A versatile solute purification cell based on the flow field-flow fractionation channel is described. Equations are obtained for impurity removal, mean solute residence time, and solute throughput. Experiments are described in which methylene blue was purged from a buffer stream and from a stream containing 10% albumin by weight using a 2.65-ml cell. Impurity removals up to about 98 to 99% were observed. Mean albumin residence time in the cell varied from about 10 to 60 min; 90% impurity removal was possible with a residence time of about 25 min.