Millipore Corp. in Billerica, MA, has developed a protocol for efficiently compartmentalizing protein solutions using ultrafiltration in a centrifugal mode. Traditional fractionation techniques use size-exclusion chromatography, which is both laborious and time intensive. The new method promises speed and efficiency through a combination of the company's Amicon Ultra centrifugal devices, which enable researchers to fractionate protein mixtures. The bi-vertical housing limits membrane polarization while the hydrophilic microstructure of the low-binding Ultracel ultrafiltration membrane enables efficient protein separation. The method expedites the fractionation process by minimizing process steps such as setting up columns, optimizing column flow rates, and collecting and concentrating various fractions.