A SDME/GC–MS methodology for determination of organophosphate and pyrethroid pesticides in water

A rapid and simultaneous method for identification and quantification of pesticides residues in water samples have been developed and applied to the analysis of real samples. Tap and San Francisco River water samples were collected from Propria town and Aracaju city in the state of Sergipe, Brazil. A new single-drop microextraction (SDME) followed by gas chromatography–mass spectrometry techniques were used to determine the dimethoate, methyl parathion, ethion (organophosphates) and permethrin (pyrethroid) pesticides in water samples. The parameters linearity, linear range, precision, accuracy, sensitivity and robustness were studied for validation of the SDME/GC–MS method. An important point to this study is that plots of relative response and logarithmic concentrations were used to verify that the measurements were within the linear dynamic range of the method. In order to enhance high linearity of analytical curve, points that do not belong to 95 to 105% of linear range were excluded. Recovery tests of pesticides in different water samples (tap water and river water) were between 76.2 and 107% and this evaluation was used to demonstrate the reliability of the method. For all pesticides the method showed the limits of detection (LOD) in a range between 0.05 and 0.38 μg L^{− 1} and the limit of quantification (LOQ) between 0.15 and 1.1 μg L^{− 1}. All these parameters demonstrate high sensitivity of the developed method and the capability for detecting and quantifying of low levels of pesticides in water samples.     

A Rheumatoid arthritis study using Raman spectroscopy

Rheumatoid arthritis (RA) is characterized by chronic inflammation of the joints and can lead to a progressive destruction of articular cartilage and bone. In this study, the specificity and sensitivity of the RA diagnostic methods based on the receiver-operating characteristic curves for monitoring C-reactive protein (CRP) and rheumatoid factor (RF) were compared with the Raman spectroscopic diagnostic method developed in this work. Sera from 24 patients with rheumatoid arthritis and from 16 healthy individuals were analyzed to assess the biochemical composition and presence of inflammatory activity by the aforementioned methods. By comparing with the clinical results for specificity and sensitivity from the RF and CRP tests, we show that the overall results from the newly developed Raman method were significantly better, with a specificity of 96%, a sensitivity of 88%, and correctly identifying 92% of the RA and healthy individuals, while the RF test gave a specificity of 100% and a sensitivity of 54%, and the CRP test gave a specificity of 87% and a sensitivity of 58%, respectively.     

Characterization of the volatile profile of Antarctic bacteria by using solid-phase microextraction-gas chromatography-mass spectrometry

Bacteria belonging to the Burkholderia cepacia complex (Bcc) are significant pathogens in Cystic Fibrosis (CF) patients and are resistant to a plethora of antibiotics. In this context, microorganisms from Antarctica are interesting because they produce antimicrobial compounds inhibiting the growth of other bacteria. This is particularly true for bacteria isolated from Antarctic sponges. The aim of this work was to characterize a set of Antarctic bacteria for their ability to produce new natural drugs that could be exploited in the control of infections in CF patients by Bcc bacteria. Hence, 11 bacterial strains allocated to different genera (e.g., Pseudoalteromonas, Arthrobacter and Psychrobacter) were tested for their ability to inhibit the growth of 21 Bcc strains and some other human pathogens. All these bacteria completely inhibited the growth of most, if not all, Bcc strains, suggesting a highly specific activity toward Bcc strains. Experimental evidences showed that the antimicrobial compounds are small volatile organic compounds, and are constitutively produced via an unknown pathway. The microbial volatile profile was obtained by SPME-GC-MS within the m/z interval of 40-450. Solid phase micro extraction technique affords the possibility to extract the volatile compounds in head space with a minimal sample perturbation. Principal component analysis and successive cluster discriminant analysis was applied to evaluate the relationships among the volatile organic compounds with the aim of classifying the microorganisms by their volatile profile. These data highlight the potentiality of Antarctic bacteria as novel sources of antibacterial substances to face Bcc infections in CF patients.     

Structural evolution during evaporation of a 3-glycidoxypropyltrimethoxysilane film studied in situ by time resolved infrared spectroscopy

Time resolved infrared spectroscopy has been applied to study in situ the evaporation process of a 3-glycidoxypropyltrimethoxysilane hybrid sol by casting a droplet on a ZnSe substrate; the analysis has been performed in the middle-infrared range and in the near-infrared range. The experiment has allowed following the structural changes induced by water evaporation and the formation of ordered structures within the cast film; the CH(2) scissoring bands have been used as a fingerprint for the disorder to order transition of the hybrid. The experiment has been done using both a fresh sol and an aged sol which produce respectively an amorphous material and a crystalline hybrid material. The analysis has shown that the epoxy groups do not react during the evaporation while the silica structure shows only a slight condensation and an increase in open cage-like species. At the end of evaporation the hybrid has a "soft-like" state which allows structural rearrangements to self-order.     

