Sequential injections as an alternative to gradient exploitation for implementing differential kinetic analysis in a flow injection system

A novel flow-based strategy for implementing simultaneous determinations of different chemical species reacting with the same reagent(s) at different rates is proposed and applied to the spectrophotometric catalytic determination of iron and vanadium in Fe-V alloys. The method relies on the influence of Fe(II) and V(IV) on the rate of the iodide oxidation by Cr(VI) under acidic conditions, the Jones reducing agent is then needed Three different plugs of the sample are sequentially inserted into an acidic KI reagent carrier stream, and a confluent Cr(VI) solution is added downstream Overlap between the inserted plugs leads to a complex sample zone with several regions of maximal and minimal absorbance values. Measurements performed on these regions reveal the different degrees of reaction development and tend to be more precise Data are treated by multivariate calibration involving the PLS algorithm The proposed system is very simple and rugged Two latent variables carried out ca 95% of the analytical information and the results are in agreement with ICP-OES. (C) 2010 Elsevier B V. All rights reserved.

An investigation of phosphate adsorption from aqueous solution onto hydrous niobium oxide prepared by co-precipitation method

The synthetic hydrous niobium oxide has been used for phosphate removal from the aqueous solutions. The kinetic data correspond very well to the pseudo second-order equation The phosphate removal tended. to increase with a decrease of pH. The equilibrium data describe very well the Langmuir isotherm. The peak appearing at 1050 cm(-1) in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The adsorption capacities are high, and increased with increasing temperature. The evaluated Delta G degrees and Delta H degrees indicate the spontaneous and endothermic nature of the reactions. The adsorptions occur with increase in entropy (Delta S positive) value suggest increase in randomness at the solid-liquid interface during the adsorption. A phosphate desorbability of approximately 60% was observed with water at pH 12, which indicated a relatively strong bonding between the adsorbed phosphate and the sorptive sites on the surface of the adsorbent. (C) 2008 Elsevier B.V. All rights reserved.

Sand bioconsolidation through the precipitation of calcium carbonate by two ureolytic bacteria

Two ureolytic strains, B. sphaericus LMG 22257 and Bacillus sp (I-001), were tested for their ability to consolidate sand by submitting them to two days` treatment using 10(7) viable cell concentrations of inocula and medium precipitation with calcium ions. The results showed that B. sphaericus LMG 22257 induced greater calcium carbonate formation. Both strains produced calcite and were able to consolidate sand. Tensile strength of consolidated sand was not a function of the amount of precipitated CaCO(3) but a linear function of the ratio bioconsolidation index (BC) defined as the ratio of CaCO(3) volume to initial sand porosity. A simple model to estimate the engineering benefits of consolidation is proposed. (C) 2011 Elsevier B.V. All rights reserved.

Spent NiMH batteries-The role of selective precipitation in the recovery of valuable metals

The production of electronic equipment, such as computers and cell phones, and, consequently, batteries, has increased dramatically. One of the types of batteries whose production and consumption has increased in recent times is the nickel metal hydride (NiMH) battery. This study evaluated a hydrometallurgical method of recovery of rare earths and a simple method to obtain a solution rich in Ni-Co from spent NiMH batteries. The active materials from both electrodes were manually removed from the accumulators and leached. Several acid and basic solutions for the recovery of rare earths were evaluated. Results showed that more than 98 wt.% of the rare earths were recovered as sulfate salts by dissolution with sulfuric acid, followed by selective precipitation at pH 1.2 using sodium hydroxide. The complete process. precipitation at pH 1.2 followed by precipitation at pH 7, removed about 100 wt.% of iron and 70 wt.% of zinc from the leaching solution. Results were similar to those found in studies that used solvent extraction. This method is easy, economic, and does not pose environmental threats of solvent extraction. (C) 2009 Elsevier B.V. All rights reserved.

Precipitation of Laves phase in a 28%Cr-4%Ni-2%Mo-Nb superferritic stainless steel

The main objective of the present work was to study the precipitation of the Laves phase in the X1 CrNiMoNb 28 4 2 (Werkstoff-Nr. DIN 1.4575) superferritic stainless steel employing several complementary techniques of microstructural analysis. The phase that precipitated in largest quantity in the DIN 1.4575 steel was the sigma (sigma) phase. However, along grain boundaries, after aging at 850 degrees C, a Laves phase of the MgZn2 type, with a hexagonal C14 crystal structure and chemical composition (Fe,Cr,Ni)(2)(Nb,Mo,Si), was also identified. Growth of the Laves phase is curtailed by exhaustion of niobium of the matrix and by the presence of the sigma phase, which also precipitates in the vicinity of the grain boundaries, however in larger amounts. No chi (chi) or austenite phases were detected in the temperature range studied. (C) 2007 Elsevier Inc. All rights reserved.

