Nos últimos anos, a Espectrometria de Emissão Atômica com Plasma induzido por Laser (LIBS) vem despertando grande interesse e pesquisas voltadas às aplicações analíticas dessa técnica tem aumentado significativamente. No entanto, sua aplicação na análise de amostras líquidas não é trivial, podendo haver comprometimento na sensibilidade e na precisão do método. Além disso, a análise quantitativa é considerada o \"calcanhar de Aquiles\" da técnica, especialmente devido à falta de materiais de referência certificados e à forte interferência de matriz. Nesse contexto, com a intenção de viabilizar a análise de matrizes líquidas por LIBS, esse trabalho propõe o uso de cerâmica como fase sólida para extração, pré-concentração e especiação de Cr em amostras de água. Foi realizado também um estudo de otimização dos parâmetros instrumentais do LIBS para o desenvolvimento de um método de medição de Cr na fase sólida, empregando cerâmica enriquecida com concentrações crescentes desse analito como material calibrante sintético. Os resultados obtidos mostraram que a cerâmica adsorve seletivamente a espécie Cr(III) em pH 7, sendo este um processo rápido, de baixo custo, cuja eficiência é pouco afetada pela presença de outros eletrólitos. Os estudos relacionados à otimização dos parâmetros instrumentais do LIBS indicaram que um diâmetro de focalização de 65 µm, um tempo de atraso de 0,75 µs, a energia por pulso de 20 mJ, uma taxa de repetição de 10 Hz e um número de pulsos igual a 403 podem ser recomendados para a quantificação de Cr no material cerâmico. Nessas condições, obteve-se uma curva de calibração analítica que possibilitou a medição Cr adsorvido em cerâmica. Uma amostra de água de torneira foi então enriquecida com 0,9 mg L-1 de Cr(III) e 0,9 mg L-1 de Cr(VI) para que um teste de recuperação fosse realizado com a finalidade de se verificar a aplicabilidade do método proposto, foi possível constatar a adsorção seletiva da espécie Cr(III), com recuperação de 105±2%. A quantificação da espécie Cr(VI) por LIBS também é possível após a redução dessa espécie a Cr(III) utilizando Fe(II) como agente redutor. Os limites de detecção (LOD) e quantificação (LOQ) estimados para o método foram respectivamente 21 mg kg-1 e 70 mg kg-1, equivalentes a 0,1 mg L-1 e 0,35 mg L-1, considerando-se o coeficiente de pré-concentração igual a 200 (m/m). / In recent years, Laser Induced Breakdown Spectroscopy (LIBS) has deserved attention of scientific community and researches using this technique have increased significantly. However, its application in the analysis of liquid samples is not trivial, because the sensitivity and accuracy of the method can be affected. In addition the quantitative analysis is considered the \"Achilles\' heel\" of the technique, especially due to the lack of certified reference materials and to the strong interference matrix. To enable the analysis of liquid matrices by LIBS, this work proposes the use of ceramic as solid phase in the extraction, preconcentration and speciation of Cr in water samples. LIBS instrumental parameters were also optimized to allow the measurement of Cr in this solid phase, for the development of a method for measuring the analyte in the solid phase, which was also used as synthetic calibrating material by the addition of increasing concentrations of the analyte. Results showed the ceramic selectively adsorbs Cr(III) species at pH 7, which is a low cost and rapid process, whose efficiency is not significantly affected by the presence of other electrolytes. Studies related to the optimization of LIBS instrumental parameters indicated that spot size of 65 µm, delay time of 0,75 µs , energy per pulse of 20 mJ, repetition rate of 10 Hz and a number of pulses equal to 403 can be recommended for the quantification of Cr the ceramic material. Under these conditions, it was obtained an analytical calibration curve which allowed a Cr measurement in ceramics. A tap water sample was enriched with 0.9 mg L-1 of Cr(III) and 0.9 mg L-1 of Cr (VI) and a recovery test was done in order to verify the applicability of the proposed method. It was observed the selective adsorption of the Cr(III) species, with recovery of 105 ± 2 %. The quantification of Cr(VI) species by LIBS was also possible, after reduction of this species to Cr(III) using Fe(II) as reducing agent. The limit of detection (LOD) and the limit of quantification (LOQ) obtained by the proposed method were respectively, 21 mg kg-1 and 70 mg kg-1, equivalent to 0.1 mg L-1 and 0.35 mg L-1, considering the preconcentration coefficient of 200 (on a w/w basis).

