Organic membranes

Membranes. Membranes comprised of activated alumina films less than 20 )J.m thick have been reported (46). These films are initially deposited via sol—gel technology (qv) from pseudoboehmite sols and are subsequently calcined to produce controlled pore sizes in the 2 to 10-nm range. Inorganic membrane systems based on this type of film and supported on soHd porous substrates have been introduced commercially. They are said to have better mechanical and thermal stabiUty than organic membranes (47). The activated alumina film comprises only a miniscule part of the total system (see Mel rane technology). 

Kawasaki et /. (1996) have used a supported membrane catalyst for extraction of erythromycin from its dilute, slightly alkaline aqueous solutions. 1-Decanol was used as an intermediate fluid membrane phase and a buffered acidic aqueous solution was used to strip the organic membrane. 

One barrel-tip contains the organic membrane phase and an internal reference electrode the other constitutes a second reference electrode. A four-barrel configuration with a 1-pm tip in which three barrels are liquid membrane electrodes for Na, Ca and and the fourth is a reference electrode has been reported Some representative applications of ion-selective electrodes for intracellular measurements are shown in Table 3. 

Theoretical insight into the interfacial charge transfer at ITIES and detection mechanism of this type of sensor were considered [61-63], In case of ionophore assisted transport for a cation I the formation of ion-ionophore complexes in the organic (membrane) phase is expected, which can be described with the appropriate complex formation constant, /3ILnI. 

The only potential that varies significantly is the phase boundary potential at the membrane/sample interface EPB-. This potential arises from an unequal equilibrium distribution of ions between the aqueous sample and organic membrane phases. The phase transfer equilibrium reaction at the interface is very rapid relative to the diffusion of ions across the aqueous sample and organic membrane phases. A separation of charge occurs at the interface where the ions partition between the two phases, which results in a buildup of potential at the sample/mem-brane interface that can be described thermodynamically in terms of the electrochemical potential. At interfacial equilibrium, the electrochemical potentials in the two phases are equal. The phase boundary potential is a result of an equilibrium distribution of ions between phases. The phase boundary potentials can be described by the following equation ... 

The equilibrium constant for this reaction depends on the stability constants of the ionophore-M+ complexes and on the distribution of ions in aqueous test solution and organic membrane phases. For a membrane of fixed composition exposed to a test solution of a given pH, the optical absorption of the membrane depends on the ratio of the protonated and deprotonated indicator which is controlled by the activity of M+ in the test solution (H,tq, is fixed by buffer). By using a to represent the fraction of total indicator (Ct) in the deprotonated form ([C]), a can be related to the absorbance values at a given wavelength as... 

The equilibrium constant for reaction 5 depends on the complex formation constant, the association constant of C in the membrane and on the distribution coefficients of H+, and ions between the organic membrane phase and aqueous sample solution, e.g. 

A commonly used simple method for determining if there are any cracks or pinholes in microporous membranes is the so-caUed bubble point test. It has been used by many organic membrane manufacturers and users alike and is also being adopted by some inorganic membrane manufacturers. The method utilizes the Washburn equation... 

Despite the fact that inorganic membranes are, in general, more stable mechanically than organic membranes, available mechanical properties data for commercial inorganic membranes are sketchy and these are not yet standardized for comparing various membranes. It appears that the methods used for obtaining various mechanical strength data are based on those for solid (nonporous) bodies and most of them arc listed as ASTM procedures. 

Determination of nAChR-Binding Sites in Torpedo Electric Organ Membrane Preparations... 

To perform in vitro transcription reaction Save 20 pi of the total volume of 100 pi (for P-UTP transcription for binding studies with uAChRs in Torpedo electric organ membranes, and in case you have to amplify the DNA again) and use 80 pi for transcription. 

Finally, cation transport through organic membranes depends inter alia, on the mobility of the carrier-cation complex. Thus, too thick ligands may decrease the efficiency of the carrier. 

Efficient extraction of proteins has been reported with reverse micellar liquid membrane systems, where the pores of the membrane are filled with the reverse micellar phase and the enzyme is extracted from the aqueous phase on one side of membrane while the back extraction into a second aqueous phase takes place at the other side. By this, both the forward and back extractions can be performed using one membrane module [132,208]. Armstrong and Li [209] confirmed the general trends observed in phase transfer using a glass diffusion cell with a reverse micellar liquid membrane. Electrostatic interactions and surfactant concentration affected the protein transfer into the organic membrane and... 

Selective ion electrodes (SIE). Selective ion electrodes are essentially variants of the well-known pH meter. They are membrane indicator types of electrodes in which a potential is developed across a membrane in the presence of the ion the size of the potential is related to the concentration and hence can be used to quantitatively detect and measure the species. However, instead of a glass membrane, as in the pH meter, the membranes consist of organics that are immersible in water. For example, anion-sensitive electrodes use a solution of an anion exchange resin in an organic solvent the liquid can be held in the form of a gel, for example, in polyvinyl chloride. The ion reacts with the organic membrane, setting up an equilibrium between the free ion in solution and the ion bound to the membrane, generating a potential difference, which is measured. 

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