Dialysis Cell Research Articles

A modified semiequilibrium dialysis method for studying solubilization in surfactant micelles: testing the semiequilibrium assumption

The detailed analysis of data obtained with the semiequilibrium dialysis (SED) method for studying solubilization in surfactant micelles requires accounting for the formation of micelles in the permeate compartment and for the presence of solubilized organic solute in these micelles. An extension of the SED method is proposed in which the concentration of surfactant is maintained well above the critical micelle concentration (cmc) in both compartments of the dialysis cell. Under these conditions, it is shown that the validity of the «semiequilibrium» assumption, viz., that the organic solute reaches equilibrium simultaneously with both surfactant solutions be demonstrated for solutions of small organic molecules and typical ionic surfactants

Design of urea-permeable anion-exchange membrane by radiation-induced graft polymerization

Strong base anion-exchange membranes were prepared by radiation-induced graft polymerization. Quaternary ammonium salts were introduced onto nonporous polyethylene films by grafting of vinyl monomers such as glycidyl methacrylate (GMA), diethylaminoethyl methacrylate (DEAEMA), and vinyl benzyl trimethyl ammonium chloride (VBTAC), followed by subsequent chemical modifications. Hydroxyethyl methacrylate (HEMA) was cografted to (a) enhance the diffusion of the VBTAC into the polymeric matrix, and (b) initiate the grafting of the VBTAC. The VBTAC/HEMA-cografted membrane was selected because of its practical physical strength. Urea permeability across the resulting anion-exchange membrane was evaluated with a diffusion dialysis cell. Anion-exchange membranes with degrees of VBTAC/HEMA grafting higher than 70% exhibited urea and phosphate ion permeation. When the VBTAC/HEMA-cografted membrane was compared with a conventional anion-exchange membrane based on a styrene-divinylbenzene matrix, higher hydrophilicity and permeability were observed.

Dissolution Profiles of Ceftizoxime Suppository

AbstractThe in vitro dissolution rates of ceftizoxime suppository were compared using a rotating dialysis cell method, a dialysis membrane method and the JP XI rotating basket method. Only small variations in the dissolution rates were found with the rotating dialysis cell method and the rotating basket method, while the dialysis membrane method indicated rather large variation than other methods. In the rotating basket method, it was observed that a part of suppository bases came out through the wire mesh of the basket and spread over the surface of the dissolution medium. In the case of dialysis membrane method, it seemed that the large variations in dissolution rate was depending on a skill of the apparatus used.As to obtain a good results, a selection of the rotating dialysis cell method was important. In vitro dissolutions of Ceftizoxime(CZX) suppository by using the rotating dialysis cell method were very rapid and also consistent with the absorption characteristics reported previously by Motohiro a...

Assessment of soluble and ionic calcium released from milk and dairy products during simulated gastro-intestinal digestion

Abstract The amounts of soluble and ionic calcium released from dairy products have been measured during simulated gastro-intestinal digestion. Different dairy products, including skim milk, evaporated milk, yogurt and cheese, containing various concentrations and forms of calcium, were submitted to pepsin and pancreatin digestion using a dialysis cell unit. Digestion products were continuously collected for quantitative determination of soluble and ionized calcium released. The results obtained showed the importance of pepsin digestion on the potential availability of dietary calcium from dairy products. Moreover, data have indicated that lower amounts of soluble and ionized calcium were released from cheese than from yogurt and evaporated milk during simulated gastro-intestinal digestion.

Scavenging effects of Fe-hydroxide-coated sand in phreatic aquifers

Sand grains coated with Fe-hydroxide were compared to uncoated sand grains as an absorbant filtration media for the treatment of metal-bearing waters. Coated and uncoated sand grains were placed into dialysis cells of a multilayer sampler and then placed into a research well. After two months of exposure, the samples were retrieved and analyzed for Cr, Pb, Ni, Cd, Mn and Co concentrations. Transmitted light and scanning electron light microscopy showed that the coating prevailed in the field and was not removed. Only Cr showed significant enrichment on the coated material compared to the uncoated material, indicating that the exposure of the Fe-coated surface to groundwater was sufficient for preferential scavenging of Cr from the water. The eight-fold enrichment of Cr may be related to its oxidation state of +3, thereby readily permitting substitution into the Fe 3+ position in the coating material. The rest of the studied metals were only slightly enriched in the coated grain.