Orientador: Edilene Cristina Ferreira / Banca: Raquel Fernandes Pupo Nogueira / Banca Marcos Yassuo Kamogawa / Resumo: A espectrometria de emissão óptica em plasma induzido por laser (LIBS) é uma técnica que vem se desenvolvendo cada vez mais para determinações analíticas multielementares, com aplicações em diversas áreas. Possui várias vantagens, como por exemplo, ser uma técnica de análise rápida, minimamente destrutiva e ambientalmente amigável, enquanto que a maior dificuldade está baseada na sua relativa baixa sensibilidade. Muitos estudos têm sido desenvolvidos com a finalidade de melhorar a sensibilidade, porém os aprimoramentos elaborados demandam equipamentos mais sofisticados, aumentando o custo e comprometendo a portabilidade da técnica. O presente trabalho avaliou estratégias simples para melhorar a sensibilidade das medidas em LIBS, permitindo o uso de instrumentos compactos de pulso simples. As estratégias desenvolvidas se baseiam na proposição da introdução de uma etapa simples de pré-tratamento da amostra, capaz de agir na fragilização de estruturas químicas que por consequência levem ao aumento das intensidades de emissão das espécies componentes da amostra. As etapas de pré-tratamentos buscam em sua essencialidade não descaracterizar as vantagens analíticas de LIBS, tais como a simplicidade e a não utilização de reagentes potencialmente tóxicos, além de serem aplicáveis à diversos tipos de amostras. A ação da temperatura sobre a modificação de estruturas químicas foi avaliada utilizando aquecimento em mufla para amostra de material vegetal, solo e liga metálica e em forno de... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Laser-induced breakdown spectroscopy (LIBS) is an analytical technique in development, increasingly applied for multielemental determinations in several areas. It shows several advantages, such as rapidity, minimally destructive and environmentally friendly, although the greatest difficulty is based on its relatively low sensitivity. Many efforts have been expended to improve LIBS sensitivity, but several proposals require more sophisticated equipment, increasing the cost and compromising the portability of the technique. The present work evaluated simple strategies to improve the sensitivity of LIBS measurements allowing the use of compact single pulse instruments. The proposed strategies are based on a simple sample pretreatment, able to promotes simplification of chemical structures, which could lead to an increase of emission intensities. The proposed pretreatment steps aimed to preserve the interesting LIBS analytical advantages, such as its simplicity and non-use of toxic reagents, and its applicability to several types of samples. Then the temperature action on the simplification of chemical structures was evaluated using conventional muffle oven, for samples of plant leaves, soil and metal alloy. Additionally, microwave oven heating was evaluated for plant leaves. The muffle oven treatments resulted in important increases of the emission intensities for all spectral region of all evaluated samples; for the plant leaves, material for which the best results were observed, the integrated peak area of the Ca I line at 612.14 nm was increased about 47x after the thermic treatment. Moreover, new emission lines, not observed before, such as Sr II line at 407.82 nm, appeared. In the alloy sample, the integrated area of Fe I line at 489.22 nm showed an increase of 8x and in soil sample the Na I line at 588.89 nm, showed an increasing of 4x. The microwave heating provided less pronounced intensity increments. / Mestre

