Navegando por Palavras-chave "Laser-induced breakdown spectroscopy"

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    Determination of Cd, Cr and Pb in phosphate fertilizers by laser-induced breakdown spectroscopy
    (Elsevier B.V., 2014-07-01) Nunes, Lidiane Cristina; Arantes de Carvalho, Gabriel Gustinelli; Santos Junior, Dario [UNIFESP]; Krug, Francisco Jose; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP)
    A validated method for quantitative determination of Cd, Cr, and Pb in phosphate fertilizers by laser-induced breakdown spectroscopy (LIBS) is presented. Laboratory samples were comminuted and homogenized by cryogenic or planetary ball milling, pressed into pellets and analyzed by LIBS. the experimental setup was designed by using a Q-switched Nd:YAG at 1064 nm with 10 Hz repetition rate, and the intensity signals from Cd II 214.441 nm, Cr II 267.716 nm and Pb II 220.353 nm emission lines were measured by using a spectrometer furnished with an intensified charge-coupled device. LIBS parameters (laser fluence, lens-to-sample distance, delay time, integration time gate, number of sites and number of laser pulses per site) were chosen after univariate experiments with a pellet of NIST SRM 695 (Trace Elements in Multi-Nutrient Fertilizer). Calibration and validation were carried out with 30 fertilizer samples from single superphosphate, triple superphosphate, monoammonium phosphate, and NPK mixtures. Good results were obtained by using 30 pulses of 50 J cm(-2) (750 mu m spot size), 2.0 mu s delay time and 5.0 mu s integration time gate. No significant differences between Cd, Cr, and Pb mass fractions determined by the proposed LIBS method and by ICP OES after microwave-assisted acid digestion (AOAC 2006.03 Official Method) were found at 95% confidence level. the limits of detection of 1 mg kg(-1) Cd, 2 mg kg(-1) Cr and 15 mg kg(-1) Pb and the precision (coefficients of variation of results ranging from 2% to 15%) indicate that the proposed LIES method can be recommended for the determination of these analytes in phosphate fertilizers. (C) 2014 Elsevier B.V. All rights reserved.
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    Determination of inorganic nutrients in wheat flour by laser-induced breakdown spectroscopy and energy dispersive X-ray fluorescence spectrometry
    (Elsevier B.V., 2014-10-01) Peruchi, Lidiane Cristina; Nunes, Lidiane Cristina; Arantes de Carvalho, Gabriel Gustinelli; Bueno Guerra, Marcelo Braga; Almeida, Eduardo de; Rufini, Iolanda Aparecida; Santos Jr., Dário [UNIFESP]; Krug, Francisco Jose; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP)
    Laser-induced breakdown spectroscopy (LIBS) and energy dispersive X-ray fluorescence spectrometry (EDXRF) were evaluated for the determination of P, K, Ca, Mg, S, Fe, Cu, Mn and Zn in pressed pellets of wheat flours. EDXRF and LIBS calibration models were built with analytes mass fractions determined by inductively coupled plasma optical emission spectrometry after microwave-assisted acid digestion in a set of 25 wheat flour laboratory samples. Test samples consisted of pressed pellets prepared from wheat flour mixed with 30% mm-1 cellulose binder. Experiments were carried out with a LIBS setup consisted of a Q-switched Nd:YAG laser and a spectrometer with Echelle optics and ICCD, and a benchtop EDXRF system fitted with a Rh target X-ray tube and a Si(Li) semiconductor detector. the correlation coefficients from the linear calibration models of P, K, Ca, Mg, S, Fe, Mn and Zn determined by LIBS and/or EDXRF varied from 0.9705 for Zn to 0.9990 for Mg by LIBS, and from 0.9306 for S to 0.9974 for K by EDXRF. the coefficients of variation of measurements varied from 1.2 to 20% for LIBS, and from 03 to 24% for EDXRF. the predictive capabilities based on RMSEP (root mean square error of prediction) values were appropriate for the determination of P, Ca, Mg, Fe, Mn and Zn by LIBS, and for P, K, S, Ca, Fe, and Zn by EDXRF. in general, results from the analysis of NIST SRM 1567a Wheat flour by LIBS and EDXRF were in agreement with their certified mass fractions. (C) 2014 Elsevier B.V. All rights reserved.
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    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.
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    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.
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    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.
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    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.
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    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.
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    Mercury Amalgam Diffusion in Human Teeth Probed Using Femtosecond LIBS
    (Sage Publications Inc, 2017) Bello, Liciane Toledo; da Ana, Patricia Aparecida; Santos, Dario, Jr. [UNIFESP]; Krug, Francisco Jose; Zezell, Denise Maria; Vieira, Nilson Dias, Jr.; Samad, Ricardo Elgul
    In this work the diffusion of mercury and other elements from amalgam tooth restorations through the surrounding dental tissue (dentin) was evaluated using femtosecond laser-induced breakdown spectroscopy (fs-LIBS). To achieve this, seven deciduous and eight permanent extracted human molar teeth with occlusal amalgam restorations were half-sectioned and analyzed using pulses from a femtosecond laser. The measurements were performed from the amalgam restoration along the amalgam/dentin interface to the apical direction. It was possible to observe the presence of metallic elements (silver, mercury, copper and tin) emission lines, as well as dental constituent ones, providing fingerprints of each material and comparable data for checking the consistence of the results. It was also shown that the elements penetration depth values in each tooth are usually similar and consistent, for both deciduous and permanent teeth, indicating that all the metals diffuse into the dentin by the same mechanism. We propose that this diffusion mechanism is mainly through liquid dragging inside the dentin tubules. The mercury diffused further in permanent teeth than in deciduous teeth, probably due to the longer diffusion times due to the age of the restorations. It was possible to conclude that the proposed femtosecond-LIBS system can detect the presence of metals in the dental tissue, among the tooth constituent elements, and map the distribution of endogenous and exogenous chemical elements, with a spatial resolution that can be brought under 100 mu m.
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    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.