Transport of 67Ga and 111In across a membrane. Role of plasma binding and concentration gradients.

If i.v. injected radiogallium does not firmly bind to circulating transferrin in plasma, the transvascular transport of the radionuclide may be affected by diffusion of unbound radionuclide and interstitial transferrin, and may therefore not be specific for transferrin transport. Using equilibrium dialysis, the avidity of 67Ga and 111In to bind to plasma transferrin was compared by evaluating transport of unbound radionuclide across a semipermeable membrane, as a function of the plasma (transferrin) concentration gradient. One chamber of a dialysis cell was filled with human plasma and 67Ga or 111In, and the other, separated by the membrane, with increasing concentrations of plasma in normal saline. The half-time (mean +/- S.D.) for reaching equilibrium between the chambers decreased (P less than 0.05) for 67Ga from 13.1 +/- 3.3 to 4.9 +/- 1.6, 3.7 +/- 1.2 and 3.0 +/- 0.5 h, at plasma concentrations of 0, 25, 50 and 100%, respectively. The equilibrium half-time for 111In did not fall at increasing plasma concentrations and was higher (P less than 0.005) than for 67Ga at 25 to 100% plasma. Hence, 67Ga is not as avidly bound to plasma transferrin as 111In, since, in contrast to 111In, dissociation of the 67Ga-transferrin complex and transmembrane diffusion of unbound 67Ga increases when the plasma transferrin concentration gradient decreases. In vivo, the transvascular transport of 67Ga may be influenced by diffusion of unbound radionuclide, depending on the interstitial transferrin concentration, and may not be a specific indicator of transvascular protein transport.

Simultaneous and rapid enzymatic determination of propylene oxide and propane-1,2-diol with flow-injection analysis

A flow-injection procedure for the rapid determination of propane-1,2-diol and propylene oxide in aqueous solutions was developed. Propane-1,2-diol can be assayed with immobilized glycerol dehydrogenase and fluorimetric detection of the NADH generated. From 0.05 to 2.5 mM propane-1,2-diol can be determined with a sampling frequency of 40–50 h −1 and a precision of better than 98%. The determination range can be extended up to 50 mmol l −1 by means of a miniaturized dialysis cell. Higher molecular weight polypropylene oxides remain in the donor sample stream. Before its enzymatic determination, propylene oxide must be hydrolysed to propane-1,2-diol. Propylene oxide is selectively separated from propane-1,2-diol by a membrane gas diffusion step into a strong acid acceptor solution. After conditioning to pH 8.5 the quantatively generated propane-1,2-diol can be assayed enzymatically. An automatically controlled flow-injection set-up gave the possibility of the simultaneous determination of propylene oxide and propane-1,2-diol.

Taurine Levels in Plasma and Blood Cells in Patients Undergoing Routine Maintenance Hemodialysis

We compared taurine levels in plasma, erythrocytes, platelets, lymphocytes, and granulocytes from 11 normal adults and 11 maintenance hemodialysis (MHD) patients immediately before and following a routine hemodialysis treatment. Taurine concentrations were elevated in plasma predialysis, as compared with normal subjects (90 +/- 16 [SEM] v 54 +/- 2 mumol/L [1.1 +/- 0.2 v 0.7 +/- 0.03, mg/dL]), but decreased with a dialysis treatment (to 34 +/- 3 mumol/L [0.4 +/- 0.04 mg/dL]). Erythrocyte taurine levels tended to be higher in MHD patients predialysis (1.2 +/- 0.2 v 0.7 +/- 0.1 nmol/10(9) cells, P less than 0.05 where P less than 0.025 is significant) as compared with controls; erythrocyte taurine was increased after dialysis (to 1.8 +/- 0.3 nmol/10(9) cells, P less than 0.006). In contrast, platelet taurine concentrations in MHD patients were lower than normal predialysis (18 +/- 2 v 27 +/- 2 nmol/10(9) cells) and declined further during the dialysis procedure (to 14 +/- 1). Granulocyte and lymphocyte taurine levels were not different in MHD patients, as compared with normal adults, either before or after dialysis. The observed differences in blood cell taurine content (expressed per 10(9) cells) could not be explained by variation in cell volumes among the groups examined. Thus, both chronic renal failure and a routine hemodialysis treatment produce changes in cell and plasma taurine levels that tend to be specific for the individual cell type.

