown spectroscopy (LIBS) to obtain water samples of spectral data. Establish water sample COD quantitative prediction model combining Partial Least Squares regression (PLS) by different spectral pretreatment method, then quantitative prediction of LIES spectrum measurement method of water COD and the relevant model parameters were analyzed. Found that the baseline correction superimposed S-Golay derivative partial least-squares model had better prediction results. The determination coefficient of calibration samples were 0. 995 8, while the determination coefficient of prediction were 0. 975 3, with RMSEC of 4. 438 7 and RMSEP of 9. 733 9. The experimental results showed that spectrum sensing technology can be used in the actual environment of water COD quantitative predictive analysis, laid the theoretical foundation for the development of portable water testing equipment.

Laser induced breakdown spectroscopy; Rice husk; Coarse rice; Cr;X-RAY-FLUORESCENCE; SPECTROMETRY; CU

To validate the feasibility of laser induced breakdown spectroscopy (LIBS) in detecting Cr in rice of polluted areas of Poyang Lake in Jiangxi province, rice husk samples, coarse rice samples and polished rice samples in the area were selected randomly as targets. In this work, these samples were tested with LIBS and the content of Cr was acquired by flame atomic absorption (AAS) in fresh samples. LIBS spectra showed that Cr I 425. 43 nm, Cr I 427. 48 nm, Cr I 428. 97 nm and abundant mineral elements such as Fe and Si were detected clearly, but they were undetectable directly in coarse rice and polished rice. The results of AAS shows that Cr in rice husk is more than the corresponding coarse rice and the Cr in polished rice does not exceed the limited content of 1 mg . kg(-1) according to qualified national standards GB 2762-2012. The ratio between rice husk and coarse rice is about 78. 95, it displayed the distribution is clear. This shows that compared with coarse rice, the concentration enrichment ratio of Cr in rice husk is higher than the coarse rice. The results demonstrate that it is feasible to detect Cr in rice husk and coarse rice. Therefore, it is helpful to predict the distribution of heavy metals in agricultural products by means of green method without pollution.

Laser-induced breakdown spectroscopy; Plastic; Partial least squares; Classification;IDENTIFICATION; LIBS; DISCRIMINATION; POLYMERS

The traditional ways of waste plastics processing mainly use the burning landfill, which lead to environmental pollution and the waste of resources. Waste plastic recycling is very important on the circulation economy and the sustainable development. The traditional instruments have some shortcomings in plastic classification, such as lower precision, higher cost, the influence of the sample color and a serious threat to operating personnel's health. Laser inducedbreakdown spectroscopy has many advantages, such as simultaneous multielement detection of elements, free from sample preparation, rapid and real-time analysis, slight damages to sample and no impact on the sample color. The method of Chemometrics combined with LIBS technique is applied to the plastic, which improves the accuracy of plastic classification. But at present, the classification has many problems, such as more parameters and the poor universality. Using on a self built LIBS instrument, we can study the laser energy, delay time, integration time and the angle of the optical fiber, which can achieve a better experiment condition. With the experimental platform, we analyze the 2 200 sample points and choose the partial least squares to analyze the spectral data. In order to achieve the correlation between the sample label and the data, we discuss the better ratio of the training set and validation set. The experimental results show that replacing the interference spectra, classification accuracy of all 11 plastic is increased to 100%, while the validation set's accuracy is only 99.8% and the test set is 99.09% without replacing the interference spectra. It can be seen that the laser induced breakdown spectroscopy combined with partial least squares method can be successfully used for the plastic sample classification.

Laser-induced breakdown spectroscopy(LIBS); Electrode enrichment; Limit of detection; Heavy metal in water;INDUCED BREAKDOWN SPECTROSCOPY

