Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PRECIPITATION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38Linked to original sources
PubMed1996

Polyelectrolyte complexes as vehicles for affinity precipitation of proteins.

Polyelectrolyte complexes (PECs) were formed with polyethylene imine (PEI) and polyacrylic acid sodium salt (PA). The aqueous solubility of such PLCs is dependent on the stoichiometry between the polymers, the charge densities of the polymers and salts present in the solution. Cibacron blue 3GA (CB) was coupled to the PEI and the PECs were used for affinity precipitation of lactate dehydrogenase (LDH) in beef heart extracts. The affinity precipitation was induced by a shift in pH, while the desorption and separation of LDH from the PECs was performed by addition of KCl combined with a shift in pH. LDH was obtained with a yield of 85% and a purification factor of approx. 11-fold. The polymers were recovered and reused once and the results became similar. Prior to the affinity precipitation, interfering nucleic acids were removed by precipitation with PEI.

Acrylic Resins↗
PubMed2003

Field intercomparison of precipitation measurements performed within the framework of the Pan European Intensive Monitoring Program of EU/ICP Forest.

A 6-month field intercomparison study on precipitation measurements was performed at Schagerbrug near the west coast in the Netherlands. Twenty bulk sampling systems and two wet-only samplers were evaluated on accuracy, sampling strategy and performance under field conditions. Bulk precipitation fluxes of NO3-, NH4+, H+ and Kjeldahl-N generally could be determined with a greater accuracy than bulk precipitation fluxes of SO4(2-), Na+, Cl-, Mg2+, Ca2+, Alkalinity and H+. Bulk precipitation fluxes of K+ generally had the lowest accuracy. Only 20% of the sampling systems differed less than 10% from the best estimate, whereas most systems (60%) differed more than 20% from the best estimate. The inaccuracy induced by the sampling system appeared to be much larger than that resulting from the analysis of the samples by different laboratories as determined by ring-tests.

Air Pollutants↗
PubMed2001

Irreversible precipitation of mercury and lead.

There are immediate concerns with current commercial reagents that are used for heavy metal precipitation; in particular the fact that the reagents are not specifically designed to bind the targeted metals. The current literature reveals that not only do commercial reagents lack sufficient ability to strongly bind the metals, but they also fail to provide long-term stability as ligand-metal complexes under a variety of moderate conditions. For this reason a new ligand was designed and synthesized: 1,3-benzenediamidoethanethiol (BDETH2). It offers multiple, concerted, bonding sites for heavy metals and forms a stable metal-ligand precipitate. In this study, the formation of compounds comprised of this ligand with the divalent metals, lead and mercury, was explored and the pH stability of the water insoluble precipitates was determined. The leaching properties of the metal-ligand precipitates were determined using inductively coupled plasma (ICP) spectroscopy and cold vapor atomic fluorescence spectroscopy (CVAF). The results indicate that a 50.00 ppm lead solution at a pH of 4.0 may be reduced to a concentration of 0.05 ppm (99.9% lead removal) and to 0.13 ppm (99.7% lead removal) at a pH 6.0. A 50.00 ppm mercury solution at pH 4.0 may be reduced to a concentration of 0.02 ppm (99.97% mercury removal) and to 0.02 ppm (99.97% mercury removal) at a pH of 6.0.

Chemical Precipitation↗
PubMed2001

Determination of Cremophor EL in plasma after sample preparation with solid phase extraction and plasma protein precipitation.

The non-ionic emulsifier Cremophor EL can be quantified using a special potentiometric titration technique with barium chloride activation and precipitation with sodium tetraphenylborate. The end point of the titration is indicated by an ionsensitive coated wire electrode which responds to an excess of tetraphenylborate ions. Sample preparation is necessary to quantify the excipient in plasma of patients receiving ciclosporin formulations with Cremophor EL (Sandimmun), since plasma proteins cause disturbances of the titration. Solid phase extraction was tested with various sorbent materials. Although some of the sorbents yielded good extraction rates of Cremophor EL from aqueous solutions, the extraction rates from plasma were significantly lower. Therefore, plasma protein precipitation with acetonitrile has been examined as an alternative to SPE and has been proved the superior method. Using the precipitation technique, a recovery rate of above 90% was achieved. Furthermore, the limit of detection from plasma was found to be 30 microg, in analogy to the determination from aqueous solutions. The combination of the plasma protein precipitation with the potentiometric titration allows quantitation and thus pharmakokinetic investigations of Cremophor EL in patients treated with Sandimmun after kidney-transplantation.