Determination of free concentration of piroxicam and naproxen in plasma. The influence of experimental conditions in equilibrium dialysis

An equilibrium dialysis method was established in order to investigate possible relationships between free drug concentrations of piroxicam and naproxen and clinical events. Therefore the influence of variations in pH, phosphate concentration and sodium azide concentration of the dialysis buffer on the free concentrations of piroxicam and naproxen was investigated. Piroxicam was found to have a pH-dependent protein binding. Therefore a good control of pH during the dialysis process is necessary. This has been achieved by increasing the buffer capacity of the dialysis buffer, by adding an antibacterial agent to the dialysis buffer and by cleansing the dialysis cells with 70% ethanol before use to prevent bacterial growth. Addition of 0.03% sodium azide as an antibacterial agent and the use of a 0.09 mol/l phosphate buffer gave good pH control. A method to correct for deviations of pH in measurements of free concentrations of piroxicam by a simple mathematical correction has been found. As naproxen was found to have a protein binding independent of pH, a pH-correction is not necessary for this drug. Standardized conditions in determination of protein binding of drugs by equilibrium dialysis are important, as composition of the dialysis buffer and pH of plasma compartment at equilibrium may influence the free concentration measurements. Comparisons of data from experiments using different methods are therefore difficult; the importance of pH-control is stressed. With the methods used in the present investigation, equilibrium dialysis in connection with HPLC, the coefficients of variation for piroxicam and naproxen free concentrations are 5.5% and 7.4%, respectively.

Drug Binding to Apparatus: A Factor Controlling Time to Equilibrium in Equilibrium Dialysis Studies

To the Editor: The time for equilibration during equilibrium dialysis studies is often considered to limit the usefulness of the technique. It is therefore important to design these studies so that the time to equilibrium is minimized. On the basis of Fick’s law, the use of dialysis cells which have a high membrane surface area to volume ratio and choice of a membrane with a high diffusivity and low effective thickness can reduce the equilibration time. Øie and Guentert have described the time advantage to be gained by introducing the drug to the protein side, rather than the buffer side of the dialysis cell. Their treatment was expanded by McNamara and Bogardus who related the time (tδ) required for the concentration in the dialysate to reach a stated fraction (δ) away from the equilibrium concentration to the membrane transport rate constant (kT) and the fraction unbound (α) in the protein compartment (eq 1), when the drug is introduced initially into the protein compartment:

Influence of storage temperature on indomethacin release from fatty-base suppositories in vitro and in vivo.

The release of indomethacin from fatty-base suppositories, which had been stored at a low (4 degrees C) and a high (25-30 degrees C) temperature for about one month, was examined in vitro and in vivo. In the in vivo experiments, the plasma indomethacin levels after administration of suppositories stored at different temperatures were measured in conscious and anesthetized rats. In the in vitro release test using a dialysis cell method, much lower amounts of indomethacin were released from the suppositories stored at a high temperature than from those stored at a low temperature. The melting point of suppositories stored at a high temperature was higher by approximately 2 degrees C than those stored at a low temperature. In conscious rats, the plasma indomethacin levels attained after the intrarectal administration of suppositories stored at a high temperature were slightly lower than those after the animals were given suppositories stored at a low temperature, but the difference was significant only 30 min after administration. In anesthetized rats, the plasma indomethacin levels were markedly lower than those in conscious rats, and the influence of the storage temperature on the plasma indomethacin levels was clearly observed. These results suggest that in conscious rats many factors such as a locomotor hyperactivity and enhancement of gastrointestinal motility caused by the rectal administration mask the real character of suppositories. The in vitro and in vivo results show that the release of indomethacin from fatty-base suppositories stored at a high temperature is less than the release from those stored at a low temperature.

