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At least 973 records · Page 54Linked to original sources

PubMed1992

Efficiency of cleaning agents for an inorganic membrane after milk ultrafiltration.

Cleaning of inorganic membranes after ultrafiltration (UF) of skim milk has been assessed using hydraulic, physicochemical and spectroscopic (i.r. and X-ray photoelectron spectroscopy) measurements. A cleaning sequence using hypochlorite alone or hypochlorite followed by HNO3 restored the membrane hydraulic resistance, in contrast to cleaning with HNO3 alone. When using NaOH, addition of Ca complexants (EDTA, gluconate, tripolyphosphate) and surfactants was required to obtain similar results. Three types of criteria (hydraulic, kinetic, chemical) are available to assess the effect of the sequestrant and surfactant types. In all the cases studied, traces of protein and Ca were detected on and within the membrane after cleaning. Nevertheless, it was concluded that it is possible to develop a single-step alkaline product to clean inorganic milk UF membranes if suitable surfactants and Ca sequestrants are included in its formula.

Animals↗

PubMed2005

Effect of chymosin and salt reduction on the quality of ultrafiltrated white-salted cheese.

This study demonstrated that both chymosin and salt-in-moisture (SM) were important factors for proteolysis in the manufacture of ultrafiltrated white-salted cheese, with significant effects on water-soluble nitrogen and nitrogen soluble in trichloroacetic acid. In contrast, the levels of free amino acids were not significantly affected by chymosin and salt treatments. The cheeses made, using high levels of chymosin with low SM had lower levels of residual alpha(S1)- and beta-casein at the end of ripening. On texture profile analysis, the hardness and fracturability of the cheeses significantly increased with SM and decreased during ripening. Increases in chymosin significantly contributed to the overall weakening of the structure throughout ripening. Bitter flavour was detected after 12 weeks in the cheese made with the higher chymosin level and lower SM, which could be the result of accumulation of gamma-casein fractions. The sensory data indicated that the hedonic responses for low chymosin with low SM cheeses were good and acceptable in flavour, which may be due to the moderate levels of proteolysis products.

Cheese↗

PubMed1998

Continuous ultraslow microdialysis and ultrafiltration for subcutaneous sampling as demonstrated by glucose and lactate measurements in rats.

Classical microdialysis has some drawbacks. Two main issues in this respect are the time-consuming calculations (due to partial recovery of an analyte) and depletion near the sampling site. In this paper we describe a sampling method, called ultraslow microdialysis (usMD), and compare this with ultrafiltration (UF) at flow rates between 100 and 300 nL/min. As an example of an application of this method, we conducted a dual-enzyme analysis for simultaneous measurement of the glucose and lactate concentrations, demonstrating these sampling techniques in the subcutaneous tissue of the rat. For UF, the flow rates in vitro and in vivo were the same. For usMD, the recovery for glucose and lactate at the applied flow rates was 100%, in contrast to conventional microdialysis. Both sampling techniques have the potential of on-line in vivo monitoring, as well as the measurement of time profiles of analytes by continuous collection and off-line analysis afterward.

Animals↗

PubMed1982

Binding isotherms of nucleosides and polynucleotides measured by continuous ultrafiltration at constant volume: a rapid and precise technique.

Equilibrium binding isotherms have been measured as a function of temperature for the interaction of 2- and 8-aminoadenosine with poly(U) by continuous, constant-volume ultrafiltration. An analytical method is described for determining the entire isotherm in a single experiment on a preequilibrated ligand--polymer solution. The method is shown to produce the same results as classical equilibrium dialysis but to be much more rapid and convenient. Values of the enthalpy, equilibrium constant, and free energy of stacking as a function of temperature are derived from the binding data. Stoichiometry of interaction is obtained from the diafiltration profiles as well as from the binding isotherms. Over the temperature range studied, the cooperativity of binding is observed to increase with rising temperature.

Adenosine↗

PubMed1980

Kinetics of binding of [3H]acetylcholine to Torpedo postsynaptic membranes: association and dissociation rate constants by rapid mixing and ultrafiltration.