In order to improve the detection sensitivity of laser-induced breakdown spectroscopy (LIES) and lower the limit of the detection of elements, LIBS combined with Aluminum electrode enrichment method is adopted to analyze heavy metals such as Pb, Cdand Ni in the water. The relationship between the characteristic spectral intensity and the key parameters-voltage of electrode method is discussed, the spectral intensity increases first and then decreases with the increase of voltage. The spectral intensity reaches-the maximum value when the enrichment voltage is 1.2 V while the optimal enrichment voltage value is 1.2 V. The stability of characteristic spectral lines of heavy metals is studied, and the relative standard deviation(RSD) of spectral intensity of Pb, Cd and Ni is 5.98%, 4.25 % and 5.27% respectively, the result shows that the spectral line obtained by this method has high stability. A series of samples in the range of 0 similar to 0.13mg.L-1 are prepared and quantitatively analyzed, the limit of detection of Pb, Cd and Ni is obtained 1.2, 3.1 and 1.7 ppb respectively. The above result shows that LTBS combined with aluminum electrode enrichment method can effectively improve the stability of characteristic spectral lines and lower the limit of detection of Pb,Cd and Ni. This research also provides a method to further improve detection sensitivity of LIES and analysis ability of heavy metal in the water.

Laser-induced breakdown spectroscopy; Orthogonal dual-pulse; Spectral enhancement; Signal-to-background ratio; Plasma temperature; Electron density;OPTICAL-EMISSION; ENHANCEMENT

In order to improve the detection sensitivity and spectral characteristic of laser-induced breakdown spectroscopy (LIES), re-heating orthogonal dual-pulse configuration is adopted to analyze Fe, Pb, Ca and Mg contained in the sample and soil sample contained different concentrations of heavy mental Cr. Variation relationship between spectral intensity, signal-to-background(SBR) of four characteristic spectral lines Fe I : 404. 581 nm, Pb I : 405. 78 nm, Ca I 422. 67 rim and Mg I : 518. 361 nm and time interval of two laser pulses is discussed, the best time interval of two laser pulses is obtained 1. 0 s. In the condition of single pulse and dual-pulse, the enhancement factor of spectral intensity of four characteristic spectral lines Fe I : 404. 581 nm, Pb I : 405. 78 nm, Ca I : 422. 67 nm and Mg I : 518. 361 nm is respectively 2. 23, 2. 31, 2. 42 and 2. 10; The time evolution characteristic of spectral intensity of characteristic spectral lines Fe I : 404. 581 nm and Ca I : 422. 67 rim is considered, and also the variation relationship between spectral acquisition delay time and SBR of-four characteristic spectral lines, dual-pulse can prolong decay time of spectral intensity and improve the SBR of characteristic spectral lines; time evolution characteristic of plasma temperature and electron density is compared in the condition of single pulse and dual-pulse, maximum elevation of plasma temperature is found to be 730 K, and the maximum increase of electron density is 1. 8 X 10(16) cm(-3). The limits of detection of heavy mental Cr are obtained 38 and 20 mu g center dot g(-1) respectively in condition of single and double pulse, limit of detection of Cr is reduced approximately 2 times by the condition of re-heating orthogonal dual pulse. Results above indicate that reheating orthogonal dual-pulse can improve detection sensibility and spectral characteristic of LIBS technique, which provides an effective method for decreasing the limit of detection of elements.

Laser induced breakdown spectroscopy; Remote detection; Partial least squares;

As a kind of spectroscopic technique, the remote laser-induced breakdown spectroscopy (Remote LIBS) can qualitatively or quantitatively measure the elemental compositions of remote targets with high-power laser and focusing optical path. In this work, a Remote LIBS system was designed and established to probe the target from 2 to 10 meters. It is characterized with Cassegrain telescope structure and automatic focusing technique. Based on this system, a method to remotely retrieve the major elemental abundance of rocks is presented. With comparative experiment, the influences on spectral signal by pulse laser energy, acquisition delay time, integration time, accumulative pulse number are analyzed to find out the optimum parameters: the wavelength of laser is 1 064 nm, pulse energy is 120 mJ, delay time is 1. 5 mu s, integration time is 1 ms, and each spectrum data acquired with averaging 30 times detection. 48 pieces of rock specimens and 6 kinds of standard rock samples (shale, granite, andesite, basalt, gneiss and pegmatite) are selected for the experiment. As to the atomic spectra database, 8 characteristic spectral lines of the major elements (Si I 390. 55 nm, Al I 394. 40 nm, Al 1396. 15 nm, Ca II396. 85 nm, Fe I 404. 6 nm, Si I 500. 60nm, Mg I 518. 36nm, Na I 589. 59 nm) were extracted for analyses. Then a PLS model is constructed to quantitatively analyze the rock elements. 48 rock specimens were selected as the training sets to serve the model. The 6 standard samples were used to test the solved model. The testing results shows that the elemental abundance of Si and Al can be predicted accurately with average relative error of only 9. 4% and 9. 6% respectively.

