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Laser-induced breakdown spectroscopy (LIBS) has been considered a promising tool for agricultural analysis in the recent years due to its advantages over traditional techniques, such as fewer sample preparations and faster measurements. An adequate choice of equipment and optimization of parameters for measurements in soils becomes an important issue aiming at a better performance of the technique. The performance of two LIBS systems, using a monomode laser at 532 nm and a multimode laser at 1064 nm, were evaluated for soil analysis. The craters formed in the sample by action of the laser pulses studied by Scanning electron microscopy (SEM) aimed to analyze the efficiency of the lasers in the ablation process. The plasma temperature and electronic density, evaluated using the Saha-Boltzmann method, were similar for both lasers. The lower boundary of the Local thermodynamic equilibrium (LTE) condition was verified for both lasers. The signal-to-noise ratio (SNR) was analyzed for many emission lines of important elements of the soil, such as C, Fe, Mg, and K. Partial least square (PLS) analysis was used to verify the performance of both lasers for the quantitative analysis. From the PLS analysis, a better performance for the elemental quantification as found to 1064 nm laser and compared to 532 nm laser, i. e, higher coefficient R, a small Root Mean Square Error of Calibration (RMSEC) for C, K and Mg, and small Root Mean Square Error of Prediction (RMSEP) for K and Mg. In conclusion, the results suggesting the use of a multimode Laser at 1064 nm hence are more accessible, and less expensive, than a monomode Laser at 532 nm.

Made available in DSpace on 2015-05-15T13:30:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2014Bitstream added on 2015-05-15T13:56:38Z : No. of bitstreams: 1 ISSN2156-8278-2014-05-11-722-729.pdf: 3517422 bytes, checksum: 8b8a6cbe5d0d0ce9ceb82e71f1519681 (MD5) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Advanced field methods of carbon (C) analysis should now be capable of providing repetitive, sequential measurements for the evaluation of spatial and temporal variation at a scale that was previously unfeasible. Some spectroscopy techniques, such as laser-induced breakdown spectroscopy (LIBS), have portable features that may potentially lead to clean and rapid alternative approaches for this purpose. The goal of this study was to quantify the C content of soils with different textures and with high iron and aluminum concentrations using LIBS. LIBS emission spectra from soil pellets were captured, and the C content was estimated (emission line of C (I) at 193.03 nm) after spectral offset and aluminum spectral interference correction. This technique is highly portable and could be ideal for providing the soil C content in a heterogeneous experiment. Dry combustion was used as a reference method, and for calibration a conventional linear model was evaluated based on soil textural classes. The correlation between reference and LIBS values showed r = 0.86 for medium-textured soils and r = 0.93 for fine-textured soils. The data showed that better correlation and lower error (14%) values were found for the fine-textured LIBS model. The limit of detection (LOD) was found to be 0.32% for medium-textured soils and 0.13% for fine-textured soils. The results indicated that LIBS quantification can be affected by the texture and chemical composition of soil. Signal treatment was shown to be very important for mitigation of these interferences and to improve quantification. Universidade Estadual Paulista Júlio de Mesquita Filho, Instituto de Química de Araraquara, Araraquara, Rua Prof. Francisco Degni, 55, Quitandinha, CEP 14800900, SP, Brasil Universidade Estadual Paulista Júlio de Mesquita Filho, Departamento de Química Analítica Instituto de Química de Araraquara FAPESP 2010/09211-6 CNPq 560292/2010-4