Filtration micro/dialysis

Chemical analysis. Succinoglycan, purified by micro-filtration and dialysis, was hydrolysed in 0.5M sulphuric acid at a concentration of approximately 5mg/ml for 16 hours at 95 C. Sugars and acids were determined by HPLC using Biorad HPX-87 columns. No pretreatment was required for acids analysis - detection was by measurement of UV... 

Hydrophobic membranes, e.g., PTFE, permit the efficient removal of volatile analytes from the sample matrix by diffusion though the micropores [257]. As these membranes have a high diffusion efficiency for many gaseous species, selectivity is usually low. For hydrophilic porous membranes, mass transference usually relies on dialysis, provided differences in donor and acceptor stream pressures are low [258] the chemical species originally in the donor stream migrate through the solvent in the interstitial volume of the membrane. Ionic species are therefore efficiently separated from the macromolecules in the sample matrix. Increasing the difference in pressures of both streams favours the micro-filtration process therefore, filtration and dialysis may occur simultaneously [259,260]. 

The individual membrane filtration processes are defined chiefly by pore size although there is some overlap. The smallest membrane pore size is used in reverse osmosis (0.0005—0.002 microns), followed by nanofiltration (0.001—0.01 microns), ultrafHtration (0.002—0.1 microns), and microfiltration (0.1—1.0 microns). Electro dialysis uses electric current to transport ionic species across a membrane. Micro- and ultrafHtration rely on pore size for material separation, reverse osmosis on pore size and diffusion, and electro dialysis on diffusion. Separation efficiency does not reach 100% for any of these membrane processes. For example, when used to desalinate—soften water for industrial processes, the concentrated salt stream (reject) from reverse osmosis can be 20% of the total flow. These concentrated, yet stiH dilute streams, may require additional treatment or special disposal methods. 

Gel filtration compares very favorably with dialysis through membranes (Kisliuk, 1960). It is rapid and can be performed on either a micro- or a macroscale. The desalting of virus by this procedure has been reported by Matheka and Wittmann (1961). 

In-line distillation has rarely been used in flow analysis, but when it has been the basic design of the distillation unit has been maintained. Some advanced micro-distillation units have been proposed, mainly for analytical procedures with electrochemical detection [309—311]. A current tendency is to place several units in the manifold for successively performing different in-line analyte separation (and/or concentration) steps, e.g., distillation, dialysis and filtration. It is also possible to perform a variant of in-line distillation under constant temperature. This approach has been called isothermal distillation, membraneless gas diffusion or thin layer distillation, and discussed in 8.5.3.2. 

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