we have sephadex g-25, sephadex g-50 and sephadex g-75 resins. our
protein is 20 Kda and we would like to desalt it for further processing.
Can some one recommend which of these will be suitable. i.e which will
cause less dilution and better desalting.



we would be packing them in XK 16/40 column and use for desalting so what amount of sample can be desalted at a time.



kindly suggest



thanks

With 20 kDa G-25 is a good bet (cut-off is around 3-5k, IIRC). G-50 is about 30k, which would not be useful to you application (assuming globular proteins that is). Maximum volume is directly dependent on the pore volume (and other factors such as particle size as it affects sample dispersion and thus peak width).

One generally tries to keep the volume of the sample in a gel filtration minimal for the best separation between two proteins. However, for protein desalting, the volume of the sample is a little less critical. I am not familiar with the type of column you are using. However, if you kept the sample volume < 10% of the column volume, that would probably work, depending on how complete the desalting has to be. I often test my desalting columns using a colored small molecule, such as riboflavin phosphate, to check the efficiency of separation.