An automated rapid-mixing ultrafiltration apparatus was constructed to measure at subsecond times the kinetics of binding of radiolabeled cholinergic ligands to nicotinic postsynaptic membranes isolated from Torpedo electric tissue. The dissociation of [3H]AcCh-receptor complexes at 7 and 23 degrees C was characterized by dissociation rate constants (kdissoc) of 0.05 s-1 and 0.15S-1, respectively. The association kinetics at low concentrations of [3H]AcCh were determined at 23 degrees C and found to be consistent with a model in which 20% of the AcCh binding sites preexist in a receptor conformation that binds AcCh with high affinity (KD = 3 nM) and with a bimolecular association constant, k+ = 5.7 x 10(7) M-1 SD-1. Initial studies of the association kinetics at higher AcCh concentrations revealed a transient low-affinity binding step that occurred relatively slowly. In the presence of 0.8 microM [3H]AcCh, this component of the association reaction was characterized by an experimental rate constant of 2 s-1. The observed binding kinetics are discussed with reference to the processes of channel activation and receptor desensitization.

Acetylcholine↗

PubMedDate not supplied

Separation of human serum albumin and human immunoglobulins using carrier phase ultrafiltration.

The fractionation of the plasma proteins human serum albumin (HSA) and human immunoglobulins (HIgG) using the combination of two newly developed techniques, pulsed sample injection technique and carrier phase ultrafiltration (CPUF), is discussed in this paper. The effects of pH and ionic strength on the transmission of a single protein (i.e., either HSA or HIgG) through 100 and 300 kDa MWCO polyethersulfone (PES) membranes were quantified using the pulsed sample injection technique. The experimental results thus obtained suggested that it would be possible to fractionate these proteins by optimizing the solution pH and ionic strength. With 100 and 300 kDa PES membranes, effective separation of HSA and HIgG was achieved by CPUF using suitable conditions, i.e., pH 4.7 and low salt concentration. The fractionation of HSA and HIgG by "reverse selectivity" using 300 kDa membranes was also examined.

Electrophoresis, Polyacrylamide Gel↗

PubMed2005

Influence of flocculation and adsorption as pretreatment on the fouling of ultrafiltration and nanofiltration membranes: application with biologically treated sewage effluent.

Membrane fouling is a critical limitation on the application of membranes to wastewater reuse. This work aims to understand the fouling phenomenon which occurs in ultrafiltration (UF; 17500 molecular weight cutoff (MWCO)) and nanofiltration (NF; 250 MWCO) membranes, with and without pretreatment. For this purpose, the molecular weight (MW) distribution of the organics has been used as a parameter to characterize the influent, the permeate, and the foulant on the membrane surface. The variation of foulant concentration on the membrane due to pretreatment of the influent by flocculation and/or adsorption was investigated in detail. With the UF membrane, the peak of the MW distribution of organics in the permeate depended on the pretreatment; for example, the weight-averaged MW (Mw) of 675 without pretreatment shifted down to 314 with pretreatment. In the case of the NF membrane, the Mw of organics in the permeate was 478 (without pretreatment) and 310 (with flocculation followed by adsorption). The Mw of the organics in the foulant on the membrane surface was 513 (UF) and 192 (NF) without pretreatment and 351 (UF) and 183 (NF) after pretreatment with flocculation followed by adsorption, respectively. Without the pretreatment, the foulant concentration was higher on both membranes. The difference was more significant on the UF membrane than on the NF membrane. For both membranes, the flocculation-and-then-adsorption pretreatment proved very effective.

Adsorption↗

PubMed2005

Partition of endocrine-disrupting chemicals between colloids and dissolved phase as determined by cross-flow ultrafiltration.

