Repositório Institucional - Unifesp :: Navegando por Palavras-chave "LIBS"

Navegando por Palavras-chave "LIBS"

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Avaliação da espectrometria de emissão óptica com plasma induzido por laser para determinação de elementos químicos em plantas medicinais
(Universidade Federal de São Paulo, 2014-04-30) Silva, Reginaldo Alexandre Valle da [UNIFESP]; Santos Junior, Dario [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
The laser-induced breakdown spectroscopy (LIBS) is a multielement technique in consolidation. The results presented in the literature highlight the major advances and potential of this technique for the direct determination of chemical elements in different samples. The technique is internationally known with acronym LIBS, and has been considered very promising for applications in quality control, materials chemistry, environmental monitoring, agriculture, forensic chemistry and biomedicine, among others. In many cases, the chemical characterization of many materials is surprisingly simple, with minimal human intervention, without the use of reagents and therefore, without generating chemical waste. The aim of this work was evaluate the LIBS technique for determination of chemical elements in medicinal plants. The experimental setup was designed by using a Q-switched Nd:YAG laser (5 ns, 360 mJ, 10 Hz,  = 1064 nm) and the emission signals were collected by lenses into an optical fiber coupled to an echelle spectrometer equipped with a high-resolution ICCD. Instrumental parameters consisted of 20 accumulated laser pulses, laser fluence 50 J/cm2, 2,0 μs delay time and 5,0 μs integration time. The results obtained showed considerable matrix effect in the interaction of the laser with different types of samples, which impaired the validation of quantification methods by LIBS. The results obtained by GFAAS showed the presence of Cd, Cr, and Pb in the samples generally in the range of 0,1 to 6,5 µg/g, 1,0 to 8,1 µg/g, and 0,4 to 1,7 µg/g respectively.
Somente Metadadados
Comparison of univariate and multivariate calibration for the determination of micronutrients in pellets of plant materials by laser induced breakdown spectrometry
(Elsevier B.V., 2010-01-01) Batista Braga, Jez Willian; Trevizan, Lilian Cristina; Nunes, Lidiane Cristina; Rufini, Iolanda Aparecida; Santos, Dario [UNIFESP]; Krug, Francisco Jose; Universidade de São Paulo (USP); Universidade de Brasília (UnB); Universidade Federal de São Carlos (UFSCar); Universidade Federal de São Paulo (UNIFESP)
The application of laser induced breakdown spectrometry (LIBS) aiming the direct analysis of plant materials is a great challenge that still needs efforts for its development and validation. in this way, a series of experimental approaches has been carried out in order to show that LIBS can be used as an alternative method to wet acid digestions based methods for analysis of agricultural and environmental samples. the large amount of information provided by LIBS spectra for these complex samples increases the difficulties for selecting the most appropriated wavelengths for each analyte. Some applications have suggested that improvements in both accuracy and precision can be achieved by the application of multivariate calibration in LIBS data when compared to the univariate regression developed with line emission intensities. in the present work, the performance of univariate and multivariate calibration, based on partial least squares regression (PLSR), was compared for analysis of pellets of plant materials made from an appropriate mixture of cryogenically ground samples with cellulose as the binding agent. the development of a specific PLSR model for each analyte and the selection of spectral regions containing only lines of the analyte of interest were the best conditions for the analysis. in this particular application, these models showed a similar performance. but PLSR seemed to be more robust due to a lower occurrence of outliers in comparison to the univariate method. Data suggests that efforts dealing with sample presentation and fitness of standards for LIBS analysis must be done in order to fulfill the boundary conditions for matrix independent development and validation. (C) 2009 Elsevier B.V. All rights reserved.