Animals↗
PubMed2000

Supercritical fluid processing of proteins. I: lysozyme precipitation from organic solution.

The solution enhanced dispersion by supercritical fluid (SEDS) process was used to evaluate the effect of the processing variables on the biological and physicochemical characteristics of lysozyme protein particles produced from an organic solution of dimethylsulfoxide (DMSO) using an experimental design procedure. The processing variables were temperature, pressure, solution concentration and the flow-rates of supercritical carbon dioxide and a protein solution. Solutions of hen egg lysozyme (0.5-1%, w/v) in DMSO were dispersed using supercritical carbon dioxide as the antisolvent, and particles precipitated in a particle formation vessel. The morphology, particle size and size distribution and biological activity of the protein were determined. The precipitates were also examined with high sensitivity differential scanning calorimetry (HSDSC) and high-performance cation-exchange chromatography. The amount of residual DMSO was determined using headspace gas chromatography. Particle size measurements showed the precipitates to be agglomerates with primary particles of size 1-5 microm, containing <20 ppm of residual solvent. The activity of the precipitates varied between 44 and 100% depending on the experimental conditions. The similarity of HSDSC data for unprocessed and processed samples indicated that the SEDS process does not cause major denaturation of lysozyme when prepared from DMSO solutions. By optimising of working conditions, the SEDS process can produce micron-sized particles of lysozyme with minimal loss of biological activity.

Carbon Dioxide↗
PubMed2003

Struvite precipitation in anaerobic swine lagoon liquid: effect of pH and Mg:P ratio and determination of rate constant.

Because of increased concern about surface water eutrophication from nutrient-enriched agricultural runoff, many swine producers are encouraged to decrease application rates of waste-based P. Precipitation and subsequent removal of magnesium ammonium phosphate (MgNH(4)PO(4) x 6H(2)O), commonly known as struvite, is a promising mechanism for N and P removal from anaerobic swine lagoon effluent. The objectives of this research were to (i) quantify the effects of adjusting pH and Mg:P ratio on struvite precipitation and (ii) determine the rate constant pH effect for struvite precipitation in anaerobic swine lagoon liquid. Concentrations of PO(4)-P in liquid from two anaerobic swine lagoons were determined after 24 h of equilibration for a pH range of 7.5-9.5 and Mg:P ratios between 1:1 and 1.6:1. Struvite formation reduced the PO(4)-P concentration in the effluents to as low as 2 mgl(-1). Minimum concentrations of PO(4)-P occurred between pH 8.9 and 9.25 at all Mg:P ratios. Struvite precipitation decreased PO(4)-P concentrations by 85% within 20 min at pH 9.0 for an initial Mg:P ratio of 1.2:1. The rate of PO(4)-P decrease was described by a first-order kinetic model, with rate constants of 3.7, 7.9, and 12.3 h(-1) at pH 8.4, 8.7 and 9.0 respectively. Our results indicate that induced struvite formation is a technically feasible method to remove N and P from swine lagoon liquid and it may allow swine producers to recover nutrients for off-farm sale.

Anaerobiosis↗
PubMed2003

Purification of single-strand DNA binding protein from an Escherichia coli lysate using counter-current chromatography, partition and precipitation.

Single-strand DNA binding protein (SSB) from Escherichia coli lysate was purified by counter-current chromatography (CCC) using the ammonium sulfate precipitation method in a coiled column. About 5 ml of E. coli lysate was separated by CCC using a polymer phase system composed of 16% (w/w) polyethylene glycol (PEG) 1000 and 17% (w/w) ammonium sulfate aqueous polymer two-phase solvent system. The precipitation of proteins in the lysate took place in the CCC column, and the SSB protein was eluted in the fraction 51-56. Many other impurities were either eluted immediately after the solvent front or precipitated in the column. The identities of the proteins in the fractions and in the precipitate were confirmed by SDS-polyacrylamide gel electrophoresis with Coomassie Brilliant Blue staining.

Chemical Precipitation↗
PubMed1975

The precipitation of proteins by carboxymethyl cellulose.

