Phosphate buffer solution (pH 5.0) used to maintain a stable mildly acidic pH in biological and chemical experiments, particularly in applications requiring pH around 5.0, such as certain enzymatic reactions, microbial cultures, or sample preparations where neutral pH is not suitable. Commonly applied in cell culture under acidic conditions, protein stabilization, and chromatography. Ideal for diluting or reconstituting lab samples without disrupting activity in acid-tolerant systems. Frequently used in diagnostic kits, pharmaceutical formulations, and laboratory research involving acid-stable nucleic acids or proteins. Also serves as a rinsing or storage solution for biological specimens due to its biocompatibility at pH 5.0.