Determination of organic and inorganic mercury species in water and sediment samples by HPLC on-line coupled with ICP-MS

This paper describes a preconcentration method for Hg²⁺ and MeHg⁺ in water samples using sodium diethyldithiocarbamate immobilized in polyurethane foam (PU-NaDDC) and an extraction method for several mercury species in sediment samples, including MeHg⁺, EtHg⁺ and PhHg⁺, which is simple, rapid, and uses a single organic solvent. Separation and measurement were done by high-performance liquid chromatography on-line with inductively coupled plasma mass spectrometry (HPLC/ICP-MS). Initially, the test of recovery was applied using procedures compatible with HPLC. Under the optimum extraction conditions, recoveries of 96.7, 96.3 and 97.3% were obtained for MeHg⁺, EtHg⁺, and PhHg⁺, respectively, from n = 4 spiked sediment samples. This study also demonstrates that the combination of solid-phase extraction on PU-NaDDC with HPLC separation and ICP-MS detection is an effective preconcentration procedure for simultaneous measurement of Hg²⁺ and MeHg⁺ at ultra-trace levels in water samples. The application of the proposed procedure to the determination of mercury species in drinking water sample was investigated. The proposed method clearly gave satisfactory average recoveries between 93.7 and 101.5%.     

Ester-additives as inhibitors of the gelification of soybean oil methyl esters in biodiesel

Biodiesel from soybean oil transesterified with methanol (TSO) becomes viscous and gelifies at low storage temperatures which makes it difficult to pump. To inhibit this behaviour bulky esters were added to reduce the crystallization temperature of TSO and to modify the rate of conversion of crystallized mass. This rate was found to follow a JMAK kinetic model. The Avrami’s parameter n was constant for TSO, while two n values were found for TSO-additive solutions, meaning that the additives first slowed down the rate of nucleation and, later on as enough nuclei had been formed, crystal growth rate dominated and the previous crystallization rate was recovered.     

Compatibility study between chlorpropamide and excipients in their physical mixtures

Chlorpropamide ((4-chloro-N-(propylamino)-carbonyl)-benzenesulfonamide) belongs to compounds having sulfonylurea group and is widely used as an oral antidiabetic agent. In this work differential scanning calorimetry (DSC) was used during pre-formulation of chlorpropamide tablets to determine the drug-excipients compatibility. The DSC curves of chlorpropamide and binary mixtures with excipients (sodium croscarmellose, sodium lauryl sulfate, microcrystalline cellulose, magnesium stearate and calcium carbonate) showed that chlorpropamide exhibited interaction with magnesium stearate and sodium lauryl sulfate. The binary mixtures of chlorpropamide–magnesium stearate presented a single endothermic process at 96–108 °C and chlorpropamide–sodium lauryl sulfate showed a wide endotherm at 99–120 °C.     

Statistical mixture design investigation of fractionated and total extracts from Erythrina speciosa Andrews leaves

The simplex centroid mixture design for the ethanol, dichloromethane, hexane and acetone solvents has been applied to the extraction of crude mass and the fiber, organic, neutral and basic fractions as well as the fractionation residues of Erythrina speciosa Andrews leaves. Binary and ternary synergic solvent interactions are seen to provide dominant contributions to the extraction of both crude mass and all the fractions. Quadratic and special cubic mixture models precisely predict the extracted quantities of each fraction and the residue as a function of the proportions of the four solvents. Different solvent mixtures are found to be the most efficient extractors for the different fractions: binary dichloromethane‐hexane mixtures for the fiber fraction, ternary ethanol‐dichloromethane‐acetone mixtures for the neutral fraction, binary ethanol‐dichloromethane mixtures for the organic fraction, crude extract and residue values and ternary ethanol‐dichloromethane‐hexane mixtures for the basic fraction. Principal component analysis shows that the ethanol‐dichloromethane mixtures are important for extracting large quantities of the basic and organic fractions as well as of the residue and crude masses.     

Efficiency and sustainability assessment for a group of farmers in the Brazilian Amazon

The aim of this paper is to use DEA models to evaluate sustainability in agriculture. Several variables are taken into account and the resulting efficiency is measured by comparison. The performance of family farms is analysed here (variables: farmed area, work force, and production). As agricultural sustainability depends on the maintenance of systems of production for long periods of time, the models were run for the years of 1986 and 2002. Tiered DEA models were used to group farmers in sustainability categories. Non-parametric regression models were used to identify the factors affecting the efficiency measurements. All the results indicate that the majority of the farmers increased their efficiency along the time. These improvements may support the existence of sustainability.     

