HI70004P is a premium quality pH 4.01 calibration buffer solution. 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 calibration buffers have been specially formulated to have an expiration of 5 years from the date of manufacture for an unopened sachet. The HI70004P is for 25 sachets containing 20 mL of buffer.