Phosphorus quantification in soil using LIBS assisted by laser-induced fluorescence.

Quantification and monitoring of phosphorus in soil plays a critical role in environmentally friendly agriculture, especially in mitigation of phosphorus leakages to water systems and subsequent risk for eutrophication. On the other hand, deficiency in phosphorus would lead to problems in development and growth of cultivated crops. Therefore, monitoring and quantification of phosphorus status in soil is essential. In this work, laser-induced breakdown spectroscopy assisted by laser-induced fluorescence (LIBS-LIF) is introduced for quantification of readily soluble phosphorus in soil and compared to the analytical performance of the conventional LIBS method. Mineral soils with variable phosphorus status were used for the analysis. The calibration curves are plotted to evaluate the detection limit of the soluble phosphorus. Compared results demonstrate improvement in detection limit from 3.74 mg/kg to 0.12 mg/kg for clay soil and from 10.94 mg/kg to 0.27 mg/kg for silt loam/loam soil in LIBS and LIBS-LIF measurements, respectively. For the LIBS-LIF measurement, detection limits are comparable with established chemical soil analyses. The proposed method would substantially reduce required sample preparation and laboratory work compared with conventional phosphorus quantification. In addition, as the calibration curves demonstrate that the calibration for soluble phosphorus holds within a soil type, LIBS-LIF has the potential to be used for high throughput soil analysis.

Tailored Langmuir-Schaefer Deposition of Few-Layer MoS2 Nanosheet Films for Electronic Applications.

Few-layer MoS2 films stay at the forefront of current research of two-dimensional materials. At present, continuous MoS2 films are prepared by chemical vapor deposition (CVD) techniques. Herein, we present a cost-effective fabrication of the large-area spatially uniform films of few-layer MoS2 flakes using a modified Langmuir-Schaefer technique. The compression of the liquid-phase exfoliated MoS2 flakes on the water subphase was used to form a continuous layer, which was subsequently transferred onto a submerged substrate by removing the subphase. After vacuum annealing, the electrical sheet resistance dropped to a level of 10 kΩ/sq, being highly competitive with that of CVD-deposited MoS2 nanosheet films. In addition, a consistent fabrication protocol of the large-area conductive MoS2 films was established. The morphology and electrical properties predetermine these films to advanced detecting, sensing, and catalytic applications. A large number of experimental techniques were used to characterize the exfoliated few-layer MoS2 flakes and to elucidate the formation of the few-layer MoS2 Langmuir film.

An elevated concentration of MoS2 lowers the efficacy of liquid-phase exfoliation and triggers the production of MoOx nanoparticles.

It is generally accepted that liquid-phase exfoliation (LPE) enables large-scale production of few-layer MoS2 flakes. In our work, we studied in detail few-layer MoS2 oxidation in the course of standard LPE in a water/ethanol solution. We demonstrate that an increase of the initial MoS2 concentration above a certain threshold triggers a pronounced oxidation and the exfoliation process starts to produce MoOx nanoparticles. A subsequent decrease of the water pH along with an increased content of SO42- suggests an oxidation scenario of few-layer MoS2 oxidation towards MoOx nanoparticles. Moreover, the lowered pH leads to agglomeration and sedimentation of the few-layer MoS2 flakes, which significantly lowers their production yield. We employed a large number of physico-chemical techniques to study the MoS2-to-MoOx transformation and found a threshold value of 10 mg ml-1 of the initial MoS2 concentration to trigger this transformation.

Determination of Metal Elements in Wine Using Laser-Induced Breakdown Spectroscopy (LIBS).

We developed a method for sensitive elemental analysis of wines using laser-induced breakdown spectroscopy (LIBS). In order to overcome the inefficiency of direct ablation of bulk wine (an organic liquid), a thin layer of wine residue was prepared on a metallic target according to an appropriated heating procedure applied to an amount of liquid wine dropped on the target surface. The obtained ensemble was thus ablated. Such a sample preparation procedure used a very small volume of 2 mL of wine and took only 30 min without reagent or solvent. The results show the detection of tens of metal and non-metal elements including majors (Na, Mg, K, Ca), minors, and traces (Li, B, Si, P, Ti, Mn, Fe, Cu, Zn, Rb, Sr, Ba, and Pb) in wines purchased from local supermarkets and from different production places in France. Commercially available wines were then spiked with certified standard solutions of Ti and Fe. Three series of laboratory reference samples were thus prepared using three different wines (a red wine and a white wine from a same production region and a red wine from another production region) with concentrations of Ti and Fe in the range of 1-40 mg/L. Calibration graphs established with the spiked samples allowed extracting the figures-of-merit parameters of the method for wine analysis such as the coefficient of determination ( R2) and the limits of detection and quantification (LOD and LOQ). The calibration curves built with the three wines were then compared. We studied the residual matrix effect between these wines in the determination of the concentrations of Ti and Fe.

Laser-induced optical breakdown spectroscopy of polymer materials based on evaluation of molecular emission bands.

Laser-induced breakdown spectroscopy (LIBS) for composition analysis of polymer materials results in optical spectra containing atomic and ionic emission lines as well as molecular emission bands. In the present work, the molecular bands are analyzed to obtain spectroscopic information about the plasma state in an effort to quantify the content of different elements in the polymers. Polyethylene (PE) and a rubber material from tire production are investigated employing 157nmF2 laser and 532nm Nd:YAG laser ablation in nitrogen and argon gas background or in air. The optical detection reaches from ultraviolet (UV) over the visible (VIS) to the near infrared (NIR) spectral range. In the UV/VIS range, intense molecular emissions, C2 Swan and CN violet bands, are measured with an Echelle spectrometer equipped with an intensified CCD camera. The measured molecular emission spectra can be fitted by vibrational-rotational transitions by open access programs and data sets with good agreement between measured and fitted spectra. The fits allow determining vibrational-rotational temperatures. A comparison to electronic temperatures Te derived earlier from atomic carbon vacuum-UV (VUV) emission lines show differences, which can be related to different locations of the atomic and molecular species in the expanding plasma plume. In the NIR spectral region, we also observe the CN red bands with a conventional CDD Czerny Turner spectrometer. The emission of the three strong atomic sulfur lines between 920 and 925nm is overlapped by these bands. Fitting of the CN red bands allows a separation of both spectral contributions. This makes a quantitative evaluation of sulfur contents in the start material in the order of 1wt% feasible.

Stable isotope composition of human fingernails from Slovakia.

Stable isotope composition of human fingernails has proven to be useful for documenting human dietary information and geographical patterns in archeological, forensic, anthropological and biological studies. Therefore, it is of interest to detect all factors influencing the stable isotopic composition in the certain regions in the world. Carbon and nitrogen isotope data of human fingernail keratin from 52 individuals from Slovakia were reported in this study. The online combustion and continuous flow isotope-ratio mass spectrometer Delta V Advantage was used for δ(13)C and δ(15)N analysis of fingernail keratin samples from 24 vegetarian and 28 omnivorous individuals. A group of people with frequent meat consumption showed enrichment in (13)C and (15)N isotopes in fingernails. A similar trend was observed with increasing seafood in an individual's diet. Moreover a significant difference was revealed between smokers and nonsmokers for both δ(13)C and δ(15)N values. These data were compared to previously published δ(13)C and δ(15)N fingernail values from across the globe. This study brings new information on the stable isotope signature of individuals from Slovakia and characterizes the Central European region for the first time. The stable isotope composition of fingernails is influenced by the frequency of meat and seafood consumption as well as smoking.