The ultrafiltration device is carried out in an airtight container, with compressed air as the driving force, pushing the piston in the container forward, making the sample liquid form internal pressure, and the bottom of the container has a strong film board.
Small molecules smaller than the diameter of the membrane pore diameter, the pressure is extruded out of the membrane, and the large molecules are trapped on the membrane plate.
At the beginning of ultrafiltration, because the solute molecules are evenly distributed in the solution, the ultrafiltration rate is faster.
But, with the continuous discharge of small molecules, macromolecules trapped accumulation in the membrane surface, the concentration is higher and higher, form concentration gradient from bottom to top, the day before ultrafiltration rate will gradually slow down, this phenomenon is called the phenomenon of concentration polarization.
In order to overcome the concentration polarization and increase the flow rate, several ultrafiltration devices were designed:
1. No stirring ultrafiltration.
This device is simple, just a certain pressure in the sealed container, the small molecule and the squeeze film, solvent concentration polarization serious without stirring device, only suitable for small ultrafiltration concentration is relatively thin.
2. Stirring ultrafiltration.
The superfilter is located above the electromagnetic agitator, and the ultrafiltration container is equipped with a magnetic rod.
During ultrafiltration to pressure container at the same time to start the magnetic stirrer, a small molecule solute and solvent molecules are membrane, large molecules to the membrane surface accumulation, were scattered electromagnetic stirrer to solution.
This method is not easy to produce the concentration polarization phenomenon, improve the speed of ultrafiltration.
3. Hollow fiber ultrafiltration.
Due to the membrane plate type ultrafiltration device, the trapped area is limited, the hollow fiber ultrafiltration is installed in a hollow column with many, hollow fiber capillary, the two ends are connected, the inner diameter of the tube is generally 0.
About 2mm, effective area can reach 1 square centimeter each fiber capillary is like a miniature dialysis bag, greatly increase the surface area of infiltration, increase the speed of ultrafiltration.