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Made available in DSpace on 2021-06-25T11:05:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Limited sensitivities of some laser-induced breakdown spectroscopy (LIBS) instruments may impair some applications. Although this drawback can be minimized by instrumental improvements, the complexity of operations and cost increases. In this work the principle of conventional dry ashing for sample preparation was evaluated as a simple and low-cost alternative to improve the sensitivity of LIBS analysis. Botanical, agronomic and industrial samples were analyzed. Samples were dry heated and their LIBS emission signals were evaluated. The results suggest the dry heating caused structural changes in samples providing greater availability of the analyte, which resulted in the enhancement of the signals. As proof of concept, the strategy was applied for Sr determination in plant leaves. Two Sr emission lines, enhanced after sample dry ashing were used. The developed methods showed similar performance featuring a good linear range (10 to 70 μg g−1) with coefficient of correlations higher than 0.99. Additionally, the accurate determination of Sr in apple and peach leaves standard materials was achieved. Department of Analytical Physical-Chemical and Inorganic Chemistry São Paulo State University - UNESP Istituto per la Scienza e Tecnologia dei Plasmi (ISTP) Sede di Bari CNR Exact and Earth Sciences Department Federal University of São Paulo - UNIFESP Department of Analytical Physical-Chemical and Inorganic Chemistry São Paulo State University - UNESP

Made available in DSpace on 2020-12-12T02:43:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-09-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The determination of N is an important demand for several sectors and the analytical features of laser-induced breakdown spectroscopy (LIBS) are very attractive to accomplish this task. In this work, a novel proposal for nitrogen determination was explored considering molecular diatomic emission lines of CN measured by LIBS. As a proof of concept, a method was developed to determine N in biochar-based fertilizers, a highly recalcitrant matrix. The fertilizers were prepared from biochar of eucalyptus pruning residues, peanut skin and fibers of banana tree and the calibration standards were prepared by matrix matching using eucalyptus biochar. Diatomic emission signals of CN at 388.3 nm showed high correlation with the levels of N in standards and samples, suggesting the molecular emission of CN is little affected by the matrix effect. The developed method is accurate since the N levels determined in the samples do not differ statistically from the expected level, with a 95% confidence level. Furthermore, the method using molecular emission is simple and highlights the potential of LIBS for N determination in complex matrices (e.g. biochar). Department of Analytical Chemistry São Paulo State University – UNESP Department of Chemistry Federal University of São Paulo – UNIFESP Department of Analytical Chemistry São Paulo State University – UNESP FAPESP: 2015/24757-9 FAPESP: 2019/18873-7 CNPq: 302414/2017-7 CNPq: 308200/2018-7

Made available in DSpace on 2018-12-11T17:33:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-09-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Biochar has gained agricultural importance as a soil amendment because of its important agricultural properties such as water retention, plant nutrient supplier, promoter of microorganism growth, sequestration action of atmospheric CO2, etc. Further, it is a low cost material being produced by recycling. Due to its active sites, biochar can adsorb nutrients so acting as a soil fertilizer. Thus the rapid assessment of nutrients in these materials is essential to ensure quality control for agricultural purposes. This work aimed to develop a simple analytical method based on Laser-Induced Breakdown Spectroscopy (LIBS) to determine Ca in biochar-based fertilizers. In particular, biochar samples enriched with Ca were prepared from peanut shells, residues of eucalyptus and banana fibers. The calibration standards were prepared by matrix matching using a biochar from eucalyptus residues. Different spectral preprocessing were evaluated to enhance the precision and accuracy of the method. However, the matrix effects demanded the use of internal standardization as the appropriate methodology to obtain the best accuracy. A linear correlation coefficient of 0.989 and a linear work range of 1.51–11.23% Ca were obtained using the proposed method, which yielded limits of detection and quantification of 0.45% e 1.51%, respectively. Calcium contents determined by LIBS in biochar-based fertilizers were in good agreement (paired t-test at 95% confidence level) with those determined by using High-Resolution Continuous Source Atomic Absorption Spectrometry (HR-CS FAAS) as the reference technique. Thus, the importance of internal standardization was demonstrated to be successful for the quantitative analysis of Ca in complex matrices like biochar-based fertilizers. São Paulo State University - UNESP Analytical Chemistry Department, P.O. Box 355 Federal University of São Paulo UNIFESP Chemistry Department, Rua São Nicolau, n° 210 - Centro - CEP CNR NANOTEC - PlasMI Lab, Via Amendola 122/D São Paulo State University - UNESP Analytical Chemistry Department, P.O. Box 355 FAPESP: 2015/24757-9