Phase equilibria of lysozyme precipitation with the volatile salt ammonium carbamate

Lysozyme precipitation induced by the addition of the volatile salt ammonium carbamate was studied through cloud-point measurements and precipitation assays. Phase equilibrium experiments were carried out at 5.0, 15.0 and 25.0 degrees C and the compositions of the coexisting phases were determined. A complete separation of the coexisting liquid and solid phases could not be achieved. Nevertheless it was possible to determine the composition of the solid precipitate through the extensions of experimental tie lines. The same precipitate was found at all temperatures. Lysozyme enzymatic activities of the supernatant and precipitate phases were also determined. The activity balance suggests that ammonium carbamate preserves lysozyme activity after the salting-out precipitation. (C) 2010 Elsevier B.V. All rights reserved.

Precipitation of Porcine Insulin With Carbon Dioxide

Recent works have pointed to the use of volatile electrolytes such as carbon dioxide (CO(2)) dissolved in aqueous solutions as a promising alternative to the precipitating agents conventionally used for protein recovery in the food and pharmaceutical industries. In this work we investigated experimental and theoretical aspects of the precipitation of porcine insulin, a biomolecule of pharmaceutical interest, using CO(2) as an acid- precipitating agent. The Solubility of porcine insulin in NaHCO(3) solutions in pressurized CO(2) was determined as a function of temperature and pressure, with a minimum being observed close to the protein isoclectric point. A thermodynamic model was developed and successfully utilized to correlate the experimental data. Insulin was considered a polyelectrolyte in the model and its self-association reactions were also taken into account. The biological activity of insulin was maintained after precipitation With CO(2), although some activity can be lost if foam is formed in the depressurization step. Biotechnol. Bioeng. 2009;103: 909-919. (C) 2009 Wiley Periodicals, Inc.

Phase equilibria for salt-induced lysozyme precipitation: Effect of salt type and temperature

The salt-induced precipitation of lysozyme from aqueous solutions was studied through precipitation assays in which the equilibrium compositions of the coexisting phases were determined. Lysozyme precipitation experiments were carried out at 5, 15 and 25 degrees C and pH 7.0 with ammonium sulfate, sodium sulfate and sodium chloride as precipitating agents. In these experiments a complete separation of the coexisting phases (liquid and solid) could not be achieved. Nevertheless it was possible to determine the composition of the precipitate. The enzymatic activity of lysozyme in the supernatant phase as well as in the precipitate phase was also determined. The activity balance suggests that there is a relationship between the composition of the true precipitate and the total activity recovery. (C) 2009 Elsevier B.V. All rights reserved.

Phase equilibria for salt-induced lysozyme precipitation: Effect of salt concentration and pH

The salt-induced precipitation of lysozyme from aqueous solutions was studied at 25 degrees C and various pH values by cloud-point investigations, precipitation experiments (analysing the compositions of the coexisting phases) and microscopic investigations of the precipitates. Sodium sulphate as well as ammonium sulphate were used to induce the precipitation. The experimental results are discussed and used to develop a scheme of the phase equilibrium in water-rich aqueous solutions of lysozyme and either Na2SO4 or (NH4)(2)SO4. (C) 2007 Elsevier B.V All rights reserved.

Metal separation from mixed types of batteries using selective precipitation and liquid-liquid extraction techniques

The purpose of this paper is to study metal separation from a sample composed of a mixture of the main types of spent household batteries, using a hydrometallurgical route, comparing selective precipitation and liquid-liquid extraction separation techniques. The preparation of the solution consisted of: grinding the waste of mixed batteries, reduction and volatile metals elimination using electric furnace and acid leaching. From this solution two different routes were studied: selective precipitation with sodium hydroxide and liquid-liquid extraction using Cyanex 272 [bis(2,4,4-trimethylpentyl) phosphoric acid] as extracting agent. The best results were obtained from liquid-liquid extraction in which Zn had a 99% extraction rate at pH 2.5. More than 95% Fe was extracted at pH 7.0, the same pH at which more than 90% Ce was extracted. About 88% Mn, Cr and Co was extracted at this pH. At pH 3.0, more than 85% Ni was extracted, and at pH 3.5 more than 80% of Cd and La was extracted. (C) 2010 Elsevier Ltd. All rights reserved.

