Membrane design, influencing factors

Liquid membrane separation systems possess great potential for performing cation separations. Many factors influence the effectiveness of a membrane separation system including complexation/ decomplexation kinetics, membrane thickness, complex diffusivity, anion type, solvent type, and the use of ionic additives. The role that each of these factors plays in determining cation selectivity and flux is discussed. In an effort to arrive at a more rational approach to liquid membrane design, the effect of varying each of these parameters is established both empirically and with theoretical models. Finally, several general liquid membrane types are reviewed, and a novel membrane type, the polymeric inclusion membrane, is discussed. 

The main chemico-analytical properties of the designed ionoselective electrodes have been determined. The work pH range of the electrodes is 1 to 5. The steepness of the electrode function is close to the idealized one calculated for two-charged ions (26-29 mV/pC). The electrode function have been established in the concentration range from 0.1 to 0.00001 mole/1. The principal advantage of such electrodes is the fact that thiocyanate ions are simultaneously both complexing ligands and the ionic power. The sensitivity (the discovery limits), selectivity (coefficient of selectivity) and the influence of the main temporal factors (drift of a potential, time of the response, lifetime of the membranes) were determined for these electrodes. 

Ultrasound can thus be used to enhance kinetics, flow, and mass and heat transfer. The overall results are that organic synthetic reactions show increased rate (sometimes even from hours to minutes, up to 25 times faster), and/or increased yield (tens of percentages, sometimes even starting from 0% yield in nonsonicated conditions). In multiphase systems, gas-liquid and solid-liquid mass transfer has been observed to increase by 5- and 20-fold, respectively [35]. Membrane fluxes have been enhanced by up to a factor of 8 [56]. Despite these results, use of acoustics, and ultrasound in particular, in chemical industry is mainly limited to the fields of cleaning and decontamination [55]. One of the main barriers to industrial application of sonochemical processes is control and scale-up of ultrasound concepts into operable processes. Therefore, a better understanding is required of the relation between a cavitation coUapse and chemical reactivity, as weU as a better understanding and reproducibility of the influence of various design and operational parameters on the cavitation process. Also, rehable mathematical models and scale-up procedures need to be developed [35, 54, 55]. 

Bioavailability is defined as the portion or fraction of a chemical that is available for biological action and is influenced by several factors including the molecular size and charge of a molecule, structural features of membranes, first pass metabolism, and therefore, bio availability can be influenced by the molecular structure of a chemical. This situation presents an opportunity for molecular designers to manipulate a chemical s structure to decrease bioavailability and consequently hazard. If the availability of a molecule can be decreased, the amount of chemical at the site of action is decreased which leads to decreased toxicity. 

The research program included also both the theory and practical aspects of ion-selective electrodes. Important part of these studies was the research oti the selectivity of such sensors and interferents and the change of selectivity imder influence of various factors. Potentiometric enzymatic sensors and sensors based oti pH-electrodes were developed and used in clinical chemistry. Kinetic model of the biosensors response with consideration of all proteolytic reactions of substrates and products of enzymatic reactions and transport processes in the membranes was elaborated. Conducting polymers and bilayer Upid membranes were used to design sensors and biosensors. 

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