Validation of the validity of the reagents after opening of containers

determine the shelf life of commercial reagents after opening, duration during which the conditions of storage data, reagent is maintained in the previously established specifications. Indeed, commercial reagents are received by the laboratory of physical chemistry for various uses. The containers are open several times. Their equilibrium chemical and/or physical state can move from static to dynamic under the action of temperature, pressure, light and contamination. As such, it is necessary to study the impact of the opening of the containers on the reliability of the analysis results and therefore, cannot keep as date expiry the expiry date before opening.

The determination of the expiration after opening date will also in the laboratory to answer away following the inspection of the national food safety agency, the environment and labour.
in your opinion what is the methodology (more effective) suitable for determining the expiration lasts?
If someone has a probation report on be subject ‘validation of the validity of the reagents’ envoyez_moi is it you more
Thanks in advance for you participation

@abdel You can validate it on your own by testing some parameters those can affect the chemicals as its description, moisture content, pH, potency etc. at different time periods (7, 15, 30, 45, 60 … days)