Separation methods dialysis

Amongst the membrane-separation methods dialysis is old enough and standardized equipment for this process has long been available. The concentration gradient existing across the membrane is the internally available driving force in the system which is responsible for the phenomenon of dialysis. 

Hamilton, P. B. Biochemical Analysis, in Anal. Chem. 38, Ann. Rev. (1966) pp. I9R and 20R have references to various separation methods dialysis, countercurrent distribution, liquid-liquid extractions, and ultrafiltration p. 21R column chromatography, electrophoretic methods, and paper and thin-layer chromatography p. 22R ion-exchange and gas chromatography. 

Purify the biotinylated protein or molecule using dialysis or gel filtration. For small molecule biotinylation where these separation methods may not be appropriate, other procedures may have to be developed, such as reverse-phase chromatography or organic precipitation techniques. 

A separation step is sometimes an essential part of an analytical method and may be as diverse as distillation, filtration, digestion, extraction, phase-separation or dialysis. These can all be performed by continuous flow analysers either by adding a specially designed glass fitting to the manifold or analytical cartridge or by the addition of a separate module to the analyser. Many biological samples contain protein and dialysis is often used to remove this protein, which would otherwise affect the analysis. 

Several variants of separation methods based on dialysis, ultrafiltration, and size exclusion chromatography have been developed that work under equilibrium conditions. Size exclusion chromatography especially has become the method of choice for binding measurements. The Hummel-Dreyer method, the vacancy peak method, and frontal analysis are variants that also apply to capillary electrophoresis. In comparison to chromatographic methods, capillary electrophoresis is faster, needs only minimal amounts of substances, and contains no stationary phase that may absorb parts of the equilibrium mixture or must be pre-equilibrated. 

Techniques can be classified into two main categories those that detect total metal concentrations and those that detect some operationally defined fraction of the total. Methods which detect total concentrations such as inductively coupled plasma spectrometry, neutron activation analysis, atomic absorption spectrometry and atomic emission spectrometry have no inherent speciation capabilities and must be combined with some other separation technique(s) to allow different species to be detected (approach A in Fig. 8.2). Such separation methods normally fractionate a sample on the basis of size, e.g. filtration/ultrafiltration, gel filtration, or a combination of size and charge, e.g. dialysis, ion exchange and solvent extraction (De Vitre et al., 1987 Badey, 1989b Berggren, 1989 1990 Buffle et al., 1992). In all instances the complexes studied must be relatively inert so that their concentrations are not appreciably modified during the fractionation procedure. 

From the great variety of methods for the determination of protein binding three separation methods, equilibrium dialysis (ED), ultrafiltration (UF), and ultracentrifugation (UC) and a non-conventional method with the binding to immobilized proteins has been chosen. The first methods are undoubtedly the most widely used because of their simplicity and general applicability to many different systems. Other methods e.g. size exclusion chromatography, capillary electrophoresis, or spectroscopic methods have been not described. Oravcova et al. (1996) gives a comprehensive review and comparison for these applications. 

All separation procedures rely on some element of differential transport the separation may be based on differences in phase equilibria, as in chromatography, or on the kinetics of transport, as in electrophoresis and centrifugation. Precipitation procedures, filtration and dialysis are also members of the broad dass of separation methods these have been discussed in an earlier chapter (Sect. 3.4). The transport processes involved in separating components are often opposed by dispersion processes such as diffusion and convection, which have to be minimised to achieve the best separation results. 

Reverse osmosis is used as a method of desalting seawater, recovering wastewater from paper mill operations, pollution control, industrial water treatment, chemical separations, and food processing. This method involves application of pressure to the surface of a saline solution, thus forcing pure water to pass from the solution through a membrane that is too dense to permit passage of sodium and chlorine ions. Hollow fibers of cellulose acetate or nylon are used as membranes, since their large surface area offers more efficient separation. See dialysis membrane diffusion desalination. 

Devis JC, Valus RJ, Lawrence EG. Aftinity dialysis— A method of continuous, rapid metal ion separation using Dialysis membranes and selective water-soluble polymers as extractants. Sep Sci Technol 1988 23, 10, 11 1039-1066. 

Dialysis is considered the reference method when studying protein binding of drugs (45) but is also useful for protein removal prior to plasma analysis. Dialysis is a classical separation method that uses semipermeable membranes to separate compounds by molecular weight. The protein sample is exposed to a buffer solution separated by the membrane. After the system is allowed to come to equilibrium, the small molecules diffuse to similar concentrations on both sides, while the sample side contains all of the protein... 

Dialysis compared with other Membrane-separation Methods... 

The most recent membrane-separation methods competitive with dialysis are essentially ultrafiltration for separation and concentration of solutes, reverse osmosis for solvent purification and electrodialysis for the separation of charged species from solvents and other solutes or from each other according to charge and mobility. Standardization of membranes and equipment for these newer methods also has more or less been accomplished during the past several decades. In all these methods it is an external driving force or source of energy which is essentially responsible for effecting the desired separation. 

Borguet, F., Cornells, R., Hilderson, H., and Lameire, N. (1991) Development of separation method for the speciation of chromium in plasma of patients on continuous ambulatory peritoneal dialysis. Trace elements in man and animals, Vol. 7, B. Momcilovic Ed., Institute for medical research and occupational health. University of Zagreb, Croatia, pp. 33-1 - 33-2. 

An automated assay for serum amylase was described. Using the Auto-Analyzer II the method employs, as substrate, a solution of dyed amylopectin which is commercially available (DyAmyl-L). After incubation of serum and substrate at 55 C, KOH (1.0 moF ) is introduced and the coloured products of enzymic hydrolysis are separated by dialysis against phosphate buffer. Absorbance is measured at 540 nm and the enzymic activity read from a standard curve obtained using calibration sera Versatol E and EN. The system provides accurate and reproducible measurement of serum amylase. The results obtained from... 

Enzymes are physiological constituents of urine, and most of them originate from renal tissue. The measurement of urinary enzymes has not yet been accepted as a routine clinical diagnostic method since urine contains many kinds of enzyme inhibitors and activators that must be removed before measurement of enzyme activity the most commonly used separation methods are gel filtration and dialysis. 

The term dialysis covers separation methods that are based on the transport of molecules or ions through a semi-permeable membrane. A differentiation is made between various types of dialysis (passive dialysis, Donnan dialysis, and electrodialysis), according to the driving force and the type of separation membrane that is used. "... 

Several techniques were described to study hydrogen-deuterium exchange in solution. The Linderstrom-Lang freeze drying method involved isolation of either isotopically enriched solvent water or protein. Methods substituting tritium for deuterium, thereby increasing the sensitivity, were developed. In this case, scintillation techniques were used for tritium analysis. Easier separation methods such as gel filtration or dialysis replace the freeze drying one. 

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