Citrate buffer for heat-induced epitope retrieval (HIER) method. HIER was used to reverse the loss of immunogenicity that occurs at partial epitopes in formalin-fixed paraffin-embedded tissue. During epitope retrieval, tissue slides are immersed in a solution and heated via a heated plate (>95° C) or other suitable heat source (such as a pressure cooker or steamer). Citrate buffer is the solution of choice for most antibodies.