Albumin may be used to eliminate background interference in ELISA's or other enzyme assay systems. It is also used in absorption, distribution, metabolism, and excretion (ADME) pharmacological research; cell culture; drug delivery research; and cryopreservation of cells. Human and bovine albumins contain 16% nitrogen and are often used as standards in protein calibration studies. Due to their free hydrophobic region fatty acid free albumins are used to solubilize lipids in tissue culture, and are also used as blocking agents in Western blots or ELISA applications. Globulin free albumins are suitable for use in applications where no other proteins should be present (e.g., electrophoresis).