[Babcock_Hall]

When I was in the laboratory every day, we had concentrators in the 3-4 mL range of starting volumes whose membranes were perpendicular to the long axis of the concentrator.  Nowadays most concentrators have membranes that are parallel to the long axis of the concentrator, and I am trying to write up a protocol for using them.  I sometimes call the former lateral-membrane concentrators, and the latter I call vertical membrane concentrators, but I don't know how universal this is.  A Pall representative once told a student of mine that there was a preferred orientation of the concentrator in the centrifuge, but my attempts to verify this using the instructions have yielded little.  The only company which mentioned this is Pierce (Thermo Scientific) product 88514.  Their instructions say:  "When using a fixed-angle rotor, position device so that the printed sample window faces outward."  I don't have these concentrators on hand; therefore, I am not quite sure how the printing relates to the membrane (the photograph is not entirely helpful).  So far, I have not found anything in the product literature for Pall or Amicon concentrators that covers this point, and I am trying to contact a representative of one of the companies.  Does anyone have any thoughts?
https://tools.thermofisher.com/content/sfs/manuals/MAN0015695_2162596_PierceProteinConcentrator_2_6mLPI.pdf

[Yggdrasil]

Whenever I have used these, I place the printed window facing outward/upwards as suggested (I think I've seen this in various manuals e.g. page 5 of http://www.vivaproducts.com/downloads/vivaspin-6-20-operating-instructions.pdf).  Because of how the liquid is designed to flow in the concentrator, I think that positioning the unit like this prevents the sample from filtering to dryness (which would be very bad for protein samples).

[Babcock_Hall]

Apparently my version of the user guide for the Amicon Ultra-4 was an older version, which did not say anything about this.  I contacted Millipore and they sent me different document, which states, "When using a fixed-angle rotor, orient the device with the membrane panel facing up."  This is odd because the membrane panel and the printed numbers are approximately 90° different, as I see things.  I don't currently have Viva or Thermofisher concentrators, but I will try to obtain some.

[Yggdrasil]

Yes, apparently the Millipore concentrators should be rotated 90° from how you would orient the Viva or Thermo concentrators.  This might reflect differences in the way the concentrators are designed.