U-Tube™ Concentrators are ultrafiltration spin devices for concentrating biological samples, including protein and nucleic acid solutions. The devices feature a vertical membrane design which limits membrane fouling and an integrated dead-stop technology to minimize the risk of concentrating to dryness. U-Tube Concentrators are available in a variety of volumes from 0.5 ml to 20 ml and molecular weight cutoffs from 3 kDA to 30 kDa with a choice of two kinds of membranes. The conventional polyethersulfone (PES) exhibits low protein binding. For quantitative sample recovery, use concentrators with ultra-low protein binding Hydrosart® membranes (Cat. No. 71875-3, 71875-4, 71881-3, 71881-4, 71882-3, 71882-4)