Tracer permeabilities underestimate transmembrane solute flux under a concentration gradient

The measured flux of sucrose across Cuprophan dialysis membrane in the presence of a concentration gradient is significantly greater than the flux predicted from radioactive tracer permeabilities measured in the absence of a concentration gradient. The difference can be explained if the membrane is heteroporous. Similar results are expected for other heterogeneous biological or artificial membranes.     

Voltage-Controlled Electric Field Gradient Focusing with Online UV Detection for Analysis of Proteins

Electric field gradient focusing (EFGF) uses a hydrodynamic flow and an electric field gradient to focus proteins in order of electrophoretic mobility. In this paper, we describe several bioanalytical applications using voltage-controlled hollow dialysis fiber-based EFGF with online UV detection. Using bovine serum albumin (BSA) as a model protein, a concentration factor as high as 15,000 and a concentration limit of detection as low as 30 pM were achieved. We also demonstrate the potential of using fiber-based EFGF for protein quantitative analysis. Simultaneous desalting and protein concentration were performed by mixing BSA with 2 M NaCl in a cell culture medium. Online concentration of ferritin and simultaneous removal of albumin from a sample matrix were performed using this EFGF system.     

Model experiments for determinations of zinc—amino acid complexes in biological fluids by polarography

The Ilkovi? constant was determined for zinc and zinc—amino acid complexes by using differential pulse polarography in 0.1 M sodium chloride—sodium diethylbarbiturate buffer at pH 7.4. A single well-behaved wave was obtained, except for cysteine and cystine for which useful calibration curves could not be obtained. The non-equilibrium dialysis of the amino acid complexes was studied in a hollow-fiber dialyzer. It is concluded that the dialysis step could be used in a method intended to measure available zinc but that the polarographic method needs further modification.     

Continuous dialysis of hydrochloric acid and lithium chloride: permeability of anion-exchange membrane to chloride ions

A counter-current two-compartment dialyzer equipped with an anion-exchange membrane Neosepta-AFN was used to study dialysis of a hydrochloric acid and lithium chloride mixture. To quantify this process, several characteristics were calculated from the data obtained at steady state. First, the dialysis process was characterized by the acid recovery yield and rejection coefficient of salt, which were in the range of 61–98% and 62–94%, respectively (for HCl and LiCl concentrations from 0.1 to 1.0 kmol m^?3 and volumetric liquid flow rates from 8 × 10^?9 to 24 × 10^?9 m³ s^?1). Furthermore, this study proved that dialysis of an HCl + LiCl mixture can be quantified by a single characteristic, i.e., the permeability coefficient of the membrane to chloride ions, which is a function of the concentration of both the components in the feed.     

Continuous dialysis of sulphuric acid in the presence of zinc sulphate

Transport of sulphuric acid in the presence of zinc sulphate through the anion-exchange membrane Neosepta-AFN (Astom Corporation, Japan) was studied in a two-compartment counter-current dialyzer with single passes at steady state. The following characteristics were used to characterize the dialysis process: recovery yield of acid, rejection coefficient of salt, and permeability coefficient of the membrane. In case of the H₂SO₄ + ZnSO₄ mixture, permeability of the membrane was quantified by four phenomenological coefficients which are functions of acid and salt concentrations in the feed. They were determined by numerical integration of differential equations describing the concentration profiles of both components in both compartments, which was combined with an optimizing procedure.     

Combining electrolysis and dialysis for regeneration of chromic acid etching solution

The technique of integrating Donnan dialysis with electrolysis was evaluated for regenerating a chromic acid solution contaminated with copper. Electrolysis converts the reduced chromium (Cr³⁺) to the active form (Cr⁶⁺, as dichromate), but cannot remove copper efficiently. A dialyzer in series greatly increases the copper removal efficiency by providing a facile route for copper ions to reach the catholyte where they are electrodeposited.     