Laser-induced breakdown spectroscopy; Proximate analysis of coal; Spectral fitting; Support vector machine;LIBS; SYSTEM

Online accurate proximate analysis of coal is vitally important to the optimization of industrial production and reduction in coal consumption. However, due to the ""matrix effect"" caused by the complex and diverse coal species in China, the measurement accuracy needs to be improved by using laser-inducedbreakdown spectroscopy (LIBS). In our experiment, both the spectral pretreatment method and the calibration model for the conversion of laser induced coal plasma spectra to the coal proximate analysis results were optimized. Experimental results showed that, compared with the traditional method, the proposed single or multiple-peak Lorentzian spectral fitting for spectral line intensity calculation reduced the mean RSD from 12. 1% to 9. 7%. For kernel function parameters optimization, the mean absolute error (MAE) of the particle swarm optimization (PSO) was smaller than that of the grid parameter (Grid) and the genetic algorithm (GA). The root mean square error (RMSEP) of support vector machine (SVM) regression model based on PSO parameter optimization was less than that of partial least squares regression (PLS). By combining the single- or multiple-peak Lorentzian spectral fitting method with the PSO based SVM for regression modeling, the average absolute errors (AAE) of predicted proximate analysis results were certified to be: 1. 37% for coal ash content of 16%similar to 30%, 1. 77% for coal ash content of 30% or more, 0. 65 MJ . kg(-1) for calorific value of 9 similar to 24 MJ . kg(-1), 1. 09% for volatile matter of 20% or less, and 1. 02% for volatile matter of 20% or more.

Long-pulse laser induced plasmas; Life-time of plasma; Relative standard deviation; Limit of detection;

Laser induced breakdown spectroscopy with long-pulse laser(500 mu s) was used to generate plasma of soil sample in air. The spectroscopy emission characteristic of soil plasma was investigated under the low power-density conditions. Intense continuum background could not be detected (402 similar to 409 and 420 similar to 436 nm) and the long-pulse laser induced plasma had a longer overall life time (about 220 similar to 270 mu s), which was different from the dynamic characteristics using nanosecond laser and ultra short pulse laser. Besides, the spectral lines of Pb I 405. 78 nm and Cr I 425. 43 nm appeared at about 210 and 190 mu s. Intensity of Pb 1405. 78 nm and Cr I 425. 43 nm increased as time passed by, reaching to its maximum at 320 and 350 mu s, respectively. The study results showed that increased interaction time between laser and sample contributed to the formation of ""quasi-stable state plasma"". The relative standard deviation was 2. 21%similar to 6. 35% concluded by 8 times repeated experiments, which showed a better stability of soil plasma by using a long-pulse laser. The detection limits of Pb and Cr were 34. 7 and 40. 0 mg . kg(-1), respectively, which was below the trace element thresholds for Class 1 soil used in the environmental quality standard in China. Parameters characterizing a laser-induced plasma were obtained with the temperature of 6612 K and electron density of 3. 7 X 10(17) cm(-3) in the condition of long-pulse laser. Experimental results showed that it was in local thermodynamic equilibrium.

Laser-induced breakdown spectroscopy (LIBS); Tobacco leaves; Plasma; Limit of detection (LOD);

