Unsupported liquid membranes

Unsupported Liquid Membranes. Very thin unsupported liquid membranes may be obtained, when the selective membrane material is stabilized by an appro-... 

Unsupported liquid membrane techniques with three phases involve an aqueous sample phase separated from another aqueous phase (called as receiver phase) by a layer of organic solvent (e.g., octane). Analyte components first diffuse from the sample into the organic liquid membrane and then back-extract out of the membrane into the receiving phase. At the same time, interferences do not diffuse into the organic membrane layer but stay in the original sample phase. 

The catalytic (supported or unsupported) interface in the vast majority of direct liquid fuel cell studies is realized in practice either as a catalyst coated membrane (CCM) or catalyst coated diffusion layer (CCDL). Both configurations in essence are part of the electrode design category, which is referred to as a gas diffusion electrode, characterized by a macroporous gas diffusion and distribution zone (thickness 100-300 pm) and a mainly mesoporous, thin reaction layer (thickness 5-50 pm). The various layers are typically hot pressed, forming the gas diffusion electrode-membrane assembly. Extensive experimental and mathematical modeling research has been performed on the gas diffusion electrode-membrane assembly, especially with respect to the H2-O2 fuel cell. It has been established fliat the catalyst utilization efficiency (defined as the electrochemically available surface area vs. total catalyst surface area measured by BET) in a typieal gas diffusion electrode is only between 10-50%, hence, flie fuel utilization eflfieieney can be low in such electrodes. Furthermore, the low fuel utilization efficiency contributes to an increased crossover rate through the membrane, which deteriorates the cathode performance. 

Determination of Ra in Groundwater. Briefly, an aliquot of the water sample was filtered using 0.45 pm membrane filter, and then 8 mL of the filtered sample was added to a 20-mL polyethylene vial. To the same vial, 12 mL of liquid scintillation cocktail, based on mineral oil (Rn measurement cocktail) was added. The vial was closed, vigorously shaken for 1 minute and stored in the fridge for about 30 days to remove unsupported Rn and to attain secular equilibrium between Ra and its daughter Rn. Ra was indirectly determined in the water sample by direct measurement of the vial by liquid scintillation spectrometry using the pulse-shape analyzer for o/p discrimination. Two control samples (blank and standard samples) were prepared, stored and measured as in case of the unknown samples. The control samples were de-ionized water and a standard Ra aqueous solution. 

---