Hanna™ buffer solutions are prepared according to precise formulas and are standardized with a pH meter calibrated according to the NIST standards. All pH 4 solutions show batch number, expiration date and the correlation table between pH and temperature. HI 5004, HI 6004, HI 7004L/C, HI 8004L/C and HI 70004C are supplied complete with certificate of analysis. This buffer value is widely used in water purification plants, in the food industry and where ever the pH is expected to be slightly acidic.