Acesso aberto (Open Access)
Desenvolvimento de métodos em espectrometria de emissão óptica com plasma induzido por laser (LIBS) para determinação de Cd, Cr e Pb em tecidos animais
(Universidade Federal de São Paulo, 2014-08-13) Abe, Claudia Naomi [UNIFESP]; Santos Junior, Dario [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
Laser-Induced Breakdown Spectroscopy (LIBS) has been considered a very promising analytical technique for applications in quality control, materials chemistry, environmental toxicology, forensic chemistry, biomedicine, among others. In this work, it was evaluated the LIBS technique for the determination of Cd, Cr, and Pb in bovine muscle, bovine liver, bovine kidney, fish muscle, mussel, and shrimp. The experimental setup was designed by using a Q-switched Nd:YAG laser at 1064 nm (5 ns, 10 Hz) and the emission signals were collected by lenses into an optical fiber coupled to an Echelle spectrometer equipped with an intensified charge-coupled device (ICCD). The effects of delay time in analytical signal collection, as well as the effect of integration time, laser fluence, sampling diameter, and number of accumulated laser pulses were evaluated. Best results were obtained when the samples were analyzed by using with laser fluence of 35 J cm?2 (1050 µm spot size), 2.0 µs of gate delay, 5,0 µs of integration time and 25 laser pulses. It was observed that the ablation of fresh tissue samples must be evaluated with higher laser energy due to the moisture content of these samples. The results obtained from the pellets analysis indicated the viability of the LIBS technique for determination of Cd, Cr, and Pb in animal tissues, but the limit of detection of Pb, 10µg/g, , must be improved for evaluations in the biomedical area.
Acesso aberto (Open Access)
Desenvolvimento de métodos para determinação de cádmio, chumbo e cromo em cosméticos por espectrometria de emissão óptica com plasma induzido por laser
(Universidade Federal de São Paulo, 2014-08-14) Matos, Simone Pires de [UNIFESP]; Santos Junior, Dario [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
Due to the increasing demand for beauty products, many cosmetic products have been marketed with dubious formulations about the safety of consumers' health. In some cases, pigments containing potentially toxic elements such as lead, chromium and cadmium are added in the formulations. Currently, there is a necessity to develop methods that allow the direct determination of these chemical elements in cosmetics. These methods are needed to assist in quality control and risk prevention, both by industry and by official regulators. In this work the optical spectrometry with laser-induced plasma emission was evaluated for determination of Cd, Cr and Pb in cosmetics. This technique, known internationally as Laser Induced Breakdown Spectroscopy with LIBS acronym, is in a consolidation phase, but the results presented in the literature highlight major advances and potential for direct determination of chemical elements in different types of samples. It was evaluated the key factors affecting the performance of LIBS, such as: sample characteristics and the ablation process, variables associated with laser, spectroscopic and matrix interference, and calibration strategies. The analytical calibration curves and the detection limits obtained initially indicate that LIBS can be a future alternative to quality control of these products.
Acesso aberto (Open Access)
Determinação da concentração de metais em solos de parques públicos da cidade de São Paulo com o uso das técnicas LIBS e ICP OES
(Universidade Federal de São Paulo, 2022-06-09) Colaço, Camila Destro [UNIFESP]; Santos Júnior, Dário [UNIFESP]; Shinzato, Mirian [UNIFESP]; http://lattes.cnpq.br/3795345587829203; http://lattes.cnpq.br/9418057647837801; http://lattes.cnpq.br/5697987164810704
Os parques são espaços fundamentais para a proteção de biodiversidade e manutenção da qualidade de vida, principalmente em grandes centros urbanos como a cidade de São Paulo. Os parques podem sofrer alterações significativas devido as atividades antrópicas e usos diversos que sofreram ao longo dos anos. Há poucos estudos sobre a qualidade dos solos desses locais. Diante disso, esse estudo propõe a avaliação da concentração de metais em solos de parques urbanos da cidade de São Paulo e compara-os com os valores orientadores fornecidos pela agencia ambiental. Para isso se utilizou a técnica de espectrometria de emissão ótica com plasma induzido por laser (LIBS) e espectrometria de emissão óptica em plasma indutivamente acoplado (ICP