Tannic acid was introduced as a secondary fixative mixture with aldehydes for biological tissues, and also as a stain. Specimens treated with Tannic acid show increased contrast and more delineation of cell membranes.
A low molecular weight, Tannic acid (LMGG) galloylglucose (C14H1009)n, provides and overcomes the previous problems of unsatisfactory penetration, extraction, and precipitation when high molecular weight Tannic acid (C76H52O46) was utilized.
It works primarily as a mordant between osmicated structures and Lead citrate of the post-staining, revealing additional ultra-cellular structures and details better delineated.
The procedure reported by Simionescu (1976) involves the following steps: (Sodium Cacodylate buffer is preferred.)
1% LMGG Tannic acid (C14H1009) in 0.05M Sodium Cacodylate buffer, freshly prepared.
Concentration of LMGG can be adjusted in a range of 0.25% to 2.0% according to the nature of the tissue and section thickness.
N. Simionescu and M. Simionescu, J. Cell Biology (1976-70), 608-621.
Tannic Acid (Lmgg), Osmium tetroxide, Sodium Cacodylate buffer, Propylene oxide, and Glutaraldehyde