Antigen Unmasking Solution, Tris-Based, 250 ml. 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. This Tris-based solution is pH 9.0 and is supplied as a convenient 100x concentrated stocks sufficient for preparation of 25 L of working solution.