Thermo Fisher, 258585000, Buffer solution pH 4, Citrate buffer

Thermo Scientific Chemicals pH 4 citrate buffer is a ready-to-use aqueous reference and reagent solution for laboratory work requiring a stable acidic pH environment. The 500 mL solution uses a citrate–sodium chloride–sodium hydroxide composition and has a specified pH range of 3.98–4.02 at 20°C. It can be used for routine pH-related checks and as an acidic buffer in compatible analytical or sample-preparation procedures, provided the method accepts the formulation and ionic composition. Unlike a certified multi-point instrument calibration set, this product is a single pH 4 buffer solution, and its suitability for formal metrological calibration depends on the relevant protocol and certificate. Minimize contamination by dispensing into a separate vessel rather than immersing used electrodes into the stock bottle. Temperature changes and air exposure can influence measured pH, so equilibrate to the procedure temperature and replace contaminated aliquots. Do not confuse this citrate solution with potassium hydrogen phthalate buffer entries that may appear in some third-party catalogs.