High-Performance Liquid Chromatographic Determination of Cefepime and Cefazolin in Human Plasma and Dialysate

A simple high-performance liquid chromatographic (HPLC) method was developed for the simultaneous determination of cefepime and cefazolin in human plasma and dialysate. For component separation, the method utilized a C₁₈ column with an aqueous mobile phase of dibasic potassium hydrogen phosphate (pH 7.0) and methanol gradient at a flow rate of 1 mL min⁻¹. The method demonstrated linearity from 2.0 to 100.0 μg mL⁻¹ (r > 0.999) with detection limit of 1 μg mL⁻¹ for both cefepime and cefazolin. The method was utilized for evaluation of plasma and dialysate samples in a clinical study evaluating the dialyzer clearance of cefepime and cefazolin using high-flux hemodialysis with varying blood flow rates in chronic kidney failure patients undergoing hemodialysis and peritoneal dialysis treatment.     

Cobalt(II) and Nickel(II) Transfer through Charged Polysulfonated Cation Exchange Membranes

The transport of Co(II) and Ni(II) ions through charged polysulfonated ion exchange membranes under Donnan dialysis conditions has been studied as a function of pH gradient at 25 degrees C. In the Donnan dialysis process, the membrane is bounded by two electrolyte solutions, the one side (donor phase) initially containing metal salts and the other H(2)SO(4) with no external potential field applied. The transport of metal ions through membranes was correlated with the flux data as well as with estimated diffusion coefficients and was found to depend on the interaction between the fixed groups in the membrane and the metal ions. It was observed that the pH gradient influences the transport of metals and the flux of ions increases with H ion concentration in the receiver phase. Copyright 2000 Academic Press.     

Label‐Free Amperometric Detection of Albumin with an Oil/Water‐type Flow Cell for Urine Protein Analysis

The 1,2‐dichloroethane (DCE)/water interface, with an anionic surfactant, dinonylnaphthalenesulfonate (DNNS^?), being present in DCE, was utilized for label‐free detection of albumin. An oil/water‐type flow cell was prepared using a porous PTFE tube and dipping the tube in the DCE solution containing DNNS^?. This flow cell provided a well‐defined current response linear to the albumin concentration up to 10 µM with a detection limit of 1.2 µM. The current response is due to the interfacial adsorption of albumin molecules depending on the Galvani potential difference. Possible interference from creatinine in the urine could be avoided by a conventional dialysis treatment.     

Electrochemical diffusion potential in a flame plasma: theory and experiment

A flame doped with an appropriate additive to produce positive ions and free electrons is a quasineutral, weak, continuum plasma. When bounded by a metallic burner upstream and a metal plate downstream, the two electrodes and flame plasma can be viewed as a gas-phase electrochemical cell. When the ion (and electron) density varies continuously along the flame axis, an expression for the diffusion potential can be derived in terms of the concentration gradient. The familiar logarithmic dependence on the ion concentration is obtained. A plasma sheath develops at the metal plate electrode; it sustains a potential difference which can be modeled by a Boltzmann distribution of the electrons in the sheath. Since the plate has to be cooled in practice, the average sheath temperature is less than the flame temperature because the sheath occurs inside the thermal boundary layer which covers the plate electrode. Inevitably, the reduced sheath temperature affects the sheath voltage. Experimental measurements of the “cell” voltage are made for the two cases of a positive concentration gradient using a sodium plasma, and a negative gradient by doping the flame with methane. As predicted theoretically, the cell voltages have opposite signs. However, the magnitude of the cell voltage seems to depend significantly on the sheath temperature which appears to decrease steadily with increasing distance downstream from the burner. It is also possible that the measured cell voltages involve unknown surface contact potentials. When compared with solution concentration cells, gas-phase flame systems exhibit both similarities and differences.     

Enzyme electrode for urea with amperometric indication: Electrode with diffusional limitation

Urea can be determined amperometrically with an enzyme electrode consisting of urease trapped in a poly(vinyl alcohol) gel and confined by a dialysis membrane. A pH-dependent hydrazine oxidation at a platinum anode is used as the detector reaction. The current is a linear function of the urea sample concentration over the range 1–80 mM with 50-μl samples injected into 2 ml of hydrazine buffer in the cell. With enzyme loadings above 20 U cm^-2, the current became limited by the rate of mass transfer in the membrane arrangement. Forty samples per hour could be analyzed with negligible carry-over when the time derivative was used for quantitation.     

