Why do we write one year expiry date for open liquid bottle and three year for open solid chemical?
Degradation of liquid chemicals is fast than the solid chemicals.
Its industrial practice. Liquid chemical loose its strenth more rapidly than solid after opening.
It is expected by regulatory agencies that sound scientifically rationale should be applied to assign lab expiry periods. You can adopt data from recognized references (USP, ASTM, AOAC, Standard Methods, ACS or compendial methods). Otherwise, you have to develop stability data during the method validation. For solid chemicals you can get the expiry dates from the supplier’s certificate of analysis, or from recognized scientifically sources. Also, once you open the chemical’s container, need to establish guideliness, according to chemical substance properties, supplier recommendatios and solution’s stability. What is important is to have scientifically proved back up data to justify any assigned expiration period.
it is our own responsibility to establish and assign the date of expiry. based on experience gained on these reagents. no guideline is preferring to address the expiry period of these reagents.
Usually , we believe that opened bottles can catch moisture easily, hence less period of expiry is assigned.
Salts/solids are usually stable. in this way we can justify.