This solution is a premium quality pH 7.01 calibration buffer that is NIST traceable and supplied with a Certificate of Analysis. Each sachet has the lot number and expiration date stamped on it and is made of light block foil ensuring freshness each time one is opened. 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 sachet. 25 sachets containing 20 mL of buffer.