OES). Os solos também foram caracterizados quanto aos indicadores textura, capacidade de troca catiônica (CTC), potencial hidrogeniônico (pH) e condutividade elétrica (CE). Foram estudados 18 solos de cinco parques. Os resultados indicaram que dos solos estudados 61% são arenosos e 39% argilosos, pH possui acidez moderada a neutra, CTC e CE indicam alta capacidade de retenção e troca de íons positivos. Com base nos indicadores, os solos possuem características similares a solos com nenhuma ou baixa intervenção antrópica. A técnica LIBS apresentou desempenho satisfatório na verificação qualitativa. Entretanto, a quantificação não foi possível para os elementos Co, Cr e Zn devido possivelmente a baixa sensibilidade, efeito matriz e opacidade do plasma, respectivamente. Para Cd e Pb foram obtidos altos valores de limites de detecção, o que inviabilizou as quantificações. Para o Cu as concentrações obtidas via LIBS e ICP OES apresentaram valores discrepantes para alguns solos, provavelmente devido as características das amostras que influenciam significativamente as análises por LIBS. Conclui-se que a técnica LIBS é uma opção prática e eficiente para avaliações qualitativas. Entretanto, para determinações quantitativas, estratégias e métodos específicos de análise devem ser adotados de acordo com a amostra, instrumentação e condições de operação. Em relação aos valores orientadores, os resultados indicaram que para Cd e Co dos 18 solos estudados, apenas 2 estão em desacordo com os valores de referência de qualidade (VRQ), porém em conformidade ao valor de prevenção (VP). Para Cu, 12 solos estão em conformidade com VRQ, apenas um excedeu os valores de VP, porém não ultrapassou o valor de intervenção (VI). Para Pb, 2 solos estão em conformidade com VRQ e 1 excedeu o VI. Para Cr, apenas 1 está em conformidade com VRQ, os restantes estão em conformidade com VP. Para Zn, 7 solos estão em conformidade com o VRQ, 7 ultrapassaram os limites de VP, mas não excederam o VI. Pelos resultados obtidos, os solos estudados fornecem qualidade suficiente para desempenhar sua função de proteção de biodiversidade e lazer aos frequentadores dos parques. Contudo, possíveis fontes antrópicas contribuírem para o aumento dos teores de metais nesses solos. Sendo assim, o monitoramento é importante para manutenção da qualidade ambiental e saúde coletiva.
Somente Metadadados
Determination of silicon in plant materials by laser-induced breakdown spectroscopy
(Elsevier B.V., 2013-05-01) Souza, Paulino Florencio de; Santos Junior, Dario [UNIFESP]; Arantes de Carvalho, Gabriel Gustinelli; Nunes, Lidiane Cristina; Gomes, Marcos da Silva; Bueno Guerra, Marcelo Braga; Krug, Francisco Jose; Universidade de São Paulo (USP); Ctr Tecnol Canavieira; Universidade Federal de São Paulo (UNIFESP); Universidade Federal de São Carlos (UFSCar)
In spite of the importance of Si for improving the productivity of many important crops, such as those from the Poaceae family (e.g. sugar cane, maize, wheat, rice), its quantitative determination in plants is seldom carried out and restricted to few laboratories in the world. There is a survey of methods in the literature, but most of them are either laborious or difficult to validate in view of the low availability of reference materials with a certified Si mass fraction. the aim of this study is to propose a method for the direct determination of Si in pellets of plant materials by laser-induced breakdown spectroscopy (LIBS). the experimental setup was designed by using a Q-switched Nd:YAG laser at 1064 nm (5 ns, 10 Hz) and the emission signals were collected by lenses into an optical fiber coupled to an Echelle spectrometer equipped with an intensified charge-coupled device. Experiments were carried out with leaves from 24 sugar cane varieties, with mass fractions varying from ca. 2 to 10 g kg(-1) Si. Pellets prepared from cryogenically ground leaves were used as test samples for both method development and validation of the calibration model. Best results were obtained when the test samples were interrogated with laser fluence of 50 J cm(-2) (750 mu m spot size) and measurements carried out at Si I 212.412 nm emission line. the results obtained by LIBS were compared with those from inductively coupled plasma optical emission spectrometry after oven-induced alkaline digestion, and no significant differences were observed after applying the Student's t-test at 95% confidence level. the trueness of the proposed LIBS method was also confirmed from the analysis of CRM GBW 07603 (Bush branches and leaves). (c) 2013 Elsevier B.V. All rights reserved.