Cross-flow ultrafiltration (CFUF) was developed first for the isolation of natural colloids and subsequently for determining the partition of selected endocrine-disrupting chemicals (EDCs) between river colloids and dissolved phase. In this study, a 1-kDa Millipore Pellicon 2 cartridge type CFUF system was validated using a range of molecular probes spiked in natural waters. Results show that good retention (>80%) of high molecular weight (HMW, >1 kDa) molecules and low retention of low molecular weight (LMW, <1 kDa) molecules can be achieved at high concentration factor (cf) values in sampling mode or over long time scales in recirculation mode. The interactions between aquatic colloids and EDCs were studied by mixing EDCs, water, and colloids previously isolated by CFUF for a certain duration, followed by the separation of the target compounds between the truly dissolved and colloid-bound phases by CFUF and analysis by gas chromatography-mass spectrometry (GC-MS). The kinetics of EDCs binding to colloids were relatively rapid, reaching equilibrium within 5 min. The mass balance of chosen EDCs through CFUF system was fully investigated, with good recovery for the relatively polar EDCs such as estrone and 17beta-estradiol. On the basis of EDC sorption by colloids, the partition coefficient normalized to colloidal organic carbon content (Kcoc) was 8.85 x 10(3), 1.50 x 10(4), 8.85 x 10(3), 4.87 x 10(4), and 1.59 x 10(4) mL/g for bisphenol A, estrone, 17beta-estradiol, 17alpha-ethynylestradiol, and 16alpha-hydroxyestrone, respectively, which are comparable with the values reported in the literature. In addition, it has been shown that the Kcoc values of EDCs were relatively independent of their octanol-water partition coefficient (Kow) values, suggesting the important role of different binding mechanisms other than nonspecific hydrophobic interaction between EDCs and natural colloids. As the CFUF-GC-MS method can be used to quantify very low concentration of pollutants and is not limited to fluorescent compounds, it has the potential to be a widely applicable separation/analytical tool for determining the partition of organic pollutants between colloidal materials and dissolved phase.

Adsorption↗

PubMed2005

Fabrication of catalytic membranes for the treatment of drinking water using combined ozonation and ultrafiltration.

The removal of disinfection byproducts and their precursors was investigated using a combined ozonation-ultrafiltration system. A commercial membrane was coated 20 or 40 times with iron oxide nanoparticles (4-6 nm in diameter). With this membrane, the concentration of dissolved organic carbon was reduced by >85% and the concentrations of simulated distribution system total trihalomethanes and simulated distribution system halo acetic acids decreased by up to 90% and 85%, respectively. When the coated membrane was used, the concentrations of aldehydes, ketones, and ketoacids in the permeate were reduced by >50% as compared to that obtained with the uncoated membranes. Hydroxyl or other radicals produced at the iron oxide coated membrane surface as a result of ozone decomposition are believed to have enhanced the degradation of the natural organic matter, thereby reducing the concentration of disinfection byproducts. While increasing the number of times the membrane was coated from 20 to 40 did not significantly reduce the concentrations of most of the parameters measured, it did result in a significant decrease in the concentrations of ozonation byproducts. Increasing the sintering temperature from 500 to 900 degrees C also resulted in an improvement in the removal of the ozonation byproducts.

Ferric Compounds↗

PubMed2006

Micellar enhanced ultrafiltration for arsenic(V) removal: effect of main operating conditions and dynamic modelling.

In this work arsenic removal by micellar enhanced ultrafiltration (MEUF) was investigated using cetylpyridinium chloride (CPC) in ceramic membrane apparatus. Permeability tests and discontinuous diafiltration tests were performed in different operating conditions to evaluate the effect of membrane pore size (20 and 50 nm), transmembrane pressure, pH, surfactant concentration (1-3 mM), and arsenic concentration (10-40 mg/L) on permeate flux decline, arsenic, and CPC rejections. These preliminary experimental results showed that a ceramic membrane with large pore size allows treament of high fluxes of concentrated arsenic-bearing solutions even by using low surfactant concentrations. Arsenic concentration in the permeate was at the 1 ppm level, with feed As concentrations (10 ppm) that are larger than those generally used in MEUF studies and with CPC amounts that are lower than the usual ones. In addition, operating conditions adopted in these tests obtained CPC concentrations in the permeate always lower than its critical micellar concentration (0.9 mM). Dynamic simulations of discontinuous two-step diafiltration tests allowed a simple and adequate representation of the performance of the process especially for 1 mM CPC, while discrepancies for 2.5 mM CPC level denoted complex interactions between CPC and As.

