Methods for purifying urease are described that make use of a precipitating agent such as ammonium sulfate to obtain urease as a precipitate. The method can involve use of a solubilizing agent, such as a citrate-containing solution, to dissolve the precipitate. The method can involve the use of a sugar to provide protected urease in a sugar-urease solution and immobilization of the urease. The method can involve freeze drying of the immobilized urease. A sugar-urease preparation and an immobilized urease, and a sorbent cartridge containing the urease are described as well as methods to conduct dialysis.