Microfluidic system for measuring neutrophil migratory responses to fast switches of chemical gradients

Experimental systems that provide temporal and spatial control of chemical gradients are required for probing into the complex mechanisms of eukaryotic cell chemotaxis. However, no current technique can simultaneously generate stable chemical gradients and allow fast gradient changes. We developed a microfluidic system with microstructured membranes for exposing neutrophils to fast and precise changes between stable, linear gradients of the known chemoattractant Interleukin-8 (IL-8). We observed that rapidly lowering the average concentration of IL-8 within a gradient, while preserving the direction of the gradient, resulted in temporary neutrophil depolarization. Fast reversal of the gradient direction while increasing or decreasing the average concentration also resulted in temporary depolarization. Neutrophils adapted and maintained their directional motility, only when the average gradient concentration was increased and the direction of the gradient preserved. Based on these observations we propose a two-component temporal sensing mechanism that uses variations of chemokine concentration averaged over the entire cell surface and localized at the leading edge, respectively, and directs neutrophil responses to changes in their chemical microenvironment.     

Electrodialysis Kinetics by Laser Interferometry

A new approach to studying electromembrane systems by the laser interferometry method is proposed. Problems in the electrodialysis kinetics that had been solved by this method are reviewed. These include the determination of the size of diffusion boundary layers, the measurement of concentration profiles of solutions at a concentration polarization of ion-selective membranes in solutions of one and two components in isothermal and nonisothermal conditions, the verification of mathematical models for electrodialysis, and the measurement of local Sherwood numbers. A method for measuring concentration profiles in solutions at the interface with bodies of spherical symmetry following the imposition of a gradient of an electric potential on the system is offered. The results of studying the concentration polarization of an ion exchanger granules are analyzed.     

Simultaneous flow-injection analysis of three components with on-line dialyzers in series. Determination of sodium, potassium and chloride in blood serum

A fast and reliable fully automated three-component flow-injection procedure for the simultaneous determination of sodium, potassium and chloride in blood serum is described. A single sample injection (100-mul blood serum) is directed to two different channels by using two dialyzers in series. To avoid interferences and blocking of the fine jet of the atomizer, sodium and potassium are dialyzed by the first dialyzer before measurement by AES with a flame photometer. A second dialyzer in series is used to eliminate interferences and for automated dilution before the dialyzed chloride is measured by UV/VIS spectrophotometry at 485 nm. The results obtained for the sodium, potassium and chloride in blood serum at a sampling rate of 106 samples per hour compared well with data obtained by standard methods.     

Determination of the endocrine disrupter bisphenol—A in the blood of uremia patients treated by dialysis

Summary Automated solid-phase extraction (SPE) then high-performance liquid chromatography have been studied for determination of the endocrine disrupter bisphenol-A (BPA) in blood. Electrochemical detection was used for selective and sensitive detection of BPA. Determination of BPA in the blood of uremia patients treated by dialysis has not yet been reported. Acidified blood and acidified SPE eluent were used to suppress the ionization of BPA and thus retain the compound on a C₁₈ column. Because artificial dialysis can be performed for periods longer than 20 years, for reasons of safety the amount of BPA migrating from the artificial dialyzer into the blood of a uremia patient was compared for different sterilization methods and for different artificial dialyzers manufactured from different materials.     

Potentiometric determination of glucose by enzymatic oxidation in a flow system

A potentiometric determination is described for glucose based on oxidation by 1,4-benzoquinone with immobilized glucose oxidase as catalyst in an enzyme reactor. The electrode is preceded by an analytical dialysis unit to remove proteins. The ratio of quinone to hydroquinone was measured with a flow-through gold electrode. Another gold electrode preceded the enzyme reactor to correct for serum components (e.g. ascorbic acid) which can also reduce quinone. The operating range is 0.04–10 × 10^-3 M β-D-glucose. The dialysis proceeds with a linear dependence on glucose concentration, and the dialysis ratio can be adjusted by changing the buffer flow rate.     

