Citrate Buffer formulated at pH 4.0 is prepared from citric acid and sodium citrate dihydrate to provide effective buffering in the acidic pH range, with functional capacity extending from approximately pH 3.0 to 6.2. This 0.5 M solution is widely used in laboratory workflows including molecular biology, histology, pathology, immunohistochemistry, and RNA extraction. In tissue-based applications, citrate buffer is commonly employed for antigen retrieval, where it facilitates the disruption of fixation-induced cross-links, improving antigen accessibility and detection in fixed tissue samples.