Arsenic↗

PubMed2006

Secondary wastewater polishing with ultrafiltration membranes for unrestricted reuse: fouling and flushing modeling.

The effects of operating parameters such astransmembrane pressure, retentate, and recirculation volumetric flow rates on the productivity of an ultrafiltration membrane were studied using field data and development of a management model. Correlation equations for predicting the volumetric permeate flow rates were derived from general membrane blocking laws and experimental data. The experimental data were obtained from a pilot study carried out in the Arad wastewater treatment system (a pilot plant operating in feed and bleed operation mode) located several kilometers west of the City of Arad, Israel. Correlation predictions were confirmed with the independent experimental results. The results enabled us to develop a mathematical expression accurately describing the decline in flux due to fouling.

Israel↗

PubMed1999

Ultrafiltration performance of heat-treated shamouti orange [Citrus sinensis (L.) Osbeck] juice.

During ultrafiltration of orange juice with inorganic membranes, heating of the juice prior to the filtration experiment resulted in a significant increase of the fouling indices. The effect of the irreversible fouling (Rif) was always high, whereas the reversible fouling (Rrf) depended on the treatment. It was clearly seen that fouling was reduced after pectin degradation, but the heat treatment applied to the juice before filtration still resulted in reduced fluxes. It is suggested that pectins and proteins that undergo flocculation/coagulation during the heat treatment tend to interact with the membrane-filtering layer and to cause reduction of permeation flux. To clean the membrane to restore its pure water flux, close to the initial one, a proteolitic enzyme detergent wash was needed.

Beverages↗

PubMed1999

Syneresis rate of cow's, ewe's, and goat's curd. Effect of thermal treatment and ultrafiltration.

The influences of ultrafiltration (UF), the intensity of heat treatment (70 degrees C for 5 or 30 min) applied to milk prior to UF processing, and species on the syneresis rate of curd from cow's, ewe's, and goat's milk were analyzed. The influence of the species was significant (P < 0.05) in the syneresis rate. The syneresis rate depended significantly on the intensity of the heat treatment applied before UF and the degree of concentration; these two parameters showed significant (P < 0.05) differences in the syneresis rate depending on the species studied. These results could indicate a possible difference in the structure of the curd formed. The differences in the curd structure could be due to the different relative composition of the retentates of the different species as well as the possible effect of the UF process on the physicochemical composition of milk.

Animals↗

PubMed2006

Ultrafiltration membrane for electrophoretic capturing of pathogens for AFM imaging.

This communication describes a simple and rapid technique for electrophoretically assisted capture of phages, viruses, and other pathogens on the surface of an ultrafiltration membrane that can be considered smooth at the nanoscale. The surface was prepared by coating commercial dialysis membrane with a micrometer-thick layer of cross-linked dextran or globular proteins. To ensure strong adherence of the coating, the surface of the dialysis membrane was activated in cold plasma. It was shown that the root-mean-square roughness of the coating was well below 1 nm when the polymer solution used for coating was allowed to slowly dry through a dialysis membrane left in direct contact with mica. Relatively small viral particles (e.g., fd phages 0.7 microm long and only 3.5 nm high in the dry state) are readily visible by AFM following electrophoretic capture from suspensions containing as few as 1 x 10(6) particles/mL onto membranes prepared as described.

Adenoviridae↗

PubMed2000

Bovine serum albumin-hemoglobin fractionation: significance of ultrafiltration system and feed solution characteristics.

This work investigates the fractionation of similar molecular weight proteins bovine serum albumin (69 kD) and bovine hemoglobin (67 kD) by ultrafiltration. Three different membranes, viz. regenerated cellulose, poly(sulfone) and surface modified poly(acrylonitrile), each with a nominal molecular cutoff rating of 100 kD, were examined. The experiments were conducted in dead end, crossflow and vortex flow filtration modes and the separation was studied as a function of feed pH and ionic strength. Under similar system hydrodynamics, the surface modified poly(acrylonitrile) membrane displayed the highest resolution with minimum membrane fouling. The separation could be improved further by operating at low applied pressure (40 kPa) and high mass transfer (> 20 x 10(-6) m/s) in a vortex flow module. Under these conditions, the highest separation factor of 40 was obtained at the pI of hemoglobin.