Made available in DSpace on 2020-12-12T01:49:17Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-05-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The present work proposes methods for detection and quantification of honey adulterants using laser-induced breakdown spectroscopy (LIBS). The sample set consisted of 6 pure honey from different botanical sources, 2 sweetener syrups and 228 fortified samples. The spectra acquired using a spark discharge coupled to the LIBS system were used for the development of the PLS-DA (classification) and PLS (calibration) models. Several data preprocessing and variable selection methods were evaluated to obtain the best fit. The detection of adulterants was performed with 100% of accuracy. The quantification of adulterants was possible through a PLS model with the variables selected by iPLS. The PLS model was validated with external samples and presented good accuracy, selectivity, sensitivity, and linearity. The proposed methods highlighted the potential of the LIBS technique for honey authenticity certification, providing fast, simple, and clean determinations since no sample pretreatment was required. Analytical Chemistry Department Institute of Chemistry São Paulo State University – UNESP, Prof. Francisco Degni 55 Department of Chemistry Federal University of São Paulo – UNIFESP, R. São Nicolau 210 Analytical Chemistry Department Institute of Chemistry São Paulo State University – UNESP, Prof. Francisco Degni 55 CNPq: 141977/2016-7 CNPq: 308200/2018-7

Made available in DSpace on 2018-12-11T17:36:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-06-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) A spark discharge system was coupled to laser-induced breakdown spectroscopy (SD-LIBS) to improve sensitivity in the determination of P in fertilizers. A LIBS system consisting of a Q-switched Nd:YAG laser operating at 1064 nm and emitting pulses at 50 mJ with a fluence of 70 J cm−2 at the focal point was used. Results of preliminary experiments suggested that the most appropriate wavelength to measure P was the P (I) line at 214.9 nm, which did not show interferences by Fe, Cu and Zn. The electrical discharge was provided by a homemade high-voltage electronic circuit consisting of two cylindrical tungsten electrodes at the optimized output voltage of 4.5 kV, with tips arranged at the optimal distances of 4 mm between them and 2 mm above the sample surface. To minimize the expected matrix effects calibration standards of P2O5 in the range of 4.8 and 33.3% were prepared by mixing various amounts of a phosphate rock reference material (SRM-120c) with a mixture of CaCO3, CaSO4, (NH2)2CO and KCl at a 1:1:1:1 mass ratio. The calibration curves obtained at a 4.5 kV SD-LIBS output voltage showed correlation coefficients ≥0.993, RSD ≤8% and LOQ 5.3% (m/m) P2O5. Data obtained by analyzing commercial samples by the proposed system were in good agreement, at 95% confidence level, with those obtained by using high-resolution continuum-source flame atomic absorption spectroscopy. São Paulo State University - UNESP Analytical Chemistry Department, P.O. Box 355 University of São Paulo – USP Department of Electrical and Computer Engineering CNR-Istituto di Nanotecnologia (NANOTEC) – PLasMI Lab, Via Amendola 122/D Federal University of São Paulo - UNIFESP Exact and Earth Sciences Department São Paulo State University - UNESP Analytical Chemistry Department, P.O. Box 355 CNPq: 141977/2016-7 FAPESP: 2004/14212-0 CNPq: 2015/24757-9 CNPq: 303255/2013-7 CNPq: 311085/2014-8

Made available in DSpace on 2018-12-11T17:37:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-10-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Laser-induced breakdown spectroscopy is an optical emission technique quite suitable for the analysis of recalcitrant materials as it eliminates complex procedures of sample preparation. However, for some simple LIBS instrumentation the detection limits are still higher compared to those of consolidated spectroscopic techniques. The aim of the present work was to develop a method for the determination of K in new biochar-based fertilizer samples using a simple single pulse LIBS arrangement. Due to the low K detectability, which made impossible to obtain calibration curves, an exploratory qualitative study was performed aiming to evaluate the influence of the addition of easily ionizable elements (EIE) on the sensitivity. To this aim different salts containing EIE (K, Li and Na) and other cations (Cu and Mg) have been evaluated. Results obtained showed that salts containing EIE cations increased the spectral emission signals of some elements in samples previously submitted to charring. In particular, the strategy of using Li+ was applied to the determination of K in biochar-based fertilizers. The addition of Li+ allowed to develop an analytical method for K determination featuring a linear dynamic range from 0.8% to 21.56% K, and limits of detection and quantification of 0.2% and 0.8%, respectively. São Paulo State University - UNESP Analytical Chemistry Department, P.O. Box 355 Federal University of São Paulo UNIFESP Chemistry Department, Rua São Nicolau, no 210 - Centro CNR-Istituto di Nanotecnologia (NANOTEC) - PLasMI Lab, Via Amendola 122/D São Paulo State University - UNESP Analytical Chemistry Department, P.O. Box 355 CAPES: 1490630 FAPESP: 2015/24757-9 CNPq: 302414/2017–7 CNPq: 311085/2014–8

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 μm spot size), 2.0 μs delay time and 5.0 μs 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 LIBS method can be recommended for the determination of these analytes in phosphate fertilizers.

