Citric Acid is an acidic compound from citrus fruits; as a starting point in the Krebs cycle, citrate is a key intermediate in metabolism. Citric acid is one of a series of compounds responsible for the physiological oxidation of fats, carbohydrates and proteins to carbon dioxide and water. Used to prepare citrate buffer for antigen retrieval of tissue samples; the citrate solution is designed to break protein cross-links; thus, unmasking antigens and epitopes in formalin-fixed and paraffin embedded tissue sections, resulting in enhancing staining intensity of antibodies. Citrate has anticoagulant activity; as a calcium chelator, it forms complexes that disrupt the tendency of blood to clot. May be used to adjust pH and as a sequestering agent for the removal of trace metals.