Nos últimos anos, a Espectrometria de Emissão Atômica com Plasma induzido por Laser (LIBS) vem despertando grande interesse e pesquisas voltadas às aplicações analíticas dessa técnica tem aumentado significativamente. No entanto, sua aplicação na análise de amostras líquidas não é trivial, podendo haver comprometimento na sensibilidade e na precisão do método. Além disso, a análise quantitativa é considerada o \"calcanhar de Aquiles\" da técnica, especialmente devido à falta de materiais de referência certificados e à forte interferência de matriz. Nesse contexto, com a intenção de viabilizar a análise de matrizes líquidas por LIBS, esse trabalho propõe o uso de cerâmica como fase sólida para extração, pré-concentração e especiação de Cr em amostras de água. Foi realizado também um estudo de otimização dos parâmetros instrumentais do LIBS para o desenvolvimento de um método de medição de Cr na fase sólida, empregando cerâmica enriquecida com concentrações crescentes desse analito como material calibrante sintético. Os resultados obtidos mostraram que a cerâmica adsorve seletivamente a espécie Cr(III) em pH 7, sendo este um processo rápido, de baixo custo, cuja eficiência é pouco afetada pela presença de outros eletrólitos. Os estudos relacionados à otimização dos parâmetros instrumentais do LIBS indicaram que um diâmetro de focalização de 65 µm, um tempo de atraso de 0,75 µs, a energia por pulso de 20 mJ, uma taxa de repetição de 10 Hz e um número de pulsos igual a 403 podem ser recomendados para a quantificação de Cr no material cerâmico. Nessas condições, obteve-se uma curva de calibração analítica que possibilitou a medição Cr adsorvido em cerâmica. Uma amostra de água de torneira foi então enriquecida com 0,9 mg L-1 de Cr(III) e 0,9 mg L-1 de Cr(VI) para que um teste de recuperação fosse realizado com a finalidade de se verificar a aplicabilidade do método proposto, foi possível constatar a adsorção seletiva da espécie Cr(III), com recuperação de 105±2%. A quantificação da espécie Cr(VI) por LIBS também é possível após a redução dessa espécie a Cr(III) utilizando Fe(II) como agente redutor. Os limites de detecção (LOD) e quantificação (LOQ) estimados para o método foram respectivamente 21 mg kg-1 e 70 mg kg-1, equivalentes a 0,1 mg L-1 e 0,35 mg L-1, considerando-se o coeficiente de pré-concentração igual a 200 (m/m). / In recent years, Laser Induced Breakdown Spectroscopy (LIBS) has deserved attention of scientific community and researches using this technique have increased significantly. However, its application in the analysis of liquid samples is not trivial, because the sensitivity and accuracy of the method can be affected. In addition the quantitative analysis is considered the \"Achilles\' heel\" of the technique, especially due to the lack of certified reference materials and to the strong interference matrix. To enable the analysis of liquid matrices by LIBS, this work proposes the use of ceramic as solid phase in the extraction, preconcentration and speciation of Cr in water samples. LIBS instrumental parameters were also optimized to allow the measurement of Cr in this solid phase, for the development of a method for measuring the analyte in the solid phase, which was also used as synthetic calibrating material by the addition of increasing concentrations of the analyte. Results showed the ceramic selectively adsorbs Cr(III) species at pH 7, which is a low cost and rapid process, whose efficiency is not significantly affected by the presence of other electrolytes. Studies related to the optimization of LIBS instrumental parameters indicated that spot size of 65 µm, delay time of 0,75 µs , energy per pulse of 20 mJ, repetition rate of 10 Hz and a number of pulses equal to 403 can be recommended for the quantification of Cr the ceramic material. Under these conditions, it was obtained an analytical calibration curve which allowed a Cr measurement in ceramics. A tap water sample was enriched with 0.9 mg L-1 of Cr(III) and 0.9 mg L-1 of Cr (VI) and a recovery test was done in order to verify the applicability of the proposed method. It was observed the selective adsorption of the Cr(III) species, with recovery of 105 ± 2 %. The quantification of Cr(VI) species by LIBS was also possible, after reduction of this species to Cr(III) using Fe(II) as reducing agent. The limit of detection (LOD) and the limit of quantification (LOQ) obtained by the proposed method were respectively, 21 mg kg-1 and 70 mg kg-1, equivalent to 0.1 mg L-1 and 0.35 mg L-1, considering the preconcentration coefficient of 200 (on a w/w basis).

The subject of this diploma thesis is the study of a sample position influence on results of an experiment in laser spectroscopy. The aim is to design an appropriate way for standardization of signal obtained at different conditions with the respect to its applicability for stand-off analysis. In the theoretical part of the diploma thesis there are the basics of LIBS method described together with the issues of stand-off experiment and both, basic and advanced approches for the processing and correction of obtained spectra. Also the experiment is designed here, which is used for the analysis of the sample inclination and distance influence on the detected signal. The choice of appropriate ways for the signal correction follows and their applicability and efficiency is then experimentally tested.