Ultra-Fast Gradient LC Method for Omeprazole Analysis Using a Monolithic Column: Assay Development, Validation, and Application to the Quality Control of Omeprazole Enteric-Coated Pellets

A method was optimized for the analysis of omeprazole (OMZ) by ultra-high speed LC with diode array detection using a monolithic Chromolith Fast Gradient RP 18 endcapped column (50 x 2.0 mm id). The analyses were performed at 30 degrees C using a mobile phase consisting of 0.15% (v/v) trifluoroacetic acid (TFA) in water (solvent A) and 0.15% (v/v) TFA in acetonitrile (solvent B) under a linear gradient of 5 to 90% B in 1 min at a flow rate of 1.0 mL/min and detection at 220 nm. Under these conditions, OMZ retention time was approximately 0.74 min. Validation parameters, such as selectivity, linearity, precision, accuracy, and robustness, showed results within the acceptable criteria. The method developed was successfully applied to OMZ enteric-coated pellets, showing that this assay can be used in the pharmaceutical industry for routine QC analysis. Moreover, the analytical conditions established allow for the simultaneous analysis of OMZ metabolites, 5-hydroxyomeprazole and omeprazole sulfone, in the same run, showing that this method can be extended to other matrixes with adequate procedures for sample preparation.

The Impacts of Inter-El Nino Variability on the Tropical Atlantic and Northeast Brazil Climate

In this study, observations and numerical simulations are used to investigate how different El Nino events affect the development of SST anomalies in the Atlantic and how this relates to the Brazilian northeast (NE) precipitation. The results show that different types of El Nino have different impacts on the SST anomalies of the equatorial and tropical South Atlantic but a similar SST response in the tropical North Atlantic. Strong and long (weak and short) El Ninos with the main heating source located in the eastern (central) Pacific generate cold (warm) anomalies in the cold tongue and Benguela upwelling regions during boreal winter and spring. When the SST anomalies in the eastern equatorial and tropical South Atlantic are cold (warm), the meridional SST gradient across the equator is positive (negative) and the ITCZ is not allowed (allowed) to move southward during the boreal spring; as a consequence, the precipitation is below (above) the average over the NE. Thus, strong and long (weak and short) El Ninos are followed by dry (wet) conditions in the NE. During strong and long El Ninos, changes in the Walker circulation over the Atlantic and in the Pacific-South Atlantic (PSA) wave train cause easterly wind anomalies in the western equatorial Atlantic, which in turn activate the Bjerknes mechanism, establishing the cold tongue in boreal spring and summer. These easterly anomalies are also responsible for the Benguela upwelling. During short and weak El Ninos, westerly wind anomalies are present in the western equatorial Atlantic accompanied by warm anomalies in the eastern equatorial and tropical South Atlantic; a positive phase of the South Atlantic dipole develops during boreal winter. The simulations highlight the importance of ocean dynamics in establishing the correct slope of the equatorial thermocline and SST anomalies, which in turn determine the correct rainfall response over the NE.

A case study of the direct radiative effect of biomass burning aerosols on precipitation in the Eastern Amazon

Numerical experiments with the Brazilian additions to the Regional Atmospheric Modeling System were performed with two nested grids (50 and 10 km horizontal resolution, respectively) with and without the effect of biomass burning for 8 different situations for 96 h integrations. Only the direct radiative effect of aerosols is considered. The results were analyzed in large areas encompassing the BR163 road (one of the main areas of deforestation in the Amazon). mainly where most of the burning takes place. The precipitation change due to the direct radiative impact of biomass burning is generally negative (i.e., there is a decrease of precipitation). However, there are a few cases with a positive impact. Two opposite forcing mechanisms were explored: (a) the thermodynamic forcing that is generally negative in the sense that the aerosol tends to stabilize the lower atmosphere and (b) the dynamic impact associated with the low level horizontal pressure gradients produced by the aerosol plumes. In order to understand the non-linear relationship between the two effects, experiments were performed with 4-fold emissions. In these cases, the dynamic effect overcomes the stabilization produced by the radiative forcing and precipitation increase is observed in comparison with the control experiment. This study suggests that. in general, the biomass burning radiative forcing decreases the precipitation. However, very large concentrations of aerosols may lead to an increase of precipitation due to the dynamical forcing associated with the horizontal pressure gradients. (C) 2009 Elsevier B.V. All rights reserved.

