How to choose the right dialysis membrane / dialysis bag / dialysis tube

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Basic principles of laboratory dialysis
Dialysis is a simple diffusion process in which small and medium molecular substances in a solution diffuse from a high concentration side through a semipermeable membrane to a low concentration solution until the osmotic pressure on both sides of the membrane reaches equilibrium.
Due to the selectivity of the porous membrane, small molecules are allowed to pass, while larger substances are trapped. Dialysis according to the molecular weight cut off (MWCO) of the semipermeable membrane can be applied to processes such as separation.
● Very mild conditions
● Easy to operate
● Wide processing capacity
● Multiple film materials and MWCO
● Low price
● Disposable membranes and devices
Dialysis application
● Purification of macromolecular substances
●pH adjustment
●Buffer replacement
●Desalting
Electric elution
●Contaminant removal
● Protein concentration
Correct selection of the appropriate molecular weight cut off ( MWCO )
Since the dialysis membrane is composed of a sponge-like laterally coupled polymer material, the retention performance is indirectly expressed by the pore size grade, ie, the molecular weight cut off (MWCO), and the solute molecular size with a rejection of 90% can more accurately represent the MWCO of the membrane.
However, the permeability of the solute also depends on the shape of the molecule, the degree of hydration, the ionic charge and the polarity. Therefore, it is generally recommended that the MWCO of the membrane be selected to be half the molecular weight of the substance to be retentate and twice the molecular size of the permeate.
Membrane shape
Depending on the grade and material of the film, there are generally tubular, ready-to-use dialysis devices (RDD) and flat sheets.
As the most conventional shape, the packaged dialysis tube is further divided into a dry type, a pre-wet type or a pre-treatment type.
The flat sheet has a square or disc shape for use in a dialysis apparatus or system.
Choose the right film
The key to successful dialysis separation is to select the most suitable membrane under the right conditions. Refer to the following 6 steps when selecting:
1. Select a grade (biotechnology or standard) according to purpose;
2. Select the membrane material (CE, RC) according to the chemical characteristics of the solution;
3. Select the product type (tubular, disposable or sheet) according to the method of use;
4. Select among MWCO according to the molecular weight of the solute;
5. Choose from a variety of sizes (disposable dialysis devices) or multiple widths (tubular) depending on the throughput;
6. Select the membrane pretreatment method according to the purpose;
Dialysis membrane selection summary guide
Membrane quality:
CE (Biotechnology)
RC (biotechnology)
RC (standard)
MWCO
(Dalton):
100-500, 500-1,000, 3.5-5K,
8-10K, 20K, 50K, 100K, 300K,
1,000K
3.5k, 8k, 10k, 15k, 25k
1k, 2k, 3.5k, 5k, 6-8k, 10k,
12-14k, 15k, 25k, 50k
Physical properties:
Opaque, hard, hydrophilic
Opaque, soft, hydrophilic
Transparent, soft, hydrophilic
Organic resistance:
medium
it is good
it is good
pH range:
2-9
2-12
2-12
Temperature limit:
37 ° C
60 ° C
121 ° C (high temperature and high pressure steam sterilization)
Flat film:
no
no
Yes
Closed clip:
ordinary
ordinary
Normal or Spectra/Por
Immediate dialysis device
Float-A-Lyzer G2
Tube-A-Lyzer
no
Dialysis bag

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