The curve selection lemma and the Morse–Sard theorem

We use an inequality due to Bochnak and Lojasiewicz, which follows from the Curve Selection Lemma of real algebraic geometry in order to prove that, given a C ^r function , we have

Identification of alkyl carbazoles and alkyl benzocarbazoles in Brazilian petroleum derivatives

The present work describes (a) the identification and characterization of an impurity, 2,4,5,7-tetrabromo-6-hydroxy-9-(2,3,4,5-tetrachlorophenyl)-3H-xanthen-3-one (BCPX), in the color additives D&C Red Nos. 27 and 28 (phloxine B) and (b) the determination of the extent and level of BCPX contamination in certified lots of these colors. For these purposes, BCPX (a compound not previously reported in the literature) was synthetically prepared. Test portions from 42 certified lots of D&C Red Nos. 27, 28 and 27 lakes were analyzed for BCPX using an HPLC method that included gradient elution and UV-vis photodiode array detection. Those lots were submitted for certification by both domestic (six) and foreign (six) manufacturers during the past 4 years. Of the test portions analyzed, 32 (76.2%) contained BCPX in amounts ranging from 0.01 to 3.21%. The remaining 10 test portions (23.8%) contained no detectable BCPX or less than 0.008%, which is the limit of quantification for the present method. The analyses revealed substantial differences in the level of BCPX across different manufacturers. The wide range of BCPX levels found in the analyzed lots suggests that the presence of BCPX in D&C Red Nos. 27 and 28 may be avoided or significantly reduced during the manufacturing process.     

Effect of combined polymers on the loss of efficiency caused by mechanical degradation in drag reducing flows through straight tubes

The mechanical molecular degradation in drag reducing flows is a huge problem in the effort to improve the efficiency of drag reducers, which is clearly increased when a combination of materials is used. Here, we analyze mixtures of three kinds of water-soluble polymers: Poly (ethylene oxide) (PEO), Polyacrylamide (PAM), and Xanthan Gum (XG). Two kinds of mixtures are tested: (a) PAM and XG; (b) PEO and XG. The synergy between the polymers is clearly noticeable. The values of the drag reduction (DR) obtained by the polymer–polymer combination was larger than that observed for a single polymer in a solution with the same total concentration of the mixture. Our tests are conducted in straight tubes where the total pressure is fixed. The values of DR are computed step-by-step, as the total amount of solution pass through the system. In doing so, we carefully took into account the loss of efficiency caused by the turbulent flow in the straight tubes. It is quite clear that the degradation of the flexible polymers (PEO and PAM) is delayed in the mixtures. In other words, besides the increase in the DR, the flexible polymers are more resistant when in the presence of the rigid one (XG). Such observation is the main conclusion of this work.     

Optically stimulated luminescence and thermoluminescence efficiencies for high-energy heavy charged particle irradiation in Al2O3:C

The thermally and optically stimulated luminescence (TL and OSL) response to high energy heavy-charged particles (HCPs) was investigated for two types of Al2O3:C luminescence dosimeters. The OSL signal was measured in both continuous-wave (CW) and pulsed mode. The efficiencies of the HCPs at producing TL or OSL, relative to gamma radiation, were obtained using four different HCPs beams (150 MeV/u 4He, 400 MeV/u 12C, 490 MeV/u 28Si, and 500 MeV/u 56Fe). The efficiencies were determined as a function of the HCP linear energy transfer (LET). It was observed that the efficiency depends on the type of detector, measurement technique, and the choice of signal. Additionally, it is shown that the shape of the CW-OSL decay curve from Al2O3:C depends on the type of radiation, and, in principle, this can be used to extract information concerning the LET of an unknown radiation field. The response of the dosimeters to low-LET radiation was also investigated for doses in the range from about 1-1000 Gy. These data were used to explain the different efficiency values obtained for the different materials and techniques, as well as the LET dependence of the CW-OSL decay curve shape.     

Determination of arsenic and antimony in seawater by voltammetric and chronopotentiometric stripping using a vibrated gold microwire electrode

The oxidation potentials of As⁰/As^III and Sb⁰/Sb^III on the gold electrode are very close to each other due to their similar chemistry. Arsenic concentration in seawater is low (10–20 nM), Sb occurring at ∼0.1 time that of As. Methods are shown here for the electroanalytical speciation of inorganic arsenic and inorganic antimony in seawater using a solid gold microwire electrode. Anodic stripping voltammetry (ASV) and chronopotentiometry (ASC) are used at pH ≤ 2 and pH 8, using a vibrating gold microwire electrode. Under vibrations, the diffusion layer size at a 5 μm diameter wire is 0.7 μm. The detection limits for the As^III and Sb^III are below 0.1 nM using 2 min and 10 min deposition times respectively. As^III and Sb^III can be determined in acidic conditions (after addition of hydrazine) or at neutral pH. In the latter case, oxidation of As⁰ to As^III was found to proceed through a transient As^III species. Adsorption of this species on the gold electrode at potentials where Sb^III diffused away is used for selective deposition of As^III. Addition of EDTA removes the interfering effect of manganese when analysing As^III. Imposition of a desorption step for Sb^III analysis is required. Total inorganic arsenic (iAs = As^V + As^III) can be determined without interference from Sb nor mono-methyl arsenious acid (MMA) at 1.6 < pH < 2 using E_dep = −1 V. Total inorganic antimony (iSb = Sb^V + Sb^III) is determined at pH 1 using E_dep = −1.8 V without interference by As.