The analytical performances of benchtop and handheld energy dispersive X-ray fluorescence spectrometry (EDXRF) systems were evaluated aiming at the direct and simultaneous determination of P, K, Ca, S, Fe, Mn, and Si in plant materials. Pressed pellets of comminuted leaves from 23 varieties of sugar cane were used as laboratory samples. Both systems presented similar figures of merit, and were able to provide useful data for plant nutrition diagnosis. Linear correlation between the elemental mass fractions in the test samples and characteristic X-ray intensities was obtained for all analytes with both types of equipment. Correlation coefficients from 0.9601 to 0.9918 and from 0.9094 to 0.9948 were attained for benchtop and handheld EDXRF, respectively. The coefficient of variation of measurements carried out in 3 different test samples was also appropriate, being lower than 13% for all analytes. Limits of detection were comparable for both systems (20 mg kg−1 for Fe and Mn, and approximately 0.1 g kg−1 for P, K, Ca, S and Si) and permit the evaluation of the mineral nutrition status of sugar cane crop taking into account the critical levels of these elements. The handheld system is a cost-effective and appealing option for those who intend to carry out faster in situ and laboratory analysis with equivalent performance of the benchtop equipment.

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 μm 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).

The effects of laser focusing and fluence on LIBS analysis of pellets of plant leaves was evaluated. A Q-switched Nd:YAG laser (5 ns, 10 Hz, 1064 nm) 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 μs delay and 5.0 μs 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 60 J cm − 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 50 J cm − 2 and 750 μm spot size. For most elements, there is an indication that accuracy is improved with higher fluences.

This review reports recent applications of the ultrasonic energy for extracting inorganic and organic analytes from diverse solid samples devoted to spectroscopic analyses. The main advantages resulting from ultrasound comprise the reduction of the procedural time and reagent consumption. In this sense, ultrasound‐assisted extractions can be considered as an efficient tool for improving the analytical performance of procedures employed in analytical chemistry and natural products chemistry. However, a rigorous experimental control is strongly recommended in order to avoid losses in precision and accuracy. Uncontrolled ultrasound‐assisted extraction procedure is also discussed, since ultrasonic irradiation can provoke decompositions of molecules, hindering organic compounds extraction.

A simple method for cadmium and lead determination in foods by beam injection flame furnace atomic absorption spectrometry (BIFF-AAS) was proposed. Food slurries were prepared by transferring an exact amount of cryogenic-ground homogenized material (50–100 mg) to centrifuge tubes, followed by addition of 5 ml (up to 2.8 mol l −1 ) nitric acid solution and sonication in an ultrasonic bath during 5–10 min. Thereafter, slurries were diluted with water to 10 ml, centrifuged during 5 min at 5400 rpm and 400 μl aliquot of the supernatant was analyzed by BIFF-AAS. The detection limits based on peak height measurements were 0.03 μg g −1 Cd and 1.6 μg g −1 Pb for 2% (m/v) slurry (200 mg/10 ml). For method validation, the certified reference materials Pig Kidney (BCR 186) and Rice Flour (NIES 10) were used. Quantitative cadmium and lead recoveries were obtained and no statistical differences were found at 95% level by applying the t -test.

Selenium is both essential and toxic to man and animals, depending on the concentration and the ingested form. Most fruits and vegetables are poor sources of selenium, but coconut can be a good selenium source. Samples were suspended (1 + 4 v/v) in a mixture of tertiary amines soluble in water (10% v/v CFA-C). This simple sample treatment avoided contamination and decreased the analysis time. The standard additions method was adopted for quantification. The action of the autosampler was improved by the presence of the amines mixture in the suspension. A Varian model AA-800 atomic absorption spectrometer equipped with a graphite furnace and a GTA 100 autosampler was used for selenium determination in coconut water and coconut milk. Background correction was performed by means of the Zeeman effect. Pyrolytically coated graphite tubes were employed. Using Pd as chemical modifier, the pyrolysis and the atomization temperatures were set at 1400 and 2200ºC, respectively. For six samples, the selenium concentration in coconut water varied from 6.5 to 21.0 mug L-1 and in coconut milk from 24.2 to 25.1 mug L-1. The accuracy of the proposed method was evaluated by an addition-recovery experiment and all recovered values are in the 99.5-102.3% range. The main advantage of the proposed method is that it can be directly applied without sample decomposition.