Thermal study of mononuclear Pd(II) complexes of the type [Pd(X)<Subscript>2</Subscript>(Rtu)(PPh<Subscript>3</Subscript>)] (X = Cl,SCN; Rtu = <Emphasis Type="Italic">N</Emphasis>-methylthiourea, <Emphasis Type="Italic">N</Emphasis>-phenylthiourea)

The synthesis, spectroscopic characterization, and thermal analysis of the compounds [Pd(X)₂(mtu)(PPh₃)] (X = Cl⁻ (1), SCN⁻ (2); mtu = N-methylthiourea; PPh₃ = triphenylphosphine) and [Pd(X)₂(phtu)(PPh₃)] (X = Cl⁻ (3), SCN⁻ (4); phtu = N-phenylthiourea) are described. The thermal decomposition of the compounds occurs in two, three, or four stages and the final decomposition products were identified as Pd⁰ by X-ray powder diffraction. The thermal stability order of the complexes is 4 > 3>2 > 1.     

Electrochemical methods for speciation of trace elements in marine waters. Dynamic aspects

The contribution of electrochemical methods to the knowledge of dynamic speciation of toxic trace elements in marine waters is critically reviewed. Due to the importance of dynamic considerations in the interpretation of the electrochemical signal, the principles and recent developments of kinetic features in the interconversion of metal complex species will be presented. As dynamic electrochemical methods, only stripping techniques (anodic stripping voltammetry and stripping chronopotentiometry) will be used because they are the most important for the determination of trace elements. Competitive ligand exchange-adsorptive cathodic stripping voltammetry, which should be considered an equilibrium technique rather than a dynamic method, will be also discussed because the complexing parameters may be affected by some kinetic limitations if equilibrium before analysis is not attained and/or the flux of the adsorbed complex is influenced by the lability of the natural complexes in the water sample. For a correct data interpretation and system characterization the comparison of results obtained from different techniques seems essential in the articulation of a serious discussion of their meaning.     

The Use of PAMAM Dendrimers as a Platform for Laccase Immobilization: Kinetic Characterization of the Enzyme

The kinetic behavior of the enzyme laccase in solution and immobilized onto carbon platforms using poly(amido amine) (PAMAM) dendrimers has been investigated. The results with the immobilized enzymes have demonstrated that almost ten times more enzyme on the carbon support is required for satisfactory kinetic rates to be achieved. Furthermore, the study as a function of the substrate concentration revealed that the kinetic behavior of the enzyme in solution fits the Michaelis?CMenten model. However, when the enzyme is immobilized onto the carbon surface, the catalyzed reaction follows a particular kinetic behavior with apparent positive cooperativity. The highest activity with laccase (in solution or immobilized) is achieved around pH?4.5, and the substrate conversion rate clearly diminishes with rising pH. The optimum temperature lies around 60?°C. The enzyme displays good catalytic activity in a wide range of pH and temperature values. The stability tests evidenced that there is no appreciable reduction in the enzymatic activity after immobilization within the first 30?days. Taking into account both the kinetic and stability tests, one can infer that the use of PAMAM dendrimers seems to be a very attractive approach for the immobilization of enzymes, as well as a feasible and useful methodology for the anchoring of enzymes with potential application in many biotechnological areas.     

Influence of plant densities and fertilization on maize grains by near-infrared spectroscopy

Near-infrared spectroscopy is a rapid process analytical technology for measuring a wide range of constituents of biological materials. The objective of the current study was to investigate maize grains grown under different levels of fertilization and plant densities using near-infrared spectroscopy. Maize grains from the same plant density had their protein content increased with doses of nitrogen. In addition, it was observed the decrease in protein content with the increase in plant densities. Except for ash content, models for the assessed parameters indicated that near-infrared spectra has the potential for fast assessment of maize grains.     

A projected gradient dynamical system modelling the dynamics of bargaining

We propose a projected gradient dynamical system as a model for a bargaining scheme for an asset for which the two interested agents have personal valuations that do not initially coincide. The personal valuations are formed using subjective beliefs concerning the future states of the world, and the reservation prices are calculated using expected utility theory. The agents are not rigid concerning their subjective probabilities and are willing to update them under the pressure to reach finally an agreement concerning the asset. The proposed projected dynamical system, on the space of probability measures, provides a model for the evolution of the agents, beliefs during the bargaining period and is constructed so that an agreement is reached under the minimum possible deviation of both agents from their initial beliefs. The convergence results are shown using techniques from convex dynamics and Lyapunov function theory.