In this review, a product series for biomolecular separation by centrifugation from Pall Life Sciences is to be discussed. Different molecular weight cut offs (MWCOs) are available (1, 3, 10, 30, 50, 100, 300 and 1000 kD). As for sample volumes, one can choose from 4 different centrifugal devices:
Nanosep™ 50 – 500 µl; 100-fold concentration
Microsep™ up to 3.5 ml; 100-fold concentration
Macrosep™ 5 – 15 ml; 15 ml can be concentrated to 0.5 ml
Jumbosep™ up to 60 ml can be concentrated to 5 ml
In principle, the protocol is easy and straightforward – assemble device, fill in sample, centrifuge, collect concentrate. The protocol also delivers images, for example, how to handle the devices properly or how to put them in the rotor correctly, which I found very helpful.
I used these products for concentration of soluble proteins in native and denatured state (using buffers containing urea). If handling denatured proteins, the MWCO should be chosen at least three times smaller than the actual molecular weight of the protein, as unfolded molecules might slip through the pores.
There is virtually no loss of sample, since the membrane paddle locks completely and all liquid is forced through the membrane. I neither experienced clogging of the pores nor adsorption of concentrated protein to the membrane. Even very small remaining volumes can be collected completely by using the provided concentrate cup. However, it is a bit difficult to handle if you try to suck up the last drop with a small pipette, because it is hard to insert the tip properly into the cavity. Finally it works anyhow.
Although Pall Life Sciences does not recommend re-use of the centrifugal devices, I found that it is no problem to utilize them at least twice (for the same protein, of course). Just rinse with water and store in 20% ethanol at 4°C.
The membrane is compatible with a wide variety of chemicals, such as guanidine HCl (6 M), sodium dodecyl sulphate (0.01 M) or urea (6 M). I concentrated proteins denatured with different concentrations of urea (up to 6 M), which worked very well.
To summarize, all Pall Centrifugal Devices can be recommended in terms of protein concentration capacity, sample recovery and handling. There is no loss of sample and no clogging of the membrane. However, I found the centrifugation times stated in the protocols were too short. For a typical concentration, it took me about twice as long (up to 3 hours). Spin time and g-force should be determined separately for each application.