The development of cancer is a complex, multistage process during which a normal cell undergoes genetic changes that result in phenotypic alterations and in the acquisition of the ability to invade other sites. Inductively coupled plasma optical emission spectroscopy was used to estimate the contents of Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, P, Pb, and Zn in healthy kidney and renal cell carcinoma (RCC), and significant differences were found for all elements. Along with the progression of the malignant disease, a progressive decrease of Cd and K was observed. In fact, for Cd, the concentration in stage T4 was 263.9 times lower than in stage T1, and for K, the concentration in stage T4 was 1.73 times lower than in stage T1. Progressive accumulation was detected for P, Pb, and Zn in stage T4. For P, the concentration in stage T4 was 11.1 times higher than in stage T1; for Pb, the concentration in stage T4 was 232.7 times higher than in T1; and for Zn, the concentration in T4 was 8.452 times higher than in T1. This study highlights the marked differences in the concentrations of selected trace metals in different malignant tumor stages. These findings indicate that some trace metals may play important roles in the pathogenesis of RCC.

article i nfo A simultaneous optimization strategy based on a neuro-genetic approach is proposed for selection of laser induced breakdown spectroscopy operational conditions for the simultaneous determination of macro- nutrients (Ca, Mg and P), micro-nutrients (B, Cu, Fe, Mn and Zn), Al and Si in plant samples. A laser induced breakdown spectroscopy system equipped with a 10 Hz Q-switched Nd:YAG laser (12 ns, 532 nm, 140 mJ) and an Echelle spectrometer with intensified coupled-charge device was used. Integration time gate, delay time, amplification gain and number of pulses were optimized. Pellets of spinach leaves (NIST 1570a) were employed as laboratory samples. In order to find a model that could correlate laser induced breakdown spectroscopy operational conditions with compromised high peak areas of all elements simultaneously, a Bayesian Regularized Artificial Neural Network approach was employed. Subsequently, a genetic algorithm was applied to find optimal conditions for the neural network model, in an approach called neuro-genetic. A single laser induced breakdown spectroscopy working condition that maximizes peak areas of all elements simultaneously, was obtained with the following optimized parameters: 9.0 µs integration time gate, 1.1 µs delay time, 225 (a.u.) amplification gain and 30 accumulated laser pulses. The proposed approach is a useful and a suitable tool for the optimization process of such a complex analytical problem.

An analytical procedure relying on micro-energy dispersive X-ray fluorescence spectrometry (μ-EDX) was evaluated for the quantitative determination of macro-, micronutrients and beneficial elements in pressed pellets of plant materials. For testing purposes, leaves from 23 varieties of sugar cane, previously analyzed by validated reference methods, based on wet decomposition procedures followed by ICP OES measurements were used. Linear correlations between analyte mass fractions in the tested samples and the corresponding μ-EDX intensities were obtained for P, K, Ca, S, Fe, Mn and Si with regression coefficients ranging from 0.9501 to 0.9933. Furthermore, the coefficients of variation of results in the 0.3 to 16% range (n = 3 sampling lines, 30 sampling sites per line), the spatial resolution of 50 μm per site and the suitable detection limits for these analytes were additional features that demonstrated the performance of the proposed procedure as a useful tool for plant nutrient diagnosis. In addition, the results also indicate that μ-EDX can be recommended as a cross-validation method for analysis of plant materials, owing to its inherent non-destructive capability and, particularly, when dealing with analytes' micro-heterogeneity evaluation within the samples.

Laser induced breakdown spectrometry (LIBS) was applied for the determination of macro (P, K, Ca, Mg) and micronutrients (B, Cu, Fe, Mn and Zn) in sugar cane leaves, which is one of the most economically important crops in Brazil. Operational conditions were previously optimized by a neuro-genetic approach, by using a laser Nd:YAG at 1064 nm with 110 mJ per pulse focused on a pellet surface prepared with ground plant samples. Emission intensities were measured after 2.0 μs delay time, with 4.5 μs integration time gate and 25 accumulated laser pulses. Measurements of LIBS spectra were based on triplicate and each replicate consisted of an average of ten spectra collected in different sites (craters) of the pellet. Quantitative determinations were carried out by using univariate calibration and chemometric methods, such as PLSR and iPLS. The calibration models were obtained by using 26 laboratory samples and the validation was carried out by using 15 test samples. For comparative purpose, these samples were also microwave-assisted digested and further analyzed by ICP OES. In general, most results obtained by LIBS did not differ significantly from ICP OES data by applying a t-test at 95% confidence level. Both LIBS multivariate and univariate calibration methods produced similar results, except for Fe where better results were achieved by the multivariate approach. Repeatability precision varied from 0.7 to 15% and 1.3 to 20% from measurements obtained by multivariate and univariate calibration, respectively. It is demonstrated that LIBS is a powerful tool for analysis of pellets of plant materials for determination of macro and micronutrients by choosing calibration and validation samples with similar matrix composition.