The rapid detection and real-time monitoring of plant elements is very important in the field of agriculture. A method using Laser Induced BreakdownSpectroscopy (LIBS) for the determination of the spectroscopy characteristics of Cu in tobacco was evaluated. To perform the calibration curve, several tobacco samples containing Cu arranged from 8. 59 to 156. 35 mu g . g(-1) were prepared. The amount of Cu prepared in laboratory was measured using atomic absorption spectroscopy. Experiments indicated that the characteristic spectrum of Cu at the wavelength of 324. 75 nm was quite clear, and easy to obtain. From the characteristic spectra obtained from Cu-contained samples, the temperature and density of the plasma induced by laser were calculated to be 39 458. 94 K and 0. 74X 10(16), respectively. The fitting curve between the intensity of the spectral lines and the sample concentrations was established with the correlation coefficient (r square) of 0. 98, the mean relative standard deviation (RSD) of 2. 59%, the limit of detection (LOD) of 7. 72 mu g . g(-1) and the spectral signal-noise ratio of 7. 86. The method was successfully applied to predict the Cu amounts in tobacco samples, which has a potential to be used in cigarette production lines and tobacco breeding.

LIBS; Plasma parameter; Quantitative analysis; Qualitative analysis;EMISSION

Laser Induced Breakdown Spectroscopic (LIBS) technique was used to detect calcium and silicon in an unknown sample. In this method plasma was generated by Nd :YAG laser of wavelength 1 064 nm with energy 400 mJ and pulse duration between 5 similar to 10 ns. The method was applied for the qualitative as well as quantitative analysis. In the qualitative analysis, the electron number density (N-e) of plasma containing calcium and silicon is determined showing that N-e of neutral particles is equivalent to 1016 (cm(-3)) whereas for ionized particles it is 10(17) (cm(-3)). Plasma temperature is measured using Boltzmann plot method which must be greater than 10 000 k. Intensity ratio method is used for the quantitative analysis shows various elements in abundance with calcium and silicon in majority.

Laser-induced breakdown spectroscopy; Quantitative analysis; Standard addition method; Curve fitting; Heavy metals;

Quantitative analysis of four heavy metals Pb, Cr, Cu and Cd in soils and solid wastes using independently developed portable system of laser-inducedbreakdown spectroscopy. A Nd: YAG pulse laser with fundamental wavelength of 1 064 nm is used as the excitation source, with the single pulse energy of 100 mJ the pulse width of 6 ns, and the operating frequency 3 Hz. The echelle spectroscopy with high resolution and wide spectral range is used as the spectral separation device, and the intensified charge coupled device GOOD) as the spectral detection device in the experiment, with the detection range of 200 similar to 500 nm and a resolution of 0.08 similar to 0.12 nm. In order to improve the spectral intensity and detection sensitivity, a device of hemisphere spatially bound is used to restrain the plasma and a optical fiber with multi-channel is used collect the signal. The reception angle is 45 degrees. The laserrepetition rate is 2 Hz while the delay is 1.5 mu s, with the gate width of 1.05 ms. Standard addition method is used to effectively solve the quantitative analysis of samples of unknown matrix. The innovation lies in the fact that, a curve fit instead of a straight line fit is used in the standard addition method to quantitative analyze the heavy metals in soils and solid wastes, which effectively improve the measurement results. Especially for the low concentrations of soil samples, linear fitting can not be used in quantitative analysis, in contrast, the correlation coefficient of curve fitting is much higher, more closer to the national standard measurement methods, to meet soil pollution detection. The result of seven soils and solid wastes samples are as follows, line fitting relative error: Pb 1.26%similar to 79.38%, Cr-22. 44%similar to 82.06%, Cu 15.09%similar to 190.50%, Cd 32.76%similar to 167.96%, and curve fitting relative error respectively Pb - 4.19%similar to 11.92%, Cr-38.31%similar to 9.26%, Cu-7.24% similar to 26.86%, Cd-10.52%similar to 12.94%, the average relative error is 10.47%.

Laser-induced breakdown spectroscopy; Soil; Calibration curve; Chemometrics analysis;LIBS; CALIBRATION