This diploma thesis deals with using laser-induced breakdown plasma spectroscopy for determining the elemental structure of unknown samples. It was necessary to design an appropriate method to qualify material by laser-induced emission spectrum. Pretreatment of data and using a variety of chemometrics methods had to be done in order to qualify the structure of elements. We achieved a required solution by projecting the data to a new PCA space, creating clusters and computing the Euclidean distance between each cluster. The experiment in the practical part was set to detect an interface of two elements. We created a data file simulating the ablation on the interface. This data set was gradually processed applying a mathematical-chemical-physical view. Several data procedures have been compiled: approximation by Lorenz, Gauss and Voigt function and also a pretreatment method such as the detection of outliers, standardization by several procedures and subsequent use of principal components analysis. A summarization of processes for input data is fully described in the thesis.

Tato diplomová práce se zabývá návrhem optomechanického modulu pro chemické mapování metodou spektroskopie laserem buzeného plazmatu (LIBS). Cílem je vyvinout modul, který bude umožňovat analýzu spektrálních čar zinku v ultrafialové (UV) oblasti. V práci jsou popsány teoretické základy metody LIBS a následně je provedena rešerše zaměřená na problematiku dálkové LIBS analýzy. V diplomové práci jsou prezentovány možné optické návrhy fokusační a sběrné optiky, z nichž jsou vybrané následně otestovány. Výsledkem práce je konstrukční návrh modulu.

This doctoral thesis investigates the application of laser-induced breakdown spectroscopy (LIBS) for detection of labeled biomolecules on nitrocellulose paper. Nitrocellulose paper is a material often used for assays involving the concentration and labeling of a target analyte, followed by label detection. Among paper-based diagnostics are lateral-flow immuno-assays (LFIAs). Research efforts have made LFIAs into accessible, portable,and low-cost tools for detecting targets such as allergens, toxins,and microbes in food and water.Gold (Au) nanoparticles are standard biomolecular labels among LFIAs, typically detected via colorimetric means.Other labels, such as quantum dots, are also often metallic, and research is ongoing to expand the number of portable instrumentations applied to their detection. A wide diversity of lanthanide-complexed polymers (LCPs) are used as immunoassay labels but have been inapt for portable paper-based assays owing to lab-bound detection instrumentation, until now. LIBS is a multi-element characterization technique which has recently developed from a bench-top to a portable/hand-held analytical tool. This is among the first studies to show that LCPs can be considered as options for biomolecule labels in paper-based assays using bench-based and hand-held LIBS as label detection modalities.<div>Chapter one reviews the importance of rapid, multiplexed detection of chemical and biological contaminants, the application of current biosensors, and the role of LIBS as an emerging biosensor. Paper-based bioassays were identified as a promising approach for contaminant detection whose capabilities could be enhanced by LIBS. The next chapter dives into LIBS system designs to address which LIBS parameters were appropriate for label detection on paper assay material. A balance of LIBS parameters was found to be important for successful analyte detection. Chaptert hree optimizes a LIBS design for sensitive detection of 17 metals and establishes limit of detection values for 7 metals. Optimal detection parameters depended on the metal being detected and were applied to the objective of the final chapter: LIBS detection of labeled antigen immobilized on a paper-based assay. Both antibody and bacteria detection assays were successfully performed and analyzed using bench top and portable LIBS,suggesting an exciting future for the use of LIBS as a biosensor.The prospect of using LIBS for multiplexed, rapid and sensitive detection of biomolecules in assays is explored, laying grounds for future work in the ever-relevant field of biological and chemical hazard detection.<br></div>