Somente Metadadados
Direct analysis of barium, calcium, potassium, and manganese concentrations in tobacco by laser-induced breakdown spectroscopy
(Elsevier Science Bv, 2016) Silvestre, Daniel Menezes; Leme, Flavio de Oliveira; Nomura, Cassiana Seimi; Nascimento, Angerson Nogueira do [UNIFESP]
This work deals with method development for the direct measurement of Ba, Ca, K, and Mn concentrations in tobacco by laser-induced breakdown spectroscopy (LIBS). Cigarette and tobacco samples from different regions of Brazil were freeze-dried and cryogenically ground for 10 min. Pellets containing 0.5 g of the ground material were prepared by applying 10 T cm(-2) pressure for 5 min in a cylindrical die set. Accurate determination of concentrations was achieved via comparison with calibration data. Calibration standards were prepared from a selected milled tobacco sample either diluted with high-purity cellulose or spiked with increasing amounts of standard solutions of the analyte, followed by freeze-drying for 48 h and cryogenic mill homogenization. After acid decomposition, inductively coupled plasma optical emission spectroscopy (ICP OES) was used to determine the mass fraction of each analyte in the calibration standards. Using the proposed method, various tobacco samples were analyzed by LIBS
Acesso aberto (Open Access)
Effect of pulse repetition rate and number of pulses in the analysis of polypropylene and high density polyethylene by nanosecond infrared laser induced breakdown spectroscopy
(Elsevier B.V., 2012-02-01) Leme, Flavio O.; Godoi, Quienly; Kiyataka, Paulo H. M.; Santos Junior, Dário [UNIFESP]; Agnelli, Jose A. M.; Krug, Francisco J.; Universidade de São Paulo (USP); Universidade Federal de São Carlos (UFSCar); Inst Tecnol Alimentos; Universidade Federal de São Paulo (UNIFESP)
Pulse repetition rates and the number of laser pulses are among the most important parameters that do affect the analysis of solid materials by laser induced breakdown spectroscopy, and the knowledge of their effects is of fundamental importance for suggesting analytical strategies when dealing with laser ablation processes of polymers. in this contribution, the influence of these parameters in the ablated mass and in the features of craters was evaluated in polypropylene and high density polyethylene plates containing pigment-based PbCrO4. Surface characterization and craters profile were carried out by perfilometry and scanning electron microscopy. Area, volume and profile of craters were obtained using Taylor Map software. A laser induced breakdown spectroscopy system consisted of a Q-Switched Nd:YAG laser (1064 nm, 5 ns) and an Echelle spectrometer equipped with ICCD detector were used. the evaluated operating conditions consisted of 10, 25 and 50 laser pulses at 1, 5 and 10 Hz, 250 mJ/pulse (85 J cm(-2)), 2 mu s delay time and 6 mu s integration time gate. Differences in the topographical features among craters of both polymers were observed. the decrease in the repetition rate resulted in irregular craters and formation of edges, especially in polypropylene sample. the differences in the topographical features and ablated masses were attributed to the influence of the degree of crystallinity, crystalline melting temperature and glass transition temperature in the ablation process of the high density polyethylene and polypropylene. It was also observed that the intensities of chromium and lead emission signals obtained at 10 Hz were two times higher than at 5 Hz by keeping the number of laser pulses constant. (C) 2011 Elsevier B. V. All rights reserved.
Somente Metadadados
Effects of laser focusing and fluence on the analysis of pellets of plant materials by laser-induced breakdown spectroscopy
(Elsevier B.V., 2012-08-01) Arantes de Carvalho, Gabriel Gustinelli; Santos Junior, Dario [UNIFESP]; Nunes, Lidiane Cristina; Gomes, Marcos da Silva; Leme, Flavio de Oliveira; Krug, Francisco Jose; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP); Universidade Federal de São Carlos (UFSCar)
The effects of laser focusing and fluence on LIBS analysis of pellets of plant leaves was evaluated. A Q-switched Nd:YAG laser (5ns, 10Hz, 1064nm) was used and the emission signals were collected by lenses into an optical fiber coupled to a spectrometer with Echelle optics and ICCD. Data were acquired from the accumulation of 20 laser pulses at 2.0 mu s delay and 5.0 mu s integration time gate. the emission signal intensities increased with both laser fluence and spot size. Higher sensitivities for Ca, K, Mg, P, Al, B, Cu, Fe, Mn, and Zn determinations were observed for fluences in the range from 25 to 60Jcm(-2). Coefficients of variation of site-to-site measurements were generally lower than 10% (n=30 sites, 20 laser pulses/site) for a fluence of 50Jcm(-2) and 750 mu m spot size. for most elements, there is an indication that accuracy is improved with higher fluences. (C) 2012 Elsevier B.V. All rights reserved.
