Dário Santos

Evaluation of Femtosecond Laser-Induced Breakdown Spectroscopy for Analysis of Animal Tissues

The aim of this work was to evaluate the performance of femtosecond laser-induced breakdown spectroscopy (fs-LIBS) for the determination of elements in animal tissues. Sample pellets were prepared from certified reference materials, such as liver, kidney, muscle, hepatopancreas, and oyster, after cryogenic grinding assisted homogenization. Individual samples were placed in a two-axis computer-controlled translation stage that moved in the plane orthogonal to a beam originating from a Ti:Sapphire chirped-pulse amplification (CPA) laser system operating at 800 nm and producing a train of 840 μJ and 40 fs pulses at 90 Hz. The plasma emission was coupled into the optical fiber of a high-resolution intensified charge-coupled device (ICCD)–echelle spectrometer. Time-resolved characteristics of the laser-produced plasmas showed that the best results were obtained with delay times between 80 and 120 ns. Data obtained indicate both that it is a matrix-independent sampling process and that fs-LIBS can be used for the determination of Ca, Cu, Fe, K, Mg, Na, and P, but efforts must be made to obtain more appropriate detection limits for Al, Sr, and Zn.

Evaluation of laser induced breakdown spectrometry for the determination of macro and micronutrients in pharmaceutical tablets

The aim of this work is to demonstrate the feasibility of laser induced breakdown spectrometry (LIBS) for the determination of macro and micronutrients in multielement tablets. The experimental setup was designed by using a laser Q-switch (Nd:YAG, 10 Hz, λ = 1064 nm) and the emission signals were collected by lenses into an optical fiber coupled to an echelle spectrometer equipped with a high-resolution intensified charge coupled device (ICCD). Tablets were cryogenically ground and thereafter pelletized before LIBS analysis. Calibration curves were made by employing samples and mixtures of commercial multielement tablets with binders at different ratios. Best results were achieved by using the following experimental conditions: 29 J cm−2 laser fluence, 165 mm lens to sample distance (f = 200 mm), 2.0 μs delay time, 5.0 μs integration time and 5 accumulated laser pulses. In general, the results obtained by the proposed LIBS procedure were in agreement with those obtained by ICP OES from the corresponding acid digests and coefficients variation of LIBS measurements varied from 2 to 16%. The metrological figures of merit indicate that LIBS fits for the intended purposes, and can be recommended for the analysis of multielement tablets and similar matrices aiming the determination of Ca, Cu, Fe, Mg, Mn, P and Zn.

Changes in phase angle and body composition induced by resistance training in older women

Background:Resistance training (RT) has selective effects on body composition that may counteract the deleterious effects of aging. Changes in phase angle (PhA) may serve to monitor the influence of RT in older people.Objectives:To describe the effect of RT in training, detraining and retraining on body composition, including PhA in older women.Subjects/methods:Thirty-three older women (⩾60 years old) participated. The RT program was carried out over 12 weeks for each stage (training, detraining and retraining). Whole-body fat-free mass and fat mass (FM) and appendicular lean soft tissue (ALST) measurements were carried out using a dual energy X-ray absorptiometry. Bioimpedance spectroscopy was used to estimate total body water (TBW), intra (ICF) and extracellular (ECF) fluids, whole-body resistance (R) and reactance (Xc) and PhA. Upper and lower body muscle strength were also assessed.Results:From baseline to after training muscle strength, ALST and PhA significantly (P<0.05) increased. In detraining, significant (P<0.05) reductions in muscle strength, TBW, ECF, ICF and PhA along with significant (P<0.05) increases in R were observed, with the greatest magnitude observed for PhA (Δ=−7.6%). From detraining to retraining a significant reduction in FM along with increases in Xc, PhA and muscle strength were observed. Although an increase was observed from detraining to retraining in PhA, the values were still lower than baseline PhA.Conclusions:In untrained older women, a RT is associated with increases in PhA, whereas detraining results in a marked decrease in PhA, and more time may be required in retraining to counteract the negative influence of absence of exercise stimulus.

