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 μs, 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 μm. 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.
a b s t r a c tThe calibration and quantitative measurement is the ''Achilles heel'' of the LIBS technique. This paper deals with a method developed for the direct measurement of K and Mg in plant samples. Instrumental parameters were optimized and the best condition found was a 50 lm spot size, 10 Hz laser repetition rate, 75 accumulated laser pulses with 25 mJ/pulse and 0.25 ls of delay time. For method calibration, the use of synthetic standard calibrating material prepared by the addition of increasing concentrations of K and Mg in wood, filter paper and babassu mesocarp was proposed in order to assess the feasibility of using these various matrices in plant samples analysis. The limits of detection of proposed method were 2-30 and 6-27 lg g À1 for K and Mg, respectively. The use of the carbon emission wavelength at 247.856 nm was used as internal standard to improve the analytical results. Certified reference materials of plants were used to check the accuracy of the proposed method and recovery around 82% and 100% were obtained in all cases. Ó 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).
Due to matrix interference and sample particle size effects, some of the most important and difficult issues in laser‐induced breakdown spectroscopy (LIBS) analysis are the calibration and quantitative measurement of a complex matrix. This study proposes the use of borate fusion as an alternative sample preparation procedure for the quantitative measurement of Al, Fe, Si and Ti in bauxite by LIBS. Analytical calibration curves were made using bauxite certified reference materials (CRM), and the precision and accuracy of the methods were evaluated by analysing an additional bauxite CRM, using two different approaches: pressed powder pellets and fused glass beads. The borate fusion method was the most suitable sample preparation technique, since particle size effects and matrix interference could be minimised, obtaining better linearity on the analytical calibration curves (r2), and more accurate and more precise results for bauxite analysis.
Mushrooms are bioaccumulating organisms commonly used in selenium (Se) enrichment studies. However, the addition of Se in the culture medium may alter the distribution of other essential elements in the mushroom fruiting body. To evaluate the effects of the Se enrichment, Ca, Mg, and K distributions in pink oyster (
Pleurotus djamor
) and K and Mg distributions in white oyster (
Pleurotus ostreatus
) mushrooms were mapped by laser-induced breakdown spectroscopy (LIBS), which can be used at room temperature and requires minimal or no sample preparation. It was verified that Se enrichment favoured the accumulation of Ca in the lower part of the pink oyster mushroom and prevented the transport of this element to the edges and tops. The Se enrichment also altered the distribution of K and Mg, decreasing the numerical correlation between the K and Mg distributions (R² = 0.5871). In the white oyster mushroom, however, despite the changes in the morphological characteristics of the fruiting bodies after enrichment, there were generally nonsignificant differences in the K and Mg distributions between the control and the Se-enriched mushrooms.
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