Hanna Solution HI7031L is a premium quality 1,413 µS/cm conductivity standard that is prepared against a NIST traceable potassium chloride solution. Hanna conductivity solutions 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 conductivity standards have been specially formulated to have an expiration of 5 years from the date of manufacture for an unopened bottle.