Hanna GroLine pH 4.01 SolutionHI7004 050 is a high quality pH 4. 01 calibration buffer that is NIST traceable and supplied with a Certificate of Analysis. Hanna calibration buffers have the lot number and expiration date clearly marked on the label and are air tight with a tamper proof seal to ensure the quality of the solution. Hanna's line of technical calibration buffers have been specially formulated to have an expiration of 5 years from the date of manufacture for an unopened