Somente Metadadados
Evaluation of Femtosecond Laser-Induced Breakdown Spectroscopy for Analysis of Animal Tissues
(Soc Applied Spectroscopy, 2008-10-01) Santos Junior, Dario [UNIFESP]; Samad, Ricardo Elgul; Trevizan, Lilian Cristina; Freitas, Anderson Zanardi de; Vieira, Nilson Dias; Krug, Francisco Jose; IPEN CNEN; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP)
The aim of this work was to evaluate the performance of femtosecond laser-induced breakdown spectroscopy (fs-LIBS) for the determination of elements in animal tissues. Sample pellets were prepared from certified reference materials, such as liver, kidney, muscle, hepatopancreas, and oyster, after cryogenic grinding assisted homogenization. Individual samples were placed in a two-axis computer-controlled translation stage that moved in the plane orthogonal to a beam originating from a Ti:Sapphire chirped-pulse amplification (CPA) laser system operating at 800 mu and producing a train of 840 mu J and 40 fs pulses at 90 Hz. The plasma emission was coupled into the optical fiber of a high-resolution intensified charge-coupled device (ICCD)-echelle spectrometer. Time-resolved characteristics of the laser-produced plasmas showed that the best results were obtained with delay times between 80 and 120 ns. Data obtained indicate both that it is a matrix-independent sampling process and that fs-LIBS can be used for the determination of Ca, Cu, Fe, K, Mg, Na, and P, but efforts must be made to obtain more appropriate detection limits for Al, Sr, and Zn.
Acesso aberto (Open Access)
Evaluation of grinding methods for pellets preparation aiming at the analysis of plant materials by laser induced breakdown spectrometry
(Elsevier B.V., 2011-09-30) Gomes, Marcos da Silva; Santos Junior, Dario [UNIFESP]; Nunes, Lidiane Cristina; Arantes de Carvalho, Gabriel Gustinelli; Leme, Flavio de Oliveira; Krug, Francisco Jose; Universidade de São Paulo (USP); Universidade Federal de São Carlos (UFSCar); Universidade Federal de São Paulo (UNIFESP)
It has been demonstrated that laser induced breakdown spectrometry (LIBS) can be used as an alternative method for the determination of macro (P, K. Ca, Mg) and micronutrients (B, Fe, Cu, Mn, Zn) in pellets of plant materials. However, information is required regarding the sample preparation for plant analysis by LIBS. in this work, methods involving cryogenic grinding and planetary ball milling were evaluated for leaves comminution before pellets preparation. the particle sizes were associated to chemical sample properties such as fiber and cellulose contents, as well as to pellets porosity and density. the pellets were ablated at 30 different sites by applying 25 laser pulses per site (Nd:YAG@1064 nm, 5 ns, 10 Hz, 25J cm(-2)). the plasma emission collected by lenses was directed through an optical fiber towards a high resolution echelle spectrometer equipped with an ICCD. Delay time and integration time gate were fixed at 2.0 and 4.5 mu s, respectively. Experiments carried out with pellets of sugarcane, orange tree and soy leaves showed a significant effect of the plant species for choosing the most appropriate grinding conditions. By using ball milling with agate materials, 20 min grinding for orange tree and soy, and 60 min for sugarcane leaves led to particle size distributions generally lower than 75 mu m. Cryogenic grinding yielded similar particle size distributions after 10 min for orange tree, 20 min for soy and 30 min for sugarcane leaves. There was up to 50% emission signal enhancement on LIBS measurements for most elements by improving particle size distribution and consequently the pellet porosity. (C) 2011 Elsevier B.V. All rights reserved.
