Concentrator systems include a circulating fluid pathway passing through a pump, a filter, and a retentate container. An effluent outlet line communicates with the circulating fluid pathway through a filtering element within a body of the filter. The systems further include a control system. In some embodiments, the pump, filter, and retentate container may be secured within a portable container. Methods for concentrating a foreign substance within a fluid sample include establishing circulation of fluid through a fluid circulation path passing through a fluid pump, a filter body, and a retentate container. Fluid is caused to exit the fluid circulation path through a filtering element within the filter body, and at least one foreign substance is prevented from passing through the filtering element. A control system may be used to control at least one of a speed of the pump and a quantity of retentate within the retentate container.
 The United States Government has certain rights in this invention pursuant to Contract No. DE-AC07-05ID14517 between the United States Department of Energy and Battelle Energy Alliance, LLC.