Abundance or deficiency of soil elements is an expression of soil fertility. Rapid detection of elements in soil is a key point of front information acquirement tools in precision agriculture, and it also provides a theoretical basis for pollution prevention of soil heavy metal and sustainable development of agriculture. This research focused on using laser-induced breakdown spectroscopy LIBS) technique combined with calibration curve and chemometrics method to conduct the simultaneous quantitative analysis of multi-elements (Al, Fe, Mg, Ca, Na and K) in soil. First of all, five certified reference materials (CRM) of soil numbered GBW07446, GBW07447, GBW07454, GBW07455, GBW07456 were ablated by a laboratorial LIBS setup in air. 50 LIBS spectra of each type of soil were averaged to reduce the error in experiment process. By integrating the acquired LIBS emission spectra and atomic spectra database from national institute of standards and technology (NIST), analytical spectral lines and corresponding spectral regions were identified. Then, calibration curves of the intensity of a peak and integrated intensity of a peak or several peaks (peak area) coupling with the element content s were fitted. The results indicated that the linear relation from the calibration curves fitted by peak areas and element contents were superior to the calibration curves fitted using intensity of a peak and element contents (except the Fe). Meanwhile, partial least-squares regression (PLSR) was employed to build the quantitative model by using the selected spectral regions and corresponding element contents, which offered a promising result with relatively high RP and showed more advantages than the calibration curve method. The approach revealed that LIES technology combined with chemometrics methods displayed a bight prospect in the field of spectrochemical analysis. The achievements of the research not only provide a guide for detecting soil nutrient spatial distribution and precision fertilization technique, but also lay a theoretical foundation for developing the portable LIBS detector used in the field.

Wear elements in engine oil; Indirect ablation laser induced breakdown spectroscopy; Matrix effect; Calibration curves;LUBRICATING OILS; CRUDE-OIL; QUANTITATIVE-DETERMINATION; MASS-SPECTROMETRY; METALS

Engine oil plays an important role in the engine operation. Elements composition and concentration in engine oil will be changed as the engine operates, which can lead to the deterioration of engine oil, and the engine thereby will be worse. A rapid and effective detection approach for oil performance, therefore, is proposed to prevent further deterioration. Indirect ablation laser induced breakdown spectroscopy (IA-LIES) is a new technology introduced specially for oil samples, which focuses on the indirect ablation of oil samples by metallic plasma with high temperature, improving the detection sensitivity and stability. In this paper, the matrix effect on calibration curves of analytical elements (Mg, Fe and Ni) in different oils was investigated. The results show that the matrix effect is quite small and reasonably negligible. A universal calibration curve can be established for analytical metals in different types of oil, and the linear fitting coefficients are all superior to 0. 99. We used the universal calibration curves to determine the concentrations of Mg, Fe and Ni in mixed oils. The IA-LIES results show a good agreement between the measured and known values. The IA-LIBS is further improved and can promote the detection of engine oil performance, which has important scientific significance for the diagnosis of engine wear.

Laser-induced breakdown spectroscopy; Vector space model; Geological cutting; Identification;SAMPLES

Vector Space Model (VSM) was originally used in document retrieval. It is characterized by extracting the texts from the document and converting the document into a text vector space. VSM compares the similarity between document text vectors and text retrieval text vectors. The document retrieval is accomplished according to the similarity based on the nearest template principle of template matching in pattern recognition. This article applied such principle into the identification of samples based on the characteristic of LIES spectrum. To create the database of characteristic peaks of training dataset, we obtained the spectra template of all kinds of samples from the training dataset and extracted the wavelength and intensity of peaks from the spectra template. In another hand, to create the database of characteristic peak vectors for all the training samples, we calculated the spectral characteristic peak weight and converted the spectra to peak vector space. The characteristic peak vector of the test data set was obtained by the same way. The cosine value between the characteristic peak vector of test data and every characteristic peak vector in the database were calculated and the maximum cosine was taken as the identification result. Geological cuttings, the research subject, were identified by the VSM in this paper. The result demonstrated that the VSM could rapidly identify the spectra from 4 kinds of geological cuttings' LIES spectral and the correct identification rate was 100% after the spectra of the test dataset were averaged. The proposed LIES spectral identification method based on VSM can be expanded to the identification of other spectral data.

