Centrisart® I is particularly suited for preparing protein-free ultrafiltrates from biological samples when deproteinising of samples is required for analysis of low molecular weight substances. Premature blocking of the membrane is efficiently prevented by filtration in the opposite direction to centrifugal force. This allows ultrafiltration even of particle-laden samples such as whole blood. The resulting ultrafiltrate is collected in the inner tube and can be easily recovered. Centrisart® I is particularly suited for preparing protein-free ultrafiltrates from biological samples when deproteinising of samples is required for analysis of low molecular weight substances. Premature blocking of the membrane is efficiently prevented by filtration in the opposite direction to centrifugal force. This allows ultrafiltration even of particle-laden samples such as whole blood. The resulting ultrafiltrate is collected in the inner tube and can be easily recovered.