Cadmium analysis in soil by microwave acid digestion and graphite furnace atomic absorption spectrometry

The need to determine micronutrients and toxic elements in soils has grown in recent years and cadmium is of special interest. A method has been developed for the determination of cadmium in soils based on a prior acid digestion of the samples with nitric acid in closed Teflon vessels, into a microwave over. The cadmium determination was carried out by graphite furnace atomic absorption spectrometry (GFAAS) with Lvov platform. Optimum operating conditions, analyte modifiers and matrix interferences have been investigated. The best matrix modifier was found to be ammonium dihydrogen phosphate. The interferences are greatly reduced under these operating conditions and calibration can be performed with simple aqueous solutions of the metal standard. The method is rapid and provides accurate and precise results that agree with certified values for two reference materials: BCR 141 (calcareous loam soil) and BCR 277 (estuarine sediment).     

A coated piezoelectric crystal detector for the determination of hydrogen sulfide

A method is presented for the detection and determination of hydrogen sulfide. It is based on the selective and reversible adsorption of hydrogen sulfide on the surface of a piezoelectric crystal coated with a cadmium iodide/urea/-glycerol solution. The proposed detector has a response time of 30 s with linear response over the concentration range 2–25 μl l^?1 (ppm).     

Complete assignments of 1H and 13C NMR spectral data for benzylidenebenzyl butyrolactone lignans

The structures of three benzylidenebenzyl butyrolactone lignans (gossypifan, carthamogenin, and savinin) have been established on basis of 1H NMR and 13C NMR spectroscopic data. The 1H NMR and 13C NMR spectra of these lignans have been fully assigned by the use of techniques such as gCOSY, non-edited gHSQC, and gHMBC. Complete assignment and most homonuclear hydrogen coupling constant measurements were performed, also providing enough data for the determination of the relative stereochemistry.     

Classification of edible vegetables affected by different traffic intensities using potential curves

Heavy metals in soils have largely been used to evaluate the impact of motorised traffic in the vicinity of motorways. Also in this field of work it is of paramount importance to analyse the vegetables grown in these areas since their consumption is one of the main sources of metal intake by people; not in vain human food is directly or indirectly derived from plants. Accordingly, a set of edible vegetable samples were first analysed and, then, classified employing different multivariate chemometric techniques; among them, SIMCA and a simplified mode of potential curves. The analytical variables were selected after a comprehensive study of roadside soil pollution where Pb, Cd and Cu were found to be the main metallic pollution tracers. Different groups of vegetables were obtained which were explained as a function of both the agricultural conditions (private versus commercial) and the different traffic intensities supported by the cultivated areas.     

Preparation and characterization of polyethylene based graft copolymers. Applications in the immobilization of enzymes

In the last few years new copolymeric supports for the immobilization of biological compounds have been developed. The graft copolymer polyethylene-g.co-hydroxyethyl methacrylate, partially hydrolyzed, has shown to be a very promising support for this purpose.

The more recent work in the preparation and characterization of this copolymer, as well as the immobilization of a lipase, is reported in this paper. Branches of poly(hydroxyethyl methacrylate) were grafted onto low density polyethylene by using gamma radiation. The influence of the presence and absence of air, as well as the monomer concentration on the yield of grafting were evaluated.

The obtained copolymers were characterized by DSC and FTIR. The influence of the support properties on the synthesis biocatalytic activity was detected.     

Multivariate optimization and validation studies in on-line pre-concentration system for lead determination in drinking water and saline waste from oil refinery

The present paper proposes an on-line pre-concentration procedure for lead determination in drinking water and saline waste from oil refinery by flame atomic absorption spectrometry (FAAS). It is based on the sorption of lead (II) ions in a minicolumn of polyurethane foam loaded with 4-(2-pyridylazo)-resorcinol (PAR) reagent. The optimization step was performed using Doehlert matrix involving the variables: sampling flow rate (SR), buffer concentration (BC), pH and eluent concentration (EC). The validation process was performed considering the parameters: linearity and other characteristics of the calibration curve, analytical features of on-line system, precision, robustness, effect of other ions in the pre-concentration system and accuracy. Using the established experimental conditions, the procedure allows lead determination with detection limit (3δ/S) of 0.4 μg l⁻¹, quantification limit (10δ/S) of 1.4 μg l⁻¹, and a precision, calculated as relative standard deviation (RSD) of 5.7 (n=8) and 2.1% (n=8) for lead concentration of 5 and 50 μg l⁻¹, respectively. The pre-concentration factor (PF) considering the ratio among the slopes of the analytical curves with and without pre-concentration is 51. The achieved recovery for lead determination in presence of several cations demonstrated that this procedure could be applied for analysis of water samples. The accuracy was confirmed by analysis of the standard reference material NIST 1640 Trace elements in natural water. The sorption process was characterized by the Langmuir isotherm. The method was applied for lead determination in drinking water collected in Salvador City, Brazil and in saline effluent samples from oil refinery. The lead content for 16 samples of drinking water analyzed varied from 0.77 to 6.98 μg l⁻¹.     