Electron-microscopic study of structurization of low-molecular inorganic compounds introduced by counter-diffusion into the porous structure of a polymer strained in adsorption-active medium

Samples were prepared of polyethyleneterephthalate (PETP) films stretched in adsorption-active medium, with their porous structure filled with silver chloride by the method of counter-diffusion from solutions of silver nitrate and sodium chloride in a dialysis cell. By subsequent treatment of this film with a photodeveloper, highly disperse blends of PETP with metallic silver were obtained. The applied counter-diffusion method is more effective than procedures previously used for filling the porous craze structure in the polymer.

Tracing the influx of sewage from a leaky sewer into a very thin and fast-flowing aquifer

Water parcels of different chemical composition were detected in a 1 m thick and up to 17 m/d fast-flowing groundwater system using a multi-layer sampler based on the dialysis cell technique. The parcels result from the infiltration of sewage effluents and also probably due to the leaching of sewage sludge from the agricultural land surface. Samples obtained at depth intervals as small as 3 cm in a natural gradient flow field revealed relative high concentrations and variable vertical profiles of Na +, NO 3 −, HCO 3 −, SO 4 2− and DOC 9 m downstream of the infiltration pipe. A pump used to obtain water samples during a 2 year period, in the same research field, proved to be an inadequate sampling technique to trace the movement of sewage effluent.

A dialysis cell for nuclear magnetic resonance spectroscopic measurement of protein-small molecule binding

A dialysis cell is described for use in an NMR spectrometer, to make spectroscopic determinations of protein-small molecule binding. The protein solution is contained within a cylindrical dialysis tube which is concentrically suspended in an NMR tube containing a protein-free dialysis buffer. Simultaneous determinations of the equilibrium transmembrane distribution of the small molecule and the chemical shifts in both compartments are made spectroscopically, providing estimates of the dissociation constant and the chemical shift of the bound species. The cell is used for 31P NMR spectroscopic measurement of the degree of binding of 2,3-diphosphoglycerate to hemoglobin in a 2.8 m m carboxyhemoglobin solution at pH 6.9 and 21°C. The K d is found to be 2.4 × 10 −3 m.

Speciation of Cadmium(II) Using Donnan Dialysis and Differential-Pulse Anodic Stripping Voltammetry in a Flow-Injection System

Abstract A flow-injection/Donnan dialysis/differential pulse anodic stripping voltammetry system was developed for the determination of free cadmium concentrations, [Cd2+], in solutions containing organically complexed Cd(II). A small dialysis cell with a strong cation-exchange membrane separating the sample and the receiver channels, was equilibrated in a flow-injection system. The ionic strength of sample and receiver solutions was 0.1 M, with NaNO3 as the bulk electrolyte. By determining a constant fraction of the Cd2+ associated with the membrane phase, [Cd2+] of the samples could be measured. Experimentally determined [Cd2+] corresponded well with those calculated, using tabulated stability constants, when citric acid, nitrilotriacetic acid, and oxalic acid were added as ligands. Thus, negatively charged and uncharged complexes were excluded from the membrane. Using the experimental design presented, [Cd2+]>5 × 10×8 M could be determined, but there is a great potential for increasing the sensitivity ...

Binding of lysozyme on the surface of entrapped phosphatidylserine—phosphatidylcholine vesicles and an example of high-performance lipid vesicle surface chromatography

Phospholipid vesicles (liposomes) composed of phosphatidylserine (PS) and phosphatidylcholine (PC) in five different molar ratios were formed and entrapped in agarose gel beads (Sepharose 6B and Superose 6). For this purpose a previous dialysis—entrapment procedure was improved by use of an apparatus with continuous buffer flow and rotating dialysis cells. By rotary dialysis combined with a method of vesicles fusion with the aid of Ca 2+ ions, the capacity of entrapped vesicles composed of 80–85% phosphatidylserine from bovine brain [denoted “PS (brain extract)”] was increased. The entrapment of PSPC vesicles increased as the content of PS was increased. Lysozyme was applied to a PSPC vesicle—Sepharose 6B column. The amount of bound lysozyme was about 9 nmol per μmole of lipids for entrapped PSPC vesicles with 20 and 45 mol-% PS contents. The amounts of bound lysozyme increased to 29, 30 and 40 nmol per μmole of lipids as the fraction of PS in the vesicles was increased to 65, 80–85 and 100 mol-% PS, respectively. The lysozyme molecules thus closely packed on the surface of the vesicles with the higher PS contents. The losses of the entrapped vesicles in the first two chromatographic lysozyme-binding experiments were 5% for 80–85% PS (brain extract) vesicles, 10–12% for vesicles with 20 to 65 mol-% PS content and 23% for pure PS vesicles. PS (brain extract) vesicles were also formed and entrapped in Superose 6 gel beads (diameter 13 μm). Ribonuclease A, lysozyme and cytochrome c were well separated on this PS-vesicle—Superose column at an ionic strength of 0.05–0.15 M.