Impact of biomass burning aerosol on the monsoon circulation transition over Amazonia

Ensemble simulations of a regional climate model (RegCM3) forced by aerosol radiative forcing suggest that biomass burning aerosols can work against the seasonal monsoon circulation transition, thus re-enforce the dry season rainfall pattern for Southern Amazonia. Strongly absorbing smoke aerosols warm and stabilize the lower troposphere within the smoke center in southern Amazonia (where aerosol optical depth >0.3). These changes increase the surface pressure in the smoke center, weaken the southward surface pressure gradient between northern and southern Amazonia, and consequently induce an anomalous moisture divergence in the smoke center and an anomalous convergence in northwestern Amazonia (5 degrees S-5 degrees N, 60 degrees W-70 degrees W). The increased atmospheric thermodynamic stability, surface pressure, and divergent flow in Southern Amazonia may inhibit synoptic cyclonic activities propagated from extratropical South America, and re-enforce winter-like synoptic cyclonic activities and rainfall in southeastern Brazil, Paraguay and northeastern Argentina. Citation: Zhang, Y., R. Fu, H. Yu, Y. Qian, R. Dickinson, M. A. F. Silva Dias, P. L. da Silva Dias, and K. Fernandes (2009), Impact of biomass burning aerosol on the monsoon circulation transition over Amazonia, Geophys. Res. Lett., 36, L10814, doi: 10.1029/2009GL037180.

Precipitation diurnal cycle and summer climatology assessment over South America: An evaluation of Regional Climate Model version 3 simulations

Regional Climate Model version 3 (RegCM3) simulations of 17 summers (1988-2004) over part of South America south of 5 degrees S were evaluated to identify model systematic errors. Model results were compared to different rainfall data sets (Climate Research Unit (CRU), Climate Prediction Center (CPC), Global Precipitation Climatology Project (GPCP), and National Centers for Environmental Prediction (NCEP) reanalysis), including the five summers mean (1998-2002) precipitation diurnal cycle observed by the Tropical Rainfall Measuring Mission (TRMM)-Precipitation Radar (PR). In spite of regional differences, the RegCM3 simulates the main observed aspects of summer climatology associated with the precipitation (northwest-southeast band of South Atlantic Convergence Zone (SACZ)) and air temperature (warmer air in the central part of the continent and colder in eastern Brazil and the Andes Mountains). At a regional scale, the main RegCM3 failures are the underestimation of the precipitation in the northern branch of the SACZ and some unrealistic intense precipitation around the Andes Mountains. However, the RegCM3 seasonal precipitation is closer to the fine-scale analyses (CPC, CRU, and TRMM-PR) than is the NCEP reanalysis, which presents an incorrect north-south orientation of SACZ and an overestimation of its intensity. The precipitation diurnal cycle observed by TRMM-PR shows pronounced contrasts between Tropics and Extratropics and land and ocean, where most of these features are simulated by RegCM3. The major similarities between the simulation and observation, especially the diurnal cycle phase, are found over the continental tropical and subtropical SACZ regions, which present afternoon maximum (1500-1800 UTC) and morning minimum (0900-1200 UTC). More specifically, over the core of SACZ, the phase and amplitude of the simulated precipitation diurnal cycle are very close to the TRMM-PR observations. Although there are amplitude differences, the RegCM3 simulates the observed nighttime rainfall in the eastern Andes Mountains, over the Atlantic Ocean, and also over northern Argentina. The main simulation deficiencies are found in the Atlantic Ocean and near the Andes Mountains. Over the Atlantic Ocean the convective scheme is not triggered; thus the rainfall arises from the grid-scale scheme and therefore differs from the TRMM-PR. Near the Andes, intense (nighttime and daytime) simulated precipitation could be a response of an incorrect circulation and topographic uplift. Finally, it is important to note that unlike most reported bias of global models, RegCM3 does not trigger the moist convection just after sunrise over the southern part of the Amazon.