Dialysis has become one of the simple and commonly used separation and purification technologies in biochemical laboratories. The main function of dialysis is to diminish inflammation, sterilize, deeply clean and detoxify, which is conducive to skin absorption. In the production process of biomacromolecule, dialysis technology should be used for desalting, removing a small amount of organic solvent, removing biomacromolecule impurities, and concentrating samples. Dialysis bags are usually bag shaped containers made of semi permeable membranes.

Selection of dialysis bag

1. Select the appropriate molecular weight.

The selection of intercepted molecular weight is based on the molecular weight of macromolecules reserved in the membrane and the molecular weight of small molecular pollutants removed. In order to achieve reasonable and effective separation, the molecular weight ratio of the two substances to be separated should be at least 25. The rule of thumb for selecting trap molecular weight: in order to obtain a retention rate of at least 90%, the value of the selected trap molecular weight is about half of the retained high molecular weight. When the molecular weight difference exceeds 100 times, high yield and high purity can be ensured at the same time.

When the molecular weight difference is 10 times, in order to pursue high yield, low molecular weight rejection can be selected; In order to pursue high purity, high molecular weight rejection can be selected. For example, in the case of products (CytC, 20KD) and impurities (vitB12, 2kd), the focus will be on the yield. The selection of graded molecules is to increase the molecular weight of the product by 80% - 100% and the yield. The use of graded molecular weight 20KD membranes for CytC and vitb12 focuses on purity, but at the cost of yield, the selection of graded membranes with high molecular weight, the sample retention rate is about 50% - 80%, and the use of graded molecular weight 50KD membranes to separate CytC and VitB12, The yield is about 76% and the residue of B12 is about 2%.

For the application of separating several molecules, the molecular weight difference between molecules must be at least 5 times to complete effective membrane dialysis. If the requirements for molecular weight difference cannot be met, other separation technologies, such as chromatography and tangential flow filtration, may be required.

2. Select the appropriate flat width (volume)

The flat width of the permeation bag depends on the sample volume and dialysis capacity. Small dialysis tube is faster; Large dialysis tubes cause slow dialysis due to long diffusion distance. For ease of use, it is recommended to use a transparent bag with a total length of about 10-15cm (including closed clips and top space).

3. Select appropriate dialysis membrane material

The affinity of each membrane varies from molecule to molecule. For globulin, the relative binding affinity is from low to high CE<; RC<； PVDF。

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