Vector Laboratories Antigen Unmasking Solutions are highly effective at revealing antigens in formalin-fixed, paraffin embedded tissue sections when used in combination with a high temperature treatment procedure. These solutions for antigen retrieval are available in two formulations. The citrate-based solution (H-3300) is pH 6.0; the Tris-based solution (H-3301) is pH 9.0. Both solutions are supplied as convenient 100x concentrated stocks, sufficient for preparation of 25 L of working solution.