A very stable buffer, used with Osmium tetroxide; provides excellent fixation, better stability and buffering capacity. The pH can be adjusted by varying the amount of hydrochloric acid in the final volume of 200 ml. Preparation Instructions: Pour 9 ml of 2N HCl; add 5.34 ml of Sym-Collidine, mix well and add distilled water up to 200 ml for a pH 7.4 solution.