Carboxymethyl cellulose (CMC) formed insoluble complexes with beta-lactoglobulin, bovine serum albumin and Na caseinate. Maximum precipitation of the beta-lactoglobulin-CMC complex occurred at pH 3-2, whereas maximum precipitation of the bovine serum albumin. The percentage of protein precipitated by CMC decreased with increasing ionic strength of the solution, the rate of decrease being least for bovine serum albumin. At a given ionic strength, more protein was precipitated by CMC of high degree of substitution than by CMC of low degree of substitution. The change in pH (delta pH) occurring on mixing CMC and unbuffered protein solutions, each initially at the same pH, was measured. delta pH was negative for beta-lactoglobulin-CMC mixtures over the pH range 7--2 (minimum at pH 5-5). For bovine serum albumin--Cmc and Na caseinate--CMC mixtures, delta pH was positive between pH 7 and 3-2 (maximum at pH 4-5), zero at pH 3-2 and negative between pH 3-2 and 2-0 (minimum at pH 2-8).

Animals↗
PubMedDate not supplied

Characterization and polyelectrolyte precipitation of beta-galactosidase containing genetic fusions of charged polypeptides.

Genetically engineered versions of beta-galactosidase were constructed through the addition of charged polypeptide fusion tails for the purpose of enhancing polyelectrolyte precipitation. Negatively charged aspartic acid tails and positively charged poly(arginine) tails were added to beta-galactosidase from Escherichia coli. These fusion proteins were all shown to possess specific activity equal to that of the native enzyme. Gel permeation and ion-exchange chromatography provided evidence concerning the integrity of the tails as well as their altered charge characteristics. All enzymes containing charged tails displayed enhanced polyelectrolyte precipitation over the native enzyme. An optimal number of charged residues, beyond which no further enhancement of precipitation was observed, was found to be approximately 10 residues for each type of tail. No interference from nucleic acids was observed in the precipitation of positively tailed beta-galactosidase.

Acrylic Resins↗
PubMedDate not supplied

Unfolding and conformational distributions during protein precipitation.

The association of misfolded proteins, or aggregation, is a critical problem in a number of human diseases as well during the expression, refolding, formulation, and delivery of therapeutic proteins. In this study, we investigate lysozyme precipitation with hydrogen exhange using nuclear magnetic resonance (NMR) and mass spectrometry (MS). We show that MS can reveal the presence of conformational distributions, albeit without the detailed structural information afforded by NMR. Further, we find that increases in precipitant concentration alter the structure and composition of precipitates. The selective unfolding of one portion of the protein in these precipitates is correlated with hydrogen exchange patterns observed under nonprecipitating conditions and in other studies of lysozyme.

Chemical Precipitation↗
PubMedDate not supplied

Optimization of poly(ethylene glycol) precipitation of hepatitis A virus used to prepare VAQTA, a highly purified inactivated vaccine.

Poly(ethylene glycol) precipitation has been successfully used to concentrate and purify hepatitis A virus from crude lysate preparations for production of VAQTA, a highly purified, formalin-inactivated hepatitis A vaccine. Initial results showed that nucleic acids present in the starting material were problematic for the performance of the poly(ethylene glycol) precipitation step. Extensive experiments were carried out to identify processing conditions suitable for vaccine manufacture which would enhance product yield and improve purity. Results of these studies indicated that the earlier practice of concentrating crude virus-containing lysate using semipermeable membranes led to aggregation of high molecular weight nucleic acids. This aggregated material coprecipitated with the virus during the subsequent poly(ethylene glycol) precipitation step; variable amounts of nucleic acids led to inconsistent virus recovery and product purity. Nuclease treatment of the crude lysate preparations decreased the molecular size of the nucleic acids and significantly reduced their coprecipitation with the virus. Further experiments demonstrated that optimal placement of the nuclease treatment was at the lysate stage followed by a capture step using anion exchange chromatography. These steps combined with optimization of the virus concentration, ionic strength, and pH of the poly(ethylene glycol) precipitation led to effective and selective concentration of the virus which significantly enhanced process reproducibility and control.

Chemical Precipitation↗
PubMed2005

Formation and dissolution of single and mixed Zn and Ni precipitates in soil: evidence from column experiments and extended X-ray absorption fine structure spectroscopy.