A new approach to pharmacokinetic parameters: Estimation of cefuroxime during haemodialysis

A linear three-compartment model is proposed as a means of estimating disposition and extracorporeal elimination pharmacokinetic parameters during haemodialysis. It was created by connecting a compartment, corresponding to the amount of drug present in the dialysis cell, to the central compartment of the standard two-compartment model from which elimination would normally take place. The transfer rate constants between the central compartment and the 'dialysis cell' and vice versa were given in terms of the plasma flow, central compartment volume, and volume of plasma contained in the dialysis cell, and thus cannot be considered to be independent parameters. The product of the rate constant for elimination from the dialysis cell, k30, and the plasma volume within the cell was used to quantify the extracorporeal elimination and termed intrinsic dialyser clearance, CLint,D. The model was used to interpret the plasma level curves obtained after administering 750 mg cefuroxime by IV bolus to a group of patients undergoing haemodialysis. The distribution parameters estimated by non-linear regression were similar to those given in the literature; however, in five of the twelve cases, no estimate of cefuroxime elimination from the central compartment (k10) could be derived. On the other hand, the estimates of the elimination rate constant (k30) from the deep peripheral compartment were greater than the values given in the literature, ranging from 50.6 h-1 to 151.0 h-1 and CLint,D ranging from 3.1 h-1 to 8.90 l h-1. The error in measuring the flow of plasma which reaches the dialyser, its influence upon the estimation of the model parameters and the relationship between the parameters themselves and those customarily used in the study of drug haemodialysis are all discussed.

Theophylline-controlled release preparations and fatty food: an in vitro study using the rotating dialysis cell method.

The in vitro dissolution behavior of four controlled-release theophylline products was investigated utilizing the rotating dialysis cell method. The effects of pH, oil, and enzymes on the dissolution profiles were studied. The wide range of pH values and the content of oil and enzymes in the dissolution media in the dialysis cell, which functioned as an in vitro model, were simulated to mimic physiological changes due to food along the entire gastrointestinal tract. Treatment with oil affected the dissolution behavior of Uniphyl and especially Theo-Dur Sprinkle but had little or no effect on the dissolution profiles of Theo-Dur tablets and Theo-24 capsules. The in vitro observations of the oil effect were related to the food effect obtained from published in vivo studies. The rotating dialysis cell can be a useful tool in studying factors which may be responsible for dissolution-related food effects on the absorption of controlled-release products.

Effect of whole blood and plasma on the permeability of glucose through different cellulose and cellulose acetate membranes

Model experiments were made with a flow-through dialysis cell to study how glucose in whole blood, plasma and aqueous standards is transferred through different membranes. Detection was via a glucose dehydrogenase reaction and NADH monitoring with a chemically modified electrode. The detector response was linear with the glucose concentration in all cases. The non-Newtonian properties of whole blood seem to be of great importance for the response. Theoretical models are proposed both for the effect of plasma viscosity and the red cell volume fraction (haematocrit) dependence on the glucose transfer rate. The models could only partially explain the differences between measurements in aqueous solutions and body fluids. Better agreement and less haematocrit dependence were obtained with low-permeability membranes.

Mass transfer in gas sparged membrane cells

Rates of mass transfer for the transfer of NaCl across a high permeability Cuprophane membrane in a gas-stirred batch dialysis cell were measured by the conductivity method. Gas sparging was found to increase the rate of mass transfer across the membrane by an amount ranging from 18 to 360% depending on the superficial gas velocity and the physical properties of the solution. The overall mass transfer coefficient was related to the superficial velocity by the equation $$K = aV_s^{0.22} .$$