Concentration with Selective Acid Removal from Americium Solutions Using Ion Exchange Membranes

Donnan dialysis and diffusion dialysis techniques are investigated for deacidification and possible concentration of actinide bearing acidic streams. Cation and anion exchange membranes are used in a two compartment dialysis cell to selectively remove acid from americium solutions. Acid concentrations, as high as 8.0M HNO₃ are used and the stability of membranes are ascertained. Possibility of simultaneous deacidification and concentration of acidic americium solutions are indicated by combining simple osmosis with diffusion dialysis. All the experiments are carried out under non stirring conditions at room temperature.     

Development of a push-pull microdialysis sampling technique for the quantitative determination of proteins

Summary An on-line push-pull sampling technique has been developed for continuous analysis of proteins of molecular weight from 5.7 to 67 kDa. The characteristics of the system include gradient elution with a total cycle time of 21 min, membrane stability, unattended automatic operation, and adjustment of the sampling mode and extraction fraction (the ratio of the concentration of analyte in the dialysate to that in the sample) by varying the effective dialysis length. The push and pull flow rates were adjusted in a manner which enabled three different modes of operation. When push-pull microdialysis was compared with conventional microdialysis sampling, significantly higher extraction fractions were obtained for all five model proteins studied. The technique has been applied to the quantification of proteins in cell samples. On-line fractionation enabled complementary MS identification of the proteins present.     

T cell chemotaxis in a simple microfluidic device

This paper describes the use of a simple microfluidic device for studying T cell chemotaxis. The microfluidic device is fabricated in poly(dimethylsiloxane) (PDMS) using soft-lithography and consists of a "Y" type fluidic channel. Solutions are infused into the device by syringe pumps and generate a concentration gradient in the channel by diffusion. We show that the experimentally measured gradient profiles agree nicely with theoretical predictions and the gradient is stable in the observation region for cell migration. Using this device, we demonstrate robust chemotaxis of human T cells in response to single and competing gradients of chemokine CCL19 and CXCL12. Because of the simplicity of the device, it can flexibly control gradient generation in space and time, and would allow generation of multiple gradient conditions in a single chip for highly parallel chemotaxis experimentation. Visualization of T cell chemotaxis has previously been limited to studies in 3D matrices or under agarose assays, which do not allow precise control or variation in conditions. Acknowledging the importance of lymphocyte homing in the adaptive immune response, the ability to study T cell chemotaxis in microfluidic devices offers a new approach for investigating lymphocyte migration and chemotaxis in vitro.     

Photosensitization reaction-induced acute electrophysiological cell response of rat myocardial cells in short loading periods of talaporfin sodium or porfimer sodium

Electrophysiological responses of rat myocardial cells to exogenous photosensitization reactions for a short period of incubation with two photosensitizers, talaporfin sodium or porfimer sodium, were measured in a subsecond time scale. The loading period of the photosensitizer when the photosensitizer might not be taken up by the cells was selected as 15min, which was determined by the fluorescence microscopic observation. We measured the intracellular Ca(2+) concentration ([Ca(2+) ](in) ) by using a fluorescent Ca(2+) indicator, Fluo-4 AM, under a high-speed confocal laser microscope to evaluate the acute electrophysiological cell response to the photosensitization reaction. The measured temporal change in Fluo-4 fluorescence intensity indicated that the response to the photosensitization reaction might be divided into two phases in both photosensitizers. The first phase is acute response: disappearance of Ca(2+) oscillation when irradiation starts, which might be caused by ion channel dysfunction. The second phase is slow response: [Ca(2+) ](in) elevation indicating influx of Ca(2+) due to the concentration gradient. The continuous Ca(2+) influx followed by changes in cell morphology suggested micropore formation on the surface of the cell membrane, resulting in necrotic cell death.