Free serum cortisol: quantification applying equilibrium dialysis or ultrafiltration and an automated immunoassay system

Background: Quantification of bioactive, free serum cortisol concentrations can characterize adrenocortical function more appropriately compared to total serum cortisol measurement. Ultrafiltration or equilibrium dialysis of serum samples allow direct measurement of free serum cortisol concentrations but respective methods have poorly been validated so far. The aim of our study was to investigate the analytical performance of free serum cortisol measurement employing equilibrium dialysis and ultrafiltration. Methods: Two commercially available ultrafiltration devices and self-assembled dialysis cells, respectively, were studied. Cortisol was quantified in filtrate or dialysate using an automated immunoassay system. Using two serum pools, the inter-assay coefficient of variation was determined for the three methods and a method comparison was performed. Results: Inter-assay coefficients of variation (n=10) between 3.2% and 14.8% were observed in the imprecision study. Method comparison demonstrated close agreement between free serum cortisol results obtained by ultrafiltration and equilibrium dialysis, respectively (equilibrium dialysis = 1.2x ultrafiltration+3.9 nmol/L; r=0.99; n=35). Conclusions: Direct quantification of free serum cortisol after equilibrium dialysis or ultrafiltration of the samples offers acceptable reproducibility and results in close agreement can be obtained. Both methods can potentially be introduced into a routine laboratory setting

Particle-by-Particle Reconstruction of Ultrafiltration Cakes in 3D from Binarized TEM Images

Transmission electron microscopy (TEM) imaging is one of the few techniques available for direct observation of the microstructure of ultrafiltration cakes. TEM images yield local microstructural information in the form of two-dimensional grayscale images of slices a few particle diameters in thickness. This work presents an innovative particle-by-particle reconstruction scheme for simulating ultrafiltration cake microstructure in three dimensions from TEM images. The scheme uses binarized TEM images, thereby permitting use of lesser-quality images. It is able to account for short- and long-range order within ultrafiltration cake structure by matching the morphology of simulated and measured microstructures at a number of resolutions and scales identifiable within the observed microstructure. In the end, simulated microstructures are intended for improving our understanding of the relationships between cake morphology, ultrafiltration performance, and operating conditions

Fouling and Rejection Behaviour of Ultrafiltration for Oil in Water Emulsion Separation

Oily waste water has been generated from food, automotive, metal processing industries as well as petroleum exploration and refinery. Polyethersulfone ultrafiltration membrane was investigated for treatment of oil in water emulsion. The emulsion models were made based on industrial oily wastewater characteristic in the oil refinery. Flux and rejection were evaluated in order study the fouling and rejection behaviour. Results showed that more than 90% of COD and 85% surfactant were rejected. The permeate flux decline was analyzed in order to study the membrane fouling. In addition, the Hermia model is adopted to investigate the fouling mechanism during ultrafiltration of oil in water emulsion. Analyze of blocking mechanism using Hermia’s model reveal that ultrafiltration of both diesel and mineral oil have good agreement with complete blocking mechanism

The Study of the Method of Fight Against Formation of Polarizing Layer at the Process of Ultrafiltration Concentration of the Skim Milk

The description of experimental set and the method of processing of the results of the study of the method of fight against formation of polarizing layer in the process of ultrafiltration concentration of skim milk raw material were presented. The results of experimental studies relative to the sparging method application for the prevention of polarizing layer in the process of membrane processing of the skim milk and its influence on the capacity of ultrafiltration membranes were offered. The mathematical models were constructed on the base of regressive equations of factorial experiment using the method of the raw material sparging above the membrane surface for selection of technological parameters of the process of ultrafiltration concentration of the skim milk. The rational working parameters of the process of ultrafiltration concentration of the skim milk using the sparging of the skim milk by the gas bubbles in the direct closeness to the membrane surface were determined. Such working parameters are: pressure– 0,4...0,5 MPa, temperature of skim milk– 40...50 ºС, frequency of sparging of skim milk– 0,10...0,15 min-1, pressure of sparging must be 0,56...0,58 MPa

Flux limitation in ultrafiltration: Osmotic pressure model and gel layer model

The characteristic permeate flux behaviour in ultrafiltration, i.e., the existence of a limiting flux which is independent of applied pressure and membrane resistance and a linear plot of the limiting flux versus the logarithm of the feed concentration, is explained by the osmotic pressure model. In the mathematical description presented here, a quantity ΔΠn/(Rmk) is introduced which is the ratio of the resistance caused by the osmotic pressure and the resistance of the membrane itself. For high values of this quantity (19) the flux is practically limited by the osmotic pressure. p]Factors leading to high values of the quantityΔΠnn/(Rmk) are discussed and it is concluded that in the ultrafiltration of medium molecular weight solutes (10,000 to 100,000 daltons) osmotic pressure limitation is more likely than gel layer limitatio

Concentration polarization phenomena during dead-end ultrafiltration of protein mixtures. The influence of solute-solute interactions