Filtration↗

PubMed2000

Cytokine levels in a patient with severe ovarian hyperstimulation syndrome before and after the ultrafiltration and reinfusion of ascitic fluid.

PURPOSE: To report serum concentrations of several cytokines (interleukin-6, interleukin-8, tumor necrosis factor-alpha, and vascular endothelial growth factor) before and after the reinfusion of ultrafiltrated ascitic fluid. METHODS: A case report of a woman hospitalized for the treatment of severe OHSS at the Department of Obstetrics and Gynecology, Tottori University Hospital. The serum concentrations of cytokines were analyzed by ELISA. RESULTS: Cytokine concentrations declined in parallel with the improvement of clinical conditions and resolution of OHSS. CONCLUSION: Measurement of serum cytokine concentrations may be useful in evaluating the severity of OHSS.

Adult↗

PubMed1988

Determination of the pH-dependent phase distribution of prostaglandin E1 in a lipid emulsion by ultrafiltration.

The distribution of prostaglandin E1 (PGE1) in a lipid emulsion has been shown to be consistent with a three-phase model which assumes that solute may reside in the bulk aqueous and oil phases and at the oil/water interface. Calculations suggest that, in a lipid emulsion having an average particle size of 0.11 micron, it is theoretically possible for a surface active species such as PGE1 to exist predominantly at the interface. Aqueous phase concentrations of PGE1 versus pH were measured in an emulsion having an oil/water phase volume ratio of 0.1 by the use of an ultrafiltration technique in order to estimate the relative percentages of PGE1 in each phase. From bulk oil/water partition coefficient determinations, the amount of PGE1 present in the bulk oil phase of the emulsion was concluded to be insignificant. At emulsion pH values less than 5, PGE1 resides preferentially (greater than 97%) at the interface. With increasing pH's, the percentage of PGE1 in the aqueous phase increases, reaching 51% at high pH's. A model which assumes that both the nonionized and the ionized PGE1 species may be present at the interface, depending on the pH, was shown to be consistent with the data. Estimates were made of the distribution coefficients of the ionized and nonionized PGE1 between the interface and the aqueous phase and their concentration dependence. The apparent pKa of PGE1 at the interface derived from these data was 6.8. The distribution coefficients were used to generate a distribution profile of the various PGE1 species as a function of the pH. This distribution profile will be useful in explaining kinetic data of PGE1 in the emulsion as a function of pH.

Alprostadil↗

PubMed2003

Modulation of nonspecific binding in ultrafiltration protein binding studies.

PURPOSE: The aim of this study was to reduce or prevent nonspecific binding (NSB) of compounds to ultrafiltration (UF) protein binding (PB) testing units. METHODS: UF units (regenerated cellulose, MWCO 10K) were used for PB and NSB measurements with or without pretreatment with 5% tween 80 (TW 80) or 5% benzalkonium chloride (BAK) on the filter membrane. Dosing solutions (10 microM) in human serum and pH 7.4 phosphate-buffered saline were centrifuged at 3,000 g and room temperature after 1-h incubation in UF testing units. In parallel, a 96-well equilibrium dialyzer was used for PB and NSB measurements in equilibrium dialysis (ED) at 37 degrees C for 4 h. Samples of UF and ED were analyzed by LC/MS or LSC. RESULTS: Severe NSB was observed for etoposide, hydrocortisone, propranolol, and vinblastine in UF. In contrast, TW 80 or BAK pre-treatment on the filter membrane decreased the NSB from 87-95% to 13-64% without causing a significant change in membrane integrity. When NSB was below 50% as a result of pretreating agents, PB data of marker compounds were comparable to those of ED. CONCLUSIONS: The pretreated membrane with TW 80 or BAK showed significantly less NSB for compounds that had a tendency toward high membrane binding. A modified UF method with pretreatment improved the performance of UF and was able to produce comparable PB results to ED.

Blood Proteins↗