Flavio de Oliveira Leme

Evaluation of grinding methods for pellets preparation aiming at the analysis of plant materials by laser induced breakdown spectrometry

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.

Feasibility of using laser induced breakdown spectroscopy for quantitative measurement of calcium, magnesium, potassium and sodium in meat

The aim of this work is to demonstrate the potential of a commercial laser induced breakdown spectroscopy (LIBS) system for quantitative determination of calcium, magnesium, potassium and sodium in bovine and chicken meat. Bovine and chicken meat are important sources of nutrients in the human diet, and Brazil is one of the major producers and exporters in the world. Measurements were performed using a commercial LIBS system designed with a Q-switched laser (Nd:YAG, 10 Hz, λ = 266 nm) and a 6 channel-CCD spectrometer. Calibration standards were produced from a selected beef and chicken sample either diluted with high-purity cellulose or spiked with increasing amounts of standard solutions of analytes. After acid decomposition, inductively coupled plasma optical emission spectroscopy (ICP OES) was used to obtain the mass fraction of each analyte in calibration standards. The accuracy of the method was checked by analysis of certified reference materials and comparison of LIBS results with ICP OES data. By applying a t-test at the 95% confidence level, LIBS results and ICP OES data presented no significant differences. The metrological figures of merit indicate the potential of a commercial LIBS system for the intended purposes and can be recommended for the analysis of beef and chicken meat aiming at the determination of Ca, Mg, K and Na.