Somente Metadadados
Evaluation of laser induced breakdown spectroscopy for cadmium determination in soils
(Elsevier B.V., 2009-10-01) Santos, Dario [UNIFESP]; Nunes, Lidiane C.; Trevizan, Lilian C.; Godoi, Quienly; Leme, Flavio O.; Braga, Jez Willian B.; Krug, Francisco Jose; Universidade Federal de São Paulo (UNIFESP); Universidade de São Paulo (USP); Universidade Federal de São Carlos (UFSCar); Universidade de Brasília (UnB)
Cadmium is known to be a toxic agent that accumulates in the living organisms and present high toxicity potential over lifetime. Efforts towards the development of methods for microanalysis of environmental samples, including the determination of this element by graphite furnace atomic absorption spectrometry (GFAAS). inductively coupled plasma optical emission spectrometry (ICP OES), and inductively coupled plasma-mass spectrometry (ICP-MS) techniques, have been increasing. Laser induced breakdown spectroscopy (UBS) is an emerging technique dedicated to microanalysis and there is a lack of information dealing with the determination of cadmium. the aim of this work is to demonstrate the feasibility of LIBS for cadmium detection in soils. the experimental setup was designed using a laser Q-switched (Nd:YAG, 10 Hz, lambda = 1064 nm) and the emission signals were collimated by lenses into an optical fiber Coupled to a high-resolution intensified charge-coupled device (ICCD)-echelle spectrometer. Samples were cryogenically ground and thereafter pelletized before LIBS analysis. Best results were achieved by exploring a test portion (i.e. sampling spots) with larger surface area, which contributes to diminish the uncertainty due to element specific microheterogeneity. Calibration curves for cadmium determination were achieved using certified reference materials. the metrological figures of merit indicate that LIBS can be recommended for screening of cadmium contamination in soils. (C) 2009 Elsevier B.V. All rights reserved.
Somente Metadadados
Evaluation of laser induced breakdown spectroscopy for the determination of macronutrients in plant materials
(Elsevier B.V., 2008-10-01) Trevizan, Lilian Cristina; Santos, Dario [UNIFESP]; Samad, Ricardo Elgul; Vieira, Nilson Dias; Nomura, Cassiana Seimi; Nunes, Lidiane Cristina; Rufini, Iolanda Aparecida; Krug, Francisco Jose; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP); IPEN CNEN SP; Universidade Federal do ABC (UFABC); Universidade Federal de São Carlos (UFSCar)
Laser induced breakdown spectroscopy (LIBS) has become an analytical tool for the direct analysis of a large variety of materials in order to provide qualitative and/or quantitative information. However, there is a lack of information for LIBS analysis of agricultural and environmental samples. in this work a LIBS system has been evaluated for the determination of macronutrients (P, K, Ca, Mg) in pellets of vegetal reference materials. An experimental setup was designed by using a Nd:YAG laser operating at 1064 nm and an Echelle spectrometer with ICCD detector. the plasma temperature was estimated by Boltzmann plots and instrumental paragmeters such as delay time, lens-to-sample distance and pulse energy were evaluated. Certified reference materials as well as reference materials were used for analytical calibrations of P, K, Ca, and Mg. Most results of the direct analysis of plant samples by LIBS were in reasonable agreement with those obtained by ICP OES after wet acid decomposition. (C) 2008 Elsevier B.V. All rights reserved.
Somente Metadadados
Evaluation of laser induced breakdown spectroscopy for the determination of micronutrients in plant materials
(Elsevier B.V., 2009-05-01) Trevizan, Lilian Cristina; Santos, Dario [UNIFESP]; Samad, Ricardo Elgul; Vieira, Nilson Dias; Nunes, Lidiane Cristina; Rufini, Iolanda Aparecida; Krug, Francisco Jose; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP); CNEN SP; Universidade Federal de São Carlos (UFSCar)
Laser induced breakdown spectroscopy (LIBS) has been evaluated for the determination of micronutrients (B, Cu, Fe, Mn and Zn) in pellets of plant materials, using NIST, BCR and GBW biological certified reference materials for analytical calibration. Pellets of approximately 2 mm thick and 15 mm diameter were prepared by transferring 0.5 g of powdered material to a 15 mm die set and applying 8.0 tons cm(-2). An experimental setup was designed by using a Nd:YAG laser operating at 1064 nm (200 mJ per pulse, 10 Hz) and an Echelle spectrometer with ICCD detector. Repeatability precision varied from 4 to 30% from measurements obtained in 10 different positions (8 laser shots per test portion) in the same sample pellet. Limits of detection were appropriate for routine analysis of plant materials and were 2.2 mg kg(-1) B, 3.0 mg kg(-1) Cu, 3.6 mg kg(-1) Fe, 1.8 mg kg(-1) Mn and 1.2 mg kg(-1) Zn. Analysis of different plant samples were carried out by LIBS and results were compared with those obtained by ICP OES after wet acid decomposition. (C) 2009 Elsevier B.V. All rights reserved.