The flux decline behaviour of some charged proteins and of binary mixtures of charged solutes during unstirred dead-end ultrafiltration has been studied. The mixtures consisted of the proteins bovine serum albumin, (BSA), α-lactalbumin and/or lysozyme. Of special interest were α-lactalbumin and lysozyme because these proteins are physico-chemically identical, except for the sign of their charge at the conditions used (pH = 7.4, I=0.125 N and T=20°C). The ultrafiltration properties were studied using the boundary layer resistance model. Ultrafiltration of single protein solutions of α-lactalbumin and of lysozyme showed identical characteristics. The fouling behaviour during ultrafiltration of binary mixtures of the three components appeared to be dependent on both the charge of the solutes and the (unequal) dimensions of the solutes. A mixture of oppositely charged proteins (i.e., BSA/lysozyme or α-lactalbumin/lysozyme) sometimes showed a considerable increase of the resistance of the concentrated layer near the membrane, depending on the mixing ratio of the two proteins. When equally charged (i.e., BSA/α-lactalbumin) proteins are ultrafiltered, a small decrease of the resistance could be observed, again depending on the mixing ratio of the proteins. The charge of the proteins, especially opposite charges, appeared to influence the flux behaviour more than the slightly denser packing of the solutes (as a result of unequal dimensions) would account for

Influence of ultrafiltration membrane characteristics on adsorptive fouling with dextrans

This paper presents a detailed investigation of fouling mechanisms for ultrafiltration membranes with polysaccharides obtained by studying membrane–solute (static adsorption) and membrane–solute–solute interactions (ultrafiltration (UF)). Two polyethersulfone (PES) membranes and one stabilized cellulose (cellulosic) membrane with a nominal cut-off of 10 kg/mol and dextrans with average molar mass (M) of 4, 10 and 15 kg/mol were used. The membranes before and after static adsorption of dextran were characterized by captive bubble contact angle and tangential streaming potential measurements as well as ultrafiltration sieving curves for polyethylene glycols. Significant water flux reductions (4–15%), which also correlated with dextran molar mass, and changes of the other membrane characteristics occurred after static dextran adsorption for the PES membranes. An empirical model to describe the correlation between the relative water flux reduction and the concentration of solute had also been proposed. In contrast, no significant changes could be detected for the cellulosic membrane. Significant membrane–solute interactions had also been confirmed in the ultrafiltration experiments with dextrans where irreversible fouling had been observed for the PES but not for the cellulosic membranes. The results provide fundamental information for a better understanding of fouling by polysaccharides. In particular, it had been confirmed that hydrophilic and neutral dextrans can significantly foul PES membranes via adsorption to the surface of the membrane polymer. On this basis, methods for control of this fouling can be properly developed

The boundary-layer resistance model for unstirred ultrafiltration. A new approach

The possibility to analyse concentration polarization phenomena during unstirred dead-end ultrafiltration by the boundary layer resistance theory has been shown by Nakao et al. [1]. Experimental data on the ultrafiltration of BSA at pH 7.4, at various concentrations and pressures, were analysed by this model and by a new version of the model in this paper. Instead of the assumption of the cake filtration theory, the new version of the model uses the unsteady state equation for solute mass transport to predict flux data by computer simulations. This approach requires no assumptions concerning the concentration at the membrane, the concentration profile or the specific resistance of the boundary layer. The computer simulations agree very well with the experimental data. Many agreements with Nakao's analyses are confirmed and some new data on the concentration polarization phenomena are obtaine

Ultrafiltration of protein solutions; the role of protein association in rejection and osmotic pressure

The monomer-dimer equilibrium of the protein β-lactoglobulin under neutral conditions appears to influence the rejection and the osmotic pressure build-up, both phenomena closely related to ultrafiltration. Rejection measurements indicate different rejections for the β-lactoglobulin monomers and dimers: the membrane rejects the dimer almost completely and the monomer only partially. The osmotic pressure turns out to be highly dependent on the protein concentration. A good agreement, up to high concentrations, is found between experimental data and theoretical osmotic pressures, calculated by taking into account the state of association, the excluded volume and the Donnan effects. The effect of changes in pH on the osmotic pressure has been measured: a minimum was found around pH = 4.5, where according to the literature, maximum protein-protein interaction occurs

A mathematical model for fluid-glucose-albumin transport in peritoneal dialysis

A mathematical model for fluid and solute transport in peritoneal dialysis is constructed. The model is based on a three-component nonlinear system of two-dimensional partial differential equations for fluid, glucose and albumin transport with the relevant boundary and initial conditions. Its aim is to model ultrafiltration of water combined with inflow of glucose to the tissue and removal of albumin from the body during dialysis, and it does this by finding the spatial distributions of glucose and albumin concentrations and hydrostatic pressure. The model is developed in one spatial dimension approximation and a governing equation for each of the variables is derived from physical principles. Under certain assumptions the model are simplified with the aim of obtaining exact formulae for spatially non-uniform steady-state solutions. As the result, the exact formulae for the fluid fluxes from blood to tissue and across the tissue are constructed together with two linear autonomous ODEs for glucose and albumin concentrations in the tissue. The obtained analytical results are checked for their applicability for the description of fluid-glucose-albumin transport during peritoneal dialysis.Comment: 28 pages, 8 figures. arXiv admin note: text overlap with arXiv:1110.128