Navegando por Palavras-chave "Plant material"

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    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.
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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 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.
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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 ablation inductively coupled plasma optical emission spectrometry for analysis of pellets of plant materials
    (Elsevier B.V., 2014-04-01) Gomes, Marcos S.; Schenk, Emily R.; Santos, Dario [UNIFESP]; Krug, Francisco Jose; Almirall, Jose R.; Universidade Federal de São Carlos (UFSCar); Universidade de São Paulo (USP); Florida Int Univ; Universidade Federal de São Paulo (UNIFESP)
    An evaluation of laser ablation inductively coupled plasma optical emission spectroscopy (LAICP OES) for the direct analysis of pelleted plant material is reported. Ground leaves of orange citrus, soy and sugarcane were comminuted using a high-speed ball mill, pressed into pellets and sampled directly with laser ablation and analyzed by ICP OES. the limits of detection (LODs) for the method ranged from as low as 0.1 mg kg(-1) for Zn to as high as 94 mg kg(-1) for K but were generally below 6 mg kg(-1) for most of the elements of interest. A certified reference material consisting of a similar matrix (NIST SRM 1547 peach leaves) was used to check the accuracy of the calibration and the reported method resulted in an average bias of similar to 5% for all the elements of interest. the precision for the reported method ranged from as low as 4% relative standard deviation (RSD) for Mn to as high as 17% RSD for Zn but averaged similar to 6.5% RSD for all the elements (n = 10). the proposed method was tested for the determination of Ca, Mg, P, K, Fe, Mn, Zn and B, and the results were in good agreement with those obtained for the corresponding acid digests by ICP-OES, no differences being observed by applying a paired t-test at the 95% confidence level. the reported direct solid sampling method provides a fast alternative to acid digestion that results in similar and appropriate analytical figures of merit with regard to sensitivity, accuracy and precision for plant material analysis. (C) 2014 Elsevier B.V. All rights reserved.