Laser-induced breakdown spectroscopy; SF6 oxygen concentration; Wavelet transform; Partial least square; Quantitative analysis;DISCHARGE

Sulfur hexafluoride (SF6) is widely used in gas-insulated high-voltage equipments due to its excellent insulation and arc extinguishing performance. However, when impurities such as trace water and oxygen are present in SF6, the by-products, which are formed due to equipment faults and partial discharge, can react with these impuriti to form stable sulfur oxyfluorides. The equipment insulation performance can be degraded significantly by those stable sulfur oxyfluorides, causing threat to the safety of the power system. The detection and analysis of the impurities such as water, oxygen and decompositions in SF6 are therefore of great importance. In this paper, laser-induced breakdown spectroscopy is employed to measure trace O in SF6. CaF2 is used as window material to solve the degradation of the excitation energy caused by the corrosion of the window material by SF6 decompositions, to eliminate the pollution problem caused by the reaction between the window material and the breakdown products of SF6 gas, and to reduce the change of plasma state caused by the change of excitation condition. By correcting the spectral baseline with an iterative wavelet transform and suppressing the noise with a wavelet transform with soft thresholding, a limit of detection of 38ppm is achieved from the experimental calibration curve. Furthermore, a quantitative model based on partial least squares (PLS) is developed to achieve better stability and precision.

Laser-induced breakdown spectroscopy (LIES); Soil; Heavy metal; Chemometrics methods; Quantitative analysis;NEURAL-NETWORK; LIBS

A large number of farm lands are contaminated by heavy metals in the process of industrialization and urbanization. Precise detection of heavy metals in soil offers valid reference for prevention and recovery of heavy metals in the field. In this research, Laser induced breakdown spectroscopy (LIBS) and chemometrics methods were employed to conduct quantitative analysis of heavy metals Pb and Cd in soil. Based on the pollution extent, soil samples with 15 concentration gradients of Pb and Cd were manually made up. Then, the LIBS emission lines of all soil samples were collected firstly. In order to eliminate errors and noise of spectral data, preprocessing methods called removal of abnormal data and normalization were used. Then, characteristic lines and spectral regions of Pb and Cd were determined based on our LIES spectra and Atomic Spectra Database (ASD) of National Institute of Standards and Technology (NIST). Quantity regression models based on multiple linear regression (MLR), partial least squares regression (PLSR), least squares support vector machine (LS-SVM) and back propagation-artificial neural network (BP-ANN) were set up and their results were compared. As a result, models based on non-linear methods (LS-SVM and BP-ANN) offered a promising results than the linear methods of MLR and PLSR. The probable reason was that non-linear methods had an advantage to deal with matrix effects of soil automatically. The results indicated that LIBS coupled with multiple chemometrics methods provided a brand-new analysis approach for heavy metals accurate detection in soil and it could be considered as an effective theoretical foundation of making protection and recovery decision for soil contaminated by heavy metals.

Laser induced breakdown spectroscopy; Coffee beans; Caffeine; Partial least squares; BP neural network;LIBS

The feasibility of fast detection of caffeine content in coffee beans based on laser induced breakdown spectroscopy (LIES) combined with chemometrics methods was studied. The coffee beans were grinded. 0.5 g of powerd material was transformed into a disk by manual tableting machine. 60 disks of coffee bean material were prepared for LIBS data acquiring. The samples were pretreated by acid wet digestion, and actual caffeine content of each sample was obtained by automic absorption spectrometer (AAS). Baseline correction was applied on the original spectral data to eliminate the negative values. Wavelet transform (WT) was used to reduce the noise, wavelet basis function is Daubechies 5 (db5) and decomposition level is 10. Normalization were employed to deal with variations caused by matrix effects and experimental conditions. The partial least squares (PLS) model on full data appeared to over-fitting. Regression coefficients and principal component analysis (PCA) were used to select characteristic variables, respectively. PLS models and back propagation (BP) neural network model were built by the variables selected. In the PLS model on the variables selected by regression coefficients, correlation coefficient of calibration set (R-c) was 0.96, correlation coefficient of prediction set (R-p) was 0.91. In the PLS model on the variables selected by PCA, R-c=0.94, R-p=0.90. In the BP neural network model on variables selected by PCA, R-c=0.96, R-p=0.96. The characteristic variables selected by two methods correspond to C, H, O, N, Na, Mg, Ca, Fe, Mn. The PLS models on the variables selected by regression coefficients and PCA both performed well on prediction samples. It demonstrated the certain relationship existing between the elements and caffeine content and the selected variables were effective. But the precise relationship bwtween C, H, O, N, Na, Mg, Ca, Fe, Mn and caffeine content needs further study. The BP neural network model on variables selected by PCA performed better than the PLS model, which demonstrated the selected variables were suitable for different modeling methods. The study showed LIBS could be applied to fast determination of caffeine content within coffee bean combined with chemometrics methods. The method of caffeine content detection presented by this study is innovative.

