Hydrochloric Acid in Ethanol (3 % / 90 %)

Hydrochloric acid alcohol (3 % / 90 %) is a solution that is frequently used in histology and microscopy. This solution consists of 3% hydrochloric acid (HCl) and 90% ethanol. The main applications of hydrochloric acid alcohol (3% / 90%) are decolorization and differentiation of stains.

In some staining protocols, such as Ziehl-Neelsen staining, hydrochloric acid alcohol is used as a decolorizer. The hydrochloric acid alcohol solution removes excess dye from non-specifically bound areas of the tissue specimen, allowing clearer and higher contrast visualization of the stained structures.

The 3% / 90% concentration is stronger than lower concentrated hydrochloric acid alcohol solutions and thus can be more effective for stubborn stains. Nevertheless, care should be taken with sensitive tissue specimens, as the higher concentration of hydrochloric acid and ethanol may affect the tissue more. In such cases, a lower concentrated hydrochloric acid-alcohol solution might be a gentler alternative.