Staining compositions and methods for use with a matrix, such as an electrophoretic gel, containing separated biopolymers. The compositions including an acid, an organic solvent, and a generally planar, fluid-permeable gel contact sheet consisting primarily of a non-cellulosic material. The acid and organic solvent may be sorbed to the fluid-permeable gel contact sheet, or may be sorbed to a layers contactable with a non-gel contact side of the gel contact sheet. In one embodiment, the composition is a source electrophoretic stain composition including a staining reagent. In one embodiment, the composition is a sink electrophoretic stain composition including a sorbent.