Laser-induced breakdown spectroscopy; Characteristic spectral lines of non-metallic elements; Support vector machine; Plastics identification;ARTIFICIAL NEURAL-NETWORKS; INDUCED PLASMA; EMISSION; POLYMERS

Laser-induced breakdown spectroscopy (LIPS) combined with support vector machine (SVM) was adopted to identify 20 kinds of different colored industrial plastics from different manufacturers in open air. The experimental parameters of spectral acquisition were optimized firstly. 100 spectra recorded under optimum conditions were randomly and equally divided into training set and test set. 6 non-metallic characteristic spectral lines were used to avoid the interference with metallic lines. And the training time of SVM model was reduced. The results show that 996 of 1000 test spectra were identified correctly and the average classification accuracy is reached to 99.6%. The classification efficiency is improved with 6 non-metallic characteristic spectral lines. The research demonstrates that, when fewer of major non-metallic characteristic spectral lines are used, laser-induced breakdown spectroscopy technique with support vector machine can identify more kinds of plastics with high accuracy and efficiency.

Laser induced plasma; Spectral line profile; Continuum intensity; Full width at half maximum (FWHM); Spectral line shift;INDUCED BREAKDOWN SPECTROSCOPY; INDUCED PLASMA DYNAMICS; ABLATION

There are many methods to characterize plasma parameters for laser-induced plasma, optical emission spectra method is a very important one to diagnose laser-induced plasma parameters. In this paper, Nd:YAG solid state laser which output 1064 nm wavelength interact with aluminum alloy sample, the temporal evolution of spectral line profile, spectral line intensity, continuum intensity, line to background intensity ratio, spectral line broadening and spectral line shift were investigated in detail for laser induced aluminum alloy plasma. The results show that the interaction of electrons between atoms and ions are very intense, which leads to electrons production of laser induced plasma at the early stage. Stark broadening effect of spectra lines are distinct and multiple spectral lines are overlapped. With temporal evolution, the electron density and electron temperature decreased quickly, the multiple spectral lines are separated slowly, and the spectral line profile is becoming thinner and symmetric. For Mg I 285.2126 nm characteristic spectral line, the intensity increased with temporal evolution at first, the intensity reached maximum value about 100 ns, and then the intensity decreased with temporal evolution, which is due to the fact that electron and ion are dominated at early stage of laser-induced plasma, atomic spectral line is very weak, with temporal evolution, the process of recombination between electrons dominated and the atomic number density increased, when the atomic number density reached maximum value, the spectral line intensity decreased with temporal evolution because excitation temperature decreased quickly. Taking wavelength in NIST database as reference wavelength, the spectral line shift for Mg I 285.212 7 nm and Zn II 206.200 4 nm take place red shift at early stage of laser induced plasma, the continuum intensity decreased dramatically by power law with temporal evolution, on the contrary, comparing with continuum intensity and spectral line intensity, continuum intensity attenuate sharply, the line to background intensity ratio increase with temporal evolution. This early phenomenon of laser inducedaluminum alloy plasma were discussed in detail from theoretical perspective.

LA-LIES; Dual-pulse; Elemental analysis; Low sample destruction;INDUCED BREAKDOWN SPECTROSCOPY; SIGNAL ENHANCEMENT; LASER-ABLATION; NANOSECOND; PLASMA

A study on elemental analysis of alloy samples under low sample destruction with dual-pulse laser-ablation laser induced breakdown spectroscopy (LA-LIES) based on one picosecond Nd : YAG laser is presented. In LA-LIBS, low pulse energy 532 nm laser was used for sample ablation and high pulse energy, time - delayed 1 064 nm laser was used for re-excitation of the ablated samples to enhance atomic emissions of the laser-induced plasma and signal detection sensitivity. The influence of pulse energies of the ablation laser and excitation laser to the signal intensities was studied experimentally. I was observed that Cu 324. 75 nm line intensity in LA-LIBS was enhanced 86 times in comparison with that obtained in SP-LIES under 10 mu J pulse energy of the ablation laser and 2. 5 mJ pulse energy of the excitation laser. The diameter of the crater generated in LA-LIES was less than 10 pin. It is demonstrated the possibility of using dual-pulse LA-LIBS to realize elemental analysis of solid sample under low sample destruction. This technique is valuable for elemental analysis of precious samples and 2D elements mapping under high spatial resolution.