The continuing need for greater energy security and energy independence has motivated researchers to develop new energy technologies for better energy resource management and efficient energy usage. The focus of this dissertation is the development of optical (spectroscopic) sensing methodologies for various fuels, and energy applications. A fiber-optic NIR sensing methodology was developed for predicting water content in bio-oil. The feasibility of using the designed near infrared (NIR) system for estimating water content in bio-oil was tested by applying multivariate analysis to NIR spectral data. The calibration results demonstrated that the spectral information can successfully predict the bio-oil water content (from 16% to 36%). The effect of ultraviolet (UV) light on the chemical stability of bio-oil was studied by employing laser-induced fluorescence (LIF) spectroscopy. To simulate the UV light exposure, a laser in the UV region (325 nm) was employed for bio-oil excitation. The LIF, as a signature of chemical change, was recorded from bio-oil. From this study, it was concluded that phenols present in the bio-oil show chemical instability, when exposed to UV light. A laser-induced breakdown spectroscopy (LIBS)-based optical sensor was designed, developed, and tested for detection of four important trace impurities in rocket fuel (hydrogen). The sensor can simultaneously measure the concentrations of nitrogen, argon, oxygen, and helium in hydrogen from storage tanks and supply lines. The sensor had estimated lower detection limits of 80 ppm for nitrogen, 97 ppm for argon, 10 ppm for oxygen, and 25 ppm for helium. A chemiluminescence-based spectroscopic diagnostics were performed to measure equivalence ratios in methane-air premixed flames. A partial least-squares regression (PLS-R)-based multivariate sensing methodology was investigated. It was found that the equivalence ratios predicted with the PLS-R-based multivariate calibration model matched with the experimentally measured equivalence ratios within 7 %. A comparative study was performed for equivalence ratios measurement in atmospheric premixed methane-air flames with ungated LIBS and chemiluminescence spectroscopy. It was reported that LIBS-based calibration, which carries spectroscopic information from a “point-like-volume,” provides better predictions of equivalence ratios compared to chemiluminescence-based calibration, which is essentially a “line-of-sight” measurement.

Laser Induced Breakdown Spectroscopy (LIBS) is showing great potential as an atomic analytical technique. With its ability to rapidly analyze all forms of matter, with little-to-no sample preparation, LIBS has many advantages over conventional atomic emission spectroscopy techniques. With the maturation of the technologies that make LIBS possible, there has been a growing movement to implement LIBS in portable analyzers for field applications. In particular, LIBS has long been considered the front-runner in the drive for stand-off detection of trace deposits of explosives. Thus there is a need for a better understanding of the relevant processes that are responsible for the LIBS signature and their relationships to the different system parameters that are helping to improve LIBS as a sensing technology. This study explores the use of LIBS as a method to detect random trace amounts of specific organic materials deposited on organic or non-metallic surfaces. This requirement forces the limitation of single-shot signal analysis. This study is both experimental and theoretical, with a sizeable component addressing data analysis using principal components analysis to reduce the dimensionality of the data, and quadratic discriminant analysis to classify the data. In addition, the alternative approach of ‘target factor analysis’ was employed to improve detection of organic residues on organic substrates. Finally, a new method of characterizing the laser-induced plasma of organics, which should lead to improved data collection and analysis, is introduced. The comparison between modeled and experimental measurements of plasma temperatures and electronic density is discussed in order to improve the present models of low-temperature laser induced plasmas.

This master’s thesis is focused on the LIBS technique for compositional differentiation and relative hardness quantification of selected geological samples. The experimental part of this thesis was conducted at the National Institute of Laser Enhanced Sciences (NILES) in Cairo, Egypt where a simple LIBS system was constructed. In parallel to the experimental work, the literature review was surveyed with the aim to give a thorough view of the history, fundamentals and all the factors related to LIBS. LIBS is a developing analytical technique, which is used to perform qualitative and semi-quantitative elemental analysis of materials (solid, liquid and gas). The fast data collection and the lack of sample preparation made LIBS be an attractive technique to be used for geological samples. This study was done to improve analytical methods for geochemical analysis of samples during different exploration phases (Mining, filed analysis, etc.), as a real-time analysis method to save money and time spent in labs. For a generation of laser induced plasma, a Q-switched Nd: YAG laser operated at 10 Hz and wavelength of 1064 nm was employed on the surface of the samples. A spectrometer fitted with an intensified charge-coupled device (ICCD) was used to disperse and detect the spectrum; then fed to a computer for recording and further processing of the data. The sample set was compiled from samples collected from different areas (South Africa and Namibia). Using principal component analysis (PCA), it was found that LIBS was able to differentiate between the samples even those of the same area. The results from the LIBS technique were correlated with subsequent analysis of the same samples by Particle-induced X-ray emission (PIXE). The feasibility of relative hardness estimation using LIBS was done by measuring the plasma excitation temperature for different samples. LIBS with its advantages as an elemental analysis technique made it possible to estimate the hardness of geological samples. Based on theory and results, an analytical technique for compositional differentiation and quantification of relative hardness of geological samples is proposed. / National Research Foundation (South Africa) / Physics / M Sc. (Physics)