A flow injection/hydride generation system for the determination of arsenic by inductively-coupled plasma atomic emission spectrometry

A flow-injection system is described for the semi-automatic determination of arsenic (10–1000 μg l^?1) by hydride generation and inductively-coupled plasma atomic emission spectrometry. The elements which were found to interfere were Co, Ni, Ag, Au, Bi, Te and Sn. Standard reference materials were analyzed with good accuracy. Approximately 200 injection h^?1 are possible. The detection limit is 1.4 ng arsenic.     

The location of tryptophan, N-acetyltryptophan and alpha-chymotrypsin in reverse micelles of AOT: a fluorescence study

The spectroscopic properties of alpha-chymotrypsin (alpha-Chym), L-tryptophan (Trp) and N-acetyl-L-tryptophan (NAT) solubilized in hydrated reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate in iso-octane were followed by fluorescence as a function of the amount of intramicellar water and initial pH. The lack of pH dependence observed for Trp in these systems, as opposed to what occurs in bulk water, and the similarities found for the protein in both media foresee different locations of these probes. In reverse micelles, fluorescence quenching studies using acrylamide emphasize the existence of structural alterations within the protein when its global charge changes from positive (pH = 7) to negative (pH = 10). The ensemble of the data points to an interfacial location of the zwitterionic Trp, an intermediate region of less tightly bound water for the location of the anionic Trp and NAT and an almost bulk water environment for alpha-Chym.     

Measurements and analysis of excess molar volumes for the ternary mixture MTBE + 1-pentanol + decane

Summary Densities at 298.15 K and atmospheric pressure have been measured, using a DMA 4500 Anton Paar densimeter, for the ternary mixture methyl tert-butyl ether (MTBE)+1-pentanol+decane and for the involved binary mixtures MTBE+1-pentanol and 1-pentanol+decane. The excess molar volumes for the binary mixture MTBE+decane was reported in an earlier work [1]. In addition, excess molar volumes were determined from the densities of the pure liquids and mixtures. Suitable fitting equations have been used in order to correlate adequately the excess molar volumes. The empirical expressions of Kohler [18], Jacob and Fitzner [19], Colinet [20], Knobeloch and Schwartz [21], Tsao and Smith [22], Toop [23], Scatchard et al. [24], Hillert [25], Mathieson and Thynne [26] were applied to estimate ternary properties from binary results.     

Effects of applied voltage on water at a gold electrode interface from ab initio molecular dynamics

Electrode–water interfaces under voltage bias demonstrate anomalous electrostatic and structural properties that are influential in their catalytic and technological applications. Mean-field and empirical models of the electrical double layer (EDL) that forms in response to an applied potential do not capture the heterogeneity that polarizable, liquid-phase water molecules engender. To illustrate the inhomogeneous nature of the electrochemical interface, Born–Oppenheimer ab initio molecular dynamics calculations of electrified Au(111) slabs interfaced with liquid water were performed using a combined explicit–implicit solvent approach. The excess charges localized on the model electrode were held constant and the electrode potentials were computed at frequent simulation times. The electrode potential in each trajectory fluctuated with changes in the atomic structure, and the trajectory-averaged potentials converged and yielded a physically reasonable differential capacitance for the system. The effects of the average applied voltages, both positive and negative, on the structural, hydrogen bonding, dynamical, and vibrational properties of water were characterized and compared to literature where applicable. Controlled-potential simulations of the interfacial solvent dynamics provide a framework for further investigation of more complex or reactive species in the EDL and broadly for understanding electrochemical interfaces in situ.

Ab initio molecular dynamics of an aqueous electrode interface reveal the electrostatic, structural, and dynamic effects of quantifiable voltage biases on water.