Laser induced breakdown spectroscopy; Liquid jet; Mixture solution; Limit of detection;

In this paper, the concentrations of Cu, Mg, Zn and Cd elements in the mixture solution consing of CuSO4, Mg(NO3)(2), Zn(NO3)(2) and Cd(NO3)(2) were measured with Laser Induced Breakdown Spectroscopy with aqueous jets which were generated within 1 064 nm wavelength of Nd: YAG laser with pulse width of 10ns and repetitive rate of 10 Hz. The mixture solutions of seven different concentrations consist of Cu, Mg, Zn and Cd were compound by adding the four solutes to the distilled water. The LIBS experiment date have been treated with the statistical exploratory data analysis method to abtain calibration curves of Cu, Mg, Zn and Cd elements, whose linear fitting coefficient R-2 were all above 0. 99, the LOD of Cu, Mg, Zn and Cd elements were determined as 5. 62, 4. 71, 13. 67 and 4. 43 ppm, respectively. The LOD of Cu element was 3. 98 ppm for pure CuSO4 solution with better experimental results than that of mixed solution, Finally, the LIBS detected differences were analyzed. The research results show that LIBS has a promising application in detecting heavy metal elements in the environmental wastewater pollution.

Laser induced breakdown spectroscopy (LIBS); Laser wavelength; Plasma time evolution; Plasma shielding effect; Coal;INDUCED BREAKDOWN SPECTROSCOPY; ELEMENTAL ANALYSIS; DEPENDENCE; PARAMETERS

In face of the complicated and changeable coal in Chinese power stations, the on-line measurement of coal elemental composition is extremely significant in terms of enhancing the safety and efficiency of boilers as well as lowering the waste emission during operation. In this work, laser induced breakdownspectroscopy (LIBS) was applied to coal quality measurement. Laser wavelength was changed as 355, 532 and 1 064 nm to investigate the influence on coal LIBS features, including plasma time evolution and the spectral lines intensity-time characteristics of different elements. Energy threshold for shielding effect was also tested to verify how it varies with laser wavelengths. Additionally, coal LIBS spectrum was analyzed under different laser wavelengths. It has been proven by experiments that higher intensity of coal LIBS spectrum and energy threshold can be easily achieved when using laser of 532 nm, making it a fantastic energy source for coal LIBS tests. Results of these experiments serve to guide the industrial application of LIBS technology in the field of coal quality measurement.

Laser-induced breakdown spectroscopy; Matcha; Green tea powder; Linear discriminant analysis (LDA);LIBS

The feasibility of using laser-induced breakdown spectroscopy (LIBS) combined with chemometrics methods for fast identification of matcha and green tea powder was investigated in this paper. The main differences between matcha and green tea powder are varieties of tea plants, cultivation management, growth time and processing technology. LIBS spectra between 230 to 880 nm of matcha produced by different manufacturers and green tea powder made with different fixation methods were selected and min-max normalization was the measure for preprocessing. Characteristic wavelengths were selected according to the X-variables loadings on the basis of principal component analysis (PCA), and then linear discriminant analysis (LDA) models were built based on characteristic wavelengths. The results showed that the LDA model based on characteristic wavelengths could identify matcha and green tea powder rapidly. Four characteristic wavelengths belong to C(I) 247. 94 nm, Mg(II) 279. 60 nm, Ca(II) 393. 45 nm and Fe(II) 766. 68 nm. The accuracy of the calibration and the prediction set all reached 100%. Laser-induced breakdown spectroscopy could accurately identify matcha produced by different manufacturers and green tea powder made with different fixation methods.