Direct analysis of plant leaves by EDXRF and LIBS: microsampling strategies and cross-validation

Microsampling strategies were evaluated for the direct analysis of dried sugar cane leaves by energy-dispersive X-ray fluorescence spectrometry (EDXRF) and laser-induced breakdown spectroscopy (LIBS). The analysis by EDXRF was carried out by irradiating each leaf fragment in its middle portion with a collimated 5 mm X-ray spot size for 50 s, allowing the determination of P, K, Ca, S, Fe, Mn and Si. EDXRF was also useful to conclude that 15 leaf fragments (37.5% of the recommended sampling area) were enough for attaining a representative analytical response from the whole diagnostic leaf. Regarding LIBS, which employs a substantial smaller ablation area (i.e., 750 µm laser spot size), sampling strategies were defined by taking into account the microchemical distribution of P, Ca, Mg, Fe, Mn, B and Si in a 9 mm × 9 mm leaf fragment area. The proposed sampling protocol relied on the interrogation (rastering) of 3 equally spaced sampling lines in each leaf fragment with 48 accumulated laser pulses per line (Nd:YAG at 1064 nm, 5 ns, 10 Hz, 50 J cm−2) perpendicular to the leaf midrib. This strategy enabled the simultaneous determination of P, K, Ca, Mg, Fe, Cu, Mn, Zn, B and Si by LIBS. Cross-validation between LIBS and EDXRF for P, K, Ca, Fe, Mn and Si predicted mass fractions presented high linear correlation coefficients of up to 0.9778 (selecting 15 leaf fragments per diagnostic leaf from 10 different sugar cane varieties). The results provide insights into a novel and promising strategy for direct and fast plant nutrition diagnosis, fostering further studies for in situ analysis of fresh leaves, strengthening the implementation of Precision Agriculture and Green Chemistry concepts.

Mercury amalgam diffusion in human teeth probed using femtosecond LIBS

In this work the diffusion of mercury and other elements from amalgam tooth restorations through the surrounding dental tissue (dentin) was evaluated using femtosecond laser-induced breakdown spectroscopy (fs-LIBS). To achieve this, seven deciduous and eight permanent extracted human molar teeth with occlusal amalgam restorations were half-sectioned and analyzed using pulses from a femtosecond laser. The measurements were performed from the amalgam restoration along the amalgam/dentin interface to the apical direction. It was possible to observe the presence of metallic elements (silver, mercury, copper and tin) emission lines, as well as dental constituent ones, providing fingerprints of each material and comparable data for checking the consistence of the results. It was also shown that the elements penetration depth values in each tooth are usually similar and consistent, for both deciduous and permanent teeth, indicating that all the metals diffuse into the dentin by the same mechanism. We propose that this diffusion mechanism is mainly through liquid dragging inside the dentin tubules. The mercury diffused further in permanent teeth than in deciduous teeth, probably due to the longer diffusion times due to the age of the restorations. It was possible to conclude that the proposed femtosecond-LIBS system can detect the presence of metals in the dental tissue, among the tooth constituent elements, and map the distribution of endogenous and exogenous chemical elements, with a spatial resolution that can be brought under 100 µm.

Recent advances in LIBS and XRF for the analysis of plants

The ability to provide a fast and multielemental analytical response directly from a solid sample makes both laser-induced breakdown spectroscopy (LIBS) and X-ray fluorescence spectrometry (XRF) very versatile tools for plant nutrition diagnosis. This review focuses on the main developments and advances in LIBS and XRF in the analysis of plant materials over the last ten years. Fundamental aspects and instrumentation are given for both techniques. The developments in the quantitative analysis of plant leaves are discussed, with special emphasis on the key aspects and challenges concerning field sampling protocols, sample preparation, and calibration strategies. Microchemical imaging applications by LIBS and XRF (including synchrotron radiation) are also presented in a broader selection of plant compartments (e.g., leaves, roots, stems, and seeds). Challenges, expectations and complementarities of LIBS and XRF towards plant nutrition diagnosis are thoroughly discussed.