Somente Metadadados
Influence of particle size distribution on the analysis of pellets of plant materials by laser-induced breakdown spectroscopy
(Elsevier B.V., 2015-03-01) Arantes de Carvalho, Gabriel Gustinelli; Santos, Dario [UNIFESP]; Gomes, Marcos da Silva; Nunes, Lidiane Cristina; Bueno Guerra, Marcelo Braga; Krug, Francisco Jose; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP)
Pellets of sieved plant materials (150, 106, 75,53 and 20 pm sieve apertures) were prepared and analyzed by laser-induced breakdown spectroscopy (LIBS), and the results for Ca, K, Mg, P, B and Mn were discussed as a function of particle size distribution. This parameter is of key importance for appropriate test sample presentation in the form of pressed pellets for quantitative analysis by LIBS. Experiments were carried out with a Q-switched Nd:YAG laser at 1064 nm, and a spectrometer with Echelle optics and an intensified charge-coupled device. Results indicated that smaller particles yielded up to 50% emission signal intensities' enhancement and attained better measurements' precision (site-to-site variation). Moreover, matrix effects were reduced by analyzing pellets prepared from <75 mu m sieved fractions (mean particle size = 32 mu m; d(95) = 102 mu m) and by using a 50 J cm(-2) laser fluence (220 mJ per pulse; 750 mu m laser spot size). the preparation of pellets from laboratory samples with monomodal particle size distributions, where most particles were smaller than 100 mu m, was decisive for improving analyte micro-homogeneity within the test samples and for attaining lower coefficients of variation of measurements, typically lower than 10% (n = 10 sites per pellet; 20 laser pulses per site). (C) 2014 Elsevier B.V. All rights reserved.
Somente Metadadados
Laser-induced breakdown spectroscopy and chemometrics for classification of toys relying on toxic elements
(Elsevier B.V., 2011-02-01) Godoi, Quienly; Leme, Flavio O.; Trevizan, Lilian C.; Pereira Filho, Edenir R.; Rufini, Iolanda A.; Santos, Dario [UNIFESP]; Krug, Francisco J.; Universidade Federal de São Carlos (UFSCar); Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP)
Quality control of toys for avoiding children exposure to potentially toxic elements is of utmost relevance and it is a common requirement in national and/or international norms for health and safety reasons. Laser-induced breakdown spectroscopy (LIBS) was recently evaluated at authors' laboratory for direct analysis of plastic toys and one of the main difficulties for the determination of Cd. Cr and Pb was the variety of mixtures and types of polymers. As most norms rely on migration (lixiviation) protocols, chemometric classification models from LIBS spectra were tested for sampling toys that present potential risk of Cd, Cr and Pb contamination. the classification models were generated from the emission spectra of 51 polymeric toys and by using Partial Least Squares - Discriminant Analysis (PLS-DA), Soft Independent Modeling of Class Analogy (SIMCA) and K-Nearest Neighbor (KNN). the classification models and validations were carried out with 40 and 11 test samples, respectively. Best results were obtained when KNN was used, with corrected predictions varying from 95% for Cd to 100% for Cr and Pb. (C) 2011 Elsevier B.V. All rights reserved.
Somente Metadadados
Laser-induced breakdown spectroscopy for analysis of plant materials: A review
(Elsevier B.V., 2012-05-01) Santos, Dario [UNIFESP]; Nunes, Lidiane Cristina; Arantes de Carvalho, Gabriel Gustinelli; Gomes, Marcos da Silva; Souza, Paulino Florencio de; Leme, Flavio de Oliveira; Cofani dos Santos, Luis Gustavo; Krug, Francisco Jose; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP); Universidade Federal de São Carlos (UFSCar); Ctr Tecnol Canavieira
Developments and contributions of laser-induced breakdown spectroscopy (LIBS) for the determination of elements in plant materials are reviewed. Several applications where the solid samples are interrogated by simply focusing the laser pulses directly onto a fresh or dried surface of leaves, roots, fruits, vegetables, wood and pollen are presented. for quantitative purposes aiming at plant nutrition diagnosis, the test sample presentation in the form of pressed pellets, prepared from clean, dried and properly ground/homogenized leaves, and the use of univariate or multivariate calibration strategies are revisited. (C) 2012 Elsevier B.V. All rights reserved.
