HI7032M is a premium quality 1,382 mg/L (ppm) TDS calibration solution that is prepared against a NIST traceable potassium chloride solution. Hanna TDS 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 TDS standards have been specially formulated to have an expiration of 5 years from the date of manufacture for an unopened bottle.