The stability and the formation and dissolution kinetics of mixed trace metal precipitates in soils are currently unknown. The objective of this study was to investigate slow sorption and release processes of Zn and Ni in a loamy soil using a combination of soil column experiments and extended X-ray absorption fine structure (EXAFS) spectroscopy. To investigate slow sorption processes, the soil material was packed into columns and leached with 5400 pore volumes of 10(-2) M CaCl2 solutions containing either ZnCl2 (5.2 x 10(-5) M) or NiCl2 (5.2 x 10(-5) M) or both ZnCl2 and NiCl2 (5.2 x 10(-5) M each). The Zn and Ni concentrations in the column effluents were monitored. The metal breakthrough curves showed that slow sorption processes lead to metal retention, whereby Zn was more strongly retained than Ni. In the experiment with both Zn and Ni present, amounts of Zn and Ni similar to those in the experiments with either Zn or Ni alone were retained. Analysis of soil samples by EXAFS spectroscopy showed that layered double hydroxide (LDH)-type precipitates had formed in all columns and that a mixed ZnNi-LDH had formed in the presence of both Zn and Ni. The dissolution of those precipitates under acidic conditions was assessed by subsequent leaching of the columns with a 10(-2) M CaCl2 solution at pH 3.0 (approximately 3000 pore volumes). When only Zn was present, 95% of the retained Zn was leached at pH 3. In contrast, only 23% of the retained Ni was leached in experiments with Ni alone. When Zn and Ni were present, 90% of the retained Zn and 87% of the retained Ni were released upon acidification. EXAFS analysis revealed that the LDH phases in the Zn experiment and the Zn-Ni experiment had been completely dissolved, while the LDH phase formed in the Ni experiment was still present. The higher resistance of Ni-LDH against dissolution at low pH could also be shown in dissolution studies with synthetic Zn-LDH, Ni-LDH, and ZnNi-LDH. Our results suggest that the individual rates at which Zn and Ni cations enter into the LDH structure determine the composition of the mixed ZnNi-LDH precipitate, and that the LDH composition determines the rate at which the LDH phase dissolves under acidic conditions.

Chemical Precipitation↗
PubMed2005

Fluoride removal by calcite: evidence for fluorite precipitation and surface adsorption.

Fluoride contamination of groundwater, both anthropogenic and natural, is a major problem worldwide. In this study, fluoride removal by crushed limestone (99% pure calcite) was investigated by batch studies and surface-sensitive techniques from solutions with fluoride concentrations from 150 micromol/L (3 mg/L) to 110 mM (approximately 2100 mg/L). Surface-sensitive techniques, including atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) as well as zeta potential measurements, confirm that, in addition to precipitation reactions, adsorption of fluoride also occurs. Results indicate that fluoride adsorption occurs immediately over the entire calcite surface with fluorite precipitating at step edges and kinks, where dissolved Ca2+ concentration is highest. The PHREEQ geochemical model was applied to the observed data and indicates that existing models, especially at low fluoride concentrations and high pH (>7.5) are not equipped to describe this complex system, largely because the PHREEQ model includes only precipitation reactions, whereas a combination of adsorption and precipitation parameters are required.

Adsorption↗
PubMed2003

Determination of trace cadmium in rice by flow injection on-line filterless precipitation-dissolution preconcentration coupled with flame atomic absorption spectrometry.

A simple, environmentally friendly, cost-effective, and sensitive method was developed for the determination of trace cadmium in rice by flow injection (FI) on-line precipitation preconcentration coupled with flame atomic absorption spectrometry (FAAS). The precipitation preconcentration of trace cadmium was achieved by on-line merging of the sample and ammonia solutions. The resultant precipitates were on-line collected by a knotted reactor (KR) without filtration. A solution of 1 mol L(-1) HNO(3) was employed to dissolve the collected precipitates and to deliver the analyte into the FAAS system for on-line detection. Preconcentration at a sample loading flow rate of 3.8 mL min(-1) for 35 s gave an enhancement factor of 44 and a detection limit (3sigma) of 0.002 microg g(-1) for the solid sample with a sample throughput of 72 h(-1). The precision (RSD, n = 11) was 2.0% at the 4.0 microg L(-1) level. The concentration of cadmium in a certified reference material (GBW 08511, rice flour) by the developed method using simple aqueous standards for calibration was in good agreement with the certified value. The proposed method was also successfully applied to the determination of trace cadmium in locally collected rice samples.

Cadmium↗
PubMed2006

Precipitation of nanostructured copper oxalate: substructure and growth mechanism.

The possibility of controlling materials properties by tailoring their substructure at the nanometer scale is a current topic of great interest. To do so, a fundamental understanding of the growth mechanism is of key importance and an analytical challenge as nanostructured materials are often produced by precipitation methods at high supersaturations where formation kinetics are fast. The current study focuses on the precipitation of copper oxalate, which has been previously shown to produce self-assembled ordered nanostructured particles with the promise of being able to tailor this nanometer substructure. In the current study we investigate in detail the growth mechanism and kinetics of precipitation by using in-situ particle size measurement or by stopping the reaction at various stages and using ex-situ methods. Combining the ex-situ methods of high-resolution scanning electron microscopy, transmission electron microscopy, and X-ray powder diffraction along with the in-situ methods, we were able to follow the growth process from 2 min to 2 weeks. The results in the 2-30 min period lead to the proposal of a core-shell growth model with a poorly ordered core and a well-structured shell of nanosized crystallites (50-70 nm), adding support to the brick-by-brick model previously proposed for this phase of particle growth. Particle evolution over long periods up to 2 weeks show a ripening which produces lens-shaped particles that eliminate the "high" surface energy faces observed in the earlier stages of growth. A more complete growth mechanism for copper oxalate precipitation at moderate supersaturations is proposed similar to recent findings for other self-assembled nanostructured particles.

Chemical Precipitation↗
PubMed2005

Use of seeds to control precipitation of calcium carbonate and determination of seed nature.

Understanding and controlling precipitation reactions is a major challenge for industrial crystallization. Calcium carbonate is a widely studied system: more than 3000 papers have been devoted to the subject over the past 10 years. The first step of the precipitation of calcium carbonate, from relatively concentrated solutions (0.01 mol/L), involves the formation of an initial gel phase which later transforms into calcite, vaterite, or a mixture of both phases. Our work aimed at controlling this first step. Nanosized seeds (8 nm), formed in situ, were used in order to control the often chaotic nucleation step which normally leads to poor phase selection and broad particle size distributions. Seeding has often been used to avoid spontaneous nucleation in metastable solutions for growth mechanism investigations of single-crystal calcium carbonate. Here the ability of a seeding method to control the precipitation reaction evolution even in the case of high supersaturation is demonstrated. The seeds and the presence of a polymeric additive (poly(acrylic acid)) allow the control of the precipitated polymorph and the specific surface area, while maintaining a narrow particle size distribution in the submicron range. Direct characterization methods did not succeed in identifying these nanoseeds; indirect methods using solubility calculations are used to demonstrate their existence and quantify size and number density of the nanosized seeds.

Calcium Carbonate↗
PubMed2004

Temperature driven morphological changes of chemically precipitated hydroxyapatite nanoparticles.

Hydroxyapatite (HA) is synthesized by a wet chemical route using calcium hydroxide and ortho-phosphoric acid at various temperatures (40, 80, and 100 degrees C). X-ray diffraction of the precipitate particles revealed HA as the predominant phase (>99%) with a small amount of beta-tricalcium phosphate. Fourier transform infrared spectroscopy indicated the presence of carbonate substitution, which decreased with increasing temperature. Transmission electron microscopy observations revealed needle-shaped particles with a high aspect ratio at 40 degrees C, which changed to spheroidal when the precipitation temperature was increased to 100 degrees C. The changes in the morphology with temperature were analyzed taking into account the driving force for the HA precipitation and the supersaturation level of Ca2+ and PO4(3-) ions with respect to HA. The analysis indicated that the supersaturation level of the reactants, especially the concentration of Ca2+ ions, played a predominant role on the precipitate morphology for this classical acid-base reaction.

Chemical Precipitation↗
PubMed2005

Influence of sodium dodecyl sulfate and static magnetic field on the properties of freshly precipitated calcium carbonate.

Properties of calcium carbonate precipitated from aqueous solutions of CaCl(2) and Na(2)CO(3) in the presence of sodium dodecyl sulfate (SDS) and S-S 0.1 T magnetic field (MF) were studied. The nucleation and precipitation processes of CaCO(3) were investigated by pH and zeta potential measurements at 20 +/- 1 degrees C up to 2 h after mixing the solutions. Also the amounts of calcium carbonate deposited on the glass surfaces and its structure were examined. It was found that SDS influences the kinetics of precipitation, crystallographic forms, and crystal size of CaCO(3). The SDS effects are more pronounced in MF presence. A small amount of SDS accelerates transformation of vaterite into calcite, whereas increasing surfactant concentration moderates such a transformation. On the other hand, in all the systems, MF in the presence of SDS causes a slower transformation of vaterite into calcite. These effects are reflected in pH and zeta potential changes, although there is no clear dependence between the SDS amount present during the precipitation and changes of the parameters investigated. It seems that MF effect is most significant at a defined optimal SDS concentration. The results, however, do not allow suggestion of any detailed mechanism of the field interaction.

Adhesiveness↗