Somente Metadadados
A novel strategy for preparing calibration standards for the analysis of plant materials by laser-induced breakdown spectroscopy: A case study with pellets of sugar cane leaves
(Elsevier B.V., 2013-08-01) Gomes, Marcos da Silva; Arantes de Carvalho, Gabriel Gustinelli; Santos Junior, Dario [UNIFESP]; Krug, Francisco Jose; Universidade de São Paulo (USP); Universidade Federal de São Carlos (UFSCar); Universidade Federal de São Paulo (UNIFESP)
Calibration is still a challenging task when dealing with the direct analysis of solids. This is particularly true for laser-induced breakdown spectroscopy (LIES), and laser ablation inductively coupled plasma optical emission spectrometry/mass spectrometry, when the calibrations are matrix-dependent and/or appropriate certified reference materials are generally not available. Looking at the analysis of plant materials in the form of pressed pellets by LIBS, a new method to overcome and/or minimize this difficulty is proposed by keeping the matrix constant in order to produce matrix-matched calibration pellets. To achieve this goal and to test this novel approach, ground sugar cane leaves were chosen and submitted to acid extractions for obtaining the corresponding blank or a material containing very low concentrations of the analytes. the resulting dried solid material was used either as a blank or a low concentration standard, and also homogeneously mixed with the original plant material at appropriate ratios as well. the corresponding pellets were used as calibration standards and ablated at 30 different sites by applying 25 laser pulses per site with a Q-switched Nd:YAG at 1064 nm. the plasma emission collected by lenses was directed through an optical fiber towards a spectrometer equipped with Echelle optics and intensified charge-coupled device. Delay time and integration time gate were fixed at 2.0 and 5.0 mu s, respectively. This calibration strategy was tested for the determination of Ca, Mg, K, P, Cu, Mn, and Zn by LIBS in pellets of leaves from 17 varieties of sugar cane and good correlations were obtained with inductively coupled plasma optical emission spectrometry results in the corresponding acid digests. the proposed approach was also useful to estimate the limits of detection based on measurements of blanks, as recommended by IUPAC, or with the aid of a low concentration standard. (C) 2013 Elsevier B.V. All rights reserved.
Somente Metadadados
Preliminary studies of laser-induced breakdown spectrometry for the determination of Ba, Cd, Cr and Pb in toys
(Elsevier B.V., 2009-06-01) Godoi, Quienly; Santos, Dario [UNIFESP]; Nunes, Lidiane C.; Leme, Flavio O.; Rufini, Iolanda A.; Agnelli, Jose A. M.; Trevizan, Lilian C.; Krug, Francisco J.; Universidade de São Paulo (USP); Universidade Federal de São Carlos (UFSCar); Universidade Federal de São Paulo (UNIFESP)
The performance of laser-induced breakdown spectrometry (LIBS) for the determination of Ba, Cd, Cr and Pb in toys has been evaluated by using a Nd:YAG laser operating at 1064 nm and an Echelle spectrometer with intensified charge-coupled device detector. Samples were purchased in different cities of São Paulo State market and analyzed directly without sample preparation. Laser-induced breakdown spectrometry experimental conditions (number of pulses, delay time. integration time gate and pulse energy) were optimized by using a Doehlert design. Laser-induced breakdown spectrometry signals correlated reasonably well with inductively coupled plasma optical emission spectrometry (ICP OES) concentrations after microwave-assisted acid digestion of selected samples. Thermal analysis was used for polymer identification and scanning electron microscopy to Visualize differences in crater geometry of different polymers employed for toy fabrication. Results indicate that laser-induced breakdown spectrometry can be proposed as a rapid screening method for investigation of potentially toxic elements in toys. the unique application of laser-induced breakdown spectrometry for identification of contaminants in successive layers of ink and polymer is also demonstrated. (C) 2009 Elsevier B.V. All rights reserved.

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