A 3% acetic acid solution is mainly used in histology to adjust the pH of tissue sections to the optimal pH range for staining. The acid solution is particularly useful in alcian blue staining, where the pH plays a crucial role in the staining result. The 3% acetic acid solution has a pH of approximately 2.5, which is ideal for typical alcian blue staining.

Alcian blue is a cationic dye that stains sulfated and carboxylated glycosaminoglycans (GAGs) and acidic mucopolysaccharides in tissue sections. The staining is dependent on the pH of the staining solution. Different GAGs can be selectively stained at different pH values. The use of a 3% acetic acid solution helps to adjust the pH of tissue sections before or after staining to ensure the binding of Alcian blue to the desired molecules.

The 3% acetic acid solution allows precise pH adjustment of tissue sections and helps to achieve clear and consistent staining results. This solution is thus